Commit | Line | Data |
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f41d911f PM |
1 | /* |
2 | * Read-Copy Update mechanism for mutual exclusion (tree-based version) | |
3 | * Internal non-public definitions that provide either classic | |
6cc68793 | 4 | * or preemptible semantics. |
f41d911f PM |
5 | * |
6 | * This program is free software; you can redistribute it and/or modify | |
7 | * it under the terms of the GNU General Public License as published by | |
8 | * the Free Software Foundation; either version 2 of the License, or | |
9 | * (at your option) any later version. | |
10 | * | |
11 | * This program is distributed in the hope that it will be useful, | |
12 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | * GNU General Public License for more details. | |
15 | * | |
16 | * You should have received a copy of the GNU General Public License | |
87de1cfd PM |
17 | * along with this program; if not, you can access it online at |
18 | * http://www.gnu.org/licenses/gpl-2.0.html. | |
f41d911f PM |
19 | * |
20 | * Copyright Red Hat, 2009 | |
21 | * Copyright IBM Corporation, 2009 | |
22 | * | |
23 | * Author: Ingo Molnar <mingo@elte.hu> | |
24 | * Paul E. McKenney <paulmck@linux.vnet.ibm.com> | |
25 | */ | |
26 | ||
d9a3da06 | 27 | #include <linux/delay.h> |
3fbfbf7a | 28 | #include <linux/gfp.h> |
b626c1b6 | 29 | #include <linux/oom.h> |
62ab7072 | 30 | #include <linux/smpboot.h> |
4102adab | 31 | #include "../time/tick-internal.h" |
f41d911f | 32 | |
5b61b0ba | 33 | #ifdef CONFIG_RCU_BOOST |
61cfd097 | 34 | |
abaa93d9 | 35 | #include "../locking/rtmutex_common.h" |
21871d7e | 36 | |
61cfd097 PM |
37 | /* |
38 | * Control variables for per-CPU and per-rcu_node kthreads. These | |
39 | * handle all flavors of RCU. | |
40 | */ | |
41 | static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task); | |
42 | DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); | |
43 | DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); | |
44 | DEFINE_PER_CPU(char, rcu_cpu_has_work); | |
45 | ||
727b705b PM |
46 | #else /* #ifdef CONFIG_RCU_BOOST */ |
47 | ||
48 | /* | |
49 | * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST, | |
50 | * all uses are in dead code. Provide a definition to keep the compiler | |
51 | * happy, but add WARN_ON_ONCE() to complain if used in the wrong place. | |
52 | * This probably needs to be excluded from -rt builds. | |
53 | */ | |
54 | #define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; }) | |
55 | ||
56 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ | |
5b61b0ba | 57 | |
3fbfbf7a PM |
58 | #ifdef CONFIG_RCU_NOCB_CPU |
59 | static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ | |
60 | static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */ | |
1b0048a4 | 61 | static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ |
3fbfbf7a PM |
62 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ |
63 | ||
26845c28 PM |
64 | /* |
65 | * Check the RCU kernel configuration parameters and print informative | |
66 | * messages about anything out of the ordinary. If you like #ifdef, you | |
67 | * will love this function. | |
68 | */ | |
69 | static void __init rcu_bootup_announce_oddness(void) | |
70 | { | |
ab6f5bd6 PM |
71 | if (IS_ENABLED(CONFIG_RCU_TRACE)) |
72 | pr_info("\tRCU debugfs-based tracing is enabled.\n"); | |
05c5df31 PM |
73 | if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) || |
74 | (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32)) | |
ab6f5bd6 | 75 | pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n", |
05c5df31 | 76 | RCU_FANOUT); |
7fa27001 | 77 | if (rcu_fanout_exact) |
ab6f5bd6 PM |
78 | pr_info("\tHierarchical RCU autobalancing is disabled.\n"); |
79 | if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ)) | |
80 | pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n"); | |
81 | if (IS_ENABLED(CONFIG_PROVE_RCU)) | |
82 | pr_info("\tRCU lockdep checking is enabled.\n"); | |
83 | if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST_RUNNABLE)) | |
84 | pr_info("\tRCU torture testing starts during boot.\n"); | |
42621697 AG |
85 | if (RCU_NUM_LVLS >= 4) |
86 | pr_info("\tFour(or more)-level hierarchy is enabled.\n"); | |
47d631af | 87 | if (RCU_FANOUT_LEAF != 16) |
a3bd2c09 | 88 | pr_info("\tBuild-time adjustment of leaf fanout to %d.\n", |
47d631af PM |
89 | RCU_FANOUT_LEAF); |
90 | if (rcu_fanout_leaf != RCU_FANOUT_LEAF) | |
9a5739d7 | 91 | pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); |
cca6f393 | 92 | if (nr_cpu_ids != NR_CPUS) |
efc151c3 | 93 | pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); |
ab6f5bd6 PM |
94 | if (IS_ENABLED(CONFIG_RCU_BOOST)) |
95 | pr_info("\tRCU kthread priority: %d.\n", kthread_prio); | |
26845c28 PM |
96 | } |
97 | ||
28f6569a | 98 | #ifdef CONFIG_PREEMPT_RCU |
f41d911f | 99 | |
a41bfeb2 | 100 | RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); |
b28a7c01 | 101 | static struct rcu_state *const rcu_state_p = &rcu_preempt_state; |
2927a689 | 102 | static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data; |
f41d911f | 103 | |
d19fb8d1 PM |
104 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
105 | bool wake); | |
d9a3da06 | 106 | |
f41d911f PM |
107 | /* |
108 | * Tell them what RCU they are running. | |
109 | */ | |
0e0fc1c2 | 110 | static void __init rcu_bootup_announce(void) |
f41d911f | 111 | { |
efc151c3 | 112 | pr_info("Preemptible hierarchical RCU implementation.\n"); |
26845c28 | 113 | rcu_bootup_announce_oddness(); |
f41d911f PM |
114 | } |
115 | ||
8203d6d0 PM |
116 | /* Flags for rcu_preempt_ctxt_queue() decision table. */ |
117 | #define RCU_GP_TASKS 0x8 | |
118 | #define RCU_EXP_TASKS 0x4 | |
119 | #define RCU_GP_BLKD 0x2 | |
120 | #define RCU_EXP_BLKD 0x1 | |
121 | ||
122 | /* | |
123 | * Queues a task preempted within an RCU-preempt read-side critical | |
124 | * section into the appropriate location within the ->blkd_tasks list, | |
125 | * depending on the states of any ongoing normal and expedited grace | |
126 | * periods. The ->gp_tasks pointer indicates which element the normal | |
127 | * grace period is waiting on (NULL if none), and the ->exp_tasks pointer | |
128 | * indicates which element the expedited grace period is waiting on (again, | |
129 | * NULL if none). If a grace period is waiting on a given element in the | |
130 | * ->blkd_tasks list, it also waits on all subsequent elements. Thus, | |
131 | * adding a task to the tail of the list blocks any grace period that is | |
132 | * already waiting on one of the elements. In contrast, adding a task | |
133 | * to the head of the list won't block any grace period that is already | |
134 | * waiting on one of the elements. | |
135 | * | |
136 | * This queuing is imprecise, and can sometimes make an ongoing grace | |
137 | * period wait for a task that is not strictly speaking blocking it. | |
138 | * Given the choice, we needlessly block a normal grace period rather than | |
139 | * blocking an expedited grace period. | |
140 | * | |
141 | * Note that an endless sequence of expedited grace periods still cannot | |
142 | * indefinitely postpone a normal grace period. Eventually, all of the | |
143 | * fixed number of preempted tasks blocking the normal grace period that are | |
144 | * not also blocking the expedited grace period will resume and complete | |
145 | * their RCU read-side critical sections. At that point, the ->gp_tasks | |
146 | * pointer will equal the ->exp_tasks pointer, at which point the end of | |
147 | * the corresponding expedited grace period will also be the end of the | |
148 | * normal grace period. | |
149 | */ | |
150 | static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp, | |
151 | unsigned long flags) __releases(rnp->lock) | |
152 | { | |
153 | int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) + | |
154 | (rnp->exp_tasks ? RCU_EXP_TASKS : 0) + | |
155 | (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) + | |
156 | (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0); | |
157 | struct task_struct *t = current; | |
158 | ||
159 | /* | |
160 | * Decide where to queue the newly blocked task. In theory, | |
161 | * this could be an if-statement. In practice, when I tried | |
162 | * that, it was quite messy. | |
163 | */ | |
164 | switch (blkd_state) { | |
165 | case 0: | |
166 | case RCU_EXP_TASKS: | |
167 | case RCU_EXP_TASKS + RCU_GP_BLKD: | |
168 | case RCU_GP_TASKS: | |
169 | case RCU_GP_TASKS + RCU_EXP_TASKS: | |
170 | ||
171 | /* | |
172 | * Blocking neither GP, or first task blocking the normal | |
173 | * GP but not blocking the already-waiting expedited GP. | |
174 | * Queue at the head of the list to avoid unnecessarily | |
175 | * blocking the already-waiting GPs. | |
176 | */ | |
177 | list_add(&t->rcu_node_entry, &rnp->blkd_tasks); | |
178 | break; | |
179 | ||
180 | case RCU_EXP_BLKD: | |
181 | case RCU_GP_BLKD: | |
182 | case RCU_GP_BLKD + RCU_EXP_BLKD: | |
183 | case RCU_GP_TASKS + RCU_EXP_BLKD: | |
184 | case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: | |
185 | case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: | |
186 | ||
187 | /* | |
188 | * First task arriving that blocks either GP, or first task | |
189 | * arriving that blocks the expedited GP (with the normal | |
190 | * GP already waiting), or a task arriving that blocks | |
191 | * both GPs with both GPs already waiting. Queue at the | |
192 | * tail of the list to avoid any GP waiting on any of the | |
193 | * already queued tasks that are not blocking it. | |
194 | */ | |
195 | list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks); | |
196 | break; | |
197 | ||
198 | case RCU_EXP_TASKS + RCU_EXP_BLKD: | |
199 | case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: | |
200 | case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD: | |
201 | ||
202 | /* | |
203 | * Second or subsequent task blocking the expedited GP. | |
204 | * The task either does not block the normal GP, or is the | |
205 | * first task blocking the normal GP. Queue just after | |
206 | * the first task blocking the expedited GP. | |
207 | */ | |
208 | list_add(&t->rcu_node_entry, rnp->exp_tasks); | |
209 | break; | |
210 | ||
211 | case RCU_GP_TASKS + RCU_GP_BLKD: | |
212 | case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD: | |
213 | ||
214 | /* | |
215 | * Second or subsequent task blocking the normal GP. | |
216 | * The task does not block the expedited GP. Queue just | |
217 | * after the first task blocking the normal GP. | |
218 | */ | |
219 | list_add(&t->rcu_node_entry, rnp->gp_tasks); | |
220 | break; | |
221 | ||
222 | default: | |
223 | ||
224 | /* Yet another exercise in excessive paranoia. */ | |
225 | WARN_ON_ONCE(1); | |
226 | break; | |
227 | } | |
228 | ||
229 | /* | |
230 | * We have now queued the task. If it was the first one to | |
231 | * block either grace period, update the ->gp_tasks and/or | |
232 | * ->exp_tasks pointers, respectively, to reference the newly | |
233 | * blocked tasks. | |
234 | */ | |
235 | if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) | |
236 | rnp->gp_tasks = &t->rcu_node_entry; | |
237 | if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD)) | |
238 | rnp->exp_tasks = &t->rcu_node_entry; | |
239 | raw_spin_unlock(&rnp->lock); | |
240 | ||
241 | /* | |
242 | * Report the quiescent state for the expedited GP. This expedited | |
243 | * GP should not be able to end until we report, so there should be | |
244 | * no need to check for a subsequent expedited GP. (Though we are | |
245 | * still in a quiescent state in any case.) | |
246 | */ | |
247 | if (blkd_state & RCU_EXP_BLKD && | |
248 | t->rcu_read_unlock_special.b.exp_need_qs) { | |
249 | t->rcu_read_unlock_special.b.exp_need_qs = false; | |
250 | rcu_report_exp_rdp(rdp->rsp, rdp, true); | |
251 | } else { | |
252 | WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs); | |
253 | } | |
254 | local_irq_restore(flags); | |
255 | } | |
256 | ||
f41d911f | 257 | /* |
6cc68793 | 258 | * Record a preemptible-RCU quiescent state for the specified CPU. Note |
f41d911f PM |
259 | * that this just means that the task currently running on the CPU is |
260 | * not in a quiescent state. There might be any number of tasks blocked | |
261 | * while in an RCU read-side critical section. | |
25502a6c | 262 | * |
1d082fd0 PM |
263 | * As with the other rcu_*_qs() functions, callers to this function |
264 | * must disable preemption. | |
f41d911f | 265 | */ |
284a8c93 | 266 | static void rcu_preempt_qs(void) |
f41d911f | 267 | { |
5b74c458 | 268 | if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) { |
284a8c93 | 269 | trace_rcu_grace_period(TPS("rcu_preempt"), |
2927a689 | 270 | __this_cpu_read(rcu_data_p->gpnum), |
284a8c93 | 271 | TPS("cpuqs")); |
5b74c458 | 272 | __this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false); |
284a8c93 PM |
273 | barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */ |
274 | current->rcu_read_unlock_special.b.need_qs = false; | |
275 | } | |
f41d911f PM |
276 | } |
277 | ||
278 | /* | |
c3422bea PM |
279 | * We have entered the scheduler, and the current task might soon be |
280 | * context-switched away from. If this task is in an RCU read-side | |
281 | * critical section, we will no longer be able to rely on the CPU to | |
12f5f524 PM |
282 | * record that fact, so we enqueue the task on the blkd_tasks list. |
283 | * The task will dequeue itself when it exits the outermost enclosing | |
284 | * RCU read-side critical section. Therefore, the current grace period | |
285 | * cannot be permitted to complete until the blkd_tasks list entries | |
286 | * predating the current grace period drain, in other words, until | |
287 | * rnp->gp_tasks becomes NULL. | |
c3422bea PM |
288 | * |
289 | * Caller must disable preemption. | |
f41d911f | 290 | */ |
38200cf2 | 291 | static void rcu_preempt_note_context_switch(void) |
f41d911f PM |
292 | { |
293 | struct task_struct *t = current; | |
c3422bea | 294 | unsigned long flags; |
f41d911f PM |
295 | struct rcu_data *rdp; |
296 | struct rcu_node *rnp; | |
297 | ||
10f39bb1 | 298 | if (t->rcu_read_lock_nesting > 0 && |
1d082fd0 | 299 | !t->rcu_read_unlock_special.b.blocked) { |
f41d911f PM |
300 | |
301 | /* Possibly blocking in an RCU read-side critical section. */ | |
e63c887c | 302 | rdp = this_cpu_ptr(rcu_state_p->rda); |
f41d911f | 303 | rnp = rdp->mynode; |
2a67e741 | 304 | raw_spin_lock_irqsave_rcu_node(rnp, flags); |
1d082fd0 | 305 | t->rcu_read_unlock_special.b.blocked = true; |
86848966 | 306 | t->rcu_blocked_node = rnp; |
f41d911f PM |
307 | |
308 | /* | |
8203d6d0 PM |
309 | * Verify the CPU's sanity, trace the preemption, and |
310 | * then queue the task as required based on the states | |
311 | * of any ongoing and expedited grace periods. | |
f41d911f | 312 | */ |
0aa04b05 | 313 | WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0); |
e7d8842e | 314 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
d4c08f2a PM |
315 | trace_rcu_preempt_task(rdp->rsp->name, |
316 | t->pid, | |
317 | (rnp->qsmask & rdp->grpmask) | |
318 | ? rnp->gpnum | |
319 | : rnp->gpnum + 1); | |
8203d6d0 | 320 | rcu_preempt_ctxt_queue(rnp, rdp, flags); |
10f39bb1 | 321 | } else if (t->rcu_read_lock_nesting < 0 && |
1d082fd0 | 322 | t->rcu_read_unlock_special.s) { |
10f39bb1 PM |
323 | |
324 | /* | |
325 | * Complete exit from RCU read-side critical section on | |
326 | * behalf of preempted instance of __rcu_read_unlock(). | |
327 | */ | |
328 | rcu_read_unlock_special(t); | |
f41d911f PM |
329 | } |
330 | ||
331 | /* | |
332 | * Either we were not in an RCU read-side critical section to | |
333 | * begin with, or we have now recorded that critical section | |
334 | * globally. Either way, we can now note a quiescent state | |
335 | * for this CPU. Again, if we were in an RCU read-side critical | |
336 | * section, and if that critical section was blocking the current | |
337 | * grace period, then the fact that the task has been enqueued | |
338 | * means that we continue to block the current grace period. | |
339 | */ | |
284a8c93 | 340 | rcu_preempt_qs(); |
f41d911f PM |
341 | } |
342 | ||
fc2219d4 PM |
343 | /* |
344 | * Check for preempted RCU readers blocking the current grace period | |
345 | * for the specified rcu_node structure. If the caller needs a reliable | |
346 | * answer, it must hold the rcu_node's ->lock. | |
347 | */ | |
27f4d280 | 348 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 | 349 | { |
12f5f524 | 350 | return rnp->gp_tasks != NULL; |
fc2219d4 PM |
351 | } |
352 | ||
12f5f524 PM |
353 | /* |
354 | * Advance a ->blkd_tasks-list pointer to the next entry, instead | |
355 | * returning NULL if at the end of the list. | |
356 | */ | |
357 | static struct list_head *rcu_next_node_entry(struct task_struct *t, | |
358 | struct rcu_node *rnp) | |
359 | { | |
360 | struct list_head *np; | |
361 | ||
362 | np = t->rcu_node_entry.next; | |
363 | if (np == &rnp->blkd_tasks) | |
364 | np = NULL; | |
365 | return np; | |
366 | } | |
367 | ||
8af3a5e7 PM |
368 | /* |
369 | * Return true if the specified rcu_node structure has tasks that were | |
370 | * preempted within an RCU read-side critical section. | |
371 | */ | |
372 | static bool rcu_preempt_has_tasks(struct rcu_node *rnp) | |
373 | { | |
374 | return !list_empty(&rnp->blkd_tasks); | |
375 | } | |
376 | ||
b668c9cf PM |
377 | /* |
378 | * Handle special cases during rcu_read_unlock(), such as needing to | |
379 | * notify RCU core processing or task having blocked during the RCU | |
380 | * read-side critical section. | |
381 | */ | |
2a3fa843 | 382 | void rcu_read_unlock_special(struct task_struct *t) |
f41d911f | 383 | { |
b6a932d1 PM |
384 | bool empty_exp; |
385 | bool empty_norm; | |
386 | bool empty_exp_now; | |
f41d911f | 387 | unsigned long flags; |
12f5f524 | 388 | struct list_head *np; |
abaa93d9 | 389 | bool drop_boost_mutex = false; |
8203d6d0 | 390 | struct rcu_data *rdp; |
f41d911f | 391 | struct rcu_node *rnp; |
1d082fd0 | 392 | union rcu_special special; |
f41d911f PM |
393 | |
394 | /* NMI handlers cannot block and cannot safely manipulate state. */ | |
395 | if (in_nmi()) | |
396 | return; | |
397 | ||
398 | local_irq_save(flags); | |
399 | ||
400 | /* | |
8203d6d0 PM |
401 | * If RCU core is waiting for this CPU to exit its critical section, |
402 | * report the fact that it has exited. Because irqs are disabled, | |
1d082fd0 | 403 | * t->rcu_read_unlock_special cannot change. |
f41d911f PM |
404 | */ |
405 | special = t->rcu_read_unlock_special; | |
1d082fd0 | 406 | if (special.b.need_qs) { |
284a8c93 | 407 | rcu_preempt_qs(); |
c0135d07 | 408 | t->rcu_read_unlock_special.b.need_qs = false; |
1d082fd0 | 409 | if (!t->rcu_read_unlock_special.s) { |
79a62f95 LJ |
410 | local_irq_restore(flags); |
411 | return; | |
412 | } | |
f41d911f PM |
413 | } |
414 | ||
8203d6d0 PM |
415 | /* |
416 | * Respond to a request for an expedited grace period, but only if | |
417 | * we were not preempted, meaning that we were running on the same | |
418 | * CPU throughout. If we were preempted, the exp_need_qs flag | |
419 | * would have been cleared at the time of the first preemption, | |
420 | * and the quiescent state would be reported when we were dequeued. | |
421 | */ | |
422 | if (special.b.exp_need_qs) { | |
423 | WARN_ON_ONCE(special.b.blocked); | |
424 | t->rcu_read_unlock_special.b.exp_need_qs = false; | |
425 | rdp = this_cpu_ptr(rcu_state_p->rda); | |
426 | rcu_report_exp_rdp(rcu_state_p, rdp, true); | |
427 | if (!t->rcu_read_unlock_special.s) { | |
428 | local_irq_restore(flags); | |
429 | return; | |
430 | } | |
431 | } | |
432 | ||
79a62f95 | 433 | /* Hardware IRQ handlers cannot block, complain if they get here. */ |
d24209bb PM |
434 | if (in_irq() || in_serving_softirq()) { |
435 | lockdep_rcu_suspicious(__FILE__, __LINE__, | |
436 | "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n"); | |
8203d6d0 | 437 | pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n", |
d24209bb PM |
438 | t->rcu_read_unlock_special.s, |
439 | t->rcu_read_unlock_special.b.blocked, | |
8203d6d0 | 440 | t->rcu_read_unlock_special.b.exp_need_qs, |
d24209bb | 441 | t->rcu_read_unlock_special.b.need_qs); |
f41d911f PM |
442 | local_irq_restore(flags); |
443 | return; | |
444 | } | |
445 | ||
446 | /* Clean up if blocked during RCU read-side critical section. */ | |
1d082fd0 PM |
447 | if (special.b.blocked) { |
448 | t->rcu_read_unlock_special.b.blocked = false; | |
f41d911f | 449 | |
dd5d19ba | 450 | /* |
0a0ba1c9 PM |
451 | * Remove this task from the list it blocked on. The task |
452 | * now remains queued on the rcu_node corresponding to | |
453 | * the CPU it first blocked on, so the first attempt to | |
454 | * acquire the task's rcu_node's ->lock will succeed. | |
455 | * Keep the loop and add a WARN_ON() out of sheer paranoia. | |
dd5d19ba PM |
456 | */ |
457 | for (;;) { | |
86848966 | 458 | rnp = t->rcu_blocked_node; |
2a67e741 | 459 | raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ |
86848966 | 460 | if (rnp == t->rcu_blocked_node) |
dd5d19ba | 461 | break; |
0a0ba1c9 | 462 | WARN_ON_ONCE(1); |
1304afb2 | 463 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
dd5d19ba | 464 | } |
74e871ac | 465 | empty_norm = !rcu_preempt_blocked_readers_cgp(rnp); |
8203d6d0 | 466 | empty_exp = sync_rcu_preempt_exp_done(rnp); |
d9a3da06 | 467 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ |
12f5f524 | 468 | np = rcu_next_node_entry(t, rnp); |
f41d911f | 469 | list_del_init(&t->rcu_node_entry); |
82e78d80 | 470 | t->rcu_blocked_node = NULL; |
f7f7bac9 | 471 | trace_rcu_unlock_preempted_task(TPS("rcu_preempt"), |
d4c08f2a | 472 | rnp->gpnum, t->pid); |
12f5f524 PM |
473 | if (&t->rcu_node_entry == rnp->gp_tasks) |
474 | rnp->gp_tasks = np; | |
475 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
476 | rnp->exp_tasks = np; | |
727b705b PM |
477 | if (IS_ENABLED(CONFIG_RCU_BOOST)) { |
478 | if (&t->rcu_node_entry == rnp->boost_tasks) | |
479 | rnp->boost_tasks = np; | |
480 | /* Snapshot ->boost_mtx ownership w/rnp->lock held. */ | |
481 | drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t; | |
482 | } | |
f41d911f PM |
483 | |
484 | /* | |
485 | * If this was the last task on the current list, and if | |
486 | * we aren't waiting on any CPUs, report the quiescent state. | |
389abd48 PM |
487 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, |
488 | * so we must take a snapshot of the expedited state. | |
f41d911f | 489 | */ |
8203d6d0 | 490 | empty_exp_now = sync_rcu_preempt_exp_done(rnp); |
74e871ac | 491 | if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) { |
f7f7bac9 | 492 | trace_rcu_quiescent_state_report(TPS("preempt_rcu"), |
d4c08f2a PM |
493 | rnp->gpnum, |
494 | 0, rnp->qsmask, | |
495 | rnp->level, | |
496 | rnp->grplo, | |
497 | rnp->grphi, | |
498 | !!rnp->gp_tasks); | |
e63c887c | 499 | rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags); |
c701d5d9 | 500 | } else { |
d4c08f2a | 501 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
c701d5d9 | 502 | } |
d9a3da06 | 503 | |
27f4d280 | 504 | /* Unboost if we were boosted. */ |
727b705b | 505 | if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) |
abaa93d9 | 506 | rt_mutex_unlock(&rnp->boost_mtx); |
27f4d280 | 507 | |
d9a3da06 PM |
508 | /* |
509 | * If this was the last task on the expedited lists, | |
510 | * then we need to report up the rcu_node hierarchy. | |
511 | */ | |
389abd48 | 512 | if (!empty_exp && empty_exp_now) |
e63c887c | 513 | rcu_report_exp_rnp(rcu_state_p, rnp, true); |
b668c9cf PM |
514 | } else { |
515 | local_irq_restore(flags); | |
f41d911f | 516 | } |
f41d911f PM |
517 | } |
518 | ||
1ed509a2 PM |
519 | /* |
520 | * Dump detailed information for all tasks blocking the current RCU | |
521 | * grace period on the specified rcu_node structure. | |
522 | */ | |
523 | static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) | |
524 | { | |
525 | unsigned long flags; | |
1ed509a2 PM |
526 | struct task_struct *t; |
527 | ||
6cf10081 | 528 | raw_spin_lock_irqsave_rcu_node(rnp, flags); |
5fd4dc06 PM |
529 | if (!rcu_preempt_blocked_readers_cgp(rnp)) { |
530 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
531 | return; | |
532 | } | |
82efed06 | 533 | t = list_entry(rnp->gp_tasks->prev, |
12f5f524 PM |
534 | struct task_struct, rcu_node_entry); |
535 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) | |
536 | sched_show_task(t); | |
537 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
1ed509a2 PM |
538 | } |
539 | ||
540 | /* | |
541 | * Dump detailed information for all tasks blocking the current RCU | |
542 | * grace period. | |
543 | */ | |
544 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
545 | { | |
546 | struct rcu_node *rnp = rcu_get_root(rsp); | |
547 | ||
548 | rcu_print_detail_task_stall_rnp(rnp); | |
549 | rcu_for_each_leaf_node(rsp, rnp) | |
550 | rcu_print_detail_task_stall_rnp(rnp); | |
551 | } | |
552 | ||
a858af28 PM |
553 | static void rcu_print_task_stall_begin(struct rcu_node *rnp) |
554 | { | |
efc151c3 | 555 | pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", |
a858af28 PM |
556 | rnp->level, rnp->grplo, rnp->grphi); |
557 | } | |
558 | ||
559 | static void rcu_print_task_stall_end(void) | |
560 | { | |
efc151c3 | 561 | pr_cont("\n"); |
a858af28 PM |
562 | } |
563 | ||
f41d911f PM |
564 | /* |
565 | * Scan the current list of tasks blocked within RCU read-side critical | |
566 | * sections, printing out the tid of each. | |
567 | */ | |
9bc8b558 | 568 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 569 | { |
f41d911f | 570 | struct task_struct *t; |
9bc8b558 | 571 | int ndetected = 0; |
f41d911f | 572 | |
27f4d280 | 573 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
9bc8b558 | 574 | return 0; |
a858af28 | 575 | rcu_print_task_stall_begin(rnp); |
82efed06 | 576 | t = list_entry(rnp->gp_tasks->prev, |
12f5f524 | 577 | struct task_struct, rcu_node_entry); |
9bc8b558 | 578 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
efc151c3 | 579 | pr_cont(" P%d", t->pid); |
9bc8b558 PM |
580 | ndetected++; |
581 | } | |
a858af28 | 582 | rcu_print_task_stall_end(); |
9bc8b558 | 583 | return ndetected; |
f41d911f PM |
584 | } |
585 | ||
74611ecb PM |
586 | /* |
587 | * Scan the current list of tasks blocked within RCU read-side critical | |
588 | * sections, printing out the tid of each that is blocking the current | |
589 | * expedited grace period. | |
590 | */ | |
591 | static int rcu_print_task_exp_stall(struct rcu_node *rnp) | |
592 | { | |
593 | struct task_struct *t; | |
594 | int ndetected = 0; | |
595 | ||
596 | if (!rnp->exp_tasks) | |
597 | return 0; | |
598 | t = list_entry(rnp->exp_tasks->prev, | |
599 | struct task_struct, rcu_node_entry); | |
600 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { | |
601 | pr_cont(" P%d", t->pid); | |
602 | ndetected++; | |
603 | } | |
604 | return ndetected; | |
605 | } | |
606 | ||
b0e165c0 PM |
607 | /* |
608 | * Check that the list of blocked tasks for the newly completed grace | |
609 | * period is in fact empty. It is a serious bug to complete a grace | |
610 | * period that still has RCU readers blocked! This function must be | |
611 | * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock | |
612 | * must be held by the caller. | |
12f5f524 PM |
613 | * |
614 | * Also, if there are blocked tasks on the list, they automatically | |
615 | * block the newly created grace period, so set up ->gp_tasks accordingly. | |
b0e165c0 PM |
616 | */ |
617 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
618 | { | |
27f4d280 | 619 | WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); |
96e92021 | 620 | if (rcu_preempt_has_tasks(rnp)) |
12f5f524 | 621 | rnp->gp_tasks = rnp->blkd_tasks.next; |
28ecd580 | 622 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
623 | } |
624 | ||
f41d911f PM |
625 | /* |
626 | * Check for a quiescent state from the current CPU. When a task blocks, | |
627 | * the task is recorded in the corresponding CPU's rcu_node structure, | |
628 | * which is checked elsewhere. | |
629 | * | |
630 | * Caller must disable hard irqs. | |
631 | */ | |
86aea0e6 | 632 | static void rcu_preempt_check_callbacks(void) |
f41d911f PM |
633 | { |
634 | struct task_struct *t = current; | |
635 | ||
636 | if (t->rcu_read_lock_nesting == 0) { | |
284a8c93 | 637 | rcu_preempt_qs(); |
f41d911f PM |
638 | return; |
639 | } | |
10f39bb1 | 640 | if (t->rcu_read_lock_nesting > 0 && |
97c668b8 | 641 | __this_cpu_read(rcu_data_p->core_needs_qs) && |
5b74c458 | 642 | __this_cpu_read(rcu_data_p->cpu_no_qs.b.norm)) |
1d082fd0 | 643 | t->rcu_read_unlock_special.b.need_qs = true; |
f41d911f PM |
644 | } |
645 | ||
a46e0899 PM |
646 | #ifdef CONFIG_RCU_BOOST |
647 | ||
09223371 SL |
648 | static void rcu_preempt_do_callbacks(void) |
649 | { | |
2927a689 | 650 | rcu_do_batch(rcu_state_p, this_cpu_ptr(rcu_data_p)); |
09223371 SL |
651 | } |
652 | ||
a46e0899 PM |
653 | #endif /* #ifdef CONFIG_RCU_BOOST */ |
654 | ||
f41d911f | 655 | /* |
6cc68793 | 656 | * Queue a preemptible-RCU callback for invocation after a grace period. |
f41d911f | 657 | */ |
b6a4ae76 | 658 | void call_rcu(struct rcu_head *head, rcu_callback_t func) |
f41d911f | 659 | { |
e63c887c | 660 | __call_rcu(head, func, rcu_state_p, -1, 0); |
f41d911f PM |
661 | } |
662 | EXPORT_SYMBOL_GPL(call_rcu); | |
663 | ||
6ebb237b PM |
664 | /** |
665 | * synchronize_rcu - wait until a grace period has elapsed. | |
666 | * | |
667 | * Control will return to the caller some time after a full grace | |
668 | * period has elapsed, in other words after all currently executing RCU | |
77d8485a PM |
669 | * read-side critical sections have completed. Note, however, that |
670 | * upon return from synchronize_rcu(), the caller might well be executing | |
671 | * concurrently with new RCU read-side critical sections that began while | |
672 | * synchronize_rcu() was waiting. RCU read-side critical sections are | |
673 | * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. | |
f0a0e6f2 PM |
674 | * |
675 | * See the description of synchronize_sched() for more detailed information | |
676 | * on memory ordering guarantees. | |
6ebb237b PM |
677 | */ |
678 | void synchronize_rcu(void) | |
679 | { | |
f78f5b90 PM |
680 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || |
681 | lock_is_held(&rcu_lock_map) || | |
682 | lock_is_held(&rcu_sched_lock_map), | |
683 | "Illegal synchronize_rcu() in RCU read-side critical section"); | |
6ebb237b PM |
684 | if (!rcu_scheduler_active) |
685 | return; | |
5afff48b | 686 | if (rcu_gp_is_expedited()) |
3705b88d AM |
687 | synchronize_rcu_expedited(); |
688 | else | |
689 | wait_rcu_gp(call_rcu); | |
6ebb237b PM |
690 | } |
691 | EXPORT_SYMBOL_GPL(synchronize_rcu); | |
692 | ||
d9a3da06 | 693 | /* |
8203d6d0 PM |
694 | * Remote handler for smp_call_function_single(). If there is an |
695 | * RCU read-side critical section in effect, request that the | |
696 | * next rcu_read_unlock() record the quiescent state up the | |
697 | * ->expmask fields in the rcu_node tree. Otherwise, immediately | |
698 | * report the quiescent state. | |
d9a3da06 | 699 | */ |
8203d6d0 | 700 | static void sync_rcu_exp_handler(void *info) |
d9a3da06 | 701 | { |
8203d6d0 PM |
702 | struct rcu_data *rdp; |
703 | struct rcu_state *rsp = info; | |
704 | struct task_struct *t = current; | |
8eb74b2b PM |
705 | |
706 | /* | |
8203d6d0 PM |
707 | * Within an RCU read-side critical section, request that the next |
708 | * rcu_read_unlock() report. Unless this RCU read-side critical | |
709 | * section has already blocked, in which case it is already set | |
710 | * up for the expedited grace period to wait on it. | |
8eb74b2b | 711 | */ |
8203d6d0 PM |
712 | if (t->rcu_read_lock_nesting > 0 && |
713 | !t->rcu_read_unlock_special.b.blocked) { | |
714 | t->rcu_read_unlock_special.b.exp_need_qs = true; | |
8eb74b2b | 715 | return; |
12f5f524 | 716 | } |
8eb74b2b | 717 | |
8203d6d0 PM |
718 | /* |
719 | * We are either exiting an RCU read-side critical section (negative | |
720 | * values of t->rcu_read_lock_nesting) or are not in one at all | |
721 | * (zero value of t->rcu_read_lock_nesting). Or we are in an RCU | |
722 | * read-side critical section that blocked before this expedited | |
723 | * grace period started. Either way, we can immediately report | |
724 | * the quiescent state. | |
725 | */ | |
726 | rdp = this_cpu_ptr(rsp->rda); | |
727 | rcu_report_exp_rdp(rsp, rdp, true); | |
d9a3da06 PM |
728 | } |
729 | ||
236fefaf PM |
730 | /** |
731 | * synchronize_rcu_expedited - Brute-force RCU grace period | |
732 | * | |
733 | * Wait for an RCU-preempt grace period, but expedite it. The basic | |
734 | * idea is to invoke synchronize_sched_expedited() to push all the tasks to | |
735 | * the ->blkd_tasks lists and wait for this list to drain. This consumes | |
736 | * significant time on all CPUs and is unfriendly to real-time workloads, | |
737 | * so is thus not recommended for any sort of common-case code. | |
738 | * In fact, if you are using synchronize_rcu_expedited() in a loop, | |
739 | * please restructure your code to batch your updates, and then Use a | |
740 | * single synchronize_rcu() instead. | |
019129d5 PM |
741 | */ |
742 | void synchronize_rcu_expedited(void) | |
743 | { | |
d9a3da06 | 744 | struct rcu_node *rnp; |
29fd9309 | 745 | struct rcu_node *rnp_unlock; |
e63c887c | 746 | struct rcu_state *rsp = rcu_state_p; |
543c6158 | 747 | unsigned long s; |
d9a3da06 | 748 | |
543c6158 | 749 | s = rcu_exp_gp_seq_snap(rsp); |
d9a3da06 | 750 | |
29fd9309 PM |
751 | rnp_unlock = exp_funnel_lock(rsp, s); |
752 | if (rnp_unlock == NULL) | |
753 | return; /* Someone else did our work for us. */ | |
1943c89d | 754 | |
543c6158 | 755 | rcu_exp_gp_seq_start(rsp); |
d9a3da06 | 756 | |
b9585e94 | 757 | /* Initialize the rcu_node tree in preparation for the wait. */ |
dcdb8807 | 758 | sync_rcu_exp_select_cpus(rsp, sync_rcu_exp_handler); |
d9a3da06 | 759 | |
12f5f524 | 760 | /* Wait for snapshotted ->blkd_tasks lists to drain. */ |
d9a3da06 | 761 | rnp = rcu_get_root(rsp); |
b08517c7 | 762 | synchronize_sched_expedited_wait(rsp); |
d9a3da06 PM |
763 | |
764 | /* Clean up and exit. */ | |
543c6158 | 765 | rcu_exp_gp_seq_end(rsp); |
29fd9309 | 766 | mutex_unlock(&rnp_unlock->exp_funnel_mutex); |
019129d5 PM |
767 | } |
768 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
769 | ||
e74f4c45 PM |
770 | /** |
771 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. | |
f0a0e6f2 PM |
772 | * |
773 | * Note that this primitive does not necessarily wait for an RCU grace period | |
774 | * to complete. For example, if there are no RCU callbacks queued anywhere | |
775 | * in the system, then rcu_barrier() is within its rights to return | |
776 | * immediately, without waiting for anything, much less an RCU grace period. | |
e74f4c45 PM |
777 | */ |
778 | void rcu_barrier(void) | |
779 | { | |
e63c887c | 780 | _rcu_barrier(rcu_state_p); |
e74f4c45 PM |
781 | } |
782 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
783 | ||
1eba8f84 | 784 | /* |
6cc68793 | 785 | * Initialize preemptible RCU's state structures. |
1eba8f84 PM |
786 | */ |
787 | static void __init __rcu_init_preempt(void) | |
788 | { | |
2927a689 | 789 | rcu_init_one(rcu_state_p, rcu_data_p); |
1eba8f84 PM |
790 | } |
791 | ||
2439b696 PM |
792 | /* |
793 | * Check for a task exiting while in a preemptible-RCU read-side | |
794 | * critical section, clean up if so. No need to issue warnings, | |
795 | * as debug_check_no_locks_held() already does this if lockdep | |
796 | * is enabled. | |
797 | */ | |
798 | void exit_rcu(void) | |
799 | { | |
800 | struct task_struct *t = current; | |
801 | ||
802 | if (likely(list_empty(¤t->rcu_node_entry))) | |
803 | return; | |
804 | t->rcu_read_lock_nesting = 1; | |
805 | barrier(); | |
1d082fd0 | 806 | t->rcu_read_unlock_special.b.blocked = true; |
2439b696 PM |
807 | __rcu_read_unlock(); |
808 | } | |
809 | ||
28f6569a | 810 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
f41d911f | 811 | |
b28a7c01 | 812 | static struct rcu_state *const rcu_state_p = &rcu_sched_state; |
2927a689 | 813 | static struct rcu_data __percpu *const rcu_data_p = &rcu_sched_data; |
27f4d280 | 814 | |
f41d911f PM |
815 | /* |
816 | * Tell them what RCU they are running. | |
817 | */ | |
0e0fc1c2 | 818 | static void __init rcu_bootup_announce(void) |
f41d911f | 819 | { |
efc151c3 | 820 | pr_info("Hierarchical RCU implementation.\n"); |
26845c28 | 821 | rcu_bootup_announce_oddness(); |
f41d911f PM |
822 | } |
823 | ||
cba6d0d6 PM |
824 | /* |
825 | * Because preemptible RCU does not exist, we never have to check for | |
826 | * CPUs being in quiescent states. | |
827 | */ | |
38200cf2 | 828 | static void rcu_preempt_note_context_switch(void) |
cba6d0d6 PM |
829 | { |
830 | } | |
831 | ||
fc2219d4 | 832 | /* |
6cc68793 | 833 | * Because preemptible RCU does not exist, there are never any preempted |
fc2219d4 PM |
834 | * RCU readers. |
835 | */ | |
27f4d280 | 836 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 PM |
837 | { |
838 | return 0; | |
839 | } | |
840 | ||
8af3a5e7 PM |
841 | /* |
842 | * Because there is no preemptible RCU, there can be no readers blocked. | |
843 | */ | |
844 | static bool rcu_preempt_has_tasks(struct rcu_node *rnp) | |
b668c9cf | 845 | { |
8af3a5e7 | 846 | return false; |
b668c9cf PM |
847 | } |
848 | ||
1ed509a2 | 849 | /* |
6cc68793 | 850 | * Because preemptible RCU does not exist, we never have to check for |
1ed509a2 PM |
851 | * tasks blocked within RCU read-side critical sections. |
852 | */ | |
853 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
854 | { | |
855 | } | |
856 | ||
f41d911f | 857 | /* |
6cc68793 | 858 | * Because preemptible RCU does not exist, we never have to check for |
f41d911f PM |
859 | * tasks blocked within RCU read-side critical sections. |
860 | */ | |
9bc8b558 | 861 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 862 | { |
9bc8b558 | 863 | return 0; |
f41d911f PM |
864 | } |
865 | ||
74611ecb PM |
866 | /* |
867 | * Because preemptible RCU does not exist, we never have to check for | |
868 | * tasks blocked within RCU read-side critical sections that are | |
869 | * blocking the current expedited grace period. | |
870 | */ | |
871 | static int rcu_print_task_exp_stall(struct rcu_node *rnp) | |
872 | { | |
873 | return 0; | |
874 | } | |
875 | ||
b0e165c0 | 876 | /* |
6cc68793 | 877 | * Because there is no preemptible RCU, there can be no readers blocked, |
49e29126 PM |
878 | * so there is no need to check for blocked tasks. So check only for |
879 | * bogus qsmask values. | |
b0e165c0 PM |
880 | */ |
881 | static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) | |
882 | { | |
49e29126 | 883 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
884 | } |
885 | ||
f41d911f | 886 | /* |
6cc68793 | 887 | * Because preemptible RCU does not exist, it never has any callbacks |
f41d911f PM |
888 | * to check. |
889 | */ | |
86aea0e6 | 890 | static void rcu_preempt_check_callbacks(void) |
f41d911f PM |
891 | { |
892 | } | |
893 | ||
019129d5 PM |
894 | /* |
895 | * Wait for an rcu-preempt grace period, but make it happen quickly. | |
6cc68793 | 896 | * But because preemptible RCU does not exist, map to rcu-sched. |
019129d5 PM |
897 | */ |
898 | void synchronize_rcu_expedited(void) | |
899 | { | |
900 | synchronize_sched_expedited(); | |
901 | } | |
902 | EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); | |
903 | ||
e74f4c45 | 904 | /* |
6cc68793 | 905 | * Because preemptible RCU does not exist, rcu_barrier() is just |
e74f4c45 PM |
906 | * another name for rcu_barrier_sched(). |
907 | */ | |
908 | void rcu_barrier(void) | |
909 | { | |
910 | rcu_barrier_sched(); | |
911 | } | |
912 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
913 | ||
1eba8f84 | 914 | /* |
6cc68793 | 915 | * Because preemptible RCU does not exist, it need not be initialized. |
1eba8f84 PM |
916 | */ |
917 | static void __init __rcu_init_preempt(void) | |
918 | { | |
919 | } | |
920 | ||
2439b696 PM |
921 | /* |
922 | * Because preemptible RCU does not exist, tasks cannot possibly exit | |
923 | * while in preemptible RCU read-side critical sections. | |
924 | */ | |
925 | void exit_rcu(void) | |
926 | { | |
927 | } | |
928 | ||
28f6569a | 929 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
8bd93a2c | 930 | |
27f4d280 PM |
931 | #ifdef CONFIG_RCU_BOOST |
932 | ||
1696a8be | 933 | #include "../locking/rtmutex_common.h" |
27f4d280 | 934 | |
0ea1f2eb PM |
935 | #ifdef CONFIG_RCU_TRACE |
936 | ||
937 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
938 | { | |
96e92021 | 939 | if (!rcu_preempt_has_tasks(rnp)) |
0ea1f2eb PM |
940 | rnp->n_balk_blkd_tasks++; |
941 | else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) | |
942 | rnp->n_balk_exp_gp_tasks++; | |
943 | else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) | |
944 | rnp->n_balk_boost_tasks++; | |
945 | else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) | |
946 | rnp->n_balk_notblocked++; | |
947 | else if (rnp->gp_tasks != NULL && | |
a9f4793d | 948 | ULONG_CMP_LT(jiffies, rnp->boost_time)) |
0ea1f2eb PM |
949 | rnp->n_balk_notyet++; |
950 | else | |
951 | rnp->n_balk_nos++; | |
952 | } | |
953 | ||
954 | #else /* #ifdef CONFIG_RCU_TRACE */ | |
955 | ||
956 | static void rcu_initiate_boost_trace(struct rcu_node *rnp) | |
957 | { | |
958 | } | |
959 | ||
960 | #endif /* #else #ifdef CONFIG_RCU_TRACE */ | |
961 | ||
5d01bbd1 TG |
962 | static void rcu_wake_cond(struct task_struct *t, int status) |
963 | { | |
964 | /* | |
965 | * If the thread is yielding, only wake it when this | |
966 | * is invoked from idle | |
967 | */ | |
968 | if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) | |
969 | wake_up_process(t); | |
970 | } | |
971 | ||
27f4d280 PM |
972 | /* |
973 | * Carry out RCU priority boosting on the task indicated by ->exp_tasks | |
974 | * or ->boost_tasks, advancing the pointer to the next task in the | |
975 | * ->blkd_tasks list. | |
976 | * | |
977 | * Note that irqs must be enabled: boosting the task can block. | |
978 | * Returns 1 if there are more tasks needing to be boosted. | |
979 | */ | |
980 | static int rcu_boost(struct rcu_node *rnp) | |
981 | { | |
982 | unsigned long flags; | |
27f4d280 PM |
983 | struct task_struct *t; |
984 | struct list_head *tb; | |
985 | ||
7d0ae808 PM |
986 | if (READ_ONCE(rnp->exp_tasks) == NULL && |
987 | READ_ONCE(rnp->boost_tasks) == NULL) | |
27f4d280 PM |
988 | return 0; /* Nothing left to boost. */ |
989 | ||
2a67e741 | 990 | raw_spin_lock_irqsave_rcu_node(rnp, flags); |
27f4d280 PM |
991 | |
992 | /* | |
993 | * Recheck under the lock: all tasks in need of boosting | |
994 | * might exit their RCU read-side critical sections on their own. | |
995 | */ | |
996 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { | |
997 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
998 | return 0; | |
999 | } | |
1000 | ||
1001 | /* | |
1002 | * Preferentially boost tasks blocking expedited grace periods. | |
1003 | * This cannot starve the normal grace periods because a second | |
1004 | * expedited grace period must boost all blocked tasks, including | |
1005 | * those blocking the pre-existing normal grace period. | |
1006 | */ | |
0ea1f2eb | 1007 | if (rnp->exp_tasks != NULL) { |
27f4d280 | 1008 | tb = rnp->exp_tasks; |
0ea1f2eb PM |
1009 | rnp->n_exp_boosts++; |
1010 | } else { | |
27f4d280 | 1011 | tb = rnp->boost_tasks; |
0ea1f2eb PM |
1012 | rnp->n_normal_boosts++; |
1013 | } | |
1014 | rnp->n_tasks_boosted++; | |
27f4d280 PM |
1015 | |
1016 | /* | |
1017 | * We boost task t by manufacturing an rt_mutex that appears to | |
1018 | * be held by task t. We leave a pointer to that rt_mutex where | |
1019 | * task t can find it, and task t will release the mutex when it | |
1020 | * exits its outermost RCU read-side critical section. Then | |
1021 | * simply acquiring this artificial rt_mutex will boost task | |
1022 | * t's priority. (Thanks to tglx for suggesting this approach!) | |
1023 | * | |
1024 | * Note that task t must acquire rnp->lock to remove itself from | |
1025 | * the ->blkd_tasks list, which it will do from exit() if from | |
1026 | * nowhere else. We therefore are guaranteed that task t will | |
1027 | * stay around at least until we drop rnp->lock. Note that | |
1028 | * rnp->lock also resolves races between our priority boosting | |
1029 | * and task t's exiting its outermost RCU read-side critical | |
1030 | * section. | |
1031 | */ | |
1032 | t = container_of(tb, struct task_struct, rcu_node_entry); | |
abaa93d9 | 1033 | rt_mutex_init_proxy_locked(&rnp->boost_mtx, t); |
27f4d280 | 1034 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
abaa93d9 PM |
1035 | /* Lock only for side effect: boosts task t's priority. */ |
1036 | rt_mutex_lock(&rnp->boost_mtx); | |
1037 | rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */ | |
27f4d280 | 1038 | |
7d0ae808 PM |
1039 | return READ_ONCE(rnp->exp_tasks) != NULL || |
1040 | READ_ONCE(rnp->boost_tasks) != NULL; | |
27f4d280 PM |
1041 | } |
1042 | ||
27f4d280 | 1043 | /* |
bc17ea10 | 1044 | * Priority-boosting kthread, one per leaf rcu_node. |
27f4d280 PM |
1045 | */ |
1046 | static int rcu_boost_kthread(void *arg) | |
1047 | { | |
1048 | struct rcu_node *rnp = (struct rcu_node *)arg; | |
1049 | int spincnt = 0; | |
1050 | int more2boost; | |
1051 | ||
f7f7bac9 | 1052 | trace_rcu_utilization(TPS("Start boost kthread@init")); |
27f4d280 | 1053 | for (;;) { |
d71df90e | 1054 | rnp->boost_kthread_status = RCU_KTHREAD_WAITING; |
f7f7bac9 | 1055 | trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); |
08bca60a | 1056 | rcu_wait(rnp->boost_tasks || rnp->exp_tasks); |
f7f7bac9 | 1057 | trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); |
d71df90e | 1058 | rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; |
27f4d280 PM |
1059 | more2boost = rcu_boost(rnp); |
1060 | if (more2boost) | |
1061 | spincnt++; | |
1062 | else | |
1063 | spincnt = 0; | |
1064 | if (spincnt > 10) { | |
5d01bbd1 | 1065 | rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; |
f7f7bac9 | 1066 | trace_rcu_utilization(TPS("End boost kthread@rcu_yield")); |
5d01bbd1 | 1067 | schedule_timeout_interruptible(2); |
f7f7bac9 | 1068 | trace_rcu_utilization(TPS("Start boost kthread@rcu_yield")); |
27f4d280 PM |
1069 | spincnt = 0; |
1070 | } | |
1071 | } | |
1217ed1b | 1072 | /* NOTREACHED */ |
f7f7bac9 | 1073 | trace_rcu_utilization(TPS("End boost kthread@notreached")); |
27f4d280 PM |
1074 | return 0; |
1075 | } | |
1076 | ||
1077 | /* | |
1078 | * Check to see if it is time to start boosting RCU readers that are | |
1079 | * blocking the current grace period, and, if so, tell the per-rcu_node | |
1080 | * kthread to start boosting them. If there is an expedited grace | |
1081 | * period in progress, it is always time to boost. | |
1082 | * | |
b065a853 PM |
1083 | * The caller must hold rnp->lock, which this function releases. |
1084 | * The ->boost_kthread_task is immortal, so we don't need to worry | |
1085 | * about it going away. | |
27f4d280 | 1086 | */ |
1217ed1b | 1087 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
615e41c6 | 1088 | __releases(rnp->lock) |
27f4d280 PM |
1089 | { |
1090 | struct task_struct *t; | |
1091 | ||
0ea1f2eb PM |
1092 | if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { |
1093 | rnp->n_balk_exp_gp_tasks++; | |
1217ed1b | 1094 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1095 | return; |
0ea1f2eb | 1096 | } |
27f4d280 PM |
1097 | if (rnp->exp_tasks != NULL || |
1098 | (rnp->gp_tasks != NULL && | |
1099 | rnp->boost_tasks == NULL && | |
1100 | rnp->qsmask == 0 && | |
1101 | ULONG_CMP_GE(jiffies, rnp->boost_time))) { | |
1102 | if (rnp->exp_tasks == NULL) | |
1103 | rnp->boost_tasks = rnp->gp_tasks; | |
1217ed1b | 1104 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 | 1105 | t = rnp->boost_kthread_task; |
5d01bbd1 TG |
1106 | if (t) |
1107 | rcu_wake_cond(t, rnp->boost_kthread_status); | |
1217ed1b | 1108 | } else { |
0ea1f2eb | 1109 | rcu_initiate_boost_trace(rnp); |
1217ed1b PM |
1110 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
1111 | } | |
27f4d280 PM |
1112 | } |
1113 | ||
a46e0899 PM |
1114 | /* |
1115 | * Wake up the per-CPU kthread to invoke RCU callbacks. | |
1116 | */ | |
1117 | static void invoke_rcu_callbacks_kthread(void) | |
1118 | { | |
1119 | unsigned long flags; | |
1120 | ||
1121 | local_irq_save(flags); | |
1122 | __this_cpu_write(rcu_cpu_has_work, 1); | |
1eb52121 | 1123 | if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && |
5d01bbd1 TG |
1124 | current != __this_cpu_read(rcu_cpu_kthread_task)) { |
1125 | rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), | |
1126 | __this_cpu_read(rcu_cpu_kthread_status)); | |
1127 | } | |
a46e0899 PM |
1128 | local_irq_restore(flags); |
1129 | } | |
1130 | ||
dff1672d PM |
1131 | /* |
1132 | * Is the current CPU running the RCU-callbacks kthread? | |
1133 | * Caller must have preemption disabled. | |
1134 | */ | |
1135 | static bool rcu_is_callbacks_kthread(void) | |
1136 | { | |
c9d4b0af | 1137 | return __this_cpu_read(rcu_cpu_kthread_task) == current; |
dff1672d PM |
1138 | } |
1139 | ||
27f4d280 PM |
1140 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) |
1141 | ||
1142 | /* | |
1143 | * Do priority-boost accounting for the start of a new grace period. | |
1144 | */ | |
1145 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) | |
1146 | { | |
1147 | rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; | |
1148 | } | |
1149 | ||
27f4d280 PM |
1150 | /* |
1151 | * Create an RCU-boost kthread for the specified node if one does not | |
1152 | * already exist. We only create this kthread for preemptible RCU. | |
1153 | * Returns zero if all is well, a negated errno otherwise. | |
1154 | */ | |
49fb4c62 | 1155 | static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, |
0aa04b05 | 1156 | struct rcu_node *rnp) |
27f4d280 | 1157 | { |
5d01bbd1 | 1158 | int rnp_index = rnp - &rsp->node[0]; |
27f4d280 PM |
1159 | unsigned long flags; |
1160 | struct sched_param sp; | |
1161 | struct task_struct *t; | |
1162 | ||
e63c887c | 1163 | if (rcu_state_p != rsp) |
27f4d280 | 1164 | return 0; |
5d01bbd1 | 1165 | |
0aa04b05 | 1166 | if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0) |
5d01bbd1 TG |
1167 | return 0; |
1168 | ||
a46e0899 | 1169 | rsp->boost = 1; |
27f4d280 PM |
1170 | if (rnp->boost_kthread_task != NULL) |
1171 | return 0; | |
1172 | t = kthread_create(rcu_boost_kthread, (void *)rnp, | |
5b61b0ba | 1173 | "rcub/%d", rnp_index); |
27f4d280 PM |
1174 | if (IS_ERR(t)) |
1175 | return PTR_ERR(t); | |
2a67e741 | 1176 | raw_spin_lock_irqsave_rcu_node(rnp, flags); |
27f4d280 PM |
1177 | rnp->boost_kthread_task = t; |
1178 | raw_spin_unlock_irqrestore(&rnp->lock, flags); | |
21871d7e | 1179 | sp.sched_priority = kthread_prio; |
27f4d280 | 1180 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
9a432736 | 1181 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ |
27f4d280 PM |
1182 | return 0; |
1183 | } | |
1184 | ||
f8b7fc6b PM |
1185 | static void rcu_kthread_do_work(void) |
1186 | { | |
c9d4b0af CL |
1187 | rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data)); |
1188 | rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data)); | |
f8b7fc6b PM |
1189 | rcu_preempt_do_callbacks(); |
1190 | } | |
1191 | ||
62ab7072 | 1192 | static void rcu_cpu_kthread_setup(unsigned int cpu) |
f8b7fc6b | 1193 | { |
f8b7fc6b | 1194 | struct sched_param sp; |
f8b7fc6b | 1195 | |
21871d7e | 1196 | sp.sched_priority = kthread_prio; |
62ab7072 | 1197 | sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); |
f8b7fc6b PM |
1198 | } |
1199 | ||
62ab7072 | 1200 | static void rcu_cpu_kthread_park(unsigned int cpu) |
f8b7fc6b | 1201 | { |
62ab7072 | 1202 | per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; |
f8b7fc6b PM |
1203 | } |
1204 | ||
62ab7072 | 1205 | static int rcu_cpu_kthread_should_run(unsigned int cpu) |
f8b7fc6b | 1206 | { |
c9d4b0af | 1207 | return __this_cpu_read(rcu_cpu_has_work); |
f8b7fc6b PM |
1208 | } |
1209 | ||
1210 | /* | |
1211 | * Per-CPU kernel thread that invokes RCU callbacks. This replaces the | |
e0f23060 PM |
1212 | * RCU softirq used in flavors and configurations of RCU that do not |
1213 | * support RCU priority boosting. | |
f8b7fc6b | 1214 | */ |
62ab7072 | 1215 | static void rcu_cpu_kthread(unsigned int cpu) |
f8b7fc6b | 1216 | { |
c9d4b0af CL |
1217 | unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status); |
1218 | char work, *workp = this_cpu_ptr(&rcu_cpu_has_work); | |
62ab7072 | 1219 | int spincnt; |
f8b7fc6b | 1220 | |
62ab7072 | 1221 | for (spincnt = 0; spincnt < 10; spincnt++) { |
f7f7bac9 | 1222 | trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); |
f8b7fc6b | 1223 | local_bh_disable(); |
f8b7fc6b | 1224 | *statusp = RCU_KTHREAD_RUNNING; |
62ab7072 PM |
1225 | this_cpu_inc(rcu_cpu_kthread_loops); |
1226 | local_irq_disable(); | |
f8b7fc6b PM |
1227 | work = *workp; |
1228 | *workp = 0; | |
62ab7072 | 1229 | local_irq_enable(); |
f8b7fc6b PM |
1230 | if (work) |
1231 | rcu_kthread_do_work(); | |
1232 | local_bh_enable(); | |
62ab7072 | 1233 | if (*workp == 0) { |
f7f7bac9 | 1234 | trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); |
62ab7072 PM |
1235 | *statusp = RCU_KTHREAD_WAITING; |
1236 | return; | |
f8b7fc6b PM |
1237 | } |
1238 | } | |
62ab7072 | 1239 | *statusp = RCU_KTHREAD_YIELDING; |
f7f7bac9 | 1240 | trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); |
62ab7072 | 1241 | schedule_timeout_interruptible(2); |
f7f7bac9 | 1242 | trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); |
62ab7072 | 1243 | *statusp = RCU_KTHREAD_WAITING; |
f8b7fc6b PM |
1244 | } |
1245 | ||
1246 | /* | |
1247 | * Set the per-rcu_node kthread's affinity to cover all CPUs that are | |
1248 | * served by the rcu_node in question. The CPU hotplug lock is still | |
1249 | * held, so the value of rnp->qsmaskinit will be stable. | |
1250 | * | |
1251 | * We don't include outgoingcpu in the affinity set, use -1 if there is | |
1252 | * no outgoing CPU. If there are no CPUs left in the affinity set, | |
1253 | * this function allows the kthread to execute on any CPU. | |
1254 | */ | |
5d01bbd1 | 1255 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b | 1256 | { |
5d01bbd1 | 1257 | struct task_struct *t = rnp->boost_kthread_task; |
0aa04b05 | 1258 | unsigned long mask = rcu_rnp_online_cpus(rnp); |
f8b7fc6b PM |
1259 | cpumask_var_t cm; |
1260 | int cpu; | |
f8b7fc6b | 1261 | |
5d01bbd1 | 1262 | if (!t) |
f8b7fc6b | 1263 | return; |
5d01bbd1 | 1264 | if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) |
f8b7fc6b | 1265 | return; |
f8b7fc6b PM |
1266 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) |
1267 | if ((mask & 0x1) && cpu != outgoingcpu) | |
1268 | cpumask_set_cpu(cpu, cm); | |
5d0b0249 | 1269 | if (cpumask_weight(cm) == 0) |
f8b7fc6b | 1270 | cpumask_setall(cm); |
5d01bbd1 | 1271 | set_cpus_allowed_ptr(t, cm); |
f8b7fc6b PM |
1272 | free_cpumask_var(cm); |
1273 | } | |
1274 | ||
62ab7072 PM |
1275 | static struct smp_hotplug_thread rcu_cpu_thread_spec = { |
1276 | .store = &rcu_cpu_kthread_task, | |
1277 | .thread_should_run = rcu_cpu_kthread_should_run, | |
1278 | .thread_fn = rcu_cpu_kthread, | |
1279 | .thread_comm = "rcuc/%u", | |
1280 | .setup = rcu_cpu_kthread_setup, | |
1281 | .park = rcu_cpu_kthread_park, | |
1282 | }; | |
f8b7fc6b PM |
1283 | |
1284 | /* | |
9386c0b7 | 1285 | * Spawn boost kthreads -- called as soon as the scheduler is running. |
f8b7fc6b | 1286 | */ |
9386c0b7 | 1287 | static void __init rcu_spawn_boost_kthreads(void) |
f8b7fc6b | 1288 | { |
f8b7fc6b | 1289 | struct rcu_node *rnp; |
5d01bbd1 | 1290 | int cpu; |
f8b7fc6b | 1291 | |
62ab7072 | 1292 | for_each_possible_cpu(cpu) |
f8b7fc6b | 1293 | per_cpu(rcu_cpu_has_work, cpu) = 0; |
62ab7072 | 1294 | BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); |
3e9f5c70 PM |
1295 | rcu_for_each_leaf_node(rcu_state_p, rnp) |
1296 | (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); | |
f8b7fc6b | 1297 | } |
f8b7fc6b | 1298 | |
49fb4c62 | 1299 | static void rcu_prepare_kthreads(int cpu) |
f8b7fc6b | 1300 | { |
e534165b | 1301 | struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu); |
f8b7fc6b PM |
1302 | struct rcu_node *rnp = rdp->mynode; |
1303 | ||
1304 | /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ | |
62ab7072 | 1305 | if (rcu_scheduler_fully_active) |
e534165b | 1306 | (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); |
f8b7fc6b PM |
1307 | } |
1308 | ||
27f4d280 PM |
1309 | #else /* #ifdef CONFIG_RCU_BOOST */ |
1310 | ||
1217ed1b | 1311 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
615e41c6 | 1312 | __releases(rnp->lock) |
27f4d280 | 1313 | { |
1217ed1b | 1314 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
27f4d280 PM |
1315 | } |
1316 | ||
a46e0899 | 1317 | static void invoke_rcu_callbacks_kthread(void) |
27f4d280 | 1318 | { |
a46e0899 | 1319 | WARN_ON_ONCE(1); |
27f4d280 PM |
1320 | } |
1321 | ||
dff1672d PM |
1322 | static bool rcu_is_callbacks_kthread(void) |
1323 | { | |
1324 | return false; | |
1325 | } | |
1326 | ||
27f4d280 PM |
1327 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
1328 | { | |
1329 | } | |
1330 | ||
5d01bbd1 | 1331 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b PM |
1332 | { |
1333 | } | |
1334 | ||
9386c0b7 | 1335 | static void __init rcu_spawn_boost_kthreads(void) |
b0d30417 | 1336 | { |
b0d30417 | 1337 | } |
b0d30417 | 1338 | |
49fb4c62 | 1339 | static void rcu_prepare_kthreads(int cpu) |
f8b7fc6b PM |
1340 | { |
1341 | } | |
1342 | ||
27f4d280 PM |
1343 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
1344 | ||
8bd93a2c PM |
1345 | #if !defined(CONFIG_RCU_FAST_NO_HZ) |
1346 | ||
1347 | /* | |
1348 | * Check to see if any future RCU-related work will need to be done | |
1349 | * by the current CPU, even if none need be done immediately, returning | |
1350 | * 1 if so. This function is part of the RCU implementation; it is -not- | |
1351 | * an exported member of the RCU API. | |
1352 | * | |
7cb92499 PM |
1353 | * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs |
1354 | * any flavor of RCU. | |
8bd93a2c | 1355 | */ |
c1ad348b | 1356 | int rcu_needs_cpu(u64 basemono, u64 *nextevt) |
8bd93a2c | 1357 | { |
c1ad348b | 1358 | *nextevt = KTIME_MAX; |
3382adbc PM |
1359 | return IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) |
1360 | ? 0 : rcu_cpu_has_callbacks(NULL); | |
7cb92499 PM |
1361 | } |
1362 | ||
1363 | /* | |
1364 | * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up | |
1365 | * after it. | |
1366 | */ | |
8fa7845d | 1367 | static void rcu_cleanup_after_idle(void) |
7cb92499 PM |
1368 | { |
1369 | } | |
1370 | ||
aea1b35e | 1371 | /* |
a858af28 | 1372 | * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, |
aea1b35e PM |
1373 | * is nothing. |
1374 | */ | |
198bbf81 | 1375 | static void rcu_prepare_for_idle(void) |
aea1b35e PM |
1376 | { |
1377 | } | |
1378 | ||
c57afe80 PM |
1379 | /* |
1380 | * Don't bother keeping a running count of the number of RCU callbacks | |
1381 | * posted because CONFIG_RCU_FAST_NO_HZ=n. | |
1382 | */ | |
1383 | static void rcu_idle_count_callbacks_posted(void) | |
1384 | { | |
1385 | } | |
1386 | ||
8bd93a2c PM |
1387 | #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1388 | ||
f23f7fa1 PM |
1389 | /* |
1390 | * This code is invoked when a CPU goes idle, at which point we want | |
1391 | * to have the CPU do everything required for RCU so that it can enter | |
1392 | * the energy-efficient dyntick-idle mode. This is handled by a | |
1393 | * state machine implemented by rcu_prepare_for_idle() below. | |
1394 | * | |
1395 | * The following three proprocessor symbols control this state machine: | |
1396 | * | |
f23f7fa1 PM |
1397 | * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted |
1398 | * to sleep in dyntick-idle mode with RCU callbacks pending. This | |
1399 | * is sized to be roughly one RCU grace period. Those energy-efficiency | |
1400 | * benchmarkers who might otherwise be tempted to set this to a large | |
1401 | * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your | |
1402 | * system. And if you are -that- concerned about energy efficiency, | |
1403 | * just power the system down and be done with it! | |
778d250a PM |
1404 | * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is |
1405 | * permitted to sleep in dyntick-idle mode with only lazy RCU | |
1406 | * callbacks pending. Setting this too high can OOM your system. | |
f23f7fa1 PM |
1407 | * |
1408 | * The values below work well in practice. If future workloads require | |
1409 | * adjustment, they can be converted into kernel config parameters, though | |
1410 | * making the state machine smarter might be a better option. | |
1411 | */ | |
e84c48ae | 1412 | #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ |
778d250a | 1413 | #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ |
f23f7fa1 | 1414 | |
5e44ce35 PM |
1415 | static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; |
1416 | module_param(rcu_idle_gp_delay, int, 0644); | |
1417 | static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; | |
1418 | module_param(rcu_idle_lazy_gp_delay, int, 0644); | |
486e2593 | 1419 | |
486e2593 | 1420 | /* |
c229828c PM |
1421 | * Try to advance callbacks for all flavors of RCU on the current CPU, but |
1422 | * only if it has been awhile since the last time we did so. Afterwards, | |
1423 | * if there are any callbacks ready for immediate invocation, return true. | |
486e2593 | 1424 | */ |
f1f399d1 | 1425 | static bool __maybe_unused rcu_try_advance_all_cbs(void) |
486e2593 | 1426 | { |
c0f4dfd4 PM |
1427 | bool cbs_ready = false; |
1428 | struct rcu_data *rdp; | |
c229828c | 1429 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
c0f4dfd4 PM |
1430 | struct rcu_node *rnp; |
1431 | struct rcu_state *rsp; | |
486e2593 | 1432 | |
c229828c PM |
1433 | /* Exit early if we advanced recently. */ |
1434 | if (jiffies == rdtp->last_advance_all) | |
d0bc90fd | 1435 | return false; |
c229828c PM |
1436 | rdtp->last_advance_all = jiffies; |
1437 | ||
c0f4dfd4 PM |
1438 | for_each_rcu_flavor(rsp) { |
1439 | rdp = this_cpu_ptr(rsp->rda); | |
1440 | rnp = rdp->mynode; | |
486e2593 | 1441 | |
c0f4dfd4 PM |
1442 | /* |
1443 | * Don't bother checking unless a grace period has | |
1444 | * completed since we last checked and there are | |
1445 | * callbacks not yet ready to invoke. | |
1446 | */ | |
e3663b10 | 1447 | if ((rdp->completed != rnp->completed || |
7d0ae808 | 1448 | unlikely(READ_ONCE(rdp->gpwrap))) && |
c0f4dfd4 | 1449 | rdp->nxttail[RCU_DONE_TAIL] != rdp->nxttail[RCU_NEXT_TAIL]) |
470716fc | 1450 | note_gp_changes(rsp, rdp); |
486e2593 | 1451 | |
c0f4dfd4 PM |
1452 | if (cpu_has_callbacks_ready_to_invoke(rdp)) |
1453 | cbs_ready = true; | |
1454 | } | |
1455 | return cbs_ready; | |
486e2593 PM |
1456 | } |
1457 | ||
aa9b1630 | 1458 | /* |
c0f4dfd4 PM |
1459 | * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready |
1460 | * to invoke. If the CPU has callbacks, try to advance them. Tell the | |
1461 | * caller to set the timeout based on whether or not there are non-lazy | |
1462 | * callbacks. | |
aa9b1630 | 1463 | * |
c0f4dfd4 | 1464 | * The caller must have disabled interrupts. |
aa9b1630 | 1465 | */ |
c1ad348b | 1466 | int rcu_needs_cpu(u64 basemono, u64 *nextevt) |
aa9b1630 | 1467 | { |
aa6da514 | 1468 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
c1ad348b | 1469 | unsigned long dj; |
aa9b1630 | 1470 | |
3382adbc | 1471 | if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL)) { |
43224b96 | 1472 | *nextevt = KTIME_MAX; |
3382adbc PM |
1473 | return 0; |
1474 | } | |
1475 | ||
c0f4dfd4 PM |
1476 | /* Snapshot to detect later posting of non-lazy callback. */ |
1477 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; | |
1478 | ||
aa9b1630 | 1479 | /* If no callbacks, RCU doesn't need the CPU. */ |
aa6da514 | 1480 | if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) { |
c1ad348b | 1481 | *nextevt = KTIME_MAX; |
aa9b1630 PM |
1482 | return 0; |
1483 | } | |
c0f4dfd4 PM |
1484 | |
1485 | /* Attempt to advance callbacks. */ | |
1486 | if (rcu_try_advance_all_cbs()) { | |
1487 | /* Some ready to invoke, so initiate later invocation. */ | |
1488 | invoke_rcu_core(); | |
aa9b1630 PM |
1489 | return 1; |
1490 | } | |
c0f4dfd4 PM |
1491 | rdtp->last_accelerate = jiffies; |
1492 | ||
1493 | /* Request timer delay depending on laziness, and round. */ | |
6faf7283 | 1494 | if (!rdtp->all_lazy) { |
c1ad348b | 1495 | dj = round_up(rcu_idle_gp_delay + jiffies, |
c0f4dfd4 | 1496 | rcu_idle_gp_delay) - jiffies; |
e84c48ae | 1497 | } else { |
c1ad348b | 1498 | dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; |
e84c48ae | 1499 | } |
c1ad348b | 1500 | *nextevt = basemono + dj * TICK_NSEC; |
aa9b1630 PM |
1501 | return 0; |
1502 | } | |
1503 | ||
21e52e15 | 1504 | /* |
c0f4dfd4 PM |
1505 | * Prepare a CPU for idle from an RCU perspective. The first major task |
1506 | * is to sense whether nohz mode has been enabled or disabled via sysfs. | |
1507 | * The second major task is to check to see if a non-lazy callback has | |
1508 | * arrived at a CPU that previously had only lazy callbacks. The third | |
1509 | * major task is to accelerate (that is, assign grace-period numbers to) | |
1510 | * any recently arrived callbacks. | |
aea1b35e PM |
1511 | * |
1512 | * The caller must have disabled interrupts. | |
8bd93a2c | 1513 | */ |
198bbf81 | 1514 | static void rcu_prepare_for_idle(void) |
8bd93a2c | 1515 | { |
48a7639c | 1516 | bool needwake; |
c0f4dfd4 | 1517 | struct rcu_data *rdp; |
198bbf81 | 1518 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
c0f4dfd4 PM |
1519 | struct rcu_node *rnp; |
1520 | struct rcu_state *rsp; | |
9d2ad243 PM |
1521 | int tne; |
1522 | ||
3382adbc PM |
1523 | if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL)) |
1524 | return; | |
1525 | ||
9d2ad243 | 1526 | /* Handle nohz enablement switches conservatively. */ |
7d0ae808 | 1527 | tne = READ_ONCE(tick_nohz_active); |
9d2ad243 | 1528 | if (tne != rdtp->tick_nohz_enabled_snap) { |
aa6da514 | 1529 | if (rcu_cpu_has_callbacks(NULL)) |
9d2ad243 PM |
1530 | invoke_rcu_core(); /* force nohz to see update. */ |
1531 | rdtp->tick_nohz_enabled_snap = tne; | |
1532 | return; | |
1533 | } | |
1534 | if (!tne) | |
1535 | return; | |
f511fc62 | 1536 | |
c0f4dfd4 | 1537 | /* If this is a no-CBs CPU, no callbacks, just return. */ |
198bbf81 | 1538 | if (rcu_is_nocb_cpu(smp_processor_id())) |
9a0c6fef | 1539 | return; |
9a0c6fef | 1540 | |
c57afe80 | 1541 | /* |
c0f4dfd4 PM |
1542 | * If a non-lazy callback arrived at a CPU having only lazy |
1543 | * callbacks, invoke RCU core for the side-effect of recalculating | |
1544 | * idle duration on re-entry to idle. | |
c57afe80 | 1545 | */ |
c0f4dfd4 PM |
1546 | if (rdtp->all_lazy && |
1547 | rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) { | |
c337f8f5 PM |
1548 | rdtp->all_lazy = false; |
1549 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; | |
c0f4dfd4 | 1550 | invoke_rcu_core(); |
c57afe80 PM |
1551 | return; |
1552 | } | |
c57afe80 | 1553 | |
3084f2f8 | 1554 | /* |
c0f4dfd4 PM |
1555 | * If we have not yet accelerated this jiffy, accelerate all |
1556 | * callbacks on this CPU. | |
3084f2f8 | 1557 | */ |
c0f4dfd4 | 1558 | if (rdtp->last_accelerate == jiffies) |
aea1b35e | 1559 | return; |
c0f4dfd4 PM |
1560 | rdtp->last_accelerate = jiffies; |
1561 | for_each_rcu_flavor(rsp) { | |
198bbf81 | 1562 | rdp = this_cpu_ptr(rsp->rda); |
c0f4dfd4 PM |
1563 | if (!*rdp->nxttail[RCU_DONE_TAIL]) |
1564 | continue; | |
1565 | rnp = rdp->mynode; | |
2a67e741 | 1566 | raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ |
48a7639c | 1567 | needwake = rcu_accelerate_cbs(rsp, rnp, rdp); |
c0f4dfd4 | 1568 | raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ |
48a7639c PM |
1569 | if (needwake) |
1570 | rcu_gp_kthread_wake(rsp); | |
77e38ed3 | 1571 | } |
c0f4dfd4 | 1572 | } |
3084f2f8 | 1573 | |
c0f4dfd4 PM |
1574 | /* |
1575 | * Clean up for exit from idle. Attempt to advance callbacks based on | |
1576 | * any grace periods that elapsed while the CPU was idle, and if any | |
1577 | * callbacks are now ready to invoke, initiate invocation. | |
1578 | */ | |
8fa7845d | 1579 | static void rcu_cleanup_after_idle(void) |
c0f4dfd4 | 1580 | { |
3382adbc PM |
1581 | if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_ALL) || |
1582 | rcu_is_nocb_cpu(smp_processor_id())) | |
aea1b35e | 1583 | return; |
7a497c96 PM |
1584 | if (rcu_try_advance_all_cbs()) |
1585 | invoke_rcu_core(); | |
8bd93a2c PM |
1586 | } |
1587 | ||
c57afe80 | 1588 | /* |
98248a0e PM |
1589 | * Keep a running count of the number of non-lazy callbacks posted |
1590 | * on this CPU. This running counter (which is never decremented) allows | |
1591 | * rcu_prepare_for_idle() to detect when something out of the idle loop | |
1592 | * posts a callback, even if an equal number of callbacks are invoked. | |
1593 | * Of course, callbacks should only be posted from within a trace event | |
1594 | * designed to be called from idle or from within RCU_NONIDLE(). | |
c57afe80 PM |
1595 | */ |
1596 | static void rcu_idle_count_callbacks_posted(void) | |
1597 | { | |
5955f7ee | 1598 | __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); |
c57afe80 PM |
1599 | } |
1600 | ||
b626c1b6 PM |
1601 | /* |
1602 | * Data for flushing lazy RCU callbacks at OOM time. | |
1603 | */ | |
1604 | static atomic_t oom_callback_count; | |
1605 | static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); | |
1606 | ||
1607 | /* | |
1608 | * RCU OOM callback -- decrement the outstanding count and deliver the | |
1609 | * wake-up if we are the last one. | |
1610 | */ | |
1611 | static void rcu_oom_callback(struct rcu_head *rhp) | |
1612 | { | |
1613 | if (atomic_dec_and_test(&oom_callback_count)) | |
1614 | wake_up(&oom_callback_wq); | |
1615 | } | |
1616 | ||
1617 | /* | |
1618 | * Post an rcu_oom_notify callback on the current CPU if it has at | |
1619 | * least one lazy callback. This will unnecessarily post callbacks | |
1620 | * to CPUs that already have a non-lazy callback at the end of their | |
1621 | * callback list, but this is an infrequent operation, so accept some | |
1622 | * extra overhead to keep things simple. | |
1623 | */ | |
1624 | static void rcu_oom_notify_cpu(void *unused) | |
1625 | { | |
1626 | struct rcu_state *rsp; | |
1627 | struct rcu_data *rdp; | |
1628 | ||
1629 | for_each_rcu_flavor(rsp) { | |
fa07a58f | 1630 | rdp = raw_cpu_ptr(rsp->rda); |
b626c1b6 PM |
1631 | if (rdp->qlen_lazy != 0) { |
1632 | atomic_inc(&oom_callback_count); | |
1633 | rsp->call(&rdp->oom_head, rcu_oom_callback); | |
1634 | } | |
1635 | } | |
1636 | } | |
1637 | ||
1638 | /* | |
1639 | * If low on memory, ensure that each CPU has a non-lazy callback. | |
1640 | * This will wake up CPUs that have only lazy callbacks, in turn | |
1641 | * ensuring that they free up the corresponding memory in a timely manner. | |
1642 | * Because an uncertain amount of memory will be freed in some uncertain | |
1643 | * timeframe, we do not claim to have freed anything. | |
1644 | */ | |
1645 | static int rcu_oom_notify(struct notifier_block *self, | |
1646 | unsigned long notused, void *nfreed) | |
1647 | { | |
1648 | int cpu; | |
1649 | ||
1650 | /* Wait for callbacks from earlier instance to complete. */ | |
1651 | wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); | |
78e4bc34 | 1652 | smp_mb(); /* Ensure callback reuse happens after callback invocation. */ |
b626c1b6 PM |
1653 | |
1654 | /* | |
1655 | * Prevent premature wakeup: ensure that all increments happen | |
1656 | * before there is a chance of the counter reaching zero. | |
1657 | */ | |
1658 | atomic_set(&oom_callback_count, 1); | |
1659 | ||
b626c1b6 PM |
1660 | for_each_online_cpu(cpu) { |
1661 | smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); | |
bde6c3aa | 1662 | cond_resched_rcu_qs(); |
b626c1b6 | 1663 | } |
b626c1b6 PM |
1664 | |
1665 | /* Unconditionally decrement: no need to wake ourselves up. */ | |
1666 | atomic_dec(&oom_callback_count); | |
1667 | ||
1668 | return NOTIFY_OK; | |
1669 | } | |
1670 | ||
1671 | static struct notifier_block rcu_oom_nb = { | |
1672 | .notifier_call = rcu_oom_notify | |
1673 | }; | |
1674 | ||
1675 | static int __init rcu_register_oom_notifier(void) | |
1676 | { | |
1677 | register_oom_notifier(&rcu_oom_nb); | |
1678 | return 0; | |
1679 | } | |
1680 | early_initcall(rcu_register_oom_notifier); | |
1681 | ||
8bd93a2c | 1682 | #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
a858af28 | 1683 | |
a858af28 PM |
1684 | #ifdef CONFIG_RCU_FAST_NO_HZ |
1685 | ||
1686 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
1687 | { | |
5955f7ee | 1688 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
c0f4dfd4 | 1689 | unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap; |
a858af28 | 1690 | |
c0f4dfd4 PM |
1691 | sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", |
1692 | rdtp->last_accelerate & 0xffff, jiffies & 0xffff, | |
1693 | ulong2long(nlpd), | |
1694 | rdtp->all_lazy ? 'L' : '.', | |
1695 | rdtp->tick_nohz_enabled_snap ? '.' : 'D'); | |
a858af28 PM |
1696 | } |
1697 | ||
1698 | #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
1699 | ||
1700 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
1701 | { | |
1c17e4d4 | 1702 | *cp = '\0'; |
a858af28 PM |
1703 | } |
1704 | ||
1705 | #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
1706 | ||
1707 | /* Initiate the stall-info list. */ | |
1708 | static void print_cpu_stall_info_begin(void) | |
1709 | { | |
efc151c3 | 1710 | pr_cont("\n"); |
a858af28 PM |
1711 | } |
1712 | ||
1713 | /* | |
1714 | * Print out diagnostic information for the specified stalled CPU. | |
1715 | * | |
1716 | * If the specified CPU is aware of the current RCU grace period | |
1717 | * (flavor specified by rsp), then print the number of scheduling | |
1718 | * clock interrupts the CPU has taken during the time that it has | |
1719 | * been aware. Otherwise, print the number of RCU grace periods | |
1720 | * that this CPU is ignorant of, for example, "1" if the CPU was | |
1721 | * aware of the previous grace period. | |
1722 | * | |
1723 | * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. | |
1724 | */ | |
1725 | static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) | |
1726 | { | |
1727 | char fast_no_hz[72]; | |
1728 | struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); | |
1729 | struct rcu_dynticks *rdtp = rdp->dynticks; | |
1730 | char *ticks_title; | |
1731 | unsigned long ticks_value; | |
1732 | ||
1733 | if (rsp->gpnum == rdp->gpnum) { | |
1734 | ticks_title = "ticks this GP"; | |
1735 | ticks_value = rdp->ticks_this_gp; | |
1736 | } else { | |
1737 | ticks_title = "GPs behind"; | |
1738 | ticks_value = rsp->gpnum - rdp->gpnum; | |
1739 | } | |
1740 | print_cpu_stall_fast_no_hz(fast_no_hz, cpu); | |
7f21aeef PM |
1741 | pr_err("\t%d-%c%c%c: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n", |
1742 | cpu, | |
1743 | "O."[!!cpu_online(cpu)], | |
1744 | "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)], | |
1745 | "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)], | |
1746 | ticks_value, ticks_title, | |
a858af28 PM |
1747 | atomic_read(&rdtp->dynticks) & 0xfff, |
1748 | rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, | |
6231069b | 1749 | rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), |
7d0ae808 | 1750 | READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart, |
a858af28 PM |
1751 | fast_no_hz); |
1752 | } | |
1753 | ||
1754 | /* Terminate the stall-info list. */ | |
1755 | static void print_cpu_stall_info_end(void) | |
1756 | { | |
efc151c3 | 1757 | pr_err("\t"); |
a858af28 PM |
1758 | } |
1759 | ||
1760 | /* Zero ->ticks_this_gp for all flavors of RCU. */ | |
1761 | static void zero_cpu_stall_ticks(struct rcu_data *rdp) | |
1762 | { | |
1763 | rdp->ticks_this_gp = 0; | |
6231069b | 1764 | rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); |
a858af28 PM |
1765 | } |
1766 | ||
1767 | /* Increment ->ticks_this_gp for all flavors of RCU. */ | |
1768 | static void increment_cpu_stall_ticks(void) | |
1769 | { | |
115f7a7c PM |
1770 | struct rcu_state *rsp; |
1771 | ||
1772 | for_each_rcu_flavor(rsp) | |
fa07a58f | 1773 | raw_cpu_inc(rsp->rda->ticks_this_gp); |
a858af28 PM |
1774 | } |
1775 | ||
3fbfbf7a PM |
1776 | #ifdef CONFIG_RCU_NOCB_CPU |
1777 | ||
1778 | /* | |
1779 | * Offload callback processing from the boot-time-specified set of CPUs | |
1780 | * specified by rcu_nocb_mask. For each CPU in the set, there is a | |
1781 | * kthread created that pulls the callbacks from the corresponding CPU, | |
1782 | * waits for a grace period to elapse, and invokes the callbacks. | |
1783 | * The no-CBs CPUs do a wake_up() on their kthread when they insert | |
1784 | * a callback into any empty list, unless the rcu_nocb_poll boot parameter | |
1785 | * has been specified, in which case each kthread actively polls its | |
1786 | * CPU. (Which isn't so great for energy efficiency, but which does | |
1787 | * reduce RCU's overhead on that CPU.) | |
1788 | * | |
1789 | * This is intended to be used in conjunction with Frederic Weisbecker's | |
1790 | * adaptive-idle work, which would seriously reduce OS jitter on CPUs | |
1791 | * running CPU-bound user-mode computations. | |
1792 | * | |
1793 | * Offloading of callback processing could also in theory be used as | |
1794 | * an energy-efficiency measure because CPUs with no RCU callbacks | |
1795 | * queued are more aggressive about entering dyntick-idle mode. | |
1796 | */ | |
1797 | ||
1798 | ||
1799 | /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ | |
1800 | static int __init rcu_nocb_setup(char *str) | |
1801 | { | |
1802 | alloc_bootmem_cpumask_var(&rcu_nocb_mask); | |
1803 | have_rcu_nocb_mask = true; | |
1804 | cpulist_parse(str, rcu_nocb_mask); | |
1805 | return 1; | |
1806 | } | |
1807 | __setup("rcu_nocbs=", rcu_nocb_setup); | |
1808 | ||
1b0048a4 PG |
1809 | static int __init parse_rcu_nocb_poll(char *arg) |
1810 | { | |
1811 | rcu_nocb_poll = 1; | |
1812 | return 0; | |
1813 | } | |
1814 | early_param("rcu_nocb_poll", parse_rcu_nocb_poll); | |
1815 | ||
dae6e64d | 1816 | /* |
0446be48 PM |
1817 | * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended |
1818 | * grace period. | |
dae6e64d | 1819 | */ |
0446be48 | 1820 | static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) |
dae6e64d | 1821 | { |
0446be48 | 1822 | wake_up_all(&rnp->nocb_gp_wq[rnp->completed & 0x1]); |
dae6e64d PM |
1823 | } |
1824 | ||
1825 | /* | |
8b425aa8 | 1826 | * Set the root rcu_node structure's ->need_future_gp field |
dae6e64d PM |
1827 | * based on the sum of those of all rcu_node structures. This does |
1828 | * double-count the root rcu_node structure's requests, but this | |
1829 | * is necessary to handle the possibility of a rcu_nocb_kthread() | |
1830 | * having awakened during the time that the rcu_node structures | |
1831 | * were being updated for the end of the previous grace period. | |
34ed6246 | 1832 | */ |
dae6e64d PM |
1833 | static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) |
1834 | { | |
8b425aa8 | 1835 | rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq; |
dae6e64d PM |
1836 | } |
1837 | ||
1838 | static void rcu_init_one_nocb(struct rcu_node *rnp) | |
34ed6246 | 1839 | { |
dae6e64d PM |
1840 | init_waitqueue_head(&rnp->nocb_gp_wq[0]); |
1841 | init_waitqueue_head(&rnp->nocb_gp_wq[1]); | |
34ed6246 PM |
1842 | } |
1843 | ||
2f33b512 | 1844 | #ifndef CONFIG_RCU_NOCB_CPU_ALL |
24342c96 | 1845 | /* Is the specified CPU a no-CBs CPU? */ |
d1e43fa5 | 1846 | bool rcu_is_nocb_cpu(int cpu) |
3fbfbf7a PM |
1847 | { |
1848 | if (have_rcu_nocb_mask) | |
1849 | return cpumask_test_cpu(cpu, rcu_nocb_mask); | |
1850 | return false; | |
1851 | } | |
2f33b512 | 1852 | #endif /* #ifndef CONFIG_RCU_NOCB_CPU_ALL */ |
3fbfbf7a | 1853 | |
fbce7497 PM |
1854 | /* |
1855 | * Kick the leader kthread for this NOCB group. | |
1856 | */ | |
1857 | static void wake_nocb_leader(struct rcu_data *rdp, bool force) | |
1858 | { | |
1859 | struct rcu_data *rdp_leader = rdp->nocb_leader; | |
1860 | ||
7d0ae808 | 1861 | if (!READ_ONCE(rdp_leader->nocb_kthread)) |
fbce7497 | 1862 | return; |
7d0ae808 | 1863 | if (READ_ONCE(rdp_leader->nocb_leader_sleep) || force) { |
39953dfd | 1864 | /* Prior smp_mb__after_atomic() orders against prior enqueue. */ |
7d0ae808 | 1865 | WRITE_ONCE(rdp_leader->nocb_leader_sleep, false); |
fbce7497 PM |
1866 | wake_up(&rdp_leader->nocb_wq); |
1867 | } | |
1868 | } | |
1869 | ||
d7e29933 PM |
1870 | /* |
1871 | * Does the specified CPU need an RCU callback for the specified flavor | |
1872 | * of rcu_barrier()? | |
1873 | */ | |
1874 | static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) | |
1875 | { | |
1876 | struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); | |
41050a00 PM |
1877 | unsigned long ret; |
1878 | #ifdef CONFIG_PROVE_RCU | |
d7e29933 | 1879 | struct rcu_head *rhp; |
41050a00 | 1880 | #endif /* #ifdef CONFIG_PROVE_RCU */ |
d7e29933 | 1881 | |
41050a00 PM |
1882 | /* |
1883 | * Check count of all no-CBs callbacks awaiting invocation. | |
1884 | * There needs to be a barrier before this function is called, | |
1885 | * but associated with a prior determination that no more | |
1886 | * callbacks would be posted. In the worst case, the first | |
1887 | * barrier in _rcu_barrier() suffices (but the caller cannot | |
1888 | * necessarily rely on this, not a substitute for the caller | |
1889 | * getting the concurrency design right!). There must also be | |
1890 | * a barrier between the following load an posting of a callback | |
1891 | * (if a callback is in fact needed). This is associated with an | |
1892 | * atomic_inc() in the caller. | |
1893 | */ | |
1894 | ret = atomic_long_read(&rdp->nocb_q_count); | |
d7e29933 | 1895 | |
41050a00 | 1896 | #ifdef CONFIG_PROVE_RCU |
7d0ae808 | 1897 | rhp = READ_ONCE(rdp->nocb_head); |
d7e29933 | 1898 | if (!rhp) |
7d0ae808 | 1899 | rhp = READ_ONCE(rdp->nocb_gp_head); |
d7e29933 | 1900 | if (!rhp) |
7d0ae808 | 1901 | rhp = READ_ONCE(rdp->nocb_follower_head); |
d7e29933 PM |
1902 | |
1903 | /* Having no rcuo kthread but CBs after scheduler starts is bad! */ | |
7d0ae808 | 1904 | if (!READ_ONCE(rdp->nocb_kthread) && rhp && |
59f792d1 | 1905 | rcu_scheduler_fully_active) { |
d7e29933 PM |
1906 | /* RCU callback enqueued before CPU first came online??? */ |
1907 | pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n", | |
1908 | cpu, rhp->func); | |
1909 | WARN_ON_ONCE(1); | |
1910 | } | |
41050a00 | 1911 | #endif /* #ifdef CONFIG_PROVE_RCU */ |
d7e29933 | 1912 | |
41050a00 | 1913 | return !!ret; |
d7e29933 PM |
1914 | } |
1915 | ||
3fbfbf7a PM |
1916 | /* |
1917 | * Enqueue the specified string of rcu_head structures onto the specified | |
1918 | * CPU's no-CBs lists. The CPU is specified by rdp, the head of the | |
1919 | * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy | |
1920 | * counts are supplied by rhcount and rhcount_lazy. | |
1921 | * | |
1922 | * If warranted, also wake up the kthread servicing this CPUs queues. | |
1923 | */ | |
1924 | static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, | |
1925 | struct rcu_head *rhp, | |
1926 | struct rcu_head **rhtp, | |
96d3fd0d PM |
1927 | int rhcount, int rhcount_lazy, |
1928 | unsigned long flags) | |
3fbfbf7a PM |
1929 | { |
1930 | int len; | |
1931 | struct rcu_head **old_rhpp; | |
1932 | struct task_struct *t; | |
1933 | ||
1934 | /* Enqueue the callback on the nocb list and update counts. */ | |
41050a00 PM |
1935 | atomic_long_add(rhcount, &rdp->nocb_q_count); |
1936 | /* rcu_barrier() relies on ->nocb_q_count add before xchg. */ | |
3fbfbf7a | 1937 | old_rhpp = xchg(&rdp->nocb_tail, rhtp); |
7d0ae808 | 1938 | WRITE_ONCE(*old_rhpp, rhp); |
3fbfbf7a | 1939 | atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); |
39953dfd | 1940 | smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */ |
3fbfbf7a PM |
1941 | |
1942 | /* If we are not being polled and there is a kthread, awaken it ... */ | |
7d0ae808 | 1943 | t = READ_ONCE(rdp->nocb_kthread); |
25e03a74 | 1944 | if (rcu_nocb_poll || !t) { |
9261dd0d PM |
1945 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
1946 | TPS("WakeNotPoll")); | |
3fbfbf7a | 1947 | return; |
9261dd0d | 1948 | } |
3fbfbf7a PM |
1949 | len = atomic_long_read(&rdp->nocb_q_count); |
1950 | if (old_rhpp == &rdp->nocb_head) { | |
96d3fd0d | 1951 | if (!irqs_disabled_flags(flags)) { |
fbce7497 PM |
1952 | /* ... if queue was empty ... */ |
1953 | wake_nocb_leader(rdp, false); | |
96d3fd0d PM |
1954 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
1955 | TPS("WakeEmpty")); | |
1956 | } else { | |
9fdd3bc9 | 1957 | rdp->nocb_defer_wakeup = RCU_NOGP_WAKE; |
96d3fd0d PM |
1958 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
1959 | TPS("WakeEmptyIsDeferred")); | |
1960 | } | |
3fbfbf7a PM |
1961 | rdp->qlen_last_fqs_check = 0; |
1962 | } else if (len > rdp->qlen_last_fqs_check + qhimark) { | |
fbce7497 | 1963 | /* ... or if many callbacks queued. */ |
9fdd3bc9 PM |
1964 | if (!irqs_disabled_flags(flags)) { |
1965 | wake_nocb_leader(rdp, true); | |
1966 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
1967 | TPS("WakeOvf")); | |
1968 | } else { | |
1969 | rdp->nocb_defer_wakeup = RCU_NOGP_WAKE_FORCE; | |
1970 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
1971 | TPS("WakeOvfIsDeferred")); | |
1972 | } | |
3fbfbf7a | 1973 | rdp->qlen_last_fqs_check = LONG_MAX / 2; |
9261dd0d PM |
1974 | } else { |
1975 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot")); | |
3fbfbf7a PM |
1976 | } |
1977 | return; | |
1978 | } | |
1979 | ||
1980 | /* | |
1981 | * This is a helper for __call_rcu(), which invokes this when the normal | |
1982 | * callback queue is inoperable. If this is not a no-CBs CPU, this | |
1983 | * function returns failure back to __call_rcu(), which can complain | |
1984 | * appropriately. | |
1985 | * | |
1986 | * Otherwise, this function queues the callback where the corresponding | |
1987 | * "rcuo" kthread can find it. | |
1988 | */ | |
1989 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, | |
96d3fd0d | 1990 | bool lazy, unsigned long flags) |
3fbfbf7a PM |
1991 | { |
1992 | ||
d1e43fa5 | 1993 | if (!rcu_is_nocb_cpu(rdp->cpu)) |
c271d3a9 | 1994 | return false; |
96d3fd0d | 1995 | __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags); |
21e7a608 PM |
1996 | if (__is_kfree_rcu_offset((unsigned long)rhp->func)) |
1997 | trace_rcu_kfree_callback(rdp->rsp->name, rhp, | |
1998 | (unsigned long)rhp->func, | |
756cbf6b PM |
1999 | -atomic_long_read(&rdp->nocb_q_count_lazy), |
2000 | -atomic_long_read(&rdp->nocb_q_count)); | |
21e7a608 PM |
2001 | else |
2002 | trace_rcu_callback(rdp->rsp->name, rhp, | |
756cbf6b PM |
2003 | -atomic_long_read(&rdp->nocb_q_count_lazy), |
2004 | -atomic_long_read(&rdp->nocb_q_count)); | |
1772947b PM |
2005 | |
2006 | /* | |
2007 | * If called from an extended quiescent state with interrupts | |
2008 | * disabled, invoke the RCU core in order to allow the idle-entry | |
2009 | * deferred-wakeup check to function. | |
2010 | */ | |
2011 | if (irqs_disabled_flags(flags) && | |
2012 | !rcu_is_watching() && | |
2013 | cpu_online(smp_processor_id())) | |
2014 | invoke_rcu_core(); | |
2015 | ||
c271d3a9 | 2016 | return true; |
3fbfbf7a PM |
2017 | } |
2018 | ||
2019 | /* | |
2020 | * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is | |
2021 | * not a no-CBs CPU. | |
2022 | */ | |
2023 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, | |
96d3fd0d PM |
2024 | struct rcu_data *rdp, |
2025 | unsigned long flags) | |
3fbfbf7a PM |
2026 | { |
2027 | long ql = rsp->qlen; | |
2028 | long qll = rsp->qlen_lazy; | |
2029 | ||
2030 | /* If this is not a no-CBs CPU, tell the caller to do it the old way. */ | |
d1e43fa5 | 2031 | if (!rcu_is_nocb_cpu(smp_processor_id())) |
0a9e1e11 | 2032 | return false; |
3fbfbf7a PM |
2033 | rsp->qlen = 0; |
2034 | rsp->qlen_lazy = 0; | |
2035 | ||
2036 | /* First, enqueue the donelist, if any. This preserves CB ordering. */ | |
2037 | if (rsp->orphan_donelist != NULL) { | |
2038 | __call_rcu_nocb_enqueue(rdp, rsp->orphan_donelist, | |
96d3fd0d | 2039 | rsp->orphan_donetail, ql, qll, flags); |
3fbfbf7a PM |
2040 | ql = qll = 0; |
2041 | rsp->orphan_donelist = NULL; | |
2042 | rsp->orphan_donetail = &rsp->orphan_donelist; | |
2043 | } | |
2044 | if (rsp->orphan_nxtlist != NULL) { | |
2045 | __call_rcu_nocb_enqueue(rdp, rsp->orphan_nxtlist, | |
96d3fd0d | 2046 | rsp->orphan_nxttail, ql, qll, flags); |
3fbfbf7a PM |
2047 | ql = qll = 0; |
2048 | rsp->orphan_nxtlist = NULL; | |
2049 | rsp->orphan_nxttail = &rsp->orphan_nxtlist; | |
2050 | } | |
0a9e1e11 | 2051 | return true; |
3fbfbf7a PM |
2052 | } |
2053 | ||
2054 | /* | |
34ed6246 PM |
2055 | * If necessary, kick off a new grace period, and either way wait |
2056 | * for a subsequent grace period to complete. | |
3fbfbf7a | 2057 | */ |
34ed6246 | 2058 | static void rcu_nocb_wait_gp(struct rcu_data *rdp) |
3fbfbf7a | 2059 | { |
34ed6246 | 2060 | unsigned long c; |
dae6e64d | 2061 | bool d; |
34ed6246 | 2062 | unsigned long flags; |
48a7639c | 2063 | bool needwake; |
34ed6246 PM |
2064 | struct rcu_node *rnp = rdp->mynode; |
2065 | ||
2a67e741 | 2066 | raw_spin_lock_irqsave_rcu_node(rnp, flags); |
48a7639c | 2067 | needwake = rcu_start_future_gp(rnp, rdp, &c); |
0446be48 | 2068 | raw_spin_unlock_irqrestore(&rnp->lock, flags); |
48a7639c PM |
2069 | if (needwake) |
2070 | rcu_gp_kthread_wake(rdp->rsp); | |
3fbfbf7a PM |
2071 | |
2072 | /* | |
34ed6246 PM |
2073 | * Wait for the grace period. Do so interruptibly to avoid messing |
2074 | * up the load average. | |
3fbfbf7a | 2075 | */ |
f7f7bac9 | 2076 | trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait")); |
34ed6246 | 2077 | for (;;) { |
dae6e64d PM |
2078 | wait_event_interruptible( |
2079 | rnp->nocb_gp_wq[c & 0x1], | |
7d0ae808 | 2080 | (d = ULONG_CMP_GE(READ_ONCE(rnp->completed), c))); |
dae6e64d | 2081 | if (likely(d)) |
34ed6246 | 2082 | break; |
73a860cd | 2083 | WARN_ON(signal_pending(current)); |
f7f7bac9 | 2084 | trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait")); |
34ed6246 | 2085 | } |
f7f7bac9 | 2086 | trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait")); |
34ed6246 | 2087 | smp_mb(); /* Ensure that CB invocation happens after GP end. */ |
3fbfbf7a PM |
2088 | } |
2089 | ||
fbce7497 PM |
2090 | /* |
2091 | * Leaders come here to wait for additional callbacks to show up. | |
2092 | * This function does not return until callbacks appear. | |
2093 | */ | |
2094 | static void nocb_leader_wait(struct rcu_data *my_rdp) | |
2095 | { | |
2096 | bool firsttime = true; | |
2097 | bool gotcbs; | |
2098 | struct rcu_data *rdp; | |
2099 | struct rcu_head **tail; | |
2100 | ||
2101 | wait_again: | |
2102 | ||
2103 | /* Wait for callbacks to appear. */ | |
2104 | if (!rcu_nocb_poll) { | |
2105 | trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Sleep"); | |
2106 | wait_event_interruptible(my_rdp->nocb_wq, | |
7d0ae808 | 2107 | !READ_ONCE(my_rdp->nocb_leader_sleep)); |
fbce7497 PM |
2108 | /* Memory barrier handled by smp_mb() calls below and repoll. */ |
2109 | } else if (firsttime) { | |
2110 | firsttime = false; /* Don't drown trace log with "Poll"! */ | |
2111 | trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, "Poll"); | |
2112 | } | |
2113 | ||
2114 | /* | |
2115 | * Each pass through the following loop checks a follower for CBs. | |
2116 | * We are our own first follower. Any CBs found are moved to | |
2117 | * nocb_gp_head, where they await a grace period. | |
2118 | */ | |
2119 | gotcbs = false; | |
2120 | for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { | |
7d0ae808 | 2121 | rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head); |
fbce7497 PM |
2122 | if (!rdp->nocb_gp_head) |
2123 | continue; /* No CBs here, try next follower. */ | |
2124 | ||
2125 | /* Move callbacks to wait-for-GP list, which is empty. */ | |
7d0ae808 | 2126 | WRITE_ONCE(rdp->nocb_head, NULL); |
fbce7497 | 2127 | rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); |
fbce7497 PM |
2128 | gotcbs = true; |
2129 | } | |
2130 | ||
2131 | /* | |
2132 | * If there were no callbacks, sleep a bit, rescan after a | |
2133 | * memory barrier, and go retry. | |
2134 | */ | |
2135 | if (unlikely(!gotcbs)) { | |
2136 | if (!rcu_nocb_poll) | |
2137 | trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, | |
2138 | "WokeEmpty"); | |
73a860cd | 2139 | WARN_ON(signal_pending(current)); |
fbce7497 PM |
2140 | schedule_timeout_interruptible(1); |
2141 | ||
2142 | /* Rescan in case we were a victim of memory ordering. */ | |
11ed7f93 PK |
2143 | my_rdp->nocb_leader_sleep = true; |
2144 | smp_mb(); /* Ensure _sleep true before scan. */ | |
fbce7497 | 2145 | for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) |
7d0ae808 | 2146 | if (READ_ONCE(rdp->nocb_head)) { |
fbce7497 | 2147 | /* Found CB, so short-circuit next wait. */ |
11ed7f93 | 2148 | my_rdp->nocb_leader_sleep = false; |
fbce7497 PM |
2149 | break; |
2150 | } | |
2151 | goto wait_again; | |
2152 | } | |
2153 | ||
2154 | /* Wait for one grace period. */ | |
2155 | rcu_nocb_wait_gp(my_rdp); | |
2156 | ||
2157 | /* | |
11ed7f93 PK |
2158 | * We left ->nocb_leader_sleep unset to reduce cache thrashing. |
2159 | * We set it now, but recheck for new callbacks while | |
fbce7497 PM |
2160 | * traversing our follower list. |
2161 | */ | |
11ed7f93 PK |
2162 | my_rdp->nocb_leader_sleep = true; |
2163 | smp_mb(); /* Ensure _sleep true before scan of ->nocb_head. */ | |
fbce7497 PM |
2164 | |
2165 | /* Each pass through the following loop wakes a follower, if needed. */ | |
2166 | for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { | |
7d0ae808 | 2167 | if (READ_ONCE(rdp->nocb_head)) |
11ed7f93 | 2168 | my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/ |
fbce7497 PM |
2169 | if (!rdp->nocb_gp_head) |
2170 | continue; /* No CBs, so no need to wake follower. */ | |
2171 | ||
2172 | /* Append callbacks to follower's "done" list. */ | |
2173 | tail = xchg(&rdp->nocb_follower_tail, rdp->nocb_gp_tail); | |
2174 | *tail = rdp->nocb_gp_head; | |
c847f142 | 2175 | smp_mb__after_atomic(); /* Store *tail before wakeup. */ |
fbce7497 PM |
2176 | if (rdp != my_rdp && tail == &rdp->nocb_follower_head) { |
2177 | /* | |
2178 | * List was empty, wake up the follower. | |
2179 | * Memory barriers supplied by atomic_long_add(). | |
2180 | */ | |
2181 | wake_up(&rdp->nocb_wq); | |
2182 | } | |
2183 | } | |
2184 | ||
2185 | /* If we (the leader) don't have CBs, go wait some more. */ | |
2186 | if (!my_rdp->nocb_follower_head) | |
2187 | goto wait_again; | |
2188 | } | |
2189 | ||
2190 | /* | |
2191 | * Followers come here to wait for additional callbacks to show up. | |
2192 | * This function does not return until callbacks appear. | |
2193 | */ | |
2194 | static void nocb_follower_wait(struct rcu_data *rdp) | |
2195 | { | |
2196 | bool firsttime = true; | |
2197 | ||
2198 | for (;;) { | |
2199 | if (!rcu_nocb_poll) { | |
2200 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
2201 | "FollowerSleep"); | |
2202 | wait_event_interruptible(rdp->nocb_wq, | |
7d0ae808 | 2203 | READ_ONCE(rdp->nocb_follower_head)); |
fbce7497 PM |
2204 | } else if (firsttime) { |
2205 | /* Don't drown trace log with "Poll"! */ | |
2206 | firsttime = false; | |
2207 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "Poll"); | |
2208 | } | |
2209 | if (smp_load_acquire(&rdp->nocb_follower_head)) { | |
2210 | /* ^^^ Ensure CB invocation follows _head test. */ | |
2211 | return; | |
2212 | } | |
2213 | if (!rcu_nocb_poll) | |
2214 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
2215 | "WokeEmpty"); | |
73a860cd | 2216 | WARN_ON(signal_pending(current)); |
fbce7497 PM |
2217 | schedule_timeout_interruptible(1); |
2218 | } | |
2219 | } | |
2220 | ||
3fbfbf7a PM |
2221 | /* |
2222 | * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes | |
fbce7497 PM |
2223 | * callbacks queued by the corresponding no-CBs CPU, however, there is |
2224 | * an optional leader-follower relationship so that the grace-period | |
2225 | * kthreads don't have to do quite so many wakeups. | |
3fbfbf7a PM |
2226 | */ |
2227 | static int rcu_nocb_kthread(void *arg) | |
2228 | { | |
2229 | int c, cl; | |
2230 | struct rcu_head *list; | |
2231 | struct rcu_head *next; | |
2232 | struct rcu_head **tail; | |
2233 | struct rcu_data *rdp = arg; | |
2234 | ||
2235 | /* Each pass through this loop invokes one batch of callbacks */ | |
2236 | for (;;) { | |
fbce7497 PM |
2237 | /* Wait for callbacks. */ |
2238 | if (rdp->nocb_leader == rdp) | |
2239 | nocb_leader_wait(rdp); | |
2240 | else | |
2241 | nocb_follower_wait(rdp); | |
2242 | ||
2243 | /* Pull the ready-to-invoke callbacks onto local list. */ | |
7d0ae808 | 2244 | list = READ_ONCE(rdp->nocb_follower_head); |
fbce7497 PM |
2245 | BUG_ON(!list); |
2246 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, "WokeNonEmpty"); | |
7d0ae808 | 2247 | WRITE_ONCE(rdp->nocb_follower_head, NULL); |
fbce7497 | 2248 | tail = xchg(&rdp->nocb_follower_tail, &rdp->nocb_follower_head); |
3fbfbf7a PM |
2249 | |
2250 | /* Each pass through the following loop invokes a callback. */ | |
41050a00 PM |
2251 | trace_rcu_batch_start(rdp->rsp->name, |
2252 | atomic_long_read(&rdp->nocb_q_count_lazy), | |
2253 | atomic_long_read(&rdp->nocb_q_count), -1); | |
3fbfbf7a PM |
2254 | c = cl = 0; |
2255 | while (list) { | |
2256 | next = list->next; | |
2257 | /* Wait for enqueuing to complete, if needed. */ | |
2258 | while (next == NULL && &list->next != tail) { | |
69a79bb1 PM |
2259 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2260 | TPS("WaitQueue")); | |
3fbfbf7a | 2261 | schedule_timeout_interruptible(1); |
69a79bb1 PM |
2262 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2263 | TPS("WokeQueue")); | |
3fbfbf7a PM |
2264 | next = list->next; |
2265 | } | |
2266 | debug_rcu_head_unqueue(list); | |
2267 | local_bh_disable(); | |
2268 | if (__rcu_reclaim(rdp->rsp->name, list)) | |
2269 | cl++; | |
2270 | c++; | |
2271 | local_bh_enable(); | |
2272 | list = next; | |
2273 | } | |
2274 | trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1); | |
41050a00 PM |
2275 | smp_mb__before_atomic(); /* _add after CB invocation. */ |
2276 | atomic_long_add(-c, &rdp->nocb_q_count); | |
2277 | atomic_long_add(-cl, &rdp->nocb_q_count_lazy); | |
c635a4e1 | 2278 | rdp->n_nocbs_invoked += c; |
3fbfbf7a PM |
2279 | } |
2280 | return 0; | |
2281 | } | |
2282 | ||
96d3fd0d | 2283 | /* Is a deferred wakeup of rcu_nocb_kthread() required? */ |
9fdd3bc9 | 2284 | static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) |
96d3fd0d | 2285 | { |
7d0ae808 | 2286 | return READ_ONCE(rdp->nocb_defer_wakeup); |
96d3fd0d PM |
2287 | } |
2288 | ||
2289 | /* Do a deferred wakeup of rcu_nocb_kthread(). */ | |
2290 | static void do_nocb_deferred_wakeup(struct rcu_data *rdp) | |
2291 | { | |
9fdd3bc9 PM |
2292 | int ndw; |
2293 | ||
96d3fd0d PM |
2294 | if (!rcu_nocb_need_deferred_wakeup(rdp)) |
2295 | return; | |
7d0ae808 PM |
2296 | ndw = READ_ONCE(rdp->nocb_defer_wakeup); |
2297 | WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOGP_WAKE_NOT); | |
9fdd3bc9 PM |
2298 | wake_nocb_leader(rdp, ndw == RCU_NOGP_WAKE_FORCE); |
2299 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake")); | |
96d3fd0d PM |
2300 | } |
2301 | ||
f4579fc5 PM |
2302 | void __init rcu_init_nohz(void) |
2303 | { | |
2304 | int cpu; | |
2305 | bool need_rcu_nocb_mask = true; | |
2306 | struct rcu_state *rsp; | |
2307 | ||
2308 | #ifdef CONFIG_RCU_NOCB_CPU_NONE | |
2309 | need_rcu_nocb_mask = false; | |
2310 | #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */ | |
2311 | ||
2312 | #if defined(CONFIG_NO_HZ_FULL) | |
2313 | if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask)) | |
2314 | need_rcu_nocb_mask = true; | |
2315 | #endif /* #if defined(CONFIG_NO_HZ_FULL) */ | |
2316 | ||
2317 | if (!have_rcu_nocb_mask && need_rcu_nocb_mask) { | |
949cccdb PK |
2318 | if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { |
2319 | pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); | |
2320 | return; | |
2321 | } | |
f4579fc5 PM |
2322 | have_rcu_nocb_mask = true; |
2323 | } | |
2324 | if (!have_rcu_nocb_mask) | |
2325 | return; | |
2326 | ||
2327 | #ifdef CONFIG_RCU_NOCB_CPU_ZERO | |
2328 | pr_info("\tOffload RCU callbacks from CPU 0\n"); | |
2329 | cpumask_set_cpu(0, rcu_nocb_mask); | |
2330 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */ | |
2331 | #ifdef CONFIG_RCU_NOCB_CPU_ALL | |
2332 | pr_info("\tOffload RCU callbacks from all CPUs\n"); | |
2333 | cpumask_copy(rcu_nocb_mask, cpu_possible_mask); | |
2334 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */ | |
2335 | #if defined(CONFIG_NO_HZ_FULL) | |
2336 | if (tick_nohz_full_running) | |
2337 | cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); | |
2338 | #endif /* #if defined(CONFIG_NO_HZ_FULL) */ | |
2339 | ||
2340 | if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { | |
2341 | pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n"); | |
2342 | cpumask_and(rcu_nocb_mask, cpu_possible_mask, | |
2343 | rcu_nocb_mask); | |
2344 | } | |
ad853b48 TH |
2345 | pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n", |
2346 | cpumask_pr_args(rcu_nocb_mask)); | |
f4579fc5 PM |
2347 | if (rcu_nocb_poll) |
2348 | pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); | |
2349 | ||
2350 | for_each_rcu_flavor(rsp) { | |
34404ca8 PM |
2351 | for_each_cpu(cpu, rcu_nocb_mask) |
2352 | init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu)); | |
35ce7f29 | 2353 | rcu_organize_nocb_kthreads(rsp); |
f4579fc5 | 2354 | } |
96d3fd0d PM |
2355 | } |
2356 | ||
3fbfbf7a PM |
2357 | /* Initialize per-rcu_data variables for no-CBs CPUs. */ |
2358 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) | |
2359 | { | |
2360 | rdp->nocb_tail = &rdp->nocb_head; | |
2361 | init_waitqueue_head(&rdp->nocb_wq); | |
fbce7497 | 2362 | rdp->nocb_follower_tail = &rdp->nocb_follower_head; |
3fbfbf7a PM |
2363 | } |
2364 | ||
35ce7f29 PM |
2365 | /* |
2366 | * If the specified CPU is a no-CBs CPU that does not already have its | |
2367 | * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are | |
2368 | * brought online out of order, this can require re-organizing the | |
2369 | * leader-follower relationships. | |
2370 | */ | |
2371 | static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu) | |
2372 | { | |
2373 | struct rcu_data *rdp; | |
2374 | struct rcu_data *rdp_last; | |
2375 | struct rcu_data *rdp_old_leader; | |
2376 | struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu); | |
2377 | struct task_struct *t; | |
2378 | ||
2379 | /* | |
2380 | * If this isn't a no-CBs CPU or if it already has an rcuo kthread, | |
2381 | * then nothing to do. | |
2382 | */ | |
2383 | if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread) | |
2384 | return; | |
2385 | ||
2386 | /* If we didn't spawn the leader first, reorganize! */ | |
2387 | rdp_old_leader = rdp_spawn->nocb_leader; | |
2388 | if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) { | |
2389 | rdp_last = NULL; | |
2390 | rdp = rdp_old_leader; | |
2391 | do { | |
2392 | rdp->nocb_leader = rdp_spawn; | |
2393 | if (rdp_last && rdp != rdp_spawn) | |
2394 | rdp_last->nocb_next_follower = rdp; | |
bbe5d7a9 PM |
2395 | if (rdp == rdp_spawn) { |
2396 | rdp = rdp->nocb_next_follower; | |
2397 | } else { | |
2398 | rdp_last = rdp; | |
2399 | rdp = rdp->nocb_next_follower; | |
2400 | rdp_last->nocb_next_follower = NULL; | |
2401 | } | |
35ce7f29 PM |
2402 | } while (rdp); |
2403 | rdp_spawn->nocb_next_follower = rdp_old_leader; | |
2404 | } | |
2405 | ||
2406 | /* Spawn the kthread for this CPU and RCU flavor. */ | |
2407 | t = kthread_run(rcu_nocb_kthread, rdp_spawn, | |
2408 | "rcuo%c/%d", rsp->abbr, cpu); | |
2409 | BUG_ON(IS_ERR(t)); | |
7d0ae808 | 2410 | WRITE_ONCE(rdp_spawn->nocb_kthread, t); |
35ce7f29 PM |
2411 | } |
2412 | ||
2413 | /* | |
2414 | * If the specified CPU is a no-CBs CPU that does not already have its | |
2415 | * rcuo kthreads, spawn them. | |
2416 | */ | |
2417 | static void rcu_spawn_all_nocb_kthreads(int cpu) | |
2418 | { | |
2419 | struct rcu_state *rsp; | |
2420 | ||
2421 | if (rcu_scheduler_fully_active) | |
2422 | for_each_rcu_flavor(rsp) | |
2423 | rcu_spawn_one_nocb_kthread(rsp, cpu); | |
2424 | } | |
2425 | ||
2426 | /* | |
2427 | * Once the scheduler is running, spawn rcuo kthreads for all online | |
2428 | * no-CBs CPUs. This assumes that the early_initcall()s happen before | |
2429 | * non-boot CPUs come online -- if this changes, we will need to add | |
2430 | * some mutual exclusion. | |
2431 | */ | |
2432 | static void __init rcu_spawn_nocb_kthreads(void) | |
2433 | { | |
2434 | int cpu; | |
2435 | ||
2436 | for_each_online_cpu(cpu) | |
2437 | rcu_spawn_all_nocb_kthreads(cpu); | |
2438 | } | |
2439 | ||
fbce7497 PM |
2440 | /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */ |
2441 | static int rcu_nocb_leader_stride = -1; | |
2442 | module_param(rcu_nocb_leader_stride, int, 0444); | |
2443 | ||
2444 | /* | |
35ce7f29 | 2445 | * Initialize leader-follower relationships for all no-CBs CPU. |
fbce7497 | 2446 | */ |
35ce7f29 | 2447 | static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp) |
3fbfbf7a PM |
2448 | { |
2449 | int cpu; | |
fbce7497 PM |
2450 | int ls = rcu_nocb_leader_stride; |
2451 | int nl = 0; /* Next leader. */ | |
3fbfbf7a | 2452 | struct rcu_data *rdp; |
fbce7497 PM |
2453 | struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */ |
2454 | struct rcu_data *rdp_prev = NULL; | |
3fbfbf7a | 2455 | |
22c2f669 | 2456 | if (!have_rcu_nocb_mask) |
3fbfbf7a | 2457 | return; |
fbce7497 PM |
2458 | if (ls == -1) { |
2459 | ls = int_sqrt(nr_cpu_ids); | |
2460 | rcu_nocb_leader_stride = ls; | |
2461 | } | |
2462 | ||
2463 | /* | |
2464 | * Each pass through this loop sets up one rcu_data structure and | |
2465 | * spawns one rcu_nocb_kthread(). | |
2466 | */ | |
3fbfbf7a PM |
2467 | for_each_cpu(cpu, rcu_nocb_mask) { |
2468 | rdp = per_cpu_ptr(rsp->rda, cpu); | |
fbce7497 PM |
2469 | if (rdp->cpu >= nl) { |
2470 | /* New leader, set up for followers & next leader. */ | |
2471 | nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls; | |
2472 | rdp->nocb_leader = rdp; | |
2473 | rdp_leader = rdp; | |
2474 | } else { | |
2475 | /* Another follower, link to previous leader. */ | |
2476 | rdp->nocb_leader = rdp_leader; | |
2477 | rdp_prev->nocb_next_follower = rdp; | |
2478 | } | |
2479 | rdp_prev = rdp; | |
3fbfbf7a PM |
2480 | } |
2481 | } | |
2482 | ||
2483 | /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ | |
34ed6246 | 2484 | static bool init_nocb_callback_list(struct rcu_data *rdp) |
3fbfbf7a | 2485 | { |
22c2f669 | 2486 | if (!rcu_is_nocb_cpu(rdp->cpu)) |
34ed6246 | 2487 | return false; |
22c2f669 | 2488 | |
34404ca8 PM |
2489 | /* If there are early-boot callbacks, move them to nocb lists. */ |
2490 | if (rdp->nxtlist) { | |
2491 | rdp->nocb_head = rdp->nxtlist; | |
2492 | rdp->nocb_tail = rdp->nxttail[RCU_NEXT_TAIL]; | |
2493 | atomic_long_set(&rdp->nocb_q_count, rdp->qlen); | |
2494 | atomic_long_set(&rdp->nocb_q_count_lazy, rdp->qlen_lazy); | |
2495 | rdp->nxtlist = NULL; | |
2496 | rdp->qlen = 0; | |
2497 | rdp->qlen_lazy = 0; | |
2498 | } | |
3fbfbf7a | 2499 | rdp->nxttail[RCU_NEXT_TAIL] = NULL; |
34ed6246 | 2500 | return true; |
3fbfbf7a PM |
2501 | } |
2502 | ||
34ed6246 PM |
2503 | #else /* #ifdef CONFIG_RCU_NOCB_CPU */ |
2504 | ||
d7e29933 PM |
2505 | static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) |
2506 | { | |
2507 | WARN_ON_ONCE(1); /* Should be dead code. */ | |
2508 | return false; | |
2509 | } | |
2510 | ||
0446be48 | 2511 | static void rcu_nocb_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) |
3fbfbf7a | 2512 | { |
3fbfbf7a PM |
2513 | } |
2514 | ||
dae6e64d PM |
2515 | static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq) |
2516 | { | |
2517 | } | |
2518 | ||
2519 | static void rcu_init_one_nocb(struct rcu_node *rnp) | |
2520 | { | |
2521 | } | |
3fbfbf7a | 2522 | |
3fbfbf7a | 2523 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, |
96d3fd0d | 2524 | bool lazy, unsigned long flags) |
3fbfbf7a | 2525 | { |
4afc7e26 | 2526 | return false; |
3fbfbf7a PM |
2527 | } |
2528 | ||
2529 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp, | |
96d3fd0d PM |
2530 | struct rcu_data *rdp, |
2531 | unsigned long flags) | |
3fbfbf7a | 2532 | { |
f4aa84ba | 2533 | return false; |
3fbfbf7a PM |
2534 | } |
2535 | ||
3fbfbf7a PM |
2536 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) |
2537 | { | |
2538 | } | |
2539 | ||
9fdd3bc9 | 2540 | static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) |
96d3fd0d PM |
2541 | { |
2542 | return false; | |
2543 | } | |
2544 | ||
2545 | static void do_nocb_deferred_wakeup(struct rcu_data *rdp) | |
2546 | { | |
2547 | } | |
2548 | ||
35ce7f29 PM |
2549 | static void rcu_spawn_all_nocb_kthreads(int cpu) |
2550 | { | |
2551 | } | |
2552 | ||
2553 | static void __init rcu_spawn_nocb_kthreads(void) | |
3fbfbf7a PM |
2554 | { |
2555 | } | |
2556 | ||
34ed6246 | 2557 | static bool init_nocb_callback_list(struct rcu_data *rdp) |
3fbfbf7a | 2558 | { |
34ed6246 | 2559 | return false; |
3fbfbf7a PM |
2560 | } |
2561 | ||
2562 | #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ | |
65d798f0 PM |
2563 | |
2564 | /* | |
2565 | * An adaptive-ticks CPU can potentially execute in kernel mode for an | |
2566 | * arbitrarily long period of time with the scheduling-clock tick turned | |
2567 | * off. RCU will be paying attention to this CPU because it is in the | |
2568 | * kernel, but the CPU cannot be guaranteed to be executing the RCU state | |
2569 | * machine because the scheduling-clock tick has been disabled. Therefore, | |
2570 | * if an adaptive-ticks CPU is failing to respond to the current grace | |
2571 | * period and has not be idle from an RCU perspective, kick it. | |
2572 | */ | |
4a81e832 | 2573 | static void __maybe_unused rcu_kick_nohz_cpu(int cpu) |
65d798f0 PM |
2574 | { |
2575 | #ifdef CONFIG_NO_HZ_FULL | |
2576 | if (tick_nohz_full_cpu(cpu)) | |
2577 | smp_send_reschedule(cpu); | |
2578 | #endif /* #ifdef CONFIG_NO_HZ_FULL */ | |
2579 | } | |
2333210b PM |
2580 | |
2581 | ||
2582 | #ifdef CONFIG_NO_HZ_FULL_SYSIDLE | |
2583 | ||
0edd1b17 | 2584 | static int full_sysidle_state; /* Current system-idle state. */ |
d4bd54fb PM |
2585 | #define RCU_SYSIDLE_NOT 0 /* Some CPU is not idle. */ |
2586 | #define RCU_SYSIDLE_SHORT 1 /* All CPUs idle for brief period. */ | |
2587 | #define RCU_SYSIDLE_LONG 2 /* All CPUs idle for long enough. */ | |
2588 | #define RCU_SYSIDLE_FULL 3 /* All CPUs idle, ready for sysidle. */ | |
2589 | #define RCU_SYSIDLE_FULL_NOTED 4 /* Actually entered sysidle state. */ | |
2590 | ||
eb348b89 PM |
2591 | /* |
2592 | * Invoked to note exit from irq or task transition to idle. Note that | |
2593 | * usermode execution does -not- count as idle here! After all, we want | |
2594 | * to detect full-system idle states, not RCU quiescent states and grace | |
2595 | * periods. The caller must have disabled interrupts. | |
2596 | */ | |
28ced795 | 2597 | static void rcu_sysidle_enter(int irq) |
eb348b89 PM |
2598 | { |
2599 | unsigned long j; | |
28ced795 | 2600 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
eb348b89 | 2601 | |
663e1310 PM |
2602 | /* If there are no nohz_full= CPUs, no need to track this. */ |
2603 | if (!tick_nohz_full_enabled()) | |
2604 | return; | |
2605 | ||
eb348b89 PM |
2606 | /* Adjust nesting, check for fully idle. */ |
2607 | if (irq) { | |
2608 | rdtp->dynticks_idle_nesting--; | |
2609 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); | |
2610 | if (rdtp->dynticks_idle_nesting != 0) | |
2611 | return; /* Still not fully idle. */ | |
2612 | } else { | |
2613 | if ((rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) == | |
2614 | DYNTICK_TASK_NEST_VALUE) { | |
2615 | rdtp->dynticks_idle_nesting = 0; | |
2616 | } else { | |
2617 | rdtp->dynticks_idle_nesting -= DYNTICK_TASK_NEST_VALUE; | |
2618 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting < 0); | |
2619 | return; /* Still not fully idle. */ | |
2620 | } | |
2621 | } | |
2622 | ||
2623 | /* Record start of fully idle period. */ | |
2624 | j = jiffies; | |
7d0ae808 | 2625 | WRITE_ONCE(rdtp->dynticks_idle_jiffies, j); |
4e857c58 | 2626 | smp_mb__before_atomic(); |
eb348b89 | 2627 | atomic_inc(&rdtp->dynticks_idle); |
4e857c58 | 2628 | smp_mb__after_atomic(); |
eb348b89 PM |
2629 | WARN_ON_ONCE(atomic_read(&rdtp->dynticks_idle) & 0x1); |
2630 | } | |
2631 | ||
0edd1b17 PM |
2632 | /* |
2633 | * Unconditionally force exit from full system-idle state. This is | |
2634 | * invoked when a normal CPU exits idle, but must be called separately | |
2635 | * for the timekeeping CPU (tick_do_timer_cpu). The reason for this | |
2636 | * is that the timekeeping CPU is permitted to take scheduling-clock | |
2637 | * interrupts while the system is in system-idle state, and of course | |
2638 | * rcu_sysidle_exit() has no way of distinguishing a scheduling-clock | |
2639 | * interrupt from any other type of interrupt. | |
2640 | */ | |
2641 | void rcu_sysidle_force_exit(void) | |
2642 | { | |
7d0ae808 | 2643 | int oldstate = READ_ONCE(full_sysidle_state); |
0edd1b17 PM |
2644 | int newoldstate; |
2645 | ||
2646 | /* | |
2647 | * Each pass through the following loop attempts to exit full | |
2648 | * system-idle state. If contention proves to be a problem, | |
2649 | * a trylock-based contention tree could be used here. | |
2650 | */ | |
2651 | while (oldstate > RCU_SYSIDLE_SHORT) { | |
2652 | newoldstate = cmpxchg(&full_sysidle_state, | |
2653 | oldstate, RCU_SYSIDLE_NOT); | |
2654 | if (oldstate == newoldstate && | |
2655 | oldstate == RCU_SYSIDLE_FULL_NOTED) { | |
2656 | rcu_kick_nohz_cpu(tick_do_timer_cpu); | |
2657 | return; /* We cleared it, done! */ | |
2658 | } | |
2659 | oldstate = newoldstate; | |
2660 | } | |
2661 | smp_mb(); /* Order initial oldstate fetch vs. later non-idle work. */ | |
2662 | } | |
2663 | ||
eb348b89 PM |
2664 | /* |
2665 | * Invoked to note entry to irq or task transition from idle. Note that | |
2666 | * usermode execution does -not- count as idle here! The caller must | |
2667 | * have disabled interrupts. | |
2668 | */ | |
28ced795 | 2669 | static void rcu_sysidle_exit(int irq) |
eb348b89 | 2670 | { |
28ced795 CL |
2671 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
2672 | ||
663e1310 PM |
2673 | /* If there are no nohz_full= CPUs, no need to track this. */ |
2674 | if (!tick_nohz_full_enabled()) | |
2675 | return; | |
2676 | ||
eb348b89 PM |
2677 | /* Adjust nesting, check for already non-idle. */ |
2678 | if (irq) { | |
2679 | rdtp->dynticks_idle_nesting++; | |
2680 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); | |
2681 | if (rdtp->dynticks_idle_nesting != 1) | |
2682 | return; /* Already non-idle. */ | |
2683 | } else { | |
2684 | /* | |
2685 | * Allow for irq misnesting. Yes, it really is possible | |
2686 | * to enter an irq handler then never leave it, and maybe | |
2687 | * also vice versa. Handle both possibilities. | |
2688 | */ | |
2689 | if (rdtp->dynticks_idle_nesting & DYNTICK_TASK_NEST_MASK) { | |
2690 | rdtp->dynticks_idle_nesting += DYNTICK_TASK_NEST_VALUE; | |
2691 | WARN_ON_ONCE(rdtp->dynticks_idle_nesting <= 0); | |
2692 | return; /* Already non-idle. */ | |
2693 | } else { | |
2694 | rdtp->dynticks_idle_nesting = DYNTICK_TASK_EXIT_IDLE; | |
2695 | } | |
2696 | } | |
2697 | ||
2698 | /* Record end of idle period. */ | |
4e857c58 | 2699 | smp_mb__before_atomic(); |
eb348b89 | 2700 | atomic_inc(&rdtp->dynticks_idle); |
4e857c58 | 2701 | smp_mb__after_atomic(); |
eb348b89 | 2702 | WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks_idle) & 0x1)); |
0edd1b17 PM |
2703 | |
2704 | /* | |
2705 | * If we are the timekeeping CPU, we are permitted to be non-idle | |
2706 | * during a system-idle state. This must be the case, because | |
2707 | * the timekeeping CPU has to take scheduling-clock interrupts | |
2708 | * during the time that the system is transitioning to full | |
2709 | * system-idle state. This means that the timekeeping CPU must | |
2710 | * invoke rcu_sysidle_force_exit() directly if it does anything | |
2711 | * more than take a scheduling-clock interrupt. | |
2712 | */ | |
2713 | if (smp_processor_id() == tick_do_timer_cpu) | |
2714 | return; | |
2715 | ||
2716 | /* Update system-idle state: We are clearly no longer fully idle! */ | |
2717 | rcu_sysidle_force_exit(); | |
2718 | } | |
2719 | ||
2720 | /* | |
2721 | * Check to see if the current CPU is idle. Note that usermode execution | |
5871968d PM |
2722 | * does not count as idle. The caller must have disabled interrupts, |
2723 | * and must be running on tick_do_timer_cpu. | |
0edd1b17 PM |
2724 | */ |
2725 | static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, | |
2726 | unsigned long *maxj) | |
2727 | { | |
2728 | int cur; | |
2729 | unsigned long j; | |
2730 | struct rcu_dynticks *rdtp = rdp->dynticks; | |
2731 | ||
663e1310 PM |
2732 | /* If there are no nohz_full= CPUs, don't check system-wide idleness. */ |
2733 | if (!tick_nohz_full_enabled()) | |
2734 | return; | |
2735 | ||
0edd1b17 PM |
2736 | /* |
2737 | * If some other CPU has already reported non-idle, if this is | |
2738 | * not the flavor of RCU that tracks sysidle state, or if this | |
2739 | * is an offline or the timekeeping CPU, nothing to do. | |
2740 | */ | |
417e8d26 | 2741 | if (!*isidle || rdp->rsp != rcu_state_p || |
0edd1b17 PM |
2742 | cpu_is_offline(rdp->cpu) || rdp->cpu == tick_do_timer_cpu) |
2743 | return; | |
5871968d PM |
2744 | /* Verify affinity of current kthread. */ |
2745 | WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu); | |
0edd1b17 PM |
2746 | |
2747 | /* Pick up current idle and NMI-nesting counter and check. */ | |
2748 | cur = atomic_read(&rdtp->dynticks_idle); | |
2749 | if (cur & 0x1) { | |
2750 | *isidle = false; /* We are not idle! */ | |
2751 | return; | |
2752 | } | |
2753 | smp_mb(); /* Read counters before timestamps. */ | |
2754 | ||
2755 | /* Pick up timestamps. */ | |
7d0ae808 | 2756 | j = READ_ONCE(rdtp->dynticks_idle_jiffies); |
0edd1b17 PM |
2757 | /* If this CPU entered idle more recently, update maxj timestamp. */ |
2758 | if (ULONG_CMP_LT(*maxj, j)) | |
2759 | *maxj = j; | |
2760 | } | |
2761 | ||
2762 | /* | |
2763 | * Is this the flavor of RCU that is handling full-system idle? | |
2764 | */ | |
2765 | static bool is_sysidle_rcu_state(struct rcu_state *rsp) | |
2766 | { | |
417e8d26 | 2767 | return rsp == rcu_state_p; |
0edd1b17 PM |
2768 | } |
2769 | ||
2770 | /* | |
2771 | * Return a delay in jiffies based on the number of CPUs, rcu_node | |
2772 | * leaf fanout, and jiffies tick rate. The idea is to allow larger | |
2773 | * systems more time to transition to full-idle state in order to | |
2774 | * avoid the cache thrashing that otherwise occur on the state variable. | |
2775 | * Really small systems (less than a couple of tens of CPUs) should | |
2776 | * instead use a single global atomically incremented counter, and later | |
2777 | * versions of this will automatically reconfigure themselves accordingly. | |
2778 | */ | |
2779 | static unsigned long rcu_sysidle_delay(void) | |
2780 | { | |
2781 | if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) | |
2782 | return 0; | |
2783 | return DIV_ROUND_UP(nr_cpu_ids * HZ, rcu_fanout_leaf * 1000); | |
2784 | } | |
2785 | ||
2786 | /* | |
2787 | * Advance the full-system-idle state. This is invoked when all of | |
2788 | * the non-timekeeping CPUs are idle. | |
2789 | */ | |
2790 | static void rcu_sysidle(unsigned long j) | |
2791 | { | |
2792 | /* Check the current state. */ | |
7d0ae808 | 2793 | switch (READ_ONCE(full_sysidle_state)) { |
0edd1b17 PM |
2794 | case RCU_SYSIDLE_NOT: |
2795 | ||
2796 | /* First time all are idle, so note a short idle period. */ | |
7d0ae808 | 2797 | WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_SHORT); |
0edd1b17 PM |
2798 | break; |
2799 | ||
2800 | case RCU_SYSIDLE_SHORT: | |
2801 | ||
2802 | /* | |
2803 | * Idle for a bit, time to advance to next state? | |
2804 | * cmpxchg failure means race with non-idle, let them win. | |
2805 | */ | |
2806 | if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) | |
2807 | (void)cmpxchg(&full_sysidle_state, | |
2808 | RCU_SYSIDLE_SHORT, RCU_SYSIDLE_LONG); | |
2809 | break; | |
2810 | ||
2811 | case RCU_SYSIDLE_LONG: | |
2812 | ||
2813 | /* | |
2814 | * Do an additional check pass before advancing to full. | |
2815 | * cmpxchg failure means race with non-idle, let them win. | |
2816 | */ | |
2817 | if (ULONG_CMP_GE(jiffies, j + rcu_sysidle_delay())) | |
2818 | (void)cmpxchg(&full_sysidle_state, | |
2819 | RCU_SYSIDLE_LONG, RCU_SYSIDLE_FULL); | |
2820 | break; | |
2821 | ||
2822 | default: | |
2823 | break; | |
2824 | } | |
2825 | } | |
2826 | ||
2827 | /* | |
2828 | * Found a non-idle non-timekeeping CPU, so kick the system-idle state | |
2829 | * back to the beginning. | |
2830 | */ | |
2831 | static void rcu_sysidle_cancel(void) | |
2832 | { | |
2833 | smp_mb(); | |
becb41bf | 2834 | if (full_sysidle_state > RCU_SYSIDLE_SHORT) |
7d0ae808 | 2835 | WRITE_ONCE(full_sysidle_state, RCU_SYSIDLE_NOT); |
0edd1b17 PM |
2836 | } |
2837 | ||
2838 | /* | |
2839 | * Update the sysidle state based on the results of a force-quiescent-state | |
2840 | * scan of the CPUs' dyntick-idle state. | |
2841 | */ | |
2842 | static void rcu_sysidle_report(struct rcu_state *rsp, int isidle, | |
2843 | unsigned long maxj, bool gpkt) | |
2844 | { | |
417e8d26 | 2845 | if (rsp != rcu_state_p) |
0edd1b17 PM |
2846 | return; /* Wrong flavor, ignore. */ |
2847 | if (gpkt && nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) | |
2848 | return; /* Running state machine from timekeeping CPU. */ | |
2849 | if (isidle) | |
2850 | rcu_sysidle(maxj); /* More idle! */ | |
2851 | else | |
2852 | rcu_sysidle_cancel(); /* Idle is over. */ | |
2853 | } | |
2854 | ||
2855 | /* | |
2856 | * Wrapper for rcu_sysidle_report() when called from the grace-period | |
2857 | * kthread's context. | |
2858 | */ | |
2859 | static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, | |
2860 | unsigned long maxj) | |
2861 | { | |
663e1310 PM |
2862 | /* If there are no nohz_full= CPUs, no need to track this. */ |
2863 | if (!tick_nohz_full_enabled()) | |
2864 | return; | |
2865 | ||
0edd1b17 PM |
2866 | rcu_sysidle_report(rsp, isidle, maxj, true); |
2867 | } | |
2868 | ||
2869 | /* Callback and function for forcing an RCU grace period. */ | |
2870 | struct rcu_sysidle_head { | |
2871 | struct rcu_head rh; | |
2872 | int inuse; | |
2873 | }; | |
2874 | ||
2875 | static void rcu_sysidle_cb(struct rcu_head *rhp) | |
2876 | { | |
2877 | struct rcu_sysidle_head *rshp; | |
2878 | ||
2879 | /* | |
2880 | * The following memory barrier is needed to replace the | |
2881 | * memory barriers that would normally be in the memory | |
2882 | * allocator. | |
2883 | */ | |
2884 | smp_mb(); /* grace period precedes setting inuse. */ | |
2885 | ||
2886 | rshp = container_of(rhp, struct rcu_sysidle_head, rh); | |
7d0ae808 | 2887 | WRITE_ONCE(rshp->inuse, 0); |
0edd1b17 PM |
2888 | } |
2889 | ||
2890 | /* | |
2891 | * Check to see if the system is fully idle, other than the timekeeping CPU. | |
663e1310 PM |
2892 | * The caller must have disabled interrupts. This is not intended to be |
2893 | * called unless tick_nohz_full_enabled(). | |
0edd1b17 PM |
2894 | */ |
2895 | bool rcu_sys_is_idle(void) | |
2896 | { | |
2897 | static struct rcu_sysidle_head rsh; | |
7d0ae808 | 2898 | int rss = READ_ONCE(full_sysidle_state); |
0edd1b17 PM |
2899 | |
2900 | if (WARN_ON_ONCE(smp_processor_id() != tick_do_timer_cpu)) | |
2901 | return false; | |
2902 | ||
2903 | /* Handle small-system case by doing a full scan of CPUs. */ | |
2904 | if (nr_cpu_ids <= CONFIG_NO_HZ_FULL_SYSIDLE_SMALL) { | |
2905 | int oldrss = rss - 1; | |
2906 | ||
2907 | /* | |
2908 | * One pass to advance to each state up to _FULL. | |
2909 | * Give up if any pass fails to advance the state. | |
2910 | */ | |
2911 | while (rss < RCU_SYSIDLE_FULL && oldrss < rss) { | |
2912 | int cpu; | |
2913 | bool isidle = true; | |
2914 | unsigned long maxj = jiffies - ULONG_MAX / 4; | |
2915 | struct rcu_data *rdp; | |
2916 | ||
2917 | /* Scan all the CPUs looking for nonidle CPUs. */ | |
2918 | for_each_possible_cpu(cpu) { | |
417e8d26 | 2919 | rdp = per_cpu_ptr(rcu_state_p->rda, cpu); |
0edd1b17 PM |
2920 | rcu_sysidle_check_cpu(rdp, &isidle, &maxj); |
2921 | if (!isidle) | |
2922 | break; | |
2923 | } | |
417e8d26 | 2924 | rcu_sysidle_report(rcu_state_p, isidle, maxj, false); |
0edd1b17 | 2925 | oldrss = rss; |
7d0ae808 | 2926 | rss = READ_ONCE(full_sysidle_state); |
0edd1b17 PM |
2927 | } |
2928 | } | |
2929 | ||
2930 | /* If this is the first observation of an idle period, record it. */ | |
2931 | if (rss == RCU_SYSIDLE_FULL) { | |
2932 | rss = cmpxchg(&full_sysidle_state, | |
2933 | RCU_SYSIDLE_FULL, RCU_SYSIDLE_FULL_NOTED); | |
2934 | return rss == RCU_SYSIDLE_FULL; | |
2935 | } | |
2936 | ||
2937 | smp_mb(); /* ensure rss load happens before later caller actions. */ | |
2938 | ||
2939 | /* If already fully idle, tell the caller (in case of races). */ | |
2940 | if (rss == RCU_SYSIDLE_FULL_NOTED) | |
2941 | return true; | |
2942 | ||
2943 | /* | |
2944 | * If we aren't there yet, and a grace period is not in flight, | |
2945 | * initiate a grace period. Either way, tell the caller that | |
2946 | * we are not there yet. We use an xchg() rather than an assignment | |
2947 | * to make up for the memory barriers that would otherwise be | |
2948 | * provided by the memory allocator. | |
2949 | */ | |
2950 | if (nr_cpu_ids > CONFIG_NO_HZ_FULL_SYSIDLE_SMALL && | |
417e8d26 | 2951 | !rcu_gp_in_progress(rcu_state_p) && |
0edd1b17 PM |
2952 | !rsh.inuse && xchg(&rsh.inuse, 1) == 0) |
2953 | call_rcu(&rsh.rh, rcu_sysidle_cb); | |
2954 | return false; | |
eb348b89 PM |
2955 | } |
2956 | ||
2333210b PM |
2957 | /* |
2958 | * Initialize dynticks sysidle state for CPUs coming online. | |
2959 | */ | |
2960 | static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) | |
2961 | { | |
2962 | rdtp->dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE; | |
2963 | } | |
2964 | ||
2965 | #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ | |
2966 | ||
28ced795 | 2967 | static void rcu_sysidle_enter(int irq) |
eb348b89 PM |
2968 | { |
2969 | } | |
2970 | ||
28ced795 | 2971 | static void rcu_sysidle_exit(int irq) |
eb348b89 PM |
2972 | { |
2973 | } | |
2974 | ||
0edd1b17 PM |
2975 | static void rcu_sysidle_check_cpu(struct rcu_data *rdp, bool *isidle, |
2976 | unsigned long *maxj) | |
2977 | { | |
2978 | } | |
2979 | ||
2980 | static bool is_sysidle_rcu_state(struct rcu_state *rsp) | |
2981 | { | |
2982 | return false; | |
2983 | } | |
2984 | ||
2985 | static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle, | |
2986 | unsigned long maxj) | |
2987 | { | |
2988 | } | |
2989 | ||
2333210b PM |
2990 | static void rcu_sysidle_init_percpu_data(struct rcu_dynticks *rdtp) |
2991 | { | |
2992 | } | |
2993 | ||
2994 | #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ | |
a096932f PM |
2995 | |
2996 | /* | |
2997 | * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the | |
2998 | * grace-period kthread will do force_quiescent_state() processing? | |
2999 | * The idea is to avoid waking up RCU core processing on such a | |
3000 | * CPU unless the grace period has extended for too long. | |
3001 | * | |
3002 | * This code relies on the fact that all NO_HZ_FULL CPUs are also | |
52e2bb95 | 3003 | * CONFIG_RCU_NOCB_CPU CPUs. |
a096932f PM |
3004 | */ |
3005 | static bool rcu_nohz_full_cpu(struct rcu_state *rsp) | |
3006 | { | |
3007 | #ifdef CONFIG_NO_HZ_FULL | |
3008 | if (tick_nohz_full_cpu(smp_processor_id()) && | |
3009 | (!rcu_gp_in_progress(rsp) || | |
7d0ae808 | 3010 | ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ))) |
5ce035fb | 3011 | return true; |
a096932f | 3012 | #endif /* #ifdef CONFIG_NO_HZ_FULL */ |
5ce035fb | 3013 | return false; |
a096932f | 3014 | } |
5057f55e PM |
3015 | |
3016 | /* | |
3017 | * Bind the grace-period kthread for the sysidle flavor of RCU to the | |
3018 | * timekeeping CPU. | |
3019 | */ | |
3020 | static void rcu_bind_gp_kthread(void) | |
3021 | { | |
c0f489d2 | 3022 | int __maybe_unused cpu; |
5057f55e | 3023 | |
c0f489d2 | 3024 | if (!tick_nohz_full_enabled()) |
5057f55e | 3025 | return; |
c0f489d2 PM |
3026 | #ifdef CONFIG_NO_HZ_FULL_SYSIDLE |
3027 | cpu = tick_do_timer_cpu; | |
5871968d | 3028 | if (cpu >= 0 && cpu < nr_cpu_ids) |
5057f55e | 3029 | set_cpus_allowed_ptr(current, cpumask_of(cpu)); |
c0f489d2 | 3030 | #else /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ |
5871968d | 3031 | housekeeping_affine(current); |
c0f489d2 | 3032 | #endif /* #else #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ |
5057f55e | 3033 | } |
176f8f7a PM |
3034 | |
3035 | /* Record the current task on dyntick-idle entry. */ | |
3036 | static void rcu_dynticks_task_enter(void) | |
3037 | { | |
3038 | #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) | |
7d0ae808 | 3039 | WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id()); |
176f8f7a PM |
3040 | #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ |
3041 | } | |
3042 | ||
3043 | /* Record no current task on dyntick-idle exit. */ | |
3044 | static void rcu_dynticks_task_exit(void) | |
3045 | { | |
3046 | #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) | |
7d0ae808 | 3047 | WRITE_ONCE(current->rcu_tasks_idle_cpu, -1); |
176f8f7a PM |
3048 | #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ |
3049 | } |