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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> |
b17b0153 | 30 | #include <linux/sched/debug.h> |
62ab7072 | 31 | #include <linux/smpboot.h> |
78634061 | 32 | #include <linux/sched/isolation.h> |
ae7e81c0 | 33 | #include <uapi/linux/sched/types.h> |
4102adab | 34 | #include "../time/tick-internal.h" |
f41d911f | 35 | |
5b61b0ba | 36 | #ifdef CONFIG_RCU_BOOST |
61cfd097 | 37 | |
abaa93d9 | 38 | #include "../locking/rtmutex_common.h" |
21871d7e | 39 | |
61cfd097 PM |
40 | /* |
41 | * Control variables for per-CPU and per-rcu_node kthreads. These | |
42 | * handle all flavors of RCU. | |
43 | */ | |
44 | static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task); | |
45 | DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status); | |
46 | DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops); | |
47 | DEFINE_PER_CPU(char, rcu_cpu_has_work); | |
48 | ||
727b705b PM |
49 | #else /* #ifdef CONFIG_RCU_BOOST */ |
50 | ||
51 | /* | |
52 | * Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST, | |
53 | * all uses are in dead code. Provide a definition to keep the compiler | |
54 | * happy, but add WARN_ON_ONCE() to complain if used in the wrong place. | |
55 | * This probably needs to be excluded from -rt builds. | |
56 | */ | |
57 | #define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; }) | |
b8869781 | 58 | #define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1) |
727b705b PM |
59 | |
60 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ | |
5b61b0ba | 61 | |
3fbfbf7a PM |
62 | #ifdef CONFIG_RCU_NOCB_CPU |
63 | static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ | |
1b0048a4 | 64 | static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ |
3fbfbf7a PM |
65 | #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ |
66 | ||
26845c28 PM |
67 | /* |
68 | * Check the RCU kernel configuration parameters and print informative | |
699d4035 | 69 | * messages about anything out of the ordinary. |
26845c28 PM |
70 | */ |
71 | static void __init rcu_bootup_announce_oddness(void) | |
72 | { | |
ab6f5bd6 | 73 | if (IS_ENABLED(CONFIG_RCU_TRACE)) |
ae91aa0a | 74 | pr_info("\tRCU event tracing is enabled.\n"); |
05c5df31 PM |
75 | if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) || |
76 | (!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32)) | |
a7538352 JP |
77 | pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d.\n", |
78 | RCU_FANOUT); | |
7fa27001 | 79 | if (rcu_fanout_exact) |
ab6f5bd6 PM |
80 | pr_info("\tHierarchical RCU autobalancing is disabled.\n"); |
81 | if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ)) | |
82 | pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n"); | |
c4a09ff7 | 83 | if (IS_ENABLED(CONFIG_PROVE_RCU)) |
ab6f5bd6 | 84 | pr_info("\tRCU lockdep checking is enabled.\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) | |
a7538352 JP |
91 | pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", |
92 | rcu_fanout_leaf); | |
cca6f393 | 93 | if (nr_cpu_ids != NR_CPUS) |
9b130ad5 | 94 | pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids); |
17c7798b | 95 | #ifdef CONFIG_RCU_BOOST |
a7538352 JP |
96 | pr_info("\tRCU priority boosting: priority %d delay %d ms.\n", |
97 | kthread_prio, CONFIG_RCU_BOOST_DELAY); | |
17c7798b PM |
98 | #endif |
99 | if (blimit != DEFAULT_RCU_BLIMIT) | |
100 | pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit); | |
101 | if (qhimark != DEFAULT_RCU_QHIMARK) | |
102 | pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark); | |
103 | if (qlowmark != DEFAULT_RCU_QLOMARK) | |
104 | pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark); | |
105 | if (jiffies_till_first_fqs != ULONG_MAX) | |
106 | pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs); | |
107 | if (jiffies_till_next_fqs != ULONG_MAX) | |
108 | pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs); | |
109 | if (rcu_kick_kthreads) | |
110 | pr_info("\tKick kthreads if too-long grace period.\n"); | |
111 | if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD)) | |
112 | pr_info("\tRCU callback double-/use-after-free debug enabled.\n"); | |
90040c9e | 113 | if (gp_preinit_delay) |
17c7798b | 114 | pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay); |
90040c9e | 115 | if (gp_init_delay) |
17c7798b | 116 | pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay); |
90040c9e | 117 | if (gp_cleanup_delay) |
17c7798b PM |
118 | pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay); |
119 | if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG)) | |
120 | pr_info("\tRCU debug extended QS entry/exit.\n"); | |
59d80fd8 | 121 | rcupdate_announce_bootup_oddness(); |
26845c28 PM |
122 | } |
123 | ||
28f6569a | 124 | #ifdef CONFIG_PREEMPT_RCU |
f41d911f | 125 | |
a41bfeb2 | 126 | RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu); |
b28a7c01 | 127 | static struct rcu_state *const rcu_state_p = &rcu_preempt_state; |
2927a689 | 128 | static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data; |
f41d911f | 129 | |
d19fb8d1 PM |
130 | static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, |
131 | bool wake); | |
3949fa9b | 132 | static void rcu_read_unlock_special(struct task_struct *t); |
d9a3da06 | 133 | |
f41d911f PM |
134 | /* |
135 | * Tell them what RCU they are running. | |
136 | */ | |
0e0fc1c2 | 137 | static void __init rcu_bootup_announce(void) |
f41d911f | 138 | { |
efc151c3 | 139 | pr_info("Preemptible hierarchical RCU implementation.\n"); |
26845c28 | 140 | rcu_bootup_announce_oddness(); |
f41d911f PM |
141 | } |
142 | ||
8203d6d0 PM |
143 | /* Flags for rcu_preempt_ctxt_queue() decision table. */ |
144 | #define RCU_GP_TASKS 0x8 | |
145 | #define RCU_EXP_TASKS 0x4 | |
146 | #define RCU_GP_BLKD 0x2 | |
147 | #define RCU_EXP_BLKD 0x1 | |
148 | ||
149 | /* | |
150 | * Queues a task preempted within an RCU-preempt read-side critical | |
151 | * section into the appropriate location within the ->blkd_tasks list, | |
152 | * depending on the states of any ongoing normal and expedited grace | |
153 | * periods. The ->gp_tasks pointer indicates which element the normal | |
154 | * grace period is waiting on (NULL if none), and the ->exp_tasks pointer | |
155 | * indicates which element the expedited grace period is waiting on (again, | |
156 | * NULL if none). If a grace period is waiting on a given element in the | |
157 | * ->blkd_tasks list, it also waits on all subsequent elements. Thus, | |
158 | * adding a task to the tail of the list blocks any grace period that is | |
159 | * already waiting on one of the elements. In contrast, adding a task | |
160 | * to the head of the list won't block any grace period that is already | |
161 | * waiting on one of the elements. | |
162 | * | |
163 | * This queuing is imprecise, and can sometimes make an ongoing grace | |
164 | * period wait for a task that is not strictly speaking blocking it. | |
165 | * Given the choice, we needlessly block a normal grace period rather than | |
166 | * blocking an expedited grace period. | |
167 | * | |
168 | * Note that an endless sequence of expedited grace periods still cannot | |
169 | * indefinitely postpone a normal grace period. Eventually, all of the | |
170 | * fixed number of preempted tasks blocking the normal grace period that are | |
171 | * not also blocking the expedited grace period will resume and complete | |
172 | * their RCU read-side critical sections. At that point, the ->gp_tasks | |
173 | * pointer will equal the ->exp_tasks pointer, at which point the end of | |
174 | * the corresponding expedited grace period will also be the end of the | |
175 | * normal grace period. | |
176 | */ | |
46a5d164 PM |
177 | static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) |
178 | __releases(rnp->lock) /* But leaves rrupts disabled. */ | |
8203d6d0 PM |
179 | { |
180 | int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) + | |
181 | (rnp->exp_tasks ? RCU_EXP_TASKS : 0) + | |
182 | (rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) + | |
183 | (rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0); | |
184 | struct task_struct *t = current; | |
185 | ||
a32e01ee | 186 | raw_lockdep_assert_held_rcu_node(rnp); |
2dee9404 | 187 | WARN_ON_ONCE(rdp->mynode != rnp); |
5b4c11d5 | 188 | WARN_ON_ONCE(!rcu_is_leaf_node(rnp)); |
1f3e5f51 PM |
189 | /* RCU better not be waiting on newly onlined CPUs! */ |
190 | WARN_ON_ONCE(rnp->qsmaskinitnext & ~rnp->qsmaskinit & rnp->qsmask & | |
191 | rdp->grpmask); | |
ea9b0c8a | 192 | |
8203d6d0 PM |
193 | /* |
194 | * Decide where to queue the newly blocked task. In theory, | |
195 | * this could be an if-statement. In practice, when I tried | |
196 | * that, it was quite messy. | |
197 | */ | |
198 | switch (blkd_state) { | |
199 | case 0: | |
200 | case RCU_EXP_TASKS: | |
201 | case RCU_EXP_TASKS + RCU_GP_BLKD: | |
202 | case RCU_GP_TASKS: | |
203 | case RCU_GP_TASKS + RCU_EXP_TASKS: | |
204 | ||
205 | /* | |
206 | * Blocking neither GP, or first task blocking the normal | |
207 | * GP but not blocking the already-waiting expedited GP. | |
208 | * Queue at the head of the list to avoid unnecessarily | |
209 | * blocking the already-waiting GPs. | |
210 | */ | |
211 | list_add(&t->rcu_node_entry, &rnp->blkd_tasks); | |
212 | break; | |
213 | ||
214 | case RCU_EXP_BLKD: | |
215 | case RCU_GP_BLKD: | |
216 | case RCU_GP_BLKD + RCU_EXP_BLKD: | |
217 | case RCU_GP_TASKS + RCU_EXP_BLKD: | |
218 | case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: | |
219 | case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: | |
220 | ||
221 | /* | |
222 | * First task arriving that blocks either GP, or first task | |
223 | * arriving that blocks the expedited GP (with the normal | |
224 | * GP already waiting), or a task arriving that blocks | |
225 | * both GPs with both GPs already waiting. Queue at the | |
226 | * tail of the list to avoid any GP waiting on any of the | |
227 | * already queued tasks that are not blocking it. | |
228 | */ | |
229 | list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks); | |
230 | break; | |
231 | ||
232 | case RCU_EXP_TASKS + RCU_EXP_BLKD: | |
233 | case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD: | |
234 | case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD: | |
235 | ||
236 | /* | |
237 | * Second or subsequent task blocking the expedited GP. | |
238 | * The task either does not block the normal GP, or is the | |
239 | * first task blocking the normal GP. Queue just after | |
240 | * the first task blocking the expedited GP. | |
241 | */ | |
242 | list_add(&t->rcu_node_entry, rnp->exp_tasks); | |
243 | break; | |
244 | ||
245 | case RCU_GP_TASKS + RCU_GP_BLKD: | |
246 | case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD: | |
247 | ||
248 | /* | |
249 | * Second or subsequent task blocking the normal GP. | |
250 | * The task does not block the expedited GP. Queue just | |
251 | * after the first task blocking the normal GP. | |
252 | */ | |
253 | list_add(&t->rcu_node_entry, rnp->gp_tasks); | |
254 | break; | |
255 | ||
256 | default: | |
257 | ||
258 | /* Yet another exercise in excessive paranoia. */ | |
259 | WARN_ON_ONCE(1); | |
260 | break; | |
261 | } | |
262 | ||
263 | /* | |
264 | * We have now queued the task. If it was the first one to | |
265 | * block either grace period, update the ->gp_tasks and/or | |
266 | * ->exp_tasks pointers, respectively, to reference the newly | |
267 | * blocked tasks. | |
268 | */ | |
4bc8d555 | 269 | if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) { |
8203d6d0 | 270 | rnp->gp_tasks = &t->rcu_node_entry; |
d43a5d32 | 271 | WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq); |
4bc8d555 | 272 | } |
8203d6d0 PM |
273 | if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD)) |
274 | rnp->exp_tasks = &t->rcu_node_entry; | |
2dee9404 PM |
275 | WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) != |
276 | !(rnp->qsmask & rdp->grpmask)); | |
277 | WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) != | |
278 | !(rnp->expmask & rdp->grpmask)); | |
67c583a7 | 279 | raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */ |
8203d6d0 PM |
280 | |
281 | /* | |
282 | * Report the quiescent state for the expedited GP. This expedited | |
283 | * GP should not be able to end until we report, so there should be | |
284 | * no need to check for a subsequent expedited GP. (Though we are | |
285 | * still in a quiescent state in any case.) | |
286 | */ | |
287 | if (blkd_state & RCU_EXP_BLKD && | |
288 | t->rcu_read_unlock_special.b.exp_need_qs) { | |
289 | t->rcu_read_unlock_special.b.exp_need_qs = false; | |
290 | rcu_report_exp_rdp(rdp->rsp, rdp, true); | |
291 | } else { | |
292 | WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs); | |
293 | } | |
8203d6d0 PM |
294 | } |
295 | ||
f41d911f | 296 | /* |
c7037ff5 PM |
297 | * Record a preemptible-RCU quiescent state for the specified CPU. |
298 | * Note that this does not necessarily mean that the task currently running | |
299 | * on the CPU is in a quiescent state: Instead, it means that the current | |
300 | * grace period need not wait on any RCU read-side critical section that | |
301 | * starts later on this CPU. It also means that if the current task is | |
302 | * in an RCU read-side critical section, it has already added itself to | |
303 | * some leaf rcu_node structure's ->blkd_tasks list. In addition to the | |
304 | * current task, there might be any number of other tasks blocked while | |
305 | * in an RCU read-side critical section. | |
25502a6c | 306 | * |
c7037ff5 | 307 | * Callers to this function must disable preemption. |
f41d911f | 308 | */ |
284a8c93 | 309 | static void rcu_preempt_qs(void) |
f41d911f | 310 | { |
ea9b0c8a | 311 | RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_qs() invoked with preemption enabled!!!\n"); |
5b74c458 | 312 | if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) { |
284a8c93 | 313 | trace_rcu_grace_period(TPS("rcu_preempt"), |
477351f7 | 314 | __this_cpu_read(rcu_data_p->gp_seq), |
284a8c93 | 315 | TPS("cpuqs")); |
5b74c458 | 316 | __this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false); |
284a8c93 PM |
317 | barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */ |
318 | current->rcu_read_unlock_special.b.need_qs = false; | |
319 | } | |
f41d911f PM |
320 | } |
321 | ||
322 | /* | |
c3422bea PM |
323 | * We have entered the scheduler, and the current task might soon be |
324 | * context-switched away from. If this task is in an RCU read-side | |
325 | * critical section, we will no longer be able to rely on the CPU to | |
12f5f524 PM |
326 | * record that fact, so we enqueue the task on the blkd_tasks list. |
327 | * The task will dequeue itself when it exits the outermost enclosing | |
328 | * RCU read-side critical section. Therefore, the current grace period | |
329 | * cannot be permitted to complete until the blkd_tasks list entries | |
330 | * predating the current grace period drain, in other words, until | |
331 | * rnp->gp_tasks becomes NULL. | |
c3422bea | 332 | * |
46a5d164 | 333 | * Caller must disable interrupts. |
f41d911f | 334 | */ |
5b72f964 | 335 | static void rcu_preempt_note_context_switch(bool preempt) |
f41d911f PM |
336 | { |
337 | struct task_struct *t = current; | |
f41d911f PM |
338 | struct rcu_data *rdp; |
339 | struct rcu_node *rnp; | |
340 | ||
b04db8e1 | 341 | lockdep_assert_irqs_disabled(); |
5b72f964 | 342 | WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0); |
10f39bb1 | 343 | if (t->rcu_read_lock_nesting > 0 && |
1d082fd0 | 344 | !t->rcu_read_unlock_special.b.blocked) { |
f41d911f PM |
345 | |
346 | /* Possibly blocking in an RCU read-side critical section. */ | |
e63c887c | 347 | rdp = this_cpu_ptr(rcu_state_p->rda); |
f41d911f | 348 | rnp = rdp->mynode; |
46a5d164 | 349 | raw_spin_lock_rcu_node(rnp); |
1d082fd0 | 350 | t->rcu_read_unlock_special.b.blocked = true; |
86848966 | 351 | t->rcu_blocked_node = rnp; |
f41d911f PM |
352 | |
353 | /* | |
8203d6d0 PM |
354 | * Verify the CPU's sanity, trace the preemption, and |
355 | * then queue the task as required based on the states | |
356 | * of any ongoing and expedited grace periods. | |
f41d911f | 357 | */ |
0aa04b05 | 358 | WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0); |
e7d8842e | 359 | WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); |
d4c08f2a PM |
360 | trace_rcu_preempt_task(rdp->rsp->name, |
361 | t->pid, | |
362 | (rnp->qsmask & rdp->grpmask) | |
598ce094 PM |
363 | ? rnp->gp_seq |
364 | : rcu_seq_snap(&rnp->gp_seq)); | |
46a5d164 | 365 | rcu_preempt_ctxt_queue(rnp, rdp); |
10f39bb1 | 366 | } else if (t->rcu_read_lock_nesting < 0 && |
1d082fd0 | 367 | t->rcu_read_unlock_special.s) { |
10f39bb1 PM |
368 | |
369 | /* | |
370 | * Complete exit from RCU read-side critical section on | |
371 | * behalf of preempted instance of __rcu_read_unlock(). | |
372 | */ | |
373 | rcu_read_unlock_special(t); | |
f41d911f PM |
374 | } |
375 | ||
376 | /* | |
377 | * Either we were not in an RCU read-side critical section to | |
378 | * begin with, or we have now recorded that critical section | |
379 | * globally. Either way, we can now note a quiescent state | |
380 | * for this CPU. Again, if we were in an RCU read-side critical | |
381 | * section, and if that critical section was blocking the current | |
382 | * grace period, then the fact that the task has been enqueued | |
383 | * means that we continue to block the current grace period. | |
384 | */ | |
284a8c93 | 385 | rcu_preempt_qs(); |
f41d911f PM |
386 | } |
387 | ||
fc2219d4 PM |
388 | /* |
389 | * Check for preempted RCU readers blocking the current grace period | |
390 | * for the specified rcu_node structure. If the caller needs a reliable | |
391 | * answer, it must hold the rcu_node's ->lock. | |
392 | */ | |
27f4d280 | 393 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 | 394 | { |
12f5f524 | 395 | return rnp->gp_tasks != NULL; |
fc2219d4 PM |
396 | } |
397 | ||
0e5da22e PM |
398 | /* |
399 | * Preemptible RCU implementation for rcu_read_lock(). | |
400 | * Just increment ->rcu_read_lock_nesting, shared state will be updated | |
401 | * if we block. | |
402 | */ | |
403 | void __rcu_read_lock(void) | |
404 | { | |
405 | current->rcu_read_lock_nesting++; | |
406 | barrier(); /* critical section after entry code. */ | |
407 | } | |
408 | EXPORT_SYMBOL_GPL(__rcu_read_lock); | |
409 | ||
410 | /* | |
411 | * Preemptible RCU implementation for rcu_read_unlock(). | |
412 | * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost | |
413 | * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then | |
414 | * invoke rcu_read_unlock_special() to clean up after a context switch | |
415 | * in an RCU read-side critical section and other special cases. | |
416 | */ | |
417 | void __rcu_read_unlock(void) | |
418 | { | |
419 | struct task_struct *t = current; | |
420 | ||
421 | if (t->rcu_read_lock_nesting != 1) { | |
422 | --t->rcu_read_lock_nesting; | |
423 | } else { | |
424 | barrier(); /* critical section before exit code. */ | |
425 | t->rcu_read_lock_nesting = INT_MIN; | |
426 | barrier(); /* assign before ->rcu_read_unlock_special load */ | |
427 | if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s))) | |
428 | rcu_read_unlock_special(t); | |
429 | barrier(); /* ->rcu_read_unlock_special load before assign */ | |
430 | t->rcu_read_lock_nesting = 0; | |
431 | } | |
432 | #ifdef CONFIG_PROVE_LOCKING | |
433 | { | |
434 | int rrln = READ_ONCE(t->rcu_read_lock_nesting); | |
435 | ||
436 | WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2); | |
437 | } | |
438 | #endif /* #ifdef CONFIG_PROVE_LOCKING */ | |
439 | } | |
440 | EXPORT_SYMBOL_GPL(__rcu_read_unlock); | |
441 | ||
12f5f524 PM |
442 | /* |
443 | * Advance a ->blkd_tasks-list pointer to the next entry, instead | |
444 | * returning NULL if at the end of the list. | |
445 | */ | |
446 | static struct list_head *rcu_next_node_entry(struct task_struct *t, | |
447 | struct rcu_node *rnp) | |
448 | { | |
449 | struct list_head *np; | |
450 | ||
451 | np = t->rcu_node_entry.next; | |
452 | if (np == &rnp->blkd_tasks) | |
453 | np = NULL; | |
454 | return np; | |
455 | } | |
456 | ||
8af3a5e7 PM |
457 | /* |
458 | * Return true if the specified rcu_node structure has tasks that were | |
459 | * preempted within an RCU read-side critical section. | |
460 | */ | |
461 | static bool rcu_preempt_has_tasks(struct rcu_node *rnp) | |
462 | { | |
463 | return !list_empty(&rnp->blkd_tasks); | |
464 | } | |
465 | ||
b668c9cf PM |
466 | /* |
467 | * Handle special cases during rcu_read_unlock(), such as needing to | |
468 | * notify RCU core processing or task having blocked during the RCU | |
469 | * read-side critical section. | |
470 | */ | |
3949fa9b | 471 | static void rcu_read_unlock_special(struct task_struct *t) |
f41d911f | 472 | { |
b6a932d1 PM |
473 | bool empty_exp; |
474 | bool empty_norm; | |
475 | bool empty_exp_now; | |
f41d911f | 476 | unsigned long flags; |
12f5f524 | 477 | struct list_head *np; |
abaa93d9 | 478 | bool drop_boost_mutex = false; |
8203d6d0 | 479 | struct rcu_data *rdp; |
f41d911f | 480 | struct rcu_node *rnp; |
1d082fd0 | 481 | union rcu_special special; |
f41d911f PM |
482 | |
483 | /* NMI handlers cannot block and cannot safely manipulate state. */ | |
484 | if (in_nmi()) | |
485 | return; | |
486 | ||
487 | local_irq_save(flags); | |
488 | ||
489 | /* | |
8203d6d0 PM |
490 | * If RCU core is waiting for this CPU to exit its critical section, |
491 | * report the fact that it has exited. Because irqs are disabled, | |
1d082fd0 | 492 | * t->rcu_read_unlock_special cannot change. |
f41d911f PM |
493 | */ |
494 | special = t->rcu_read_unlock_special; | |
1d082fd0 | 495 | if (special.b.need_qs) { |
284a8c93 | 496 | rcu_preempt_qs(); |
c0135d07 | 497 | t->rcu_read_unlock_special.b.need_qs = false; |
1d082fd0 | 498 | if (!t->rcu_read_unlock_special.s) { |
79a62f95 LJ |
499 | local_irq_restore(flags); |
500 | return; | |
501 | } | |
f41d911f PM |
502 | } |
503 | ||
8203d6d0 PM |
504 | /* |
505 | * Respond to a request for an expedited grace period, but only if | |
506 | * we were not preempted, meaning that we were running on the same | |
507 | * CPU throughout. If we were preempted, the exp_need_qs flag | |
508 | * would have been cleared at the time of the first preemption, | |
509 | * and the quiescent state would be reported when we were dequeued. | |
510 | */ | |
511 | if (special.b.exp_need_qs) { | |
512 | WARN_ON_ONCE(special.b.blocked); | |
513 | t->rcu_read_unlock_special.b.exp_need_qs = false; | |
514 | rdp = this_cpu_ptr(rcu_state_p->rda); | |
515 | rcu_report_exp_rdp(rcu_state_p, rdp, true); | |
516 | if (!t->rcu_read_unlock_special.s) { | |
517 | local_irq_restore(flags); | |
518 | return; | |
519 | } | |
520 | } | |
521 | ||
79a62f95 | 522 | /* Hardware IRQ handlers cannot block, complain if they get here. */ |
d24209bb PM |
523 | if (in_irq() || in_serving_softirq()) { |
524 | lockdep_rcu_suspicious(__FILE__, __LINE__, | |
525 | "rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n"); | |
8203d6d0 | 526 | pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n", |
d24209bb PM |
527 | t->rcu_read_unlock_special.s, |
528 | t->rcu_read_unlock_special.b.blocked, | |
8203d6d0 | 529 | t->rcu_read_unlock_special.b.exp_need_qs, |
d24209bb | 530 | t->rcu_read_unlock_special.b.need_qs); |
f41d911f PM |
531 | local_irq_restore(flags); |
532 | return; | |
533 | } | |
534 | ||
535 | /* Clean up if blocked during RCU read-side critical section. */ | |
1d082fd0 PM |
536 | if (special.b.blocked) { |
537 | t->rcu_read_unlock_special.b.blocked = false; | |
f41d911f | 538 | |
dd5d19ba | 539 | /* |
0a0ba1c9 | 540 | * Remove this task from the list it blocked on. The task |
8ba9153b PM |
541 | * now remains queued on the rcu_node corresponding to the |
542 | * CPU it first blocked on, so there is no longer any need | |
543 | * to loop. Retain a WARN_ON_ONCE() out of sheer paranoia. | |
dd5d19ba | 544 | */ |
8ba9153b PM |
545 | rnp = t->rcu_blocked_node; |
546 | raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ | |
547 | WARN_ON_ONCE(rnp != t->rcu_blocked_node); | |
5b4c11d5 | 548 | WARN_ON_ONCE(!rcu_is_leaf_node(rnp)); |
74e871ac | 549 | empty_norm = !rcu_preempt_blocked_readers_cgp(rnp); |
d43a5d32 | 550 | WARN_ON_ONCE(rnp->completedqs == rnp->gp_seq && |
4bc8d555 | 551 | (!empty_norm || rnp->qsmask)); |
8203d6d0 | 552 | empty_exp = sync_rcu_preempt_exp_done(rnp); |
d9a3da06 | 553 | smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ |
12f5f524 | 554 | np = rcu_next_node_entry(t, rnp); |
f41d911f | 555 | list_del_init(&t->rcu_node_entry); |
82e78d80 | 556 | t->rcu_blocked_node = NULL; |
f7f7bac9 | 557 | trace_rcu_unlock_preempted_task(TPS("rcu_preempt"), |
865aa1e0 | 558 | rnp->gp_seq, t->pid); |
12f5f524 PM |
559 | if (&t->rcu_node_entry == rnp->gp_tasks) |
560 | rnp->gp_tasks = np; | |
561 | if (&t->rcu_node_entry == rnp->exp_tasks) | |
562 | rnp->exp_tasks = np; | |
727b705b | 563 | if (IS_ENABLED(CONFIG_RCU_BOOST)) { |
727b705b PM |
564 | /* Snapshot ->boost_mtx ownership w/rnp->lock held. */ |
565 | drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t; | |
2dee9404 PM |
566 | if (&t->rcu_node_entry == rnp->boost_tasks) |
567 | rnp->boost_tasks = np; | |
727b705b | 568 | } |
f41d911f PM |
569 | |
570 | /* | |
571 | * If this was the last task on the current list, and if | |
572 | * we aren't waiting on any CPUs, report the quiescent state. | |
389abd48 PM |
573 | * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, |
574 | * so we must take a snapshot of the expedited state. | |
f41d911f | 575 | */ |
8203d6d0 | 576 | empty_exp_now = sync_rcu_preempt_exp_done(rnp); |
74e871ac | 577 | if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) { |
f7f7bac9 | 578 | trace_rcu_quiescent_state_report(TPS("preempt_rcu"), |
db023296 | 579 | rnp->gp_seq, |
d4c08f2a PM |
580 | 0, rnp->qsmask, |
581 | rnp->level, | |
582 | rnp->grplo, | |
583 | rnp->grphi, | |
584 | !!rnp->gp_tasks); | |
e63c887c | 585 | rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags); |
c701d5d9 | 586 | } else { |
67c583a7 | 587 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
c701d5d9 | 588 | } |
d9a3da06 | 589 | |
27f4d280 | 590 | /* Unboost if we were boosted. */ |
727b705b | 591 | if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) |
02a7c234 | 592 | rt_mutex_futex_unlock(&rnp->boost_mtx); |
27f4d280 | 593 | |
d9a3da06 PM |
594 | /* |
595 | * If this was the last task on the expedited lists, | |
596 | * then we need to report up the rcu_node hierarchy. | |
597 | */ | |
389abd48 | 598 | if (!empty_exp && empty_exp_now) |
e63c887c | 599 | rcu_report_exp_rnp(rcu_state_p, rnp, true); |
b668c9cf PM |
600 | } else { |
601 | local_irq_restore(flags); | |
f41d911f | 602 | } |
f41d911f PM |
603 | } |
604 | ||
1ed509a2 PM |
605 | /* |
606 | * Dump detailed information for all tasks blocking the current RCU | |
607 | * grace period on the specified rcu_node structure. | |
608 | */ | |
609 | static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) | |
610 | { | |
611 | unsigned long flags; | |
1ed509a2 PM |
612 | struct task_struct *t; |
613 | ||
6cf10081 | 614 | raw_spin_lock_irqsave_rcu_node(rnp, flags); |
5fd4dc06 | 615 | if (!rcu_preempt_blocked_readers_cgp(rnp)) { |
67c583a7 | 616 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
5fd4dc06 PM |
617 | return; |
618 | } | |
82efed06 | 619 | t = list_entry(rnp->gp_tasks->prev, |
12f5f524 | 620 | struct task_struct, rcu_node_entry); |
3caa973b TH |
621 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
622 | /* | |
623 | * We could be printing a lot while holding a spinlock. | |
624 | * Avoid triggering hard lockup. | |
625 | */ | |
626 | touch_nmi_watchdog(); | |
12f5f524 | 627 | sched_show_task(t); |
3caa973b | 628 | } |
67c583a7 | 629 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
1ed509a2 PM |
630 | } |
631 | ||
632 | /* | |
633 | * Dump detailed information for all tasks blocking the current RCU | |
634 | * grace period. | |
635 | */ | |
636 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
637 | { | |
638 | struct rcu_node *rnp = rcu_get_root(rsp); | |
639 | ||
640 | rcu_print_detail_task_stall_rnp(rnp); | |
641 | rcu_for_each_leaf_node(rsp, rnp) | |
642 | rcu_print_detail_task_stall_rnp(rnp); | |
643 | } | |
644 | ||
a858af28 PM |
645 | static void rcu_print_task_stall_begin(struct rcu_node *rnp) |
646 | { | |
efc151c3 | 647 | pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", |
a858af28 PM |
648 | rnp->level, rnp->grplo, rnp->grphi); |
649 | } | |
650 | ||
651 | static void rcu_print_task_stall_end(void) | |
652 | { | |
efc151c3 | 653 | pr_cont("\n"); |
a858af28 PM |
654 | } |
655 | ||
f41d911f PM |
656 | /* |
657 | * Scan the current list of tasks blocked within RCU read-side critical | |
658 | * sections, printing out the tid of each. | |
659 | */ | |
9bc8b558 | 660 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 661 | { |
f41d911f | 662 | struct task_struct *t; |
9bc8b558 | 663 | int ndetected = 0; |
f41d911f | 664 | |
27f4d280 | 665 | if (!rcu_preempt_blocked_readers_cgp(rnp)) |
9bc8b558 | 666 | return 0; |
a858af28 | 667 | rcu_print_task_stall_begin(rnp); |
82efed06 | 668 | t = list_entry(rnp->gp_tasks->prev, |
12f5f524 | 669 | struct task_struct, rcu_node_entry); |
9bc8b558 | 670 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { |
efc151c3 | 671 | pr_cont(" P%d", t->pid); |
9bc8b558 PM |
672 | ndetected++; |
673 | } | |
a858af28 | 674 | rcu_print_task_stall_end(); |
9bc8b558 | 675 | return ndetected; |
f41d911f PM |
676 | } |
677 | ||
74611ecb PM |
678 | /* |
679 | * Scan the current list of tasks blocked within RCU read-side critical | |
680 | * sections, printing out the tid of each that is blocking the current | |
681 | * expedited grace period. | |
682 | */ | |
683 | static int rcu_print_task_exp_stall(struct rcu_node *rnp) | |
684 | { | |
685 | struct task_struct *t; | |
686 | int ndetected = 0; | |
687 | ||
688 | if (!rnp->exp_tasks) | |
689 | return 0; | |
690 | t = list_entry(rnp->exp_tasks->prev, | |
691 | struct task_struct, rcu_node_entry); | |
692 | list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { | |
693 | pr_cont(" P%d", t->pid); | |
694 | ndetected++; | |
695 | } | |
696 | return ndetected; | |
697 | } | |
698 | ||
b0e165c0 PM |
699 | /* |
700 | * Check that the list of blocked tasks for the newly completed grace | |
701 | * period is in fact empty. It is a serious bug to complete a grace | |
702 | * period that still has RCU readers blocked! This function must be | |
ff3bb6f4 | 703 | * invoked -before- updating this rnp's ->gp_seq, and the rnp's ->lock |
b0e165c0 | 704 | * must be held by the caller. |
12f5f524 PM |
705 | * |
706 | * Also, if there are blocked tasks on the list, they automatically | |
707 | * block the newly created grace period, so set up ->gp_tasks accordingly. | |
b0e165c0 | 708 | */ |
57738942 PM |
709 | static void |
710 | rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp) | |
b0e165c0 | 711 | { |
c5ebe66c PM |
712 | struct task_struct *t; |
713 | ||
ea9b0c8a | 714 | RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n"); |
4bc8d555 | 715 | if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp))) |
57738942 | 716 | dump_blkd_tasks(rsp, rnp, 10); |
0b107d24 PM |
717 | if (rcu_preempt_has_tasks(rnp) && |
718 | (rnp->qsmaskinit || rnp->wait_blkd_tasks)) { | |
12f5f524 | 719 | rnp->gp_tasks = rnp->blkd_tasks.next; |
c5ebe66c PM |
720 | t = container_of(rnp->gp_tasks, struct task_struct, |
721 | rcu_node_entry); | |
722 | trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"), | |
865aa1e0 | 723 | rnp->gp_seq, t->pid); |
c5ebe66c | 724 | } |
28ecd580 | 725 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
726 | } |
727 | ||
f41d911f PM |
728 | /* |
729 | * Check for a quiescent state from the current CPU. When a task blocks, | |
730 | * the task is recorded in the corresponding CPU's rcu_node structure, | |
731 | * which is checked elsewhere. | |
732 | * | |
733 | * Caller must disable hard irqs. | |
734 | */ | |
86aea0e6 | 735 | static void rcu_preempt_check_callbacks(void) |
f41d911f | 736 | { |
15651201 | 737 | struct rcu_state *rsp = &rcu_preempt_state; |
f41d911f PM |
738 | struct task_struct *t = current; |
739 | ||
740 | if (t->rcu_read_lock_nesting == 0) { | |
284a8c93 | 741 | rcu_preempt_qs(); |
f41d911f PM |
742 | return; |
743 | } | |
10f39bb1 | 744 | if (t->rcu_read_lock_nesting > 0 && |
97c668b8 | 745 | __this_cpu_read(rcu_data_p->core_needs_qs) && |
15651201 PM |
746 | __this_cpu_read(rcu_data_p->cpu_no_qs.b.norm) && |
747 | !t->rcu_read_unlock_special.b.need_qs && | |
748 | time_after(jiffies, rsp->gp_start + HZ)) | |
1d082fd0 | 749 | t->rcu_read_unlock_special.b.need_qs = true; |
f41d911f PM |
750 | } |
751 | ||
a68a2bb2 PM |
752 | /** |
753 | * call_rcu() - Queue an RCU callback for invocation after a grace period. | |
754 | * @head: structure to be used for queueing the RCU updates. | |
755 | * @func: actual callback function to be invoked after the grace period | |
756 | * | |
757 | * The callback function will be invoked some time after a full grace | |
758 | * period elapses, in other words after all pre-existing RCU read-side | |
759 | * critical sections have completed. However, the callback function | |
760 | * might well execute concurrently with RCU read-side critical sections | |
761 | * that started after call_rcu() was invoked. RCU read-side critical | |
762 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
763 | * and may be nested. | |
764 | * | |
765 | * Note that all CPUs must agree that the grace period extended beyond | |
766 | * all pre-existing RCU read-side critical section. On systems with more | |
767 | * than one CPU, this means that when "func()" is invoked, each CPU is | |
768 | * guaranteed to have executed a full memory barrier since the end of its | |
769 | * last RCU read-side critical section whose beginning preceded the call | |
770 | * to call_rcu(). It also means that each CPU executing an RCU read-side | |
771 | * critical section that continues beyond the start of "func()" must have | |
772 | * executed a memory barrier after the call_rcu() but before the beginning | |
773 | * of that RCU read-side critical section. Note that these guarantees | |
774 | * include CPUs that are offline, idle, or executing in user mode, as | |
775 | * well as CPUs that are executing in the kernel. | |
776 | * | |
777 | * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the | |
778 | * resulting RCU callback function "func()", then both CPU A and CPU B are | |
779 | * guaranteed to execute a full memory barrier during the time interval | |
780 | * between the call to call_rcu() and the invocation of "func()" -- even | |
781 | * if CPU A and CPU B are the same CPU (but again only if the system has | |
782 | * more than one CPU). | |
f41d911f | 783 | */ |
b6a4ae76 | 784 | void call_rcu(struct rcu_head *head, rcu_callback_t func) |
f41d911f | 785 | { |
e63c887c | 786 | __call_rcu(head, func, rcu_state_p, -1, 0); |
f41d911f PM |
787 | } |
788 | EXPORT_SYMBOL_GPL(call_rcu); | |
789 | ||
6ebb237b PM |
790 | /** |
791 | * synchronize_rcu - wait until a grace period has elapsed. | |
792 | * | |
793 | * Control will return to the caller some time after a full grace | |
794 | * period has elapsed, in other words after all currently executing RCU | |
77d8485a PM |
795 | * read-side critical sections have completed. Note, however, that |
796 | * upon return from synchronize_rcu(), the caller might well be executing | |
797 | * concurrently with new RCU read-side critical sections that began while | |
798 | * synchronize_rcu() was waiting. RCU read-side critical sections are | |
799 | * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. | |
f0a0e6f2 | 800 | * |
e28371c8 PM |
801 | * See the description of synchronize_sched() for more detailed |
802 | * information on memory-ordering guarantees. However, please note | |
803 | * that -only- the memory-ordering guarantees apply. For example, | |
804 | * synchronize_rcu() is -not- guaranteed to wait on things like code | |
805 | * protected by preempt_disable(), instead, synchronize_rcu() is -only- | |
806 | * guaranteed to wait on RCU read-side critical sections, that is, sections | |
807 | * of code protected by rcu_read_lock(). | |
6ebb237b PM |
808 | */ |
809 | void synchronize_rcu(void) | |
810 | { | |
f78f5b90 PM |
811 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || |
812 | lock_is_held(&rcu_lock_map) || | |
813 | lock_is_held(&rcu_sched_lock_map), | |
814 | "Illegal synchronize_rcu() in RCU read-side critical section"); | |
52d7e48b | 815 | if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) |
6ebb237b | 816 | return; |
5afff48b | 817 | if (rcu_gp_is_expedited()) |
3705b88d AM |
818 | synchronize_rcu_expedited(); |
819 | else | |
820 | wait_rcu_gp(call_rcu); | |
6ebb237b PM |
821 | } |
822 | EXPORT_SYMBOL_GPL(synchronize_rcu); | |
823 | ||
e74f4c45 PM |
824 | /** |
825 | * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. | |
f0a0e6f2 PM |
826 | * |
827 | * Note that this primitive does not necessarily wait for an RCU grace period | |
828 | * to complete. For example, if there are no RCU callbacks queued anywhere | |
829 | * in the system, then rcu_barrier() is within its rights to return | |
830 | * immediately, without waiting for anything, much less an RCU grace period. | |
e74f4c45 PM |
831 | */ |
832 | void rcu_barrier(void) | |
833 | { | |
e63c887c | 834 | _rcu_barrier(rcu_state_p); |
e74f4c45 PM |
835 | } |
836 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
837 | ||
1eba8f84 | 838 | /* |
6cc68793 | 839 | * Initialize preemptible RCU's state structures. |
1eba8f84 PM |
840 | */ |
841 | static void __init __rcu_init_preempt(void) | |
842 | { | |
a87f203e | 843 | rcu_init_one(rcu_state_p); |
1eba8f84 PM |
844 | } |
845 | ||
2439b696 PM |
846 | /* |
847 | * Check for a task exiting while in a preemptible-RCU read-side | |
848 | * critical section, clean up if so. No need to issue warnings, | |
849 | * as debug_check_no_locks_held() already does this if lockdep | |
850 | * is enabled. | |
851 | */ | |
852 | void exit_rcu(void) | |
853 | { | |
854 | struct task_struct *t = current; | |
855 | ||
856 | if (likely(list_empty(¤t->rcu_node_entry))) | |
857 | return; | |
858 | t->rcu_read_lock_nesting = 1; | |
859 | barrier(); | |
1d082fd0 | 860 | t->rcu_read_unlock_special.b.blocked = true; |
2439b696 PM |
861 | __rcu_read_unlock(); |
862 | } | |
863 | ||
4bc8d555 PM |
864 | /* |
865 | * Dump the blocked-tasks state, but limit the list dump to the | |
866 | * specified number of elements. | |
867 | */ | |
57738942 PM |
868 | static void |
869 | dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck) | |
4bc8d555 | 870 | { |
57738942 | 871 | int cpu; |
4bc8d555 PM |
872 | int i; |
873 | struct list_head *lhp; | |
57738942 PM |
874 | bool onl; |
875 | struct rcu_data *rdp; | |
ff3cee39 | 876 | struct rcu_node *rnp1; |
4bc8d555 | 877 | |
ce11fae8 | 878 | raw_lockdep_assert_held_rcu_node(rnp); |
ff3cee39 | 879 | pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n", |
77cfc7bf | 880 | __func__, rnp->grplo, rnp->grphi, rnp->level, |
ff3cee39 PM |
881 | (long)rnp->gp_seq, (long)rnp->completedqs); |
882 | for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent) | |
883 | pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n", | |
884 | __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext); | |
77cfc7bf PM |
885 | pr_info("%s: ->gp_tasks %p ->boost_tasks %p ->exp_tasks %p\n", |
886 | __func__, rnp->gp_tasks, rnp->boost_tasks, rnp->exp_tasks); | |
887 | pr_info("%s: ->blkd_tasks", __func__); | |
4bc8d555 PM |
888 | i = 0; |
889 | list_for_each(lhp, &rnp->blkd_tasks) { | |
890 | pr_cont(" %p", lhp); | |
891 | if (++i >= 10) | |
892 | break; | |
893 | } | |
894 | pr_cont("\n"); | |
57738942 PM |
895 | for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) { |
896 | rdp = per_cpu_ptr(rsp->rda, cpu); | |
897 | onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp)); | |
898 | pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n", | |
899 | cpu, ".o"[onl], | |
900 | (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags, | |
901 | (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags); | |
902 | } | |
4bc8d555 PM |
903 | } |
904 | ||
28f6569a | 905 | #else /* #ifdef CONFIG_PREEMPT_RCU */ |
f41d911f | 906 | |
b28a7c01 | 907 | static struct rcu_state *const rcu_state_p = &rcu_sched_state; |
27f4d280 | 908 | |
f41d911f PM |
909 | /* |
910 | * Tell them what RCU they are running. | |
911 | */ | |
0e0fc1c2 | 912 | static void __init rcu_bootup_announce(void) |
f41d911f | 913 | { |
efc151c3 | 914 | pr_info("Hierarchical RCU implementation.\n"); |
26845c28 | 915 | rcu_bootup_announce_oddness(); |
f41d911f PM |
916 | } |
917 | ||
cba6d0d6 PM |
918 | /* |
919 | * Because preemptible RCU does not exist, we never have to check for | |
920 | * CPUs being in quiescent states. | |
921 | */ | |
5b72f964 | 922 | static void rcu_preempt_note_context_switch(bool preempt) |
cba6d0d6 PM |
923 | { |
924 | } | |
925 | ||
fc2219d4 | 926 | /* |
6cc68793 | 927 | * Because preemptible RCU does not exist, there are never any preempted |
fc2219d4 PM |
928 | * RCU readers. |
929 | */ | |
27f4d280 | 930 | static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) |
fc2219d4 PM |
931 | { |
932 | return 0; | |
933 | } | |
934 | ||
8af3a5e7 PM |
935 | /* |
936 | * Because there is no preemptible RCU, there can be no readers blocked. | |
937 | */ | |
938 | static bool rcu_preempt_has_tasks(struct rcu_node *rnp) | |
b668c9cf | 939 | { |
8af3a5e7 | 940 | return false; |
b668c9cf PM |
941 | } |
942 | ||
1ed509a2 | 943 | /* |
6cc68793 | 944 | * Because preemptible RCU does not exist, we never have to check for |
1ed509a2 PM |
945 | * tasks blocked within RCU read-side critical sections. |
946 | */ | |
947 | static void rcu_print_detail_task_stall(struct rcu_state *rsp) | |
948 | { | |
949 | } | |
950 | ||
f41d911f | 951 | /* |
6cc68793 | 952 | * Because preemptible RCU does not exist, we never have to check for |
f41d911f PM |
953 | * tasks blocked within RCU read-side critical sections. |
954 | */ | |
9bc8b558 | 955 | static int rcu_print_task_stall(struct rcu_node *rnp) |
f41d911f | 956 | { |
9bc8b558 | 957 | return 0; |
f41d911f PM |
958 | } |
959 | ||
74611ecb PM |
960 | /* |
961 | * Because preemptible RCU does not exist, we never have to check for | |
962 | * tasks blocked within RCU read-side critical sections that are | |
963 | * blocking the current expedited grace period. | |
964 | */ | |
965 | static int rcu_print_task_exp_stall(struct rcu_node *rnp) | |
966 | { | |
967 | return 0; | |
968 | } | |
969 | ||
b0e165c0 | 970 | /* |
6cc68793 | 971 | * Because there is no preemptible RCU, there can be no readers blocked, |
49e29126 PM |
972 | * so there is no need to check for blocked tasks. So check only for |
973 | * bogus qsmask values. | |
b0e165c0 | 974 | */ |
57738942 PM |
975 | static void |
976 | rcu_preempt_check_blocked_tasks(struct rcu_state *rsp, struct rcu_node *rnp) | |
b0e165c0 | 977 | { |
49e29126 | 978 | WARN_ON_ONCE(rnp->qsmask); |
b0e165c0 PM |
979 | } |
980 | ||
f41d911f | 981 | /* |
6cc68793 | 982 | * Because preemptible RCU does not exist, it never has any callbacks |
f41d911f PM |
983 | * to check. |
984 | */ | |
86aea0e6 | 985 | static void rcu_preempt_check_callbacks(void) |
f41d911f PM |
986 | { |
987 | } | |
988 | ||
e74f4c45 | 989 | /* |
6cc68793 | 990 | * Because preemptible RCU does not exist, rcu_barrier() is just |
e74f4c45 PM |
991 | * another name for rcu_barrier_sched(). |
992 | */ | |
993 | void rcu_barrier(void) | |
994 | { | |
995 | rcu_barrier_sched(); | |
996 | } | |
997 | EXPORT_SYMBOL_GPL(rcu_barrier); | |
998 | ||
1eba8f84 | 999 | /* |
6cc68793 | 1000 | * Because preemptible RCU does not exist, it need not be initialized. |
1eba8f84 PM |
1001 | */ |
1002 | static void __init __rcu_init_preempt(void) | |
1003 | { | |
1004 | } | |
1005 | ||
2439b696 PM |
1006 | /* |
1007 | * Because preemptible RCU does not exist, tasks cannot possibly exit | |
1008 | * while in preemptible RCU read-side critical sections. | |
1009 | */ | |
1010 | void exit_rcu(void) | |
1011 | { | |
1012 | } | |
1013 | ||
4bc8d555 PM |
1014 | /* |
1015 | * Dump the guaranteed-empty blocked-tasks state. Trust but verify. | |
1016 | */ | |
57738942 PM |
1017 | static void |
1018 | dump_blkd_tasks(struct rcu_state *rsp, struct rcu_node *rnp, int ncheck) | |
4bc8d555 PM |
1019 | { |
1020 | WARN_ON_ONCE(!list_empty(&rnp->blkd_tasks)); | |
1021 | } | |
1022 | ||
28f6569a | 1023 | #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ |
8bd93a2c | 1024 | |
27f4d280 PM |
1025 | #ifdef CONFIG_RCU_BOOST |
1026 | ||
5d01bbd1 TG |
1027 | static void rcu_wake_cond(struct task_struct *t, int status) |
1028 | { | |
1029 | /* | |
1030 | * If the thread is yielding, only wake it when this | |
1031 | * is invoked from idle | |
1032 | */ | |
1033 | if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) | |
1034 | wake_up_process(t); | |
1035 | } | |
1036 | ||
27f4d280 PM |
1037 | /* |
1038 | * Carry out RCU priority boosting on the task indicated by ->exp_tasks | |
1039 | * or ->boost_tasks, advancing the pointer to the next task in the | |
1040 | * ->blkd_tasks list. | |
1041 | * | |
1042 | * Note that irqs must be enabled: boosting the task can block. | |
1043 | * Returns 1 if there are more tasks needing to be boosted. | |
1044 | */ | |
1045 | static int rcu_boost(struct rcu_node *rnp) | |
1046 | { | |
1047 | unsigned long flags; | |
27f4d280 PM |
1048 | struct task_struct *t; |
1049 | struct list_head *tb; | |
1050 | ||
7d0ae808 PM |
1051 | if (READ_ONCE(rnp->exp_tasks) == NULL && |
1052 | READ_ONCE(rnp->boost_tasks) == NULL) | |
27f4d280 PM |
1053 | return 0; /* Nothing left to boost. */ |
1054 | ||
2a67e741 | 1055 | raw_spin_lock_irqsave_rcu_node(rnp, flags); |
27f4d280 PM |
1056 | |
1057 | /* | |
1058 | * Recheck under the lock: all tasks in need of boosting | |
1059 | * might exit their RCU read-side critical sections on their own. | |
1060 | */ | |
1061 | if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { | |
67c583a7 | 1062 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
27f4d280 PM |
1063 | return 0; |
1064 | } | |
1065 | ||
1066 | /* | |
1067 | * Preferentially boost tasks blocking expedited grace periods. | |
1068 | * This cannot starve the normal grace periods because a second | |
1069 | * expedited grace period must boost all blocked tasks, including | |
1070 | * those blocking the pre-existing normal grace period. | |
1071 | */ | |
bec06785 | 1072 | if (rnp->exp_tasks != NULL) |
27f4d280 | 1073 | tb = rnp->exp_tasks; |
bec06785 | 1074 | else |
27f4d280 PM |
1075 | tb = rnp->boost_tasks; |
1076 | ||
1077 | /* | |
1078 | * We boost task t by manufacturing an rt_mutex that appears to | |
1079 | * be held by task t. We leave a pointer to that rt_mutex where | |
1080 | * task t can find it, and task t will release the mutex when it | |
1081 | * exits its outermost RCU read-side critical section. Then | |
1082 | * simply acquiring this artificial rt_mutex will boost task | |
1083 | * t's priority. (Thanks to tglx for suggesting this approach!) | |
1084 | * | |
1085 | * Note that task t must acquire rnp->lock to remove itself from | |
1086 | * the ->blkd_tasks list, which it will do from exit() if from | |
1087 | * nowhere else. We therefore are guaranteed that task t will | |
1088 | * stay around at least until we drop rnp->lock. Note that | |
1089 | * rnp->lock also resolves races between our priority boosting | |
1090 | * and task t's exiting its outermost RCU read-side critical | |
1091 | * section. | |
1092 | */ | |
1093 | t = container_of(tb, struct task_struct, rcu_node_entry); | |
abaa93d9 | 1094 | rt_mutex_init_proxy_locked(&rnp->boost_mtx, t); |
67c583a7 | 1095 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
abaa93d9 PM |
1096 | /* Lock only for side effect: boosts task t's priority. */ |
1097 | rt_mutex_lock(&rnp->boost_mtx); | |
1098 | rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */ | |
27f4d280 | 1099 | |
7d0ae808 PM |
1100 | return READ_ONCE(rnp->exp_tasks) != NULL || |
1101 | READ_ONCE(rnp->boost_tasks) != NULL; | |
27f4d280 PM |
1102 | } |
1103 | ||
27f4d280 | 1104 | /* |
bc17ea10 | 1105 | * Priority-boosting kthread, one per leaf rcu_node. |
27f4d280 PM |
1106 | */ |
1107 | static int rcu_boost_kthread(void *arg) | |
1108 | { | |
1109 | struct rcu_node *rnp = (struct rcu_node *)arg; | |
1110 | int spincnt = 0; | |
1111 | int more2boost; | |
1112 | ||
f7f7bac9 | 1113 | trace_rcu_utilization(TPS("Start boost kthread@init")); |
27f4d280 | 1114 | for (;;) { |
d71df90e | 1115 | rnp->boost_kthread_status = RCU_KTHREAD_WAITING; |
f7f7bac9 | 1116 | trace_rcu_utilization(TPS("End boost kthread@rcu_wait")); |
08bca60a | 1117 | rcu_wait(rnp->boost_tasks || rnp->exp_tasks); |
f7f7bac9 | 1118 | trace_rcu_utilization(TPS("Start boost kthread@rcu_wait")); |
d71df90e | 1119 | rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; |
27f4d280 PM |
1120 | more2boost = rcu_boost(rnp); |
1121 | if (more2boost) | |
1122 | spincnt++; | |
1123 | else | |
1124 | spincnt = 0; | |
1125 | if (spincnt > 10) { | |
5d01bbd1 | 1126 | rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; |
f7f7bac9 | 1127 | trace_rcu_utilization(TPS("End boost kthread@rcu_yield")); |
5d01bbd1 | 1128 | schedule_timeout_interruptible(2); |
f7f7bac9 | 1129 | trace_rcu_utilization(TPS("Start boost kthread@rcu_yield")); |
27f4d280 PM |
1130 | spincnt = 0; |
1131 | } | |
1132 | } | |
1217ed1b | 1133 | /* NOTREACHED */ |
f7f7bac9 | 1134 | trace_rcu_utilization(TPS("End boost kthread@notreached")); |
27f4d280 PM |
1135 | return 0; |
1136 | } | |
1137 | ||
1138 | /* | |
1139 | * Check to see if it is time to start boosting RCU readers that are | |
1140 | * blocking the current grace period, and, if so, tell the per-rcu_node | |
1141 | * kthread to start boosting them. If there is an expedited grace | |
1142 | * period in progress, it is always time to boost. | |
1143 | * | |
b065a853 PM |
1144 | * The caller must hold rnp->lock, which this function releases. |
1145 | * The ->boost_kthread_task is immortal, so we don't need to worry | |
1146 | * about it going away. | |
27f4d280 | 1147 | */ |
1217ed1b | 1148 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
615e41c6 | 1149 | __releases(rnp->lock) |
27f4d280 PM |
1150 | { |
1151 | struct task_struct *t; | |
1152 | ||
a32e01ee | 1153 | raw_lockdep_assert_held_rcu_node(rnp); |
0ea1f2eb | 1154 | if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { |
67c583a7 | 1155 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
27f4d280 | 1156 | return; |
0ea1f2eb | 1157 | } |
27f4d280 PM |
1158 | if (rnp->exp_tasks != NULL || |
1159 | (rnp->gp_tasks != NULL && | |
1160 | rnp->boost_tasks == NULL && | |
1161 | rnp->qsmask == 0 && | |
1162 | ULONG_CMP_GE(jiffies, rnp->boost_time))) { | |
1163 | if (rnp->exp_tasks == NULL) | |
1164 | rnp->boost_tasks = rnp->gp_tasks; | |
67c583a7 | 1165 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
27f4d280 | 1166 | t = rnp->boost_kthread_task; |
5d01bbd1 TG |
1167 | if (t) |
1168 | rcu_wake_cond(t, rnp->boost_kthread_status); | |
1217ed1b | 1169 | } else { |
67c583a7 | 1170 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
1217ed1b | 1171 | } |
27f4d280 PM |
1172 | } |
1173 | ||
a46e0899 PM |
1174 | /* |
1175 | * Wake up the per-CPU kthread to invoke RCU callbacks. | |
1176 | */ | |
1177 | static void invoke_rcu_callbacks_kthread(void) | |
1178 | { | |
1179 | unsigned long flags; | |
1180 | ||
1181 | local_irq_save(flags); | |
1182 | __this_cpu_write(rcu_cpu_has_work, 1); | |
1eb52121 | 1183 | if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && |
5d01bbd1 TG |
1184 | current != __this_cpu_read(rcu_cpu_kthread_task)) { |
1185 | rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), | |
1186 | __this_cpu_read(rcu_cpu_kthread_status)); | |
1187 | } | |
a46e0899 PM |
1188 | local_irq_restore(flags); |
1189 | } | |
1190 | ||
dff1672d PM |
1191 | /* |
1192 | * Is the current CPU running the RCU-callbacks kthread? | |
1193 | * Caller must have preemption disabled. | |
1194 | */ | |
1195 | static bool rcu_is_callbacks_kthread(void) | |
1196 | { | |
c9d4b0af | 1197 | return __this_cpu_read(rcu_cpu_kthread_task) == current; |
dff1672d PM |
1198 | } |
1199 | ||
27f4d280 PM |
1200 | #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) |
1201 | ||
1202 | /* | |
1203 | * Do priority-boost accounting for the start of a new grace period. | |
1204 | */ | |
1205 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) | |
1206 | { | |
1207 | rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; | |
1208 | } | |
1209 | ||
27f4d280 PM |
1210 | /* |
1211 | * Create an RCU-boost kthread for the specified node if one does not | |
1212 | * already exist. We only create this kthread for preemptible RCU. | |
1213 | * Returns zero if all is well, a negated errno otherwise. | |
1214 | */ | |
49fb4c62 | 1215 | static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp, |
0aa04b05 | 1216 | struct rcu_node *rnp) |
27f4d280 | 1217 | { |
5d01bbd1 | 1218 | int rnp_index = rnp - &rsp->node[0]; |
27f4d280 PM |
1219 | unsigned long flags; |
1220 | struct sched_param sp; | |
1221 | struct task_struct *t; | |
1222 | ||
e63c887c | 1223 | if (rcu_state_p != rsp) |
27f4d280 | 1224 | return 0; |
5d01bbd1 | 1225 | |
0aa04b05 | 1226 | if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0) |
5d01bbd1 TG |
1227 | return 0; |
1228 | ||
a46e0899 | 1229 | rsp->boost = 1; |
27f4d280 PM |
1230 | if (rnp->boost_kthread_task != NULL) |
1231 | return 0; | |
1232 | t = kthread_create(rcu_boost_kthread, (void *)rnp, | |
5b61b0ba | 1233 | "rcub/%d", rnp_index); |
27f4d280 PM |
1234 | if (IS_ERR(t)) |
1235 | return PTR_ERR(t); | |
2a67e741 | 1236 | raw_spin_lock_irqsave_rcu_node(rnp, flags); |
27f4d280 | 1237 | rnp->boost_kthread_task = t; |
67c583a7 | 1238 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
21871d7e | 1239 | sp.sched_priority = kthread_prio; |
27f4d280 | 1240 | sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); |
9a432736 | 1241 | wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ |
27f4d280 PM |
1242 | return 0; |
1243 | } | |
1244 | ||
f8b7fc6b PM |
1245 | static void rcu_kthread_do_work(void) |
1246 | { | |
c9d4b0af CL |
1247 | rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data)); |
1248 | rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data)); | |
be01b4ca | 1249 | rcu_do_batch(&rcu_preempt_state, this_cpu_ptr(&rcu_preempt_data)); |
f8b7fc6b PM |
1250 | } |
1251 | ||
62ab7072 | 1252 | static void rcu_cpu_kthread_setup(unsigned int cpu) |
f8b7fc6b | 1253 | { |
f8b7fc6b | 1254 | struct sched_param sp; |
f8b7fc6b | 1255 | |
21871d7e | 1256 | sp.sched_priority = kthread_prio; |
62ab7072 | 1257 | sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); |
f8b7fc6b PM |
1258 | } |
1259 | ||
62ab7072 | 1260 | static void rcu_cpu_kthread_park(unsigned int cpu) |
f8b7fc6b | 1261 | { |
62ab7072 | 1262 | per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; |
f8b7fc6b PM |
1263 | } |
1264 | ||
62ab7072 | 1265 | static int rcu_cpu_kthread_should_run(unsigned int cpu) |
f8b7fc6b | 1266 | { |
c9d4b0af | 1267 | return __this_cpu_read(rcu_cpu_has_work); |
f8b7fc6b PM |
1268 | } |
1269 | ||
1270 | /* | |
1271 | * Per-CPU kernel thread that invokes RCU callbacks. This replaces the | |
e0f23060 PM |
1272 | * RCU softirq used in flavors and configurations of RCU that do not |
1273 | * support RCU priority boosting. | |
f8b7fc6b | 1274 | */ |
62ab7072 | 1275 | static void rcu_cpu_kthread(unsigned int cpu) |
f8b7fc6b | 1276 | { |
c9d4b0af CL |
1277 | unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status); |
1278 | char work, *workp = this_cpu_ptr(&rcu_cpu_has_work); | |
62ab7072 | 1279 | int spincnt; |
f8b7fc6b | 1280 | |
62ab7072 | 1281 | for (spincnt = 0; spincnt < 10; spincnt++) { |
f7f7bac9 | 1282 | trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait")); |
f8b7fc6b | 1283 | local_bh_disable(); |
f8b7fc6b | 1284 | *statusp = RCU_KTHREAD_RUNNING; |
62ab7072 PM |
1285 | this_cpu_inc(rcu_cpu_kthread_loops); |
1286 | local_irq_disable(); | |
f8b7fc6b PM |
1287 | work = *workp; |
1288 | *workp = 0; | |
62ab7072 | 1289 | local_irq_enable(); |
f8b7fc6b PM |
1290 | if (work) |
1291 | rcu_kthread_do_work(); | |
1292 | local_bh_enable(); | |
62ab7072 | 1293 | if (*workp == 0) { |
f7f7bac9 | 1294 | trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); |
62ab7072 PM |
1295 | *statusp = RCU_KTHREAD_WAITING; |
1296 | return; | |
f8b7fc6b PM |
1297 | } |
1298 | } | |
62ab7072 | 1299 | *statusp = RCU_KTHREAD_YIELDING; |
f7f7bac9 | 1300 | trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); |
62ab7072 | 1301 | schedule_timeout_interruptible(2); |
f7f7bac9 | 1302 | trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); |
62ab7072 | 1303 | *statusp = RCU_KTHREAD_WAITING; |
f8b7fc6b PM |
1304 | } |
1305 | ||
1306 | /* | |
1307 | * Set the per-rcu_node kthread's affinity to cover all CPUs that are | |
1308 | * served by the rcu_node in question. The CPU hotplug lock is still | |
1309 | * held, so the value of rnp->qsmaskinit will be stable. | |
1310 | * | |
1311 | * We don't include outgoingcpu in the affinity set, use -1 if there is | |
1312 | * no outgoing CPU. If there are no CPUs left in the affinity set, | |
1313 | * this function allows the kthread to execute on any CPU. | |
1314 | */ | |
5d01bbd1 | 1315 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b | 1316 | { |
5d01bbd1 | 1317 | struct task_struct *t = rnp->boost_kthread_task; |
0aa04b05 | 1318 | unsigned long mask = rcu_rnp_online_cpus(rnp); |
f8b7fc6b PM |
1319 | cpumask_var_t cm; |
1320 | int cpu; | |
f8b7fc6b | 1321 | |
5d01bbd1 | 1322 | if (!t) |
f8b7fc6b | 1323 | return; |
5d01bbd1 | 1324 | if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) |
f8b7fc6b | 1325 | return; |
bc75e999 MR |
1326 | for_each_leaf_node_possible_cpu(rnp, cpu) |
1327 | if ((mask & leaf_node_cpu_bit(rnp, cpu)) && | |
1328 | cpu != outgoingcpu) | |
f8b7fc6b | 1329 | cpumask_set_cpu(cpu, cm); |
5d0b0249 | 1330 | if (cpumask_weight(cm) == 0) |
f8b7fc6b | 1331 | cpumask_setall(cm); |
5d01bbd1 | 1332 | set_cpus_allowed_ptr(t, cm); |
f8b7fc6b PM |
1333 | free_cpumask_var(cm); |
1334 | } | |
1335 | ||
62ab7072 PM |
1336 | static struct smp_hotplug_thread rcu_cpu_thread_spec = { |
1337 | .store = &rcu_cpu_kthread_task, | |
1338 | .thread_should_run = rcu_cpu_kthread_should_run, | |
1339 | .thread_fn = rcu_cpu_kthread, | |
1340 | .thread_comm = "rcuc/%u", | |
1341 | .setup = rcu_cpu_kthread_setup, | |
1342 | .park = rcu_cpu_kthread_park, | |
1343 | }; | |
f8b7fc6b PM |
1344 | |
1345 | /* | |
9386c0b7 | 1346 | * Spawn boost kthreads -- called as soon as the scheduler is running. |
f8b7fc6b | 1347 | */ |
9386c0b7 | 1348 | static void __init rcu_spawn_boost_kthreads(void) |
f8b7fc6b | 1349 | { |
f8b7fc6b | 1350 | struct rcu_node *rnp; |
5d01bbd1 | 1351 | int cpu; |
f8b7fc6b | 1352 | |
62ab7072 | 1353 | for_each_possible_cpu(cpu) |
f8b7fc6b | 1354 | per_cpu(rcu_cpu_has_work, cpu) = 0; |
62ab7072 | 1355 | BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); |
3e9f5c70 PM |
1356 | rcu_for_each_leaf_node(rcu_state_p, rnp) |
1357 | (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); | |
f8b7fc6b | 1358 | } |
f8b7fc6b | 1359 | |
49fb4c62 | 1360 | static void rcu_prepare_kthreads(int cpu) |
f8b7fc6b | 1361 | { |
e534165b | 1362 | struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu); |
f8b7fc6b PM |
1363 | struct rcu_node *rnp = rdp->mynode; |
1364 | ||
1365 | /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ | |
62ab7072 | 1366 | if (rcu_scheduler_fully_active) |
e534165b | 1367 | (void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp); |
f8b7fc6b PM |
1368 | } |
1369 | ||
27f4d280 PM |
1370 | #else /* #ifdef CONFIG_RCU_BOOST */ |
1371 | ||
1217ed1b | 1372 | static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) |
615e41c6 | 1373 | __releases(rnp->lock) |
27f4d280 | 1374 | { |
67c583a7 | 1375 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); |
27f4d280 PM |
1376 | } |
1377 | ||
a46e0899 | 1378 | static void invoke_rcu_callbacks_kthread(void) |
27f4d280 | 1379 | { |
a46e0899 | 1380 | WARN_ON_ONCE(1); |
27f4d280 PM |
1381 | } |
1382 | ||
dff1672d PM |
1383 | static bool rcu_is_callbacks_kthread(void) |
1384 | { | |
1385 | return false; | |
1386 | } | |
1387 | ||
27f4d280 PM |
1388 | static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) |
1389 | { | |
1390 | } | |
1391 | ||
5d01bbd1 | 1392 | static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) |
f8b7fc6b PM |
1393 | { |
1394 | } | |
1395 | ||
9386c0b7 | 1396 | static void __init rcu_spawn_boost_kthreads(void) |
b0d30417 | 1397 | { |
b0d30417 | 1398 | } |
b0d30417 | 1399 | |
49fb4c62 | 1400 | static void rcu_prepare_kthreads(int cpu) |
f8b7fc6b PM |
1401 | { |
1402 | } | |
1403 | ||
27f4d280 PM |
1404 | #endif /* #else #ifdef CONFIG_RCU_BOOST */ |
1405 | ||
8bd93a2c PM |
1406 | #if !defined(CONFIG_RCU_FAST_NO_HZ) |
1407 | ||
1408 | /* | |
1409 | * Check to see if any future RCU-related work will need to be done | |
1410 | * by the current CPU, even if none need be done immediately, returning | |
1411 | * 1 if so. This function is part of the RCU implementation; it is -not- | |
1412 | * an exported member of the RCU API. | |
1413 | * | |
7cb92499 PM |
1414 | * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs |
1415 | * any flavor of RCU. | |
8bd93a2c | 1416 | */ |
c1ad348b | 1417 | int rcu_needs_cpu(u64 basemono, u64 *nextevt) |
8bd93a2c | 1418 | { |
c1ad348b | 1419 | *nextevt = KTIME_MAX; |
44c65ff2 | 1420 | return rcu_cpu_has_callbacks(NULL); |
7cb92499 PM |
1421 | } |
1422 | ||
1423 | /* | |
1424 | * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up | |
1425 | * after it. | |
1426 | */ | |
8fa7845d | 1427 | static void rcu_cleanup_after_idle(void) |
7cb92499 PM |
1428 | { |
1429 | } | |
1430 | ||
aea1b35e | 1431 | /* |
a858af28 | 1432 | * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, |
aea1b35e PM |
1433 | * is nothing. |
1434 | */ | |
198bbf81 | 1435 | static void rcu_prepare_for_idle(void) |
aea1b35e PM |
1436 | { |
1437 | } | |
1438 | ||
c57afe80 PM |
1439 | /* |
1440 | * Don't bother keeping a running count of the number of RCU callbacks | |
1441 | * posted because CONFIG_RCU_FAST_NO_HZ=n. | |
1442 | */ | |
1443 | static void rcu_idle_count_callbacks_posted(void) | |
1444 | { | |
1445 | } | |
1446 | ||
8bd93a2c PM |
1447 | #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
1448 | ||
f23f7fa1 PM |
1449 | /* |
1450 | * This code is invoked when a CPU goes idle, at which point we want | |
1451 | * to have the CPU do everything required for RCU so that it can enter | |
1452 | * the energy-efficient dyntick-idle mode. This is handled by a | |
1453 | * state machine implemented by rcu_prepare_for_idle() below. | |
1454 | * | |
1455 | * The following three proprocessor symbols control this state machine: | |
1456 | * | |
f23f7fa1 PM |
1457 | * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted |
1458 | * to sleep in dyntick-idle mode with RCU callbacks pending. This | |
1459 | * is sized to be roughly one RCU grace period. Those energy-efficiency | |
1460 | * benchmarkers who might otherwise be tempted to set this to a large | |
1461 | * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your | |
1462 | * system. And if you are -that- concerned about energy efficiency, | |
1463 | * just power the system down and be done with it! | |
778d250a PM |
1464 | * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is |
1465 | * permitted to sleep in dyntick-idle mode with only lazy RCU | |
1466 | * callbacks pending. Setting this too high can OOM your system. | |
f23f7fa1 PM |
1467 | * |
1468 | * The values below work well in practice. If future workloads require | |
1469 | * adjustment, they can be converted into kernel config parameters, though | |
1470 | * making the state machine smarter might be a better option. | |
1471 | */ | |
e84c48ae | 1472 | #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ |
778d250a | 1473 | #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ |
f23f7fa1 | 1474 | |
5e44ce35 PM |
1475 | static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; |
1476 | module_param(rcu_idle_gp_delay, int, 0644); | |
1477 | static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY; | |
1478 | module_param(rcu_idle_lazy_gp_delay, int, 0644); | |
486e2593 | 1479 | |
486e2593 | 1480 | /* |
c229828c PM |
1481 | * Try to advance callbacks for all flavors of RCU on the current CPU, but |
1482 | * only if it has been awhile since the last time we did so. Afterwards, | |
1483 | * if there are any callbacks ready for immediate invocation, return true. | |
486e2593 | 1484 | */ |
f1f399d1 | 1485 | static bool __maybe_unused rcu_try_advance_all_cbs(void) |
486e2593 | 1486 | { |
c0f4dfd4 PM |
1487 | bool cbs_ready = false; |
1488 | struct rcu_data *rdp; | |
c229828c | 1489 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
c0f4dfd4 PM |
1490 | struct rcu_node *rnp; |
1491 | struct rcu_state *rsp; | |
486e2593 | 1492 | |
c229828c PM |
1493 | /* Exit early if we advanced recently. */ |
1494 | if (jiffies == rdtp->last_advance_all) | |
d0bc90fd | 1495 | return false; |
c229828c PM |
1496 | rdtp->last_advance_all = jiffies; |
1497 | ||
c0f4dfd4 PM |
1498 | for_each_rcu_flavor(rsp) { |
1499 | rdp = this_cpu_ptr(rsp->rda); | |
1500 | rnp = rdp->mynode; | |
486e2593 | 1501 | |
c0f4dfd4 PM |
1502 | /* |
1503 | * Don't bother checking unless a grace period has | |
1504 | * completed since we last checked and there are | |
1505 | * callbacks not yet ready to invoke. | |
1506 | */ | |
03c8cb76 PM |
1507 | if ((rcu_seq_completed_gp(rdp->gp_seq, |
1508 | rcu_seq_current(&rnp->gp_seq)) || | |
7d0ae808 | 1509 | unlikely(READ_ONCE(rdp->gpwrap))) && |
15fecf89 | 1510 | rcu_segcblist_pend_cbs(&rdp->cblist)) |
470716fc | 1511 | note_gp_changes(rsp, rdp); |
486e2593 | 1512 | |
15fecf89 | 1513 | if (rcu_segcblist_ready_cbs(&rdp->cblist)) |
c0f4dfd4 PM |
1514 | cbs_ready = true; |
1515 | } | |
1516 | return cbs_ready; | |
486e2593 PM |
1517 | } |
1518 | ||
aa9b1630 | 1519 | /* |
c0f4dfd4 PM |
1520 | * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready |
1521 | * to invoke. If the CPU has callbacks, try to advance them. Tell the | |
1522 | * caller to set the timeout based on whether or not there are non-lazy | |
1523 | * callbacks. | |
aa9b1630 | 1524 | * |
c0f4dfd4 | 1525 | * The caller must have disabled interrupts. |
aa9b1630 | 1526 | */ |
c1ad348b | 1527 | int rcu_needs_cpu(u64 basemono, u64 *nextevt) |
aa9b1630 | 1528 | { |
aa6da514 | 1529 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
c1ad348b | 1530 | unsigned long dj; |
aa9b1630 | 1531 | |
b04db8e1 | 1532 | lockdep_assert_irqs_disabled(); |
3382adbc | 1533 | |
c0f4dfd4 PM |
1534 | /* Snapshot to detect later posting of non-lazy callback. */ |
1535 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; | |
1536 | ||
aa9b1630 | 1537 | /* If no callbacks, RCU doesn't need the CPU. */ |
aa6da514 | 1538 | if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) { |
c1ad348b | 1539 | *nextevt = KTIME_MAX; |
aa9b1630 PM |
1540 | return 0; |
1541 | } | |
c0f4dfd4 PM |
1542 | |
1543 | /* Attempt to advance callbacks. */ | |
1544 | if (rcu_try_advance_all_cbs()) { | |
1545 | /* Some ready to invoke, so initiate later invocation. */ | |
1546 | invoke_rcu_core(); | |
aa9b1630 PM |
1547 | return 1; |
1548 | } | |
c0f4dfd4 PM |
1549 | rdtp->last_accelerate = jiffies; |
1550 | ||
1551 | /* Request timer delay depending on laziness, and round. */ | |
6faf7283 | 1552 | if (!rdtp->all_lazy) { |
c1ad348b | 1553 | dj = round_up(rcu_idle_gp_delay + jiffies, |
c0f4dfd4 | 1554 | rcu_idle_gp_delay) - jiffies; |
e84c48ae | 1555 | } else { |
c1ad348b | 1556 | dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies; |
e84c48ae | 1557 | } |
c1ad348b | 1558 | *nextevt = basemono + dj * TICK_NSEC; |
aa9b1630 PM |
1559 | return 0; |
1560 | } | |
1561 | ||
21e52e15 | 1562 | /* |
c0f4dfd4 PM |
1563 | * Prepare a CPU for idle from an RCU perspective. The first major task |
1564 | * is to sense whether nohz mode has been enabled or disabled via sysfs. | |
1565 | * The second major task is to check to see if a non-lazy callback has | |
1566 | * arrived at a CPU that previously had only lazy callbacks. The third | |
1567 | * major task is to accelerate (that is, assign grace-period numbers to) | |
1568 | * any recently arrived callbacks. | |
aea1b35e PM |
1569 | * |
1570 | * The caller must have disabled interrupts. | |
8bd93a2c | 1571 | */ |
198bbf81 | 1572 | static void rcu_prepare_for_idle(void) |
8bd93a2c | 1573 | { |
48a7639c | 1574 | bool needwake; |
c0f4dfd4 | 1575 | struct rcu_data *rdp; |
198bbf81 | 1576 | struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); |
c0f4dfd4 PM |
1577 | struct rcu_node *rnp; |
1578 | struct rcu_state *rsp; | |
9d2ad243 PM |
1579 | int tne; |
1580 | ||
b04db8e1 | 1581 | lockdep_assert_irqs_disabled(); |
44c65ff2 | 1582 | if (rcu_is_nocb_cpu(smp_processor_id())) |
3382adbc PM |
1583 | return; |
1584 | ||
9d2ad243 | 1585 | /* Handle nohz enablement switches conservatively. */ |
7d0ae808 | 1586 | tne = READ_ONCE(tick_nohz_active); |
9d2ad243 | 1587 | if (tne != rdtp->tick_nohz_enabled_snap) { |
aa6da514 | 1588 | if (rcu_cpu_has_callbacks(NULL)) |
9d2ad243 PM |
1589 | invoke_rcu_core(); /* force nohz to see update. */ |
1590 | rdtp->tick_nohz_enabled_snap = tne; | |
1591 | return; | |
1592 | } | |
1593 | if (!tne) | |
1594 | return; | |
f511fc62 | 1595 | |
c57afe80 | 1596 | /* |
c0f4dfd4 PM |
1597 | * If a non-lazy callback arrived at a CPU having only lazy |
1598 | * callbacks, invoke RCU core for the side-effect of recalculating | |
1599 | * idle duration on re-entry to idle. | |
c57afe80 | 1600 | */ |
c0f4dfd4 PM |
1601 | if (rdtp->all_lazy && |
1602 | rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) { | |
c337f8f5 PM |
1603 | rdtp->all_lazy = false; |
1604 | rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; | |
c0f4dfd4 | 1605 | invoke_rcu_core(); |
c57afe80 PM |
1606 | return; |
1607 | } | |
c57afe80 | 1608 | |
3084f2f8 | 1609 | /* |
c0f4dfd4 PM |
1610 | * If we have not yet accelerated this jiffy, accelerate all |
1611 | * callbacks on this CPU. | |
3084f2f8 | 1612 | */ |
c0f4dfd4 | 1613 | if (rdtp->last_accelerate == jiffies) |
aea1b35e | 1614 | return; |
c0f4dfd4 PM |
1615 | rdtp->last_accelerate = jiffies; |
1616 | for_each_rcu_flavor(rsp) { | |
198bbf81 | 1617 | rdp = this_cpu_ptr(rsp->rda); |
135bd1a2 | 1618 | if (!rcu_segcblist_pend_cbs(&rdp->cblist)) |
c0f4dfd4 PM |
1619 | continue; |
1620 | rnp = rdp->mynode; | |
2a67e741 | 1621 | raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ |
48a7639c | 1622 | needwake = rcu_accelerate_cbs(rsp, rnp, rdp); |
67c583a7 | 1623 | raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ |
48a7639c PM |
1624 | if (needwake) |
1625 | rcu_gp_kthread_wake(rsp); | |
77e38ed3 | 1626 | } |
c0f4dfd4 | 1627 | } |
3084f2f8 | 1628 | |
c0f4dfd4 PM |
1629 | /* |
1630 | * Clean up for exit from idle. Attempt to advance callbacks based on | |
1631 | * any grace periods that elapsed while the CPU was idle, and if any | |
1632 | * callbacks are now ready to invoke, initiate invocation. | |
1633 | */ | |
8fa7845d | 1634 | static void rcu_cleanup_after_idle(void) |
c0f4dfd4 | 1635 | { |
b04db8e1 | 1636 | lockdep_assert_irqs_disabled(); |
44c65ff2 | 1637 | if (rcu_is_nocb_cpu(smp_processor_id())) |
aea1b35e | 1638 | return; |
7a497c96 PM |
1639 | if (rcu_try_advance_all_cbs()) |
1640 | invoke_rcu_core(); | |
8bd93a2c PM |
1641 | } |
1642 | ||
c57afe80 | 1643 | /* |
98248a0e PM |
1644 | * Keep a running count of the number of non-lazy callbacks posted |
1645 | * on this CPU. This running counter (which is never decremented) allows | |
1646 | * rcu_prepare_for_idle() to detect when something out of the idle loop | |
1647 | * posts a callback, even if an equal number of callbacks are invoked. | |
1648 | * Of course, callbacks should only be posted from within a trace event | |
1649 | * designed to be called from idle or from within RCU_NONIDLE(). | |
c57afe80 PM |
1650 | */ |
1651 | static void rcu_idle_count_callbacks_posted(void) | |
1652 | { | |
5955f7ee | 1653 | __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); |
c57afe80 PM |
1654 | } |
1655 | ||
b626c1b6 PM |
1656 | /* |
1657 | * Data for flushing lazy RCU callbacks at OOM time. | |
1658 | */ | |
1659 | static atomic_t oom_callback_count; | |
1660 | static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); | |
1661 | ||
1662 | /* | |
1663 | * RCU OOM callback -- decrement the outstanding count and deliver the | |
1664 | * wake-up if we are the last one. | |
1665 | */ | |
1666 | static void rcu_oom_callback(struct rcu_head *rhp) | |
1667 | { | |
1668 | if (atomic_dec_and_test(&oom_callback_count)) | |
1669 | wake_up(&oom_callback_wq); | |
1670 | } | |
1671 | ||
1672 | /* | |
1673 | * Post an rcu_oom_notify callback on the current CPU if it has at | |
1674 | * least one lazy callback. This will unnecessarily post callbacks | |
1675 | * to CPUs that already have a non-lazy callback at the end of their | |
1676 | * callback list, but this is an infrequent operation, so accept some | |
1677 | * extra overhead to keep things simple. | |
1678 | */ | |
1679 | static void rcu_oom_notify_cpu(void *unused) | |
1680 | { | |
1681 | struct rcu_state *rsp; | |
1682 | struct rcu_data *rdp; | |
1683 | ||
1684 | for_each_rcu_flavor(rsp) { | |
fa07a58f | 1685 | rdp = raw_cpu_ptr(rsp->rda); |
15fecf89 | 1686 | if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) { |
b626c1b6 PM |
1687 | atomic_inc(&oom_callback_count); |
1688 | rsp->call(&rdp->oom_head, rcu_oom_callback); | |
1689 | } | |
1690 | } | |
1691 | } | |
1692 | ||
1693 | /* | |
1694 | * If low on memory, ensure that each CPU has a non-lazy callback. | |
1695 | * This will wake up CPUs that have only lazy callbacks, in turn | |
1696 | * ensuring that they free up the corresponding memory in a timely manner. | |
1697 | * Because an uncertain amount of memory will be freed in some uncertain | |
1698 | * timeframe, we do not claim to have freed anything. | |
1699 | */ | |
1700 | static int rcu_oom_notify(struct notifier_block *self, | |
1701 | unsigned long notused, void *nfreed) | |
1702 | { | |
1703 | int cpu; | |
1704 | ||
1705 | /* Wait for callbacks from earlier instance to complete. */ | |
1706 | wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); | |
78e4bc34 | 1707 | smp_mb(); /* Ensure callback reuse happens after callback invocation. */ |
b626c1b6 PM |
1708 | |
1709 | /* | |
1710 | * Prevent premature wakeup: ensure that all increments happen | |
1711 | * before there is a chance of the counter reaching zero. | |
1712 | */ | |
1713 | atomic_set(&oom_callback_count, 1); | |
1714 | ||
b626c1b6 PM |
1715 | for_each_online_cpu(cpu) { |
1716 | smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); | |
cee43939 | 1717 | cond_resched_tasks_rcu_qs(); |
b626c1b6 | 1718 | } |
b626c1b6 PM |
1719 | |
1720 | /* Unconditionally decrement: no need to wake ourselves up. */ | |
1721 | atomic_dec(&oom_callback_count); | |
1722 | ||
1723 | return NOTIFY_OK; | |
1724 | } | |
1725 | ||
1726 | static struct notifier_block rcu_oom_nb = { | |
1727 | .notifier_call = rcu_oom_notify | |
1728 | }; | |
1729 | ||
1730 | static int __init rcu_register_oom_notifier(void) | |
1731 | { | |
1732 | register_oom_notifier(&rcu_oom_nb); | |
1733 | return 0; | |
1734 | } | |
1735 | early_initcall(rcu_register_oom_notifier); | |
1736 | ||
8bd93a2c | 1737 | #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |
a858af28 | 1738 | |
a858af28 PM |
1739 | #ifdef CONFIG_RCU_FAST_NO_HZ |
1740 | ||
1741 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
1742 | { | |
5955f7ee | 1743 | struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); |
c0f4dfd4 | 1744 | unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap; |
a858af28 | 1745 | |
c0f4dfd4 PM |
1746 | sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c", |
1747 | rdtp->last_accelerate & 0xffff, jiffies & 0xffff, | |
1748 | ulong2long(nlpd), | |
1749 | rdtp->all_lazy ? 'L' : '.', | |
1750 | rdtp->tick_nohz_enabled_snap ? '.' : 'D'); | |
a858af28 PM |
1751 | } |
1752 | ||
1753 | #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
1754 | ||
1755 | static void print_cpu_stall_fast_no_hz(char *cp, int cpu) | |
1756 | { | |
1c17e4d4 | 1757 | *cp = '\0'; |
a858af28 PM |
1758 | } |
1759 | ||
1760 | #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ | |
1761 | ||
1762 | /* Initiate the stall-info list. */ | |
1763 | static void print_cpu_stall_info_begin(void) | |
1764 | { | |
efc151c3 | 1765 | pr_cont("\n"); |
a858af28 PM |
1766 | } |
1767 | ||
1768 | /* | |
1769 | * Print out diagnostic information for the specified stalled CPU. | |
1770 | * | |
1771 | * If the specified CPU is aware of the current RCU grace period | |
1772 | * (flavor specified by rsp), then print the number of scheduling | |
1773 | * clock interrupts the CPU has taken during the time that it has | |
1774 | * been aware. Otherwise, print the number of RCU grace periods | |
1775 | * that this CPU is ignorant of, for example, "1" if the CPU was | |
1776 | * aware of the previous grace period. | |
1777 | * | |
1778 | * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. | |
1779 | */ | |
1780 | static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) | |
1781 | { | |
9b9500da | 1782 | unsigned long delta; |
a858af28 PM |
1783 | char fast_no_hz[72]; |
1784 | struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); | |
1785 | struct rcu_dynticks *rdtp = rdp->dynticks; | |
1786 | char *ticks_title; | |
1787 | unsigned long ticks_value; | |
1788 | ||
3caa973b TH |
1789 | /* |
1790 | * We could be printing a lot while holding a spinlock. Avoid | |
1791 | * triggering hard lockup. | |
1792 | */ | |
1793 | touch_nmi_watchdog(); | |
1794 | ||
471f87c3 PM |
1795 | ticks_value = rcu_seq_ctr(rsp->gp_seq - rdp->gp_seq); |
1796 | if (ticks_value) { | |
1797 | ticks_title = "GPs behind"; | |
1798 | } else { | |
a858af28 PM |
1799 | ticks_title = "ticks this GP"; |
1800 | ticks_value = rdp->ticks_this_gp; | |
a858af28 PM |
1801 | } |
1802 | print_cpu_stall_fast_no_hz(fast_no_hz, cpu); | |
8aa670cd | 1803 | delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq); |
89b4cd4b | 1804 | pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n", |
7f21aeef PM |
1805 | cpu, |
1806 | "O."[!!cpu_online(cpu)], | |
1807 | "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)], | |
1808 | "N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)], | |
9b9500da PM |
1809 | !IS_ENABLED(CONFIG_IRQ_WORK) ? '?' : |
1810 | rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' : | |
1811 | "!."[!delta], | |
7f21aeef | 1812 | ticks_value, ticks_title, |
02a5c550 | 1813 | rcu_dynticks_snap(rdtp) & 0xfff, |
a858af28 | 1814 | rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, |
6231069b | 1815 | rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), |
7d0ae808 | 1816 | READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart, |
a858af28 PM |
1817 | fast_no_hz); |
1818 | } | |
1819 | ||
1820 | /* Terminate the stall-info list. */ | |
1821 | static void print_cpu_stall_info_end(void) | |
1822 | { | |
efc151c3 | 1823 | pr_err("\t"); |
a858af28 PM |
1824 | } |
1825 | ||
1826 | /* Zero ->ticks_this_gp for all flavors of RCU. */ | |
1827 | static void zero_cpu_stall_ticks(struct rcu_data *rdp) | |
1828 | { | |
1829 | rdp->ticks_this_gp = 0; | |
6231069b | 1830 | rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id()); |
a858af28 PM |
1831 | } |
1832 | ||
1833 | /* Increment ->ticks_this_gp for all flavors of RCU. */ | |
1834 | static void increment_cpu_stall_ticks(void) | |
1835 | { | |
115f7a7c PM |
1836 | struct rcu_state *rsp; |
1837 | ||
1838 | for_each_rcu_flavor(rsp) | |
fa07a58f | 1839 | raw_cpu_inc(rsp->rda->ticks_this_gp); |
a858af28 PM |
1840 | } |
1841 | ||
3fbfbf7a PM |
1842 | #ifdef CONFIG_RCU_NOCB_CPU |
1843 | ||
1844 | /* | |
1845 | * Offload callback processing from the boot-time-specified set of CPUs | |
1846 | * specified by rcu_nocb_mask. For each CPU in the set, there is a | |
1847 | * kthread created that pulls the callbacks from the corresponding CPU, | |
1848 | * waits for a grace period to elapse, and invokes the callbacks. | |
1849 | * The no-CBs CPUs do a wake_up() on their kthread when they insert | |
1850 | * a callback into any empty list, unless the rcu_nocb_poll boot parameter | |
1851 | * has been specified, in which case each kthread actively polls its | |
1852 | * CPU. (Which isn't so great for energy efficiency, but which does | |
1853 | * reduce RCU's overhead on that CPU.) | |
1854 | * | |
1855 | * This is intended to be used in conjunction with Frederic Weisbecker's | |
1856 | * adaptive-idle work, which would seriously reduce OS jitter on CPUs | |
1857 | * running CPU-bound user-mode computations. | |
1858 | * | |
1859 | * Offloading of callback processing could also in theory be used as | |
1860 | * an energy-efficiency measure because CPUs with no RCU callbacks | |
1861 | * queued are more aggressive about entering dyntick-idle mode. | |
1862 | */ | |
1863 | ||
1864 | ||
1865 | /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */ | |
1866 | static int __init rcu_nocb_setup(char *str) | |
1867 | { | |
1868 | alloc_bootmem_cpumask_var(&rcu_nocb_mask); | |
3fbfbf7a PM |
1869 | cpulist_parse(str, rcu_nocb_mask); |
1870 | return 1; | |
1871 | } | |
1872 | __setup("rcu_nocbs=", rcu_nocb_setup); | |
1873 | ||
1b0048a4 PG |
1874 | static int __init parse_rcu_nocb_poll(char *arg) |
1875 | { | |
5455a7f6 | 1876 | rcu_nocb_poll = true; |
1b0048a4 PG |
1877 | return 0; |
1878 | } | |
1879 | early_param("rcu_nocb_poll", parse_rcu_nocb_poll); | |
1880 | ||
dae6e64d | 1881 | /* |
0446be48 PM |
1882 | * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended |
1883 | * grace period. | |
dae6e64d | 1884 | */ |
abedf8e2 | 1885 | static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) |
dae6e64d | 1886 | { |
abedf8e2 | 1887 | swake_up_all(sq); |
dae6e64d PM |
1888 | } |
1889 | ||
abedf8e2 | 1890 | static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) |
065bb78c | 1891 | { |
e0da2374 | 1892 | return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1]; |
065bb78c DW |
1893 | } |
1894 | ||
dae6e64d | 1895 | static void rcu_init_one_nocb(struct rcu_node *rnp) |
34ed6246 | 1896 | { |
abedf8e2 PG |
1897 | init_swait_queue_head(&rnp->nocb_gp_wq[0]); |
1898 | init_swait_queue_head(&rnp->nocb_gp_wq[1]); | |
34ed6246 PM |
1899 | } |
1900 | ||
24342c96 | 1901 | /* Is the specified CPU a no-CBs CPU? */ |
d1e43fa5 | 1902 | bool rcu_is_nocb_cpu(int cpu) |
3fbfbf7a | 1903 | { |
84b12b75 | 1904 | if (cpumask_available(rcu_nocb_mask)) |
3fbfbf7a PM |
1905 | return cpumask_test_cpu(cpu, rcu_nocb_mask); |
1906 | return false; | |
1907 | } | |
1908 | ||
fbce7497 | 1909 | /* |
8be6e1b1 PM |
1910 | * Kick the leader kthread for this NOCB group. Caller holds ->nocb_lock |
1911 | * and this function releases it. | |
fbce7497 | 1912 | */ |
8be6e1b1 PM |
1913 | static void __wake_nocb_leader(struct rcu_data *rdp, bool force, |
1914 | unsigned long flags) | |
1915 | __releases(rdp->nocb_lock) | |
fbce7497 PM |
1916 | { |
1917 | struct rcu_data *rdp_leader = rdp->nocb_leader; | |
1918 | ||
8be6e1b1 PM |
1919 | lockdep_assert_held(&rdp->nocb_lock); |
1920 | if (!READ_ONCE(rdp_leader->nocb_kthread)) { | |
1921 | raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); | |
fbce7497 | 1922 | return; |
8be6e1b1 PM |
1923 | } |
1924 | if (rdp_leader->nocb_leader_sleep || force) { | |
39953dfd | 1925 | /* Prior smp_mb__after_atomic() orders against prior enqueue. */ |
7d0ae808 | 1926 | WRITE_ONCE(rdp_leader->nocb_leader_sleep, false); |
8be6e1b1 PM |
1927 | del_timer(&rdp->nocb_timer); |
1928 | raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); | |
b3dae109 PZ |
1929 | smp_mb(); /* ->nocb_leader_sleep before swake_up_one(). */ |
1930 | swake_up_one(&rdp_leader->nocb_wq); | |
8be6e1b1 PM |
1931 | } else { |
1932 | raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); | |
fbce7497 PM |
1933 | } |
1934 | } | |
1935 | ||
8be6e1b1 PM |
1936 | /* |
1937 | * Kick the leader kthread for this NOCB group, but caller has not | |
1938 | * acquired locks. | |
1939 | */ | |
1940 | static void wake_nocb_leader(struct rcu_data *rdp, bool force) | |
1941 | { | |
1942 | unsigned long flags; | |
1943 | ||
1944 | raw_spin_lock_irqsave(&rdp->nocb_lock, flags); | |
1945 | __wake_nocb_leader(rdp, force, flags); | |
1946 | } | |
1947 | ||
1948 | /* | |
1949 | * Arrange to wake the leader kthread for this NOCB group at some | |
1950 | * future time when it is safe to do so. | |
1951 | */ | |
1952 | static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype, | |
1953 | const char *reason) | |
1954 | { | |
1955 | unsigned long flags; | |
1956 | ||
1957 | raw_spin_lock_irqsave(&rdp->nocb_lock, flags); | |
1958 | if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) | |
1959 | mod_timer(&rdp->nocb_timer, jiffies + 1); | |
1960 | WRITE_ONCE(rdp->nocb_defer_wakeup, waketype); | |
1961 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, reason); | |
1962 | raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); | |
1963 | } | |
1964 | ||
d7e29933 PM |
1965 | /* |
1966 | * Does the specified CPU need an RCU callback for the specified flavor | |
1967 | * of rcu_barrier()? | |
1968 | */ | |
1969 | static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) | |
1970 | { | |
1971 | struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); | |
41050a00 PM |
1972 | unsigned long ret; |
1973 | #ifdef CONFIG_PROVE_RCU | |
d7e29933 | 1974 | struct rcu_head *rhp; |
41050a00 | 1975 | #endif /* #ifdef CONFIG_PROVE_RCU */ |
d7e29933 | 1976 | |
41050a00 PM |
1977 | /* |
1978 | * Check count of all no-CBs callbacks awaiting invocation. | |
1979 | * There needs to be a barrier before this function is called, | |
1980 | * but associated with a prior determination that no more | |
1981 | * callbacks would be posted. In the worst case, the first | |
1982 | * barrier in _rcu_barrier() suffices (but the caller cannot | |
1983 | * necessarily rely on this, not a substitute for the caller | |
1984 | * getting the concurrency design right!). There must also be | |
1985 | * a barrier between the following load an posting of a callback | |
1986 | * (if a callback is in fact needed). This is associated with an | |
1987 | * atomic_inc() in the caller. | |
1988 | */ | |
1989 | ret = atomic_long_read(&rdp->nocb_q_count); | |
d7e29933 | 1990 | |
41050a00 | 1991 | #ifdef CONFIG_PROVE_RCU |
7d0ae808 | 1992 | rhp = READ_ONCE(rdp->nocb_head); |
d7e29933 | 1993 | if (!rhp) |
7d0ae808 | 1994 | rhp = READ_ONCE(rdp->nocb_gp_head); |
d7e29933 | 1995 | if (!rhp) |
7d0ae808 | 1996 | rhp = READ_ONCE(rdp->nocb_follower_head); |
d7e29933 PM |
1997 | |
1998 | /* Having no rcuo kthread but CBs after scheduler starts is bad! */ | |
7d0ae808 | 1999 | if (!READ_ONCE(rdp->nocb_kthread) && rhp && |
59f792d1 | 2000 | rcu_scheduler_fully_active) { |
d7e29933 PM |
2001 | /* RCU callback enqueued before CPU first came online??? */ |
2002 | pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n", | |
2003 | cpu, rhp->func); | |
2004 | WARN_ON_ONCE(1); | |
2005 | } | |
41050a00 | 2006 | #endif /* #ifdef CONFIG_PROVE_RCU */ |
d7e29933 | 2007 | |
41050a00 | 2008 | return !!ret; |
d7e29933 PM |
2009 | } |
2010 | ||
3fbfbf7a PM |
2011 | /* |
2012 | * Enqueue the specified string of rcu_head structures onto the specified | |
2013 | * CPU's no-CBs lists. The CPU is specified by rdp, the head of the | |
2014 | * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy | |
2015 | * counts are supplied by rhcount and rhcount_lazy. | |
2016 | * | |
2017 | * If warranted, also wake up the kthread servicing this CPUs queues. | |
2018 | */ | |
2019 | static void __call_rcu_nocb_enqueue(struct rcu_data *rdp, | |
2020 | struct rcu_head *rhp, | |
2021 | struct rcu_head **rhtp, | |
96d3fd0d PM |
2022 | int rhcount, int rhcount_lazy, |
2023 | unsigned long flags) | |
3fbfbf7a PM |
2024 | { |
2025 | int len; | |
2026 | struct rcu_head **old_rhpp; | |
2027 | struct task_struct *t; | |
2028 | ||
2029 | /* Enqueue the callback on the nocb list and update counts. */ | |
41050a00 PM |
2030 | atomic_long_add(rhcount, &rdp->nocb_q_count); |
2031 | /* rcu_barrier() relies on ->nocb_q_count add before xchg. */ | |
3fbfbf7a | 2032 | old_rhpp = xchg(&rdp->nocb_tail, rhtp); |
7d0ae808 | 2033 | WRITE_ONCE(*old_rhpp, rhp); |
3fbfbf7a | 2034 | atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy); |
39953dfd | 2035 | smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */ |
3fbfbf7a PM |
2036 | |
2037 | /* If we are not being polled and there is a kthread, awaken it ... */ | |
7d0ae808 | 2038 | t = READ_ONCE(rdp->nocb_kthread); |
25e03a74 | 2039 | if (rcu_nocb_poll || !t) { |
9261dd0d PM |
2040 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2041 | TPS("WakeNotPoll")); | |
3fbfbf7a | 2042 | return; |
9261dd0d | 2043 | } |
3fbfbf7a PM |
2044 | len = atomic_long_read(&rdp->nocb_q_count); |
2045 | if (old_rhpp == &rdp->nocb_head) { | |
96d3fd0d | 2046 | if (!irqs_disabled_flags(flags)) { |
fbce7497 PM |
2047 | /* ... if queue was empty ... */ |
2048 | wake_nocb_leader(rdp, false); | |
96d3fd0d PM |
2049 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2050 | TPS("WakeEmpty")); | |
2051 | } else { | |
8be6e1b1 PM |
2052 | wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE, |
2053 | TPS("WakeEmptyIsDeferred")); | |
96d3fd0d | 2054 | } |
3fbfbf7a PM |
2055 | rdp->qlen_last_fqs_check = 0; |
2056 | } else if (len > rdp->qlen_last_fqs_check + qhimark) { | |
fbce7497 | 2057 | /* ... or if many callbacks queued. */ |
9fdd3bc9 PM |
2058 | if (!irqs_disabled_flags(flags)) { |
2059 | wake_nocb_leader(rdp, true); | |
2060 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, | |
2061 | TPS("WakeOvf")); | |
2062 | } else { | |
efcd2d54 | 2063 | wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE_FORCE, |
8be6e1b1 | 2064 | TPS("WakeOvfIsDeferred")); |
9fdd3bc9 | 2065 | } |
3fbfbf7a | 2066 | rdp->qlen_last_fqs_check = LONG_MAX / 2; |
9261dd0d PM |
2067 | } else { |
2068 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot")); | |
3fbfbf7a PM |
2069 | } |
2070 | return; | |
2071 | } | |
2072 | ||
2073 | /* | |
2074 | * This is a helper for __call_rcu(), which invokes this when the normal | |
2075 | * callback queue is inoperable. If this is not a no-CBs CPU, this | |
2076 | * function returns failure back to __call_rcu(), which can complain | |
2077 | * appropriately. | |
2078 | * | |
2079 | * Otherwise, this function queues the callback where the corresponding | |
2080 | * "rcuo" kthread can find it. | |
2081 | */ | |
2082 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, | |
96d3fd0d | 2083 | bool lazy, unsigned long flags) |
3fbfbf7a PM |
2084 | { |
2085 | ||
d1e43fa5 | 2086 | if (!rcu_is_nocb_cpu(rdp->cpu)) |
c271d3a9 | 2087 | return false; |
96d3fd0d | 2088 | __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags); |
21e7a608 PM |
2089 | if (__is_kfree_rcu_offset((unsigned long)rhp->func)) |
2090 | trace_rcu_kfree_callback(rdp->rsp->name, rhp, | |
2091 | (unsigned long)rhp->func, | |
756cbf6b PM |
2092 | -atomic_long_read(&rdp->nocb_q_count_lazy), |
2093 | -atomic_long_read(&rdp->nocb_q_count)); | |
21e7a608 PM |
2094 | else |
2095 | trace_rcu_callback(rdp->rsp->name, rhp, | |
756cbf6b PM |
2096 | -atomic_long_read(&rdp->nocb_q_count_lazy), |
2097 | -atomic_long_read(&rdp->nocb_q_count)); | |
1772947b PM |
2098 | |
2099 | /* | |
2100 | * If called from an extended quiescent state with interrupts | |
2101 | * disabled, invoke the RCU core in order to allow the idle-entry | |
2102 | * deferred-wakeup check to function. | |
2103 | */ | |
2104 | if (irqs_disabled_flags(flags) && | |
2105 | !rcu_is_watching() && | |
2106 | cpu_online(smp_processor_id())) | |
2107 | invoke_rcu_core(); | |
2108 | ||
c271d3a9 | 2109 | return true; |
3fbfbf7a PM |
2110 | } |
2111 | ||
2112 | /* | |
2113 | * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is | |
2114 | * not a no-CBs CPU. | |
2115 | */ | |
b1a2d79f | 2116 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp, |
96d3fd0d PM |
2117 | struct rcu_data *rdp, |
2118 | unsigned long flags) | |
3fbfbf7a | 2119 | { |
b04db8e1 | 2120 | lockdep_assert_irqs_disabled(); |
d1e43fa5 | 2121 | if (!rcu_is_nocb_cpu(smp_processor_id())) |
b1a2d79f PM |
2122 | return false; /* Not NOCBs CPU, caller must migrate CBs. */ |
2123 | __call_rcu_nocb_enqueue(my_rdp, rcu_segcblist_head(&rdp->cblist), | |
2124 | rcu_segcblist_tail(&rdp->cblist), | |
2125 | rcu_segcblist_n_cbs(&rdp->cblist), | |
2126 | rcu_segcblist_n_lazy_cbs(&rdp->cblist), flags); | |
2127 | rcu_segcblist_init(&rdp->cblist); | |
2128 | rcu_segcblist_disable(&rdp->cblist); | |
0a9e1e11 | 2129 | return true; |
3fbfbf7a PM |
2130 | } |
2131 | ||
2132 | /* | |
34ed6246 PM |
2133 | * If necessary, kick off a new grace period, and either way wait |
2134 | * for a subsequent grace period to complete. | |
3fbfbf7a | 2135 | */ |
34ed6246 | 2136 | static void rcu_nocb_wait_gp(struct rcu_data *rdp) |
3fbfbf7a | 2137 | { |
34ed6246 | 2138 | unsigned long c; |
dae6e64d | 2139 | bool d; |
34ed6246 | 2140 | unsigned long flags; |
48a7639c | 2141 | bool needwake; |
34ed6246 PM |
2142 | struct rcu_node *rnp = rdp->mynode; |
2143 | ||
ab5e869c | 2144 | local_irq_save(flags); |
29365e56 | 2145 | c = rcu_seq_snap(&rdp->rsp->gp_seq); |
ab5e869c PM |
2146 | if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) { |
2147 | local_irq_restore(flags); | |
2148 | } else { | |
2149 | raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ | |
2150 | needwake = rcu_start_this_gp(rnp, rdp, c); | |
2151 | raw_spin_unlock_irqrestore_rcu_node(rnp, flags); | |
2152 | if (needwake) | |
2153 | rcu_gp_kthread_wake(rdp->rsp); | |
2154 | } | |
3fbfbf7a PM |
2155 | |
2156 | /* | |
34ed6246 PM |
2157 | * Wait for the grace period. Do so interruptibly to avoid messing |
2158 | * up the load average. | |
3fbfbf7a | 2159 | */ |
41e80595 | 2160 | trace_rcu_this_gp(rnp, rdp, c, TPS("StartWait")); |
34ed6246 | 2161 | for (;;) { |
b3dae109 | 2162 | swait_event_interruptible_exclusive( |
29365e56 PM |
2163 | rnp->nocb_gp_wq[rcu_seq_ctr(c) & 0x1], |
2164 | (d = rcu_seq_done(&rnp->gp_seq, c))); | |
dae6e64d | 2165 | if (likely(d)) |
34ed6246 | 2166 | break; |
73a860cd | 2167 | WARN_ON(signal_pending(current)); |
41e80595 | 2168 | trace_rcu_this_gp(rnp, rdp, c, TPS("ResumeWait")); |
34ed6246 | 2169 | } |
41e80595 | 2170 | trace_rcu_this_gp(rnp, rdp, c, TPS("EndWait")); |
34ed6246 | 2171 | smp_mb(); /* Ensure that CB invocation happens after GP end. */ |
3fbfbf7a PM |
2172 | } |
2173 | ||
fbce7497 PM |
2174 | /* |
2175 | * Leaders come here to wait for additional callbacks to show up. | |
2176 | * This function does not return until callbacks appear. | |
2177 | */ | |
2178 | static void nocb_leader_wait(struct rcu_data *my_rdp) | |
2179 | { | |
2180 | bool firsttime = true; | |
8be6e1b1 | 2181 | unsigned long flags; |
fbce7497 PM |
2182 | bool gotcbs; |
2183 | struct rcu_data *rdp; | |
2184 | struct rcu_head **tail; | |
2185 | ||
2186 | wait_again: | |
2187 | ||
2188 | /* Wait for callbacks to appear. */ | |
2189 | if (!rcu_nocb_poll) { | |
bedbb648 | 2190 | trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Sleep")); |
b3dae109 | 2191 | swait_event_interruptible_exclusive(my_rdp->nocb_wq, |
7d0ae808 | 2192 | !READ_ONCE(my_rdp->nocb_leader_sleep)); |
8be6e1b1 PM |
2193 | raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags); |
2194 | my_rdp->nocb_leader_sleep = true; | |
2195 | WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT); | |
2196 | del_timer(&my_rdp->nocb_timer); | |
2197 | raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags); | |
fbce7497 PM |
2198 | } else if (firsttime) { |
2199 | firsttime = false; /* Don't drown trace log with "Poll"! */ | |
bedbb648 | 2200 | trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Poll")); |
fbce7497 PM |
2201 | } |
2202 | ||
2203 | /* | |
2204 | * Each pass through the following loop checks a follower for CBs. | |
2205 | * We are our own first follower. Any CBs found are moved to | |
2206 | * nocb_gp_head, where they await a grace period. | |
2207 | */ | |
2208 | gotcbs = false; | |
8be6e1b1 | 2209 | smp_mb(); /* wakeup and _sleep before ->nocb_head reads. */ |
fbce7497 | 2210 | for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { |
7d0ae808 | 2211 | rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head); |
fbce7497 PM |
2212 | if (!rdp->nocb_gp_head) |
2213 | continue; /* No CBs here, try next follower. */ | |
2214 | ||
2215 | /* Move callbacks to wait-for-GP list, which is empty. */ | |
7d0ae808 | 2216 | WRITE_ONCE(rdp->nocb_head, NULL); |
fbce7497 | 2217 | rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head); |
fbce7497 PM |
2218 | gotcbs = true; |
2219 | } | |
2220 | ||
8be6e1b1 | 2221 | /* No callbacks? Sleep a bit if polling, and go retry. */ |
fbce7497 | 2222 | if (unlikely(!gotcbs)) { |
73a860cd | 2223 | WARN_ON(signal_pending(current)); |
8be6e1b1 PM |
2224 | if (rcu_nocb_poll) { |
2225 | schedule_timeout_interruptible(1); | |
2226 | } else { | |
fbce7497 | 2227 | trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, |
bedbb648 | 2228 | TPS("WokeEmpty")); |
8be6e1b1 | 2229 | } |
fbce7497 PM |
2230 | goto wait_again; |
2231 | } | |
2232 | ||
2233 | /* Wait for one grace period. */ | |
2234 | rcu_nocb_wait_gp(my_rdp); | |
2235 | ||
fbce7497 PM |
2236 | /* Each pass through the following loop wakes a follower, if needed. */ |
2237 | for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) { | |
8be6e1b1 PM |
2238 | if (!rcu_nocb_poll && |
2239 | READ_ONCE(rdp->nocb_head) && | |
2240 | READ_ONCE(my_rdp->nocb_leader_sleep)) { | |
2241 | raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags); | |
11ed7f93 | 2242 | my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/ |
8be6e1b1 PM |
2243 | raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags); |
2244 | } | |
fbce7497 PM |
2245 | if (!rdp->nocb_gp_head) |
2246 | continue; /* No CBs, so no need to wake follower. */ | |
2247 | ||
2248 | /* Append callbacks to follower's "done" list. */ | |
8be6e1b1 PM |
2249 | raw_spin_lock_irqsave(&rdp->nocb_lock, flags); |
2250 | tail = rdp->nocb_follower_tail; | |
2251 | rdp->nocb_follower_tail = rdp->nocb_gp_tail; | |
fbce7497 | 2252 | *tail = rdp->nocb_gp_head; |
8be6e1b1 | 2253 | raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); |
fbce7497 | 2254 | if (rdp != my_rdp && tail == &rdp->nocb_follower_head) { |
8be6e1b1 | 2255 | /* List was empty, so wake up the follower. */ |
b3dae109 | 2256 | swake_up_one(&rdp->nocb_wq); |
fbce7497 PM |
2257 | } |
2258 | } | |
2259 | ||
2260 | /* If we (the leader) don't have CBs, go wait some more. */ | |
2261 | if (!my_rdp->nocb_follower_head) | |
2262 | goto wait_again; | |
2263 | } | |
2264 | ||
2265 | /* | |
2266 | * Followers come here to wait for additional callbacks to show up. | |
2267 | * This function does not return until callbacks appear. | |
2268 | */ | |
2269 | static void nocb_follower_wait(struct rcu_data *rdp) | |
2270 | { | |
fbce7497 | 2271 | for (;;) { |
bedbb648 | 2272 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("FollowerSleep")); |
b3dae109 | 2273 | swait_event_interruptible_exclusive(rdp->nocb_wq, |
8be6e1b1 | 2274 | READ_ONCE(rdp->nocb_follower_head)); |
fbce7497 PM |
2275 | if (smp_load_acquire(&rdp->nocb_follower_head)) { |
2276 | /* ^^^ Ensure CB invocation follows _head test. */ | |
2277 | return; | |
2278 | } | |
73a860cd | 2279 | WARN_ON(signal_pending(current)); |
bedbb648 | 2280 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeEmpty")); |
fbce7497 PM |
2281 | } |
2282 | } | |
2283 | ||
3fbfbf7a PM |
2284 | /* |
2285 | * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes | |
fbce7497 PM |
2286 | * callbacks queued by the corresponding no-CBs CPU, however, there is |
2287 | * an optional leader-follower relationship so that the grace-period | |
2288 | * kthreads don't have to do quite so many wakeups. | |
3fbfbf7a PM |
2289 | */ |
2290 | static int rcu_nocb_kthread(void *arg) | |
2291 | { | |
2292 | int c, cl; | |
8be6e1b1 | 2293 | unsigned long flags; |
3fbfbf7a PM |
2294 | struct rcu_head *list; |
2295 | struct rcu_head *next; | |
2296 | struct rcu_head **tail; | |
2297 | struct rcu_data *rdp = arg; | |
2298 | ||
2299 | /* Each pass through this loop invokes one batch of callbacks */ | |
2300 | for (;;) { | |
fbce7497 PM |
2301 | /* Wait for callbacks. */ |
2302 | if (rdp->nocb_leader == rdp) | |
2303 | nocb_leader_wait(rdp); | |
2304 | else | |
2305 | nocb_follower_wait(rdp); | |
2306 | ||
2307 | /* Pull the ready-to-invoke callbacks onto local list. */ | |
8be6e1b1 PM |
2308 | raw_spin_lock_irqsave(&rdp->nocb_lock, flags); |
2309 | list = rdp->nocb_follower_head; | |
2310 | rdp->nocb_follower_head = NULL; | |
2311 | tail = rdp->nocb_follower_tail; | |
2312 | rdp->nocb_follower_tail = &rdp->nocb_follower_head; | |
2313 | raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); | |
fbce7497 | 2314 | BUG_ON(!list); |
bedbb648 | 2315 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeNonEmpty")); |
3fbfbf7a PM |
2316 | |
2317 | /* Each pass through the following loop invokes a callback. */ | |
41050a00 PM |
2318 | trace_rcu_batch_start(rdp->rsp->name, |
2319 | atomic_long_read(&rdp->nocb_q_count_lazy), | |
2320 | atomic_long_read(&rdp->nocb_q_count), -1); | |
3fbfbf7a PM |
2321 | c = cl = 0; |
2322 | while (list) { | |
2323 | next = list->next; | |
2324 | /* Wait for enqueuing to complete, if needed. */ | |
2325 | while (next == NULL && &list->next != tail) { | |
69a79bb1 PM |
2326 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2327 | TPS("WaitQueue")); | |
3fbfbf7a | 2328 | schedule_timeout_interruptible(1); |
69a79bb1 PM |
2329 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, |
2330 | TPS("WokeQueue")); | |
3fbfbf7a PM |
2331 | next = list->next; |
2332 | } | |
2333 | debug_rcu_head_unqueue(list); | |
2334 | local_bh_disable(); | |
2335 | if (__rcu_reclaim(rdp->rsp->name, list)) | |
2336 | cl++; | |
2337 | c++; | |
2338 | local_bh_enable(); | |
cee43939 | 2339 | cond_resched_tasks_rcu_qs(); |
3fbfbf7a PM |
2340 | list = next; |
2341 | } | |
2342 | trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1); | |
41050a00 PM |
2343 | smp_mb__before_atomic(); /* _add after CB invocation. */ |
2344 | atomic_long_add(-c, &rdp->nocb_q_count); | |
2345 | atomic_long_add(-cl, &rdp->nocb_q_count_lazy); | |
3fbfbf7a PM |
2346 | } |
2347 | return 0; | |
2348 | } | |
2349 | ||
96d3fd0d | 2350 | /* Is a deferred wakeup of rcu_nocb_kthread() required? */ |
9fdd3bc9 | 2351 | static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) |
96d3fd0d | 2352 | { |
7d0ae808 | 2353 | return READ_ONCE(rdp->nocb_defer_wakeup); |
96d3fd0d PM |
2354 | } |
2355 | ||
2356 | /* Do a deferred wakeup of rcu_nocb_kthread(). */ | |
8be6e1b1 | 2357 | static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp) |
96d3fd0d | 2358 | { |
8be6e1b1 | 2359 | unsigned long flags; |
9fdd3bc9 PM |
2360 | int ndw; |
2361 | ||
8be6e1b1 PM |
2362 | raw_spin_lock_irqsave(&rdp->nocb_lock, flags); |
2363 | if (!rcu_nocb_need_deferred_wakeup(rdp)) { | |
2364 | raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); | |
96d3fd0d | 2365 | return; |
8be6e1b1 | 2366 | } |
7d0ae808 | 2367 | ndw = READ_ONCE(rdp->nocb_defer_wakeup); |
511324e4 | 2368 | WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT); |
8be6e1b1 | 2369 | __wake_nocb_leader(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags); |
9fdd3bc9 | 2370 | trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake")); |
96d3fd0d PM |
2371 | } |
2372 | ||
8be6e1b1 | 2373 | /* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */ |
fd30b717 | 2374 | static void do_nocb_deferred_wakeup_timer(struct timer_list *t) |
8be6e1b1 | 2375 | { |
fd30b717 KC |
2376 | struct rcu_data *rdp = from_timer(rdp, t, nocb_timer); |
2377 | ||
2378 | do_nocb_deferred_wakeup_common(rdp); | |
8be6e1b1 PM |
2379 | } |
2380 | ||
2381 | /* | |
2382 | * Do a deferred wakeup of rcu_nocb_kthread() from fastpath. | |
2383 | * This means we do an inexact common-case check. Note that if | |
2384 | * we miss, ->nocb_timer will eventually clean things up. | |
2385 | */ | |
2386 | static void do_nocb_deferred_wakeup(struct rcu_data *rdp) | |
2387 | { | |
2388 | if (rcu_nocb_need_deferred_wakeup(rdp)) | |
2389 | do_nocb_deferred_wakeup_common(rdp); | |
2390 | } | |
2391 | ||
f4579fc5 PM |
2392 | void __init rcu_init_nohz(void) |
2393 | { | |
2394 | int cpu; | |
ef126206 | 2395 | bool need_rcu_nocb_mask = false; |
f4579fc5 PM |
2396 | struct rcu_state *rsp; |
2397 | ||
f4579fc5 PM |
2398 | #if defined(CONFIG_NO_HZ_FULL) |
2399 | if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask)) | |
2400 | need_rcu_nocb_mask = true; | |
2401 | #endif /* #if defined(CONFIG_NO_HZ_FULL) */ | |
2402 | ||
84b12b75 | 2403 | if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) { |
949cccdb PK |
2404 | if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { |
2405 | pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); | |
2406 | return; | |
2407 | } | |
f4579fc5 | 2408 | } |
84b12b75 | 2409 | if (!cpumask_available(rcu_nocb_mask)) |
f4579fc5 PM |
2410 | return; |
2411 | ||
f4579fc5 PM |
2412 | #if defined(CONFIG_NO_HZ_FULL) |
2413 | if (tick_nohz_full_running) | |
2414 | cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); | |
2415 | #endif /* #if defined(CONFIG_NO_HZ_FULL) */ | |
2416 | ||
2417 | if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { | |
ef126206 | 2418 | pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n"); |
f4579fc5 PM |
2419 | cpumask_and(rcu_nocb_mask, cpu_possible_mask, |
2420 | rcu_nocb_mask); | |
2421 | } | |
3016611e PM |
2422 | if (cpumask_empty(rcu_nocb_mask)) |
2423 | pr_info("\tOffload RCU callbacks from CPUs: (none).\n"); | |
2424 | else | |
2425 | pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n", | |
2426 | cpumask_pr_args(rcu_nocb_mask)); | |
f4579fc5 PM |
2427 | if (rcu_nocb_poll) |
2428 | pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); | |
2429 | ||
2430 | for_each_rcu_flavor(rsp) { | |
34404ca8 PM |
2431 | for_each_cpu(cpu, rcu_nocb_mask) |
2432 | init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu)); | |
35ce7f29 | 2433 | rcu_organize_nocb_kthreads(rsp); |
f4579fc5 | 2434 | } |
96d3fd0d PM |
2435 | } |
2436 | ||
3fbfbf7a PM |
2437 | /* Initialize per-rcu_data variables for no-CBs CPUs. */ |
2438 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) | |
2439 | { | |
2440 | rdp->nocb_tail = &rdp->nocb_head; | |
abedf8e2 | 2441 | init_swait_queue_head(&rdp->nocb_wq); |
fbce7497 | 2442 | rdp->nocb_follower_tail = &rdp->nocb_follower_head; |
8be6e1b1 | 2443 | raw_spin_lock_init(&rdp->nocb_lock); |
fd30b717 | 2444 | timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0); |
3fbfbf7a PM |
2445 | } |
2446 | ||
35ce7f29 PM |
2447 | /* |
2448 | * If the specified CPU is a no-CBs CPU that does not already have its | |
2449 | * rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are | |
2450 | * brought online out of order, this can require re-organizing the | |
2451 | * leader-follower relationships. | |
2452 | */ | |
2453 | static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu) | |
2454 | { | |
2455 | struct rcu_data *rdp; | |
2456 | struct rcu_data *rdp_last; | |
2457 | struct rcu_data *rdp_old_leader; | |
2458 | struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu); | |
2459 | struct task_struct *t; | |
2460 | ||
2461 | /* | |
2462 | * If this isn't a no-CBs CPU or if it already has an rcuo kthread, | |
2463 | * then nothing to do. | |
2464 | */ | |
2465 | if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread) | |
2466 | return; | |
2467 | ||
2468 | /* If we didn't spawn the leader first, reorganize! */ | |
2469 | rdp_old_leader = rdp_spawn->nocb_leader; | |
2470 | if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) { | |
2471 | rdp_last = NULL; | |
2472 | rdp = rdp_old_leader; | |
2473 | do { | |
2474 | rdp->nocb_leader = rdp_spawn; | |
2475 | if (rdp_last && rdp != rdp_spawn) | |
2476 | rdp_last->nocb_next_follower = rdp; | |
bbe5d7a9 PM |
2477 | if (rdp == rdp_spawn) { |
2478 | rdp = rdp->nocb_next_follower; | |
2479 | } else { | |
2480 | rdp_last = rdp; | |
2481 | rdp = rdp->nocb_next_follower; | |
2482 | rdp_last->nocb_next_follower = NULL; | |
2483 | } | |
35ce7f29 PM |
2484 | } while (rdp); |
2485 | rdp_spawn->nocb_next_follower = rdp_old_leader; | |
2486 | } | |
2487 | ||
2488 | /* Spawn the kthread for this CPU and RCU flavor. */ | |
2489 | t = kthread_run(rcu_nocb_kthread, rdp_spawn, | |
2490 | "rcuo%c/%d", rsp->abbr, cpu); | |
2491 | BUG_ON(IS_ERR(t)); | |
7d0ae808 | 2492 | WRITE_ONCE(rdp_spawn->nocb_kthread, t); |
35ce7f29 PM |
2493 | } |
2494 | ||
2495 | /* | |
2496 | * If the specified CPU is a no-CBs CPU that does not already have its | |
2497 | * rcuo kthreads, spawn them. | |
2498 | */ | |
2499 | static void rcu_spawn_all_nocb_kthreads(int cpu) | |
2500 | { | |
2501 | struct rcu_state *rsp; | |
2502 | ||
2503 | if (rcu_scheduler_fully_active) | |
2504 | for_each_rcu_flavor(rsp) | |
2505 | rcu_spawn_one_nocb_kthread(rsp, cpu); | |
2506 | } | |
2507 | ||
2508 | /* | |
2509 | * Once the scheduler is running, spawn rcuo kthreads for all online | |
2510 | * no-CBs CPUs. This assumes that the early_initcall()s happen before | |
2511 | * non-boot CPUs come online -- if this changes, we will need to add | |
2512 | * some mutual exclusion. | |
2513 | */ | |
2514 | static void __init rcu_spawn_nocb_kthreads(void) | |
2515 | { | |
2516 | int cpu; | |
2517 | ||
2518 | for_each_online_cpu(cpu) | |
2519 | rcu_spawn_all_nocb_kthreads(cpu); | |
2520 | } | |
2521 | ||
fbce7497 PM |
2522 | /* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */ |
2523 | static int rcu_nocb_leader_stride = -1; | |
2524 | module_param(rcu_nocb_leader_stride, int, 0444); | |
2525 | ||
2526 | /* | |
35ce7f29 | 2527 | * Initialize leader-follower relationships for all no-CBs CPU. |
fbce7497 | 2528 | */ |
35ce7f29 | 2529 | static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp) |
3fbfbf7a PM |
2530 | { |
2531 | int cpu; | |
fbce7497 PM |
2532 | int ls = rcu_nocb_leader_stride; |
2533 | int nl = 0; /* Next leader. */ | |
3fbfbf7a | 2534 | struct rcu_data *rdp; |
fbce7497 PM |
2535 | struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */ |
2536 | struct rcu_data *rdp_prev = NULL; | |
3fbfbf7a | 2537 | |
84b12b75 | 2538 | if (!cpumask_available(rcu_nocb_mask)) |
3fbfbf7a | 2539 | return; |
fbce7497 PM |
2540 | if (ls == -1) { |
2541 | ls = int_sqrt(nr_cpu_ids); | |
2542 | rcu_nocb_leader_stride = ls; | |
2543 | } | |
2544 | ||
2545 | /* | |
9831ce3b PM |
2546 | * Each pass through this loop sets up one rcu_data structure. |
2547 | * Should the corresponding CPU come online in the future, then | |
2548 | * we will spawn the needed set of rcu_nocb_kthread() kthreads. | |
fbce7497 | 2549 | */ |
3fbfbf7a PM |
2550 | for_each_cpu(cpu, rcu_nocb_mask) { |
2551 | rdp = per_cpu_ptr(rsp->rda, cpu); | |
fbce7497 PM |
2552 | if (rdp->cpu >= nl) { |
2553 | /* New leader, set up for followers & next leader. */ | |
2554 | nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls; | |
2555 | rdp->nocb_leader = rdp; | |
2556 | rdp_leader = rdp; | |
2557 | } else { | |
2558 | /* Another follower, link to previous leader. */ | |
2559 | rdp->nocb_leader = rdp_leader; | |
2560 | rdp_prev->nocb_next_follower = rdp; | |
2561 | } | |
2562 | rdp_prev = rdp; | |
3fbfbf7a PM |
2563 | } |
2564 | } | |
2565 | ||
2566 | /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */ | |
34ed6246 | 2567 | static bool init_nocb_callback_list(struct rcu_data *rdp) |
3fbfbf7a | 2568 | { |
22c2f669 | 2569 | if (!rcu_is_nocb_cpu(rdp->cpu)) |
34ed6246 | 2570 | return false; |
22c2f669 | 2571 | |
34404ca8 | 2572 | /* If there are early-boot callbacks, move them to nocb lists. */ |
15fecf89 PM |
2573 | if (!rcu_segcblist_empty(&rdp->cblist)) { |
2574 | rdp->nocb_head = rcu_segcblist_head(&rdp->cblist); | |
2575 | rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist); | |
2576 | atomic_long_set(&rdp->nocb_q_count, | |
2577 | rcu_segcblist_n_cbs(&rdp->cblist)); | |
2578 | atomic_long_set(&rdp->nocb_q_count_lazy, | |
2579 | rcu_segcblist_n_lazy_cbs(&rdp->cblist)); | |
2580 | rcu_segcblist_init(&rdp->cblist); | |
34404ca8 | 2581 | } |
15fecf89 | 2582 | rcu_segcblist_disable(&rdp->cblist); |
34ed6246 | 2583 | return true; |
3fbfbf7a PM |
2584 | } |
2585 | ||
34ed6246 PM |
2586 | #else /* #ifdef CONFIG_RCU_NOCB_CPU */ |
2587 | ||
d7e29933 PM |
2588 | static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu) |
2589 | { | |
2590 | WARN_ON_ONCE(1); /* Should be dead code. */ | |
2591 | return false; | |
2592 | } | |
2593 | ||
abedf8e2 | 2594 | static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) |
3fbfbf7a | 2595 | { |
3fbfbf7a PM |
2596 | } |
2597 | ||
abedf8e2 | 2598 | static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) |
065bb78c DW |
2599 | { |
2600 | return NULL; | |
2601 | } | |
2602 | ||
dae6e64d PM |
2603 | static void rcu_init_one_nocb(struct rcu_node *rnp) |
2604 | { | |
2605 | } | |
3fbfbf7a | 2606 | |
3fbfbf7a | 2607 | static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp, |
96d3fd0d | 2608 | bool lazy, unsigned long flags) |
3fbfbf7a | 2609 | { |
4afc7e26 | 2610 | return false; |
3fbfbf7a PM |
2611 | } |
2612 | ||
b1a2d79f | 2613 | static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp, |
96d3fd0d PM |
2614 | struct rcu_data *rdp, |
2615 | unsigned long flags) | |
3fbfbf7a | 2616 | { |
f4aa84ba | 2617 | return false; |
3fbfbf7a PM |
2618 | } |
2619 | ||
3fbfbf7a PM |
2620 | static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) |
2621 | { | |
2622 | } | |
2623 | ||
9fdd3bc9 | 2624 | static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) |
96d3fd0d PM |
2625 | { |
2626 | return false; | |
2627 | } | |
2628 | ||
2629 | static void do_nocb_deferred_wakeup(struct rcu_data *rdp) | |
2630 | { | |
2631 | } | |
2632 | ||
35ce7f29 PM |
2633 | static void rcu_spawn_all_nocb_kthreads(int cpu) |
2634 | { | |
2635 | } | |
2636 | ||
2637 | static void __init rcu_spawn_nocb_kthreads(void) | |
3fbfbf7a PM |
2638 | { |
2639 | } | |
2640 | ||
34ed6246 | 2641 | static bool init_nocb_callback_list(struct rcu_data *rdp) |
3fbfbf7a | 2642 | { |
34ed6246 | 2643 | return false; |
3fbfbf7a PM |
2644 | } |
2645 | ||
2646 | #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ | |
65d798f0 | 2647 | |
a096932f PM |
2648 | /* |
2649 | * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the | |
2650 | * grace-period kthread will do force_quiescent_state() processing? | |
2651 | * The idea is to avoid waking up RCU core processing on such a | |
2652 | * CPU unless the grace period has extended for too long. | |
2653 | * | |
2654 | * This code relies on the fact that all NO_HZ_FULL CPUs are also | |
52e2bb95 | 2655 | * CONFIG_RCU_NOCB_CPU CPUs. |
a096932f PM |
2656 | */ |
2657 | static bool rcu_nohz_full_cpu(struct rcu_state *rsp) | |
2658 | { | |
2659 | #ifdef CONFIG_NO_HZ_FULL | |
2660 | if (tick_nohz_full_cpu(smp_processor_id()) && | |
2661 | (!rcu_gp_in_progress(rsp) || | |
7d0ae808 | 2662 | ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ))) |
5ce035fb | 2663 | return true; |
a096932f | 2664 | #endif /* #ifdef CONFIG_NO_HZ_FULL */ |
5ce035fb | 2665 | return false; |
a096932f | 2666 | } |
5057f55e PM |
2667 | |
2668 | /* | |
265f5f28 | 2669 | * Bind the RCU grace-period kthreads to the housekeeping CPU. |
5057f55e PM |
2670 | */ |
2671 | static void rcu_bind_gp_kthread(void) | |
2672 | { | |
c0f489d2 | 2673 | if (!tick_nohz_full_enabled()) |
5057f55e | 2674 | return; |
de201559 | 2675 | housekeeping_affine(current, HK_FLAG_RCU); |
5057f55e | 2676 | } |
176f8f7a PM |
2677 | |
2678 | /* Record the current task on dyntick-idle entry. */ | |
2679 | static void rcu_dynticks_task_enter(void) | |
2680 | { | |
2681 | #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) | |
7d0ae808 | 2682 | WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id()); |
176f8f7a PM |
2683 | #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ |
2684 | } | |
2685 | ||
2686 | /* Record no current task on dyntick-idle exit. */ | |
2687 | static void rcu_dynticks_task_exit(void) | |
2688 | { | |
2689 | #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) | |
7d0ae808 | 2690 | WRITE_ONCE(current->rcu_tasks_idle_cpu, -1); |
176f8f7a PM |
2691 | #endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ |
2692 | } |