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eacd6f04 PM |
1 | /* SPDX-License-Identifier: GPL-2.0+ */ |
2 | /* | |
3 | * Task-based RCU implementations. | |
4 | * | |
5 | * Copyright (C) 2020 Paul E. McKenney | |
6 | */ | |
7 | ||
8fd8ca38 | 8 | #ifdef CONFIG_TASKS_RCU_GENERIC |
5873b8a9 PM |
9 | |
10 | //////////////////////////////////////////////////////////////////////// | |
11 | // | |
12 | // Generic data structures. | |
13 | ||
14 | struct rcu_tasks; | |
15 | typedef void (*rcu_tasks_gp_func_t)(struct rcu_tasks *rtp); | |
e4fe5dd6 PM |
16 | typedef void (*pregp_func_t)(void); |
17 | typedef void (*pertask_func_t)(struct task_struct *t, struct list_head *hop); | |
9796e1ae | 18 | typedef void (*postscan_func_t)(struct list_head *hop); |
e4fe5dd6 | 19 | typedef void (*holdouts_func_t)(struct list_head *hop, bool ndrpt, bool *frptp); |
af051ca4 | 20 | typedef void (*postgp_func_t)(struct rcu_tasks *rtp); |
eacd6f04 | 21 | |
07e10515 | 22 | /** |
85b86994 | 23 | * struct rcu_tasks - Definition for a Tasks-RCU-like mechanism. |
07e10515 PM |
24 | * @cbs_head: Head of callback list. |
25 | * @cbs_tail: Tail pointer for callback list. | |
a616aec9 | 26 | * @cbs_wq: Wait queue allowing new callback to get kthread's attention. |
07e10515 PM |
27 | * @cbs_lock: Lock protecting callback list. |
28 | * @kthread_ptr: This flavor's grace-period/callback-invocation kthread. | |
5873b8a9 | 29 | * @gp_func: This flavor's grace-period-wait function. |
af051ca4 | 30 | * @gp_state: Grace period's most recent state transition (debugging). |
4fe192df | 31 | * @gp_sleep: Per-grace-period sleep to prevent CPU-bound looping. |
2393a613 | 32 | * @init_fract: Initial backoff sleep interval. |
af051ca4 PM |
33 | * @gp_jiffies: Time of last @gp_state transition. |
34 | * @gp_start: Most recent grace-period start in jiffies. | |
238dbce3 PM |
35 | * @n_gps: Number of grace periods completed since boot. |
36 | * @n_ipis: Number of IPIs sent to encourage grace periods to end. | |
7e0669c3 | 37 | * @n_ipis_fails: Number of IPI-send failures. |
e4fe5dd6 PM |
38 | * @pregp_func: This flavor's pre-grace-period function (optional). |
39 | * @pertask_func: This flavor's per-task scan function (optional). | |
40 | * @postscan_func: This flavor's post-task scan function (optional). | |
85b86994 | 41 | * @holdouts_func: This flavor's holdout-list scan function (optional). |
e4fe5dd6 | 42 | * @postgp_func: This flavor's post-grace-period function (optional). |
5873b8a9 | 43 | * @call_func: This flavor's call_rcu()-equivalent function. |
c97d12a6 PM |
44 | * @name: This flavor's textual name. |
45 | * @kname: This flavor's kthread name. | |
07e10515 PM |
46 | */ |
47 | struct rcu_tasks { | |
48 | struct rcu_head *cbs_head; | |
49 | struct rcu_head **cbs_tail; | |
50 | struct wait_queue_head cbs_wq; | |
51 | raw_spinlock_t cbs_lock; | |
af051ca4 | 52 | int gp_state; |
4fe192df | 53 | int gp_sleep; |
2393a613 | 54 | int init_fract; |
af051ca4 | 55 | unsigned long gp_jiffies; |
88092d0c | 56 | unsigned long gp_start; |
238dbce3 PM |
57 | unsigned long n_gps; |
58 | unsigned long n_ipis; | |
7e0669c3 | 59 | unsigned long n_ipis_fails; |
07e10515 | 60 | struct task_struct *kthread_ptr; |
5873b8a9 | 61 | rcu_tasks_gp_func_t gp_func; |
e4fe5dd6 PM |
62 | pregp_func_t pregp_func; |
63 | pertask_func_t pertask_func; | |
64 | postscan_func_t postscan_func; | |
65 | holdouts_func_t holdouts_func; | |
66 | postgp_func_t postgp_func; | |
5873b8a9 | 67 | call_rcu_func_t call_func; |
c97d12a6 PM |
68 | char *name; |
69 | char *kname; | |
07e10515 PM |
70 | }; |
71 | ||
c97d12a6 PM |
72 | #define DEFINE_RCU_TASKS(rt_name, gp, call, n) \ |
73 | static struct rcu_tasks rt_name = \ | |
07e10515 | 74 | { \ |
c97d12a6 PM |
75 | .cbs_tail = &rt_name.cbs_head, \ |
76 | .cbs_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rt_name.cbs_wq), \ | |
77 | .cbs_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_lock), \ | |
5873b8a9 PM |
78 | .gp_func = gp, \ |
79 | .call_func = call, \ | |
c97d12a6 PM |
80 | .name = n, \ |
81 | .kname = #rt_name, \ | |
07e10515 PM |
82 | } |
83 | ||
eacd6f04 PM |
84 | /* Track exiting tasks in order to allow them to be waited for. */ |
85 | DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu); | |
86 | ||
b0afa0f0 | 87 | /* Avoid IPIing CPUs early in the grace period. */ |
574de876 | 88 | #define RCU_TASK_IPI_DELAY (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) ? HZ / 2 : 0) |
b0afa0f0 PM |
89 | static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY; |
90 | module_param(rcu_task_ipi_delay, int, 0644); | |
91 | ||
eacd6f04 PM |
92 | /* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */ |
93 | #define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10) | |
94 | static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT; | |
95 | module_param(rcu_task_stall_timeout, int, 0644); | |
96 | ||
af051ca4 PM |
97 | /* RCU tasks grace-period state for debugging. */ |
98 | #define RTGS_INIT 0 | |
99 | #define RTGS_WAIT_WAIT_CBS 1 | |
100 | #define RTGS_WAIT_GP 2 | |
101 | #define RTGS_PRE_WAIT_GP 3 | |
102 | #define RTGS_SCAN_TASKLIST 4 | |
103 | #define RTGS_POST_SCAN_TASKLIST 5 | |
104 | #define RTGS_WAIT_SCAN_HOLDOUTS 6 | |
105 | #define RTGS_SCAN_HOLDOUTS 7 | |
106 | #define RTGS_POST_GP 8 | |
107 | #define RTGS_WAIT_READERS 9 | |
108 | #define RTGS_INVOKE_CBS 10 | |
109 | #define RTGS_WAIT_CBS 11 | |
8344496e | 110 | #ifndef CONFIG_TINY_RCU |
af051ca4 PM |
111 | static const char * const rcu_tasks_gp_state_names[] = { |
112 | "RTGS_INIT", | |
113 | "RTGS_WAIT_WAIT_CBS", | |
114 | "RTGS_WAIT_GP", | |
115 | "RTGS_PRE_WAIT_GP", | |
116 | "RTGS_SCAN_TASKLIST", | |
117 | "RTGS_POST_SCAN_TASKLIST", | |
118 | "RTGS_WAIT_SCAN_HOLDOUTS", | |
119 | "RTGS_SCAN_HOLDOUTS", | |
120 | "RTGS_POST_GP", | |
121 | "RTGS_WAIT_READERS", | |
122 | "RTGS_INVOKE_CBS", | |
123 | "RTGS_WAIT_CBS", | |
124 | }; | |
8344496e | 125 | #endif /* #ifndef CONFIG_TINY_RCU */ |
af051ca4 | 126 | |
5873b8a9 PM |
127 | //////////////////////////////////////////////////////////////////////// |
128 | // | |
129 | // Generic code. | |
130 | ||
af051ca4 PM |
131 | /* Record grace-period phase and time. */ |
132 | static void set_tasks_gp_state(struct rcu_tasks *rtp, int newstate) | |
133 | { | |
134 | rtp->gp_state = newstate; | |
135 | rtp->gp_jiffies = jiffies; | |
136 | } | |
137 | ||
8344496e | 138 | #ifndef CONFIG_TINY_RCU |
af051ca4 PM |
139 | /* Return state name. */ |
140 | static const char *tasks_gp_state_getname(struct rcu_tasks *rtp) | |
141 | { | |
142 | int i = data_race(rtp->gp_state); // Let KCSAN detect update races | |
143 | int j = READ_ONCE(i); // Prevent the compiler from reading twice | |
144 | ||
145 | if (j >= ARRAY_SIZE(rcu_tasks_gp_state_names)) | |
146 | return "???"; | |
147 | return rcu_tasks_gp_state_names[j]; | |
148 | } | |
8344496e | 149 | #endif /* #ifndef CONFIG_TINY_RCU */ |
af051ca4 | 150 | |
5873b8a9 PM |
151 | // Enqueue a callback for the specified flavor of Tasks RCU. |
152 | static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, | |
153 | struct rcu_tasks *rtp) | |
eacd6f04 PM |
154 | { |
155 | unsigned long flags; | |
156 | bool needwake; | |
157 | ||
158 | rhp->next = NULL; | |
159 | rhp->func = func; | |
07e10515 PM |
160 | raw_spin_lock_irqsave(&rtp->cbs_lock, flags); |
161 | needwake = !rtp->cbs_head; | |
162 | WRITE_ONCE(*rtp->cbs_tail, rhp); | |
163 | rtp->cbs_tail = &rhp->next; | |
164 | raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags); | |
eacd6f04 | 165 | /* We can't create the thread unless interrupts are enabled. */ |
07e10515 PM |
166 | if (needwake && READ_ONCE(rtp->kthread_ptr)) |
167 | wake_up(&rtp->cbs_wq); | |
eacd6f04 | 168 | } |
eacd6f04 | 169 | |
5873b8a9 PM |
170 | // Wait for a grace period for the specified flavor of Tasks RCU. |
171 | static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp) | |
eacd6f04 PM |
172 | { |
173 | /* Complain if the scheduler has not started. */ | |
174 | RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE, | |
175 | "synchronize_rcu_tasks called too soon"); | |
176 | ||
177 | /* Wait for the grace period. */ | |
5873b8a9 | 178 | wait_rcu_gp(rtp->call_func); |
eacd6f04 PM |
179 | } |
180 | ||
181 | /* RCU-tasks kthread that detects grace periods and invokes callbacks. */ | |
182 | static int __noreturn rcu_tasks_kthread(void *arg) | |
183 | { | |
184 | unsigned long flags; | |
eacd6f04 PM |
185 | struct rcu_head *list; |
186 | struct rcu_head *next; | |
07e10515 | 187 | struct rcu_tasks *rtp = arg; |
eacd6f04 PM |
188 | |
189 | /* Run on housekeeping CPUs by default. Sysadm can move if desired. */ | |
190 | housekeeping_affine(current, HK_FLAG_RCU); | |
07e10515 | 191 | WRITE_ONCE(rtp->kthread_ptr, current); // Let GPs start! |
eacd6f04 PM |
192 | |
193 | /* | |
194 | * Each pass through the following loop makes one check for | |
195 | * newly arrived callbacks, and, if there are some, waits for | |
196 | * one RCU-tasks grace period and then invokes the callbacks. | |
197 | * This loop is terminated by the system going down. ;-) | |
198 | */ | |
199 | for (;;) { | |
200 | ||
201 | /* Pick up any new callbacks. */ | |
07e10515 | 202 | raw_spin_lock_irqsave(&rtp->cbs_lock, flags); |
43766c3e | 203 | smp_mb__after_spinlock(); // Order updates vs. GP. |
07e10515 PM |
204 | list = rtp->cbs_head; |
205 | rtp->cbs_head = NULL; | |
206 | rtp->cbs_tail = &rtp->cbs_head; | |
207 | raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags); | |
eacd6f04 PM |
208 | |
209 | /* If there were none, wait a bit and start over. */ | |
210 | if (!list) { | |
07e10515 PM |
211 | wait_event_interruptible(rtp->cbs_wq, |
212 | READ_ONCE(rtp->cbs_head)); | |
213 | if (!rtp->cbs_head) { | |
eacd6f04 | 214 | WARN_ON(signal_pending(current)); |
af051ca4 | 215 | set_tasks_gp_state(rtp, RTGS_WAIT_WAIT_CBS); |
ea6eed9f | 216 | schedule_timeout_idle(HZ/10); |
eacd6f04 PM |
217 | } |
218 | continue; | |
219 | } | |
220 | ||
5873b8a9 | 221 | // Wait for one grace period. |
af051ca4 | 222 | set_tasks_gp_state(rtp, RTGS_WAIT_GP); |
88092d0c | 223 | rtp->gp_start = jiffies; |
5873b8a9 | 224 | rtp->gp_func(rtp); |
238dbce3 | 225 | rtp->n_gps++; |
eacd6f04 PM |
226 | |
227 | /* Invoke the callbacks. */ | |
af051ca4 | 228 | set_tasks_gp_state(rtp, RTGS_INVOKE_CBS); |
eacd6f04 PM |
229 | while (list) { |
230 | next = list->next; | |
231 | local_bh_disable(); | |
232 | list->func(list); | |
233 | local_bh_enable(); | |
234 | list = next; | |
235 | cond_resched(); | |
236 | } | |
237 | /* Paranoid sleep to keep this from entering a tight loop */ | |
4fe192df | 238 | schedule_timeout_idle(rtp->gp_sleep); |
af051ca4 PM |
239 | |
240 | set_tasks_gp_state(rtp, RTGS_WAIT_CBS); | |
eacd6f04 PM |
241 | } |
242 | } | |
243 | ||
1b04fa99 | 244 | /* Spawn RCU-tasks grace-period kthread. */ |
5873b8a9 | 245 | static void __init rcu_spawn_tasks_kthread_generic(struct rcu_tasks *rtp) |
eacd6f04 PM |
246 | { |
247 | struct task_struct *t; | |
248 | ||
c97d12a6 PM |
249 | t = kthread_run(rcu_tasks_kthread, rtp, "%s_kthread", rtp->kname); |
250 | if (WARN_ONCE(IS_ERR(t), "%s: Could not start %s grace-period kthread, OOM is now expected behavior\n", __func__, rtp->name)) | |
5873b8a9 | 251 | return; |
eacd6f04 | 252 | smp_mb(); /* Ensure others see full kthread. */ |
eacd6f04 | 253 | } |
eacd6f04 | 254 | |
eacd6f04 PM |
255 | #ifndef CONFIG_TINY_RCU |
256 | ||
257 | /* | |
258 | * Print any non-default Tasks RCU settings. | |
259 | */ | |
260 | static void __init rcu_tasks_bootup_oddness(void) | |
261 | { | |
d5f177d3 | 262 | #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) |
eacd6f04 PM |
263 | if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT) |
264 | pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout); | |
d5f177d3 PM |
265 | #endif /* #ifdef CONFIG_TASKS_RCU */ |
266 | #ifdef CONFIG_TASKS_RCU | |
267 | pr_info("\tTrampoline variant of Tasks RCU enabled.\n"); | |
eacd6f04 | 268 | #endif /* #ifdef CONFIG_TASKS_RCU */ |
c84aad76 PM |
269 | #ifdef CONFIG_TASKS_RUDE_RCU |
270 | pr_info("\tRude variant of Tasks RCU enabled.\n"); | |
271 | #endif /* #ifdef CONFIG_TASKS_RUDE_RCU */ | |
d5f177d3 PM |
272 | #ifdef CONFIG_TASKS_TRACE_RCU |
273 | pr_info("\tTracing variant of Tasks RCU enabled.\n"); | |
274 | #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */ | |
eacd6f04 PM |
275 | } |
276 | ||
277 | #endif /* #ifndef CONFIG_TINY_RCU */ | |
5873b8a9 | 278 | |
8344496e | 279 | #ifndef CONFIG_TINY_RCU |
e21408ce PM |
280 | /* Dump out rcutorture-relevant state common to all RCU-tasks flavors. */ |
281 | static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s) | |
282 | { | |
7e0669c3 | 283 | pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c %s\n", |
e21408ce | 284 | rtp->kname, |
7e0669c3 | 285 | tasks_gp_state_getname(rtp), data_race(rtp->gp_state), |
af051ca4 | 286 | jiffies - data_race(rtp->gp_jiffies), |
7e0669c3 PM |
287 | data_race(rtp->n_gps), |
288 | data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis), | |
e21408ce PM |
289 | ".k"[!!data_race(rtp->kthread_ptr)], |
290 | ".C"[!!data_race(rtp->cbs_head)], | |
291 | s); | |
292 | } | |
27c0f144 | 293 | #endif // #ifndef CONFIG_TINY_RCU |
e21408ce | 294 | |
25246fc8 PM |
295 | static void exit_tasks_rcu_finish_trace(struct task_struct *t); |
296 | ||
297 | #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) | |
5873b8a9 | 298 | |
d01aa263 PM |
299 | //////////////////////////////////////////////////////////////////////// |
300 | // | |
301 | // Shared code between task-list-scanning variants of Tasks RCU. | |
302 | ||
303 | /* Wait for one RCU-tasks grace period. */ | |
304 | static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) | |
305 | { | |
306 | struct task_struct *g, *t; | |
307 | unsigned long lastreport; | |
308 | LIST_HEAD(holdouts); | |
309 | int fract; | |
310 | ||
af051ca4 | 311 | set_tasks_gp_state(rtp, RTGS_PRE_WAIT_GP); |
d01aa263 PM |
312 | rtp->pregp_func(); |
313 | ||
314 | /* | |
315 | * There were callbacks, so we need to wait for an RCU-tasks | |
316 | * grace period. Start off by scanning the task list for tasks | |
317 | * that are not already voluntarily blocked. Mark these tasks | |
318 | * and make a list of them in holdouts. | |
319 | */ | |
af051ca4 | 320 | set_tasks_gp_state(rtp, RTGS_SCAN_TASKLIST); |
d01aa263 PM |
321 | rcu_read_lock(); |
322 | for_each_process_thread(g, t) | |
323 | rtp->pertask_func(t, &holdouts); | |
324 | rcu_read_unlock(); | |
325 | ||
af051ca4 | 326 | set_tasks_gp_state(rtp, RTGS_POST_SCAN_TASKLIST); |
9796e1ae | 327 | rtp->postscan_func(&holdouts); |
d01aa263 PM |
328 | |
329 | /* | |
330 | * Each pass through the following loop scans the list of holdout | |
331 | * tasks, removing any that are no longer holdouts. When the list | |
332 | * is empty, we are done. | |
333 | */ | |
334 | lastreport = jiffies; | |
335 | ||
2393a613 PM |
336 | // Start off with initial wait and slowly back off to 1 HZ wait. |
337 | fract = rtp->init_fract; | |
d01aa263 | 338 | |
77dc1741 | 339 | while (!list_empty(&holdouts)) { |
d01aa263 PM |
340 | bool firstreport; |
341 | bool needreport; | |
342 | int rtst; | |
343 | ||
d01aa263 | 344 | /* Slowly back off waiting for holdouts */ |
af051ca4 | 345 | set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS); |
75dc2da5 | 346 | schedule_timeout_idle(fract); |
d01aa263 | 347 | |
75dc2da5 PM |
348 | if (fract < HZ) |
349 | fract++; | |
d01aa263 PM |
350 | |
351 | rtst = READ_ONCE(rcu_task_stall_timeout); | |
352 | needreport = rtst > 0 && time_after(jiffies, lastreport + rtst); | |
353 | if (needreport) | |
354 | lastreport = jiffies; | |
355 | firstreport = true; | |
356 | WARN_ON(signal_pending(current)); | |
af051ca4 | 357 | set_tasks_gp_state(rtp, RTGS_SCAN_HOLDOUTS); |
d01aa263 PM |
358 | rtp->holdouts_func(&holdouts, needreport, &firstreport); |
359 | } | |
360 | ||
af051ca4 PM |
361 | set_tasks_gp_state(rtp, RTGS_POST_GP); |
362 | rtp->postgp_func(rtp); | |
d01aa263 PM |
363 | } |
364 | ||
25246fc8 PM |
365 | #endif /* #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) */ |
366 | ||
367 | #ifdef CONFIG_TASKS_RCU | |
368 | ||
5873b8a9 PM |
369 | //////////////////////////////////////////////////////////////////////// |
370 | // | |
371 | // Simple variant of RCU whose quiescent states are voluntary context | |
372 | // switch, cond_resched_rcu_qs(), user-space execution, and idle. | |
373 | // As such, grace periods can take one good long time. There are no | |
374 | // read-side primitives similar to rcu_read_lock() and rcu_read_unlock() | |
375 | // because this implementation is intended to get the system into a safe | |
376 | // state for some of the manipulations involved in tracing and the like. | |
377 | // Finally, this implementation does not support high call_rcu_tasks() | |
378 | // rates from multiple CPUs. If this is required, per-CPU callback lists | |
379 | // will be needed. | |
06a3ec92 PM |
380 | // |
381 | // The implementation uses rcu_tasks_wait_gp(), which relies on function | |
382 | // pointers in the rcu_tasks structure. The rcu_spawn_tasks_kthread() | |
383 | // function sets these function pointers up so that rcu_tasks_wait_gp() | |
384 | // invokes these functions in this order: | |
385 | // | |
386 | // rcu_tasks_pregp_step(): | |
387 | // Invokes synchronize_rcu() in order to wait for all in-flight | |
388 | // t->on_rq and t->nvcsw transitions to complete. This works because | |
389 | // all such transitions are carried out with interrupts disabled. | |
390 | // rcu_tasks_pertask(), invoked on every non-idle task: | |
391 | // For every runnable non-idle task other than the current one, use | |
392 | // get_task_struct() to pin down that task, snapshot that task's | |
393 | // number of voluntary context switches, and add that task to the | |
394 | // holdout list. | |
395 | // rcu_tasks_postscan(): | |
396 | // Invoke synchronize_srcu() to ensure that all tasks that were | |
397 | // in the process of exiting (and which thus might not know to | |
398 | // synchronize with this RCU Tasks grace period) have completed | |
399 | // exiting. | |
400 | // check_all_holdout_tasks(), repeatedly until holdout list is empty: | |
401 | // Scans the holdout list, attempting to identify a quiescent state | |
402 | // for each task on the list. If there is a quiescent state, the | |
403 | // corresponding task is removed from the holdout list. | |
404 | // rcu_tasks_postgp(): | |
405 | // Invokes synchronize_rcu() in order to ensure that all prior | |
406 | // t->on_rq and t->nvcsw transitions are seen by all CPUs and tasks | |
407 | // to have happened before the end of this RCU Tasks grace period. | |
408 | // Again, this works because all such transitions are carried out | |
409 | // with interrupts disabled. | |
410 | // | |
411 | // For each exiting task, the exit_tasks_rcu_start() and | |
412 | // exit_tasks_rcu_finish() functions begin and end, respectively, the SRCU | |
413 | // read-side critical sections waited for by rcu_tasks_postscan(). | |
414 | // | |
415 | // Pre-grace-period update-side code is ordered before the grace via the | |
416 | // ->cbs_lock and the smp_mb__after_spinlock(). Pre-grace-period read-side | |
417 | // code is ordered before the grace period via synchronize_rcu() call | |
418 | // in rcu_tasks_pregp_step() and by the scheduler's locks and interrupt | |
419 | // disabling. | |
5873b8a9 | 420 | |
e4fe5dd6 PM |
421 | /* Pre-grace-period preparation. */ |
422 | static void rcu_tasks_pregp_step(void) | |
423 | { | |
424 | /* | |
425 | * Wait for all pre-existing t->on_rq and t->nvcsw transitions | |
426 | * to complete. Invoking synchronize_rcu() suffices because all | |
427 | * these transitions occur with interrupts disabled. Without this | |
428 | * synchronize_rcu(), a read-side critical section that started | |
429 | * before the grace period might be incorrectly seen as having | |
430 | * started after the grace period. | |
431 | * | |
432 | * This synchronize_rcu() also dispenses with the need for a | |
433 | * memory barrier on the first store to t->rcu_tasks_holdout, | |
434 | * as it forces the store to happen after the beginning of the | |
435 | * grace period. | |
436 | */ | |
437 | synchronize_rcu(); | |
438 | } | |
439 | ||
440 | /* Per-task initial processing. */ | |
441 | static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop) | |
442 | { | |
443 | if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) { | |
444 | get_task_struct(t); | |
445 | t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw); | |
446 | WRITE_ONCE(t->rcu_tasks_holdout, true); | |
447 | list_add(&t->rcu_tasks_holdout_list, hop); | |
448 | } | |
449 | } | |
450 | ||
451 | /* Processing between scanning taskslist and draining the holdout list. */ | |
04a3c5aa | 452 | static void rcu_tasks_postscan(struct list_head *hop) |
e4fe5dd6 PM |
453 | { |
454 | /* | |
455 | * Wait for tasks that are in the process of exiting. This | |
456 | * does only part of the job, ensuring that all tasks that were | |
457 | * previously exiting reach the point where they have disabled | |
458 | * preemption, allowing the later synchronize_rcu() to finish | |
459 | * the job. | |
460 | */ | |
461 | synchronize_srcu(&tasks_rcu_exit_srcu); | |
462 | } | |
463 | ||
5873b8a9 PM |
464 | /* See if tasks are still holding out, complain if so. */ |
465 | static void check_holdout_task(struct task_struct *t, | |
466 | bool needreport, bool *firstreport) | |
467 | { | |
468 | int cpu; | |
469 | ||
470 | if (!READ_ONCE(t->rcu_tasks_holdout) || | |
471 | t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) || | |
472 | !READ_ONCE(t->on_rq) || | |
473 | (IS_ENABLED(CONFIG_NO_HZ_FULL) && | |
474 | !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) { | |
475 | WRITE_ONCE(t->rcu_tasks_holdout, false); | |
476 | list_del_init(&t->rcu_tasks_holdout_list); | |
477 | put_task_struct(t); | |
478 | return; | |
479 | } | |
480 | rcu_request_urgent_qs_task(t); | |
481 | if (!needreport) | |
482 | return; | |
483 | if (*firstreport) { | |
484 | pr_err("INFO: rcu_tasks detected stalls on tasks:\n"); | |
485 | *firstreport = false; | |
486 | } | |
487 | cpu = task_cpu(t); | |
488 | pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n", | |
489 | t, ".I"[is_idle_task(t)], | |
490 | "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)], | |
491 | t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout, | |
492 | t->rcu_tasks_idle_cpu, cpu); | |
493 | sched_show_task(t); | |
494 | } | |
495 | ||
e4fe5dd6 PM |
496 | /* Scan the holdout lists for tasks no longer holding out. */ |
497 | static void check_all_holdout_tasks(struct list_head *hop, | |
498 | bool needreport, bool *firstreport) | |
499 | { | |
500 | struct task_struct *t, *t1; | |
501 | ||
502 | list_for_each_entry_safe(t, t1, hop, rcu_tasks_holdout_list) { | |
503 | check_holdout_task(t, needreport, firstreport); | |
504 | cond_resched(); | |
505 | } | |
506 | } | |
507 | ||
508 | /* Finish off the Tasks-RCU grace period. */ | |
af051ca4 | 509 | static void rcu_tasks_postgp(struct rcu_tasks *rtp) |
e4fe5dd6 PM |
510 | { |
511 | /* | |
512 | * Because ->on_rq and ->nvcsw are not guaranteed to have a full | |
513 | * memory barriers prior to them in the schedule() path, memory | |
514 | * reordering on other CPUs could cause their RCU-tasks read-side | |
515 | * critical sections to extend past the end of the grace period. | |
516 | * However, because these ->nvcsw updates are carried out with | |
517 | * interrupts disabled, we can use synchronize_rcu() to force the | |
518 | * needed ordering on all such CPUs. | |
519 | * | |
520 | * This synchronize_rcu() also confines all ->rcu_tasks_holdout | |
521 | * accesses to be within the grace period, avoiding the need for | |
522 | * memory barriers for ->rcu_tasks_holdout accesses. | |
523 | * | |
524 | * In addition, this synchronize_rcu() waits for exiting tasks | |
525 | * to complete their final preempt_disable() region of execution, | |
526 | * cleaning up after the synchronize_srcu() above. | |
527 | */ | |
528 | synchronize_rcu(); | |
529 | } | |
530 | ||
5873b8a9 | 531 | void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func); |
c97d12a6 | 532 | DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks"); |
5873b8a9 PM |
533 | |
534 | /** | |
535 | * call_rcu_tasks() - Queue an RCU for invocation task-based grace period | |
536 | * @rhp: structure to be used for queueing the RCU updates. | |
537 | * @func: actual callback function to be invoked after the grace period | |
538 | * | |
539 | * The callback function will be invoked some time after a full grace | |
540 | * period elapses, in other words after all currently executing RCU | |
541 | * read-side critical sections have completed. call_rcu_tasks() assumes | |
542 | * that the read-side critical sections end at a voluntary context | |
543 | * switch (not a preemption!), cond_resched_rcu_qs(), entry into idle, | |
544 | * or transition to usermode execution. As such, there are no read-side | |
545 | * primitives analogous to rcu_read_lock() and rcu_read_unlock() because | |
546 | * this primitive is intended to determine that all tasks have passed | |
a616aec9 | 547 | * through a safe state, not so much for data-structure synchronization. |
5873b8a9 PM |
548 | * |
549 | * See the description of call_rcu() for more detailed information on | |
550 | * memory ordering guarantees. | |
551 | */ | |
552 | void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) | |
553 | { | |
554 | call_rcu_tasks_generic(rhp, func, &rcu_tasks); | |
555 | } | |
556 | EXPORT_SYMBOL_GPL(call_rcu_tasks); | |
557 | ||
558 | /** | |
559 | * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed. | |
560 | * | |
561 | * Control will return to the caller some time after a full rcu-tasks | |
562 | * grace period has elapsed, in other words after all currently | |
563 | * executing rcu-tasks read-side critical sections have elapsed. These | |
564 | * read-side critical sections are delimited by calls to schedule(), | |
565 | * cond_resched_tasks_rcu_qs(), idle execution, userspace execution, calls | |
566 | * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched(). | |
567 | * | |
568 | * This is a very specialized primitive, intended only for a few uses in | |
569 | * tracing and other situations requiring manipulation of function | |
570 | * preambles and profiling hooks. The synchronize_rcu_tasks() function | |
571 | * is not (yet) intended for heavy use from multiple CPUs. | |
572 | * | |
573 | * See the description of synchronize_rcu() for more detailed information | |
574 | * on memory ordering guarantees. | |
575 | */ | |
576 | void synchronize_rcu_tasks(void) | |
577 | { | |
578 | synchronize_rcu_tasks_generic(&rcu_tasks); | |
579 | } | |
580 | EXPORT_SYMBOL_GPL(synchronize_rcu_tasks); | |
581 | ||
582 | /** | |
583 | * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks. | |
584 | * | |
585 | * Although the current implementation is guaranteed to wait, it is not | |
586 | * obligated to, for example, if there are no pending callbacks. | |
587 | */ | |
588 | void rcu_barrier_tasks(void) | |
589 | { | |
590 | /* There is only one callback queue, so this is easy. ;-) */ | |
591 | synchronize_rcu_tasks(); | |
592 | } | |
593 | EXPORT_SYMBOL_GPL(rcu_barrier_tasks); | |
594 | ||
595 | static int __init rcu_spawn_tasks_kthread(void) | |
596 | { | |
4fe192df | 597 | rcu_tasks.gp_sleep = HZ / 10; |
75dc2da5 | 598 | rcu_tasks.init_fract = HZ / 10; |
e4fe5dd6 PM |
599 | rcu_tasks.pregp_func = rcu_tasks_pregp_step; |
600 | rcu_tasks.pertask_func = rcu_tasks_pertask; | |
601 | rcu_tasks.postscan_func = rcu_tasks_postscan; | |
602 | rcu_tasks.holdouts_func = check_all_holdout_tasks; | |
603 | rcu_tasks.postgp_func = rcu_tasks_postgp; | |
5873b8a9 PM |
604 | rcu_spawn_tasks_kthread_generic(&rcu_tasks); |
605 | return 0; | |
606 | } | |
5873b8a9 | 607 | |
27c0f144 PM |
608 | #if !defined(CONFIG_TINY_RCU) |
609 | void show_rcu_tasks_classic_gp_kthread(void) | |
e21408ce PM |
610 | { |
611 | show_rcu_tasks_generic_gp_kthread(&rcu_tasks, ""); | |
612 | } | |
27c0f144 PM |
613 | EXPORT_SYMBOL_GPL(show_rcu_tasks_classic_gp_kthread); |
614 | #endif // !defined(CONFIG_TINY_RCU) | |
e21408ce | 615 | |
25246fc8 PM |
616 | /* Do the srcu_read_lock() for the above synchronize_srcu(). */ |
617 | void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu) | |
618 | { | |
619 | preempt_disable(); | |
620 | current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu); | |
621 | preempt_enable(); | |
622 | } | |
623 | ||
624 | /* Do the srcu_read_unlock() for the above synchronize_srcu(). */ | |
625 | void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu) | |
626 | { | |
627 | struct task_struct *t = current; | |
628 | ||
629 | preempt_disable(); | |
630 | __srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx); | |
631 | preempt_enable(); | |
632 | exit_tasks_rcu_finish_trace(t); | |
633 | } | |
634 | ||
e21408ce | 635 | #else /* #ifdef CONFIG_TASKS_RCU */ |
25246fc8 PM |
636 | void exit_tasks_rcu_start(void) { } |
637 | void exit_tasks_rcu_finish(void) { exit_tasks_rcu_finish_trace(current); } | |
e21408ce | 638 | #endif /* #else #ifdef CONFIG_TASKS_RCU */ |
c84aad76 PM |
639 | |
640 | #ifdef CONFIG_TASKS_RUDE_RCU | |
641 | ||
642 | //////////////////////////////////////////////////////////////////////// | |
643 | // | |
644 | // "Rude" variant of Tasks RCU, inspired by Steve Rostedt's trick of | |
645 | // passing an empty function to schedule_on_each_cpu(). This approach | |
e4be1f44 PM |
646 | // provides an asynchronous call_rcu_tasks_rude() API and batching of |
647 | // concurrent calls to the synchronous synchronize_rcu_tasks_rude() API. | |
9fc98e31 PM |
648 | // This invokes schedule_on_each_cpu() in order to send IPIs far and wide |
649 | // and induces otherwise unnecessary context switches on all online CPUs, | |
650 | // whether idle or not. | |
651 | // | |
652 | // Callback handling is provided by the rcu_tasks_kthread() function. | |
653 | // | |
654 | // Ordering is provided by the scheduler's context-switch code. | |
c84aad76 PM |
655 | |
656 | // Empty function to allow workqueues to force a context switch. | |
657 | static void rcu_tasks_be_rude(struct work_struct *work) | |
658 | { | |
659 | } | |
660 | ||
661 | // Wait for one rude RCU-tasks grace period. | |
662 | static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp) | |
663 | { | |
238dbce3 | 664 | rtp->n_ipis += cpumask_weight(cpu_online_mask); |
c84aad76 PM |
665 | schedule_on_each_cpu(rcu_tasks_be_rude); |
666 | } | |
667 | ||
668 | void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func); | |
c97d12a6 PM |
669 | DEFINE_RCU_TASKS(rcu_tasks_rude, rcu_tasks_rude_wait_gp, call_rcu_tasks_rude, |
670 | "RCU Tasks Rude"); | |
c84aad76 PM |
671 | |
672 | /** | |
673 | * call_rcu_tasks_rude() - Queue a callback rude task-based grace period | |
674 | * @rhp: structure to be used for queueing the RCU updates. | |
675 | * @func: actual callback function to be invoked after the grace period | |
676 | * | |
677 | * The callback function will be invoked some time after a full grace | |
678 | * period elapses, in other words after all currently executing RCU | |
679 | * read-side critical sections have completed. call_rcu_tasks_rude() | |
680 | * assumes that the read-side critical sections end at context switch, | |
681 | * cond_resched_rcu_qs(), or transition to usermode execution. As such, | |
682 | * there are no read-side primitives analogous to rcu_read_lock() and | |
683 | * rcu_read_unlock() because this primitive is intended to determine | |
684 | * that all tasks have passed through a safe state, not so much for | |
a616aec9 | 685 | * data-structure synchronization. |
c84aad76 PM |
686 | * |
687 | * See the description of call_rcu() for more detailed information on | |
688 | * memory ordering guarantees. | |
689 | */ | |
690 | void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func) | |
691 | { | |
692 | call_rcu_tasks_generic(rhp, func, &rcu_tasks_rude); | |
693 | } | |
694 | EXPORT_SYMBOL_GPL(call_rcu_tasks_rude); | |
695 | ||
696 | /** | |
697 | * synchronize_rcu_tasks_rude - wait for a rude rcu-tasks grace period | |
698 | * | |
699 | * Control will return to the caller some time after a rude rcu-tasks | |
700 | * grace period has elapsed, in other words after all currently | |
701 | * executing rcu-tasks read-side critical sections have elapsed. These | |
702 | * read-side critical sections are delimited by calls to schedule(), | |
703 | * cond_resched_tasks_rcu_qs(), userspace execution, and (in theory, | |
704 | * anyway) cond_resched(). | |
705 | * | |
706 | * This is a very specialized primitive, intended only for a few uses in | |
707 | * tracing and other situations requiring manipulation of function preambles | |
708 | * and profiling hooks. The synchronize_rcu_tasks_rude() function is not | |
709 | * (yet) intended for heavy use from multiple CPUs. | |
710 | * | |
711 | * See the description of synchronize_rcu() for more detailed information | |
712 | * on memory ordering guarantees. | |
713 | */ | |
714 | void synchronize_rcu_tasks_rude(void) | |
715 | { | |
716 | synchronize_rcu_tasks_generic(&rcu_tasks_rude); | |
717 | } | |
718 | EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_rude); | |
719 | ||
720 | /** | |
721 | * rcu_barrier_tasks_rude - Wait for in-flight call_rcu_tasks_rude() callbacks. | |
722 | * | |
723 | * Although the current implementation is guaranteed to wait, it is not | |
724 | * obligated to, for example, if there are no pending callbacks. | |
725 | */ | |
726 | void rcu_barrier_tasks_rude(void) | |
727 | { | |
728 | /* There is only one callback queue, so this is easy. ;-) */ | |
729 | synchronize_rcu_tasks_rude(); | |
730 | } | |
731 | EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude); | |
732 | ||
733 | static int __init rcu_spawn_tasks_rude_kthread(void) | |
734 | { | |
4fe192df | 735 | rcu_tasks_rude.gp_sleep = HZ / 10; |
c84aad76 PM |
736 | rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude); |
737 | return 0; | |
738 | } | |
c84aad76 | 739 | |
27c0f144 PM |
740 | #if !defined(CONFIG_TINY_RCU) |
741 | void show_rcu_tasks_rude_gp_kthread(void) | |
e21408ce PM |
742 | { |
743 | show_rcu_tasks_generic_gp_kthread(&rcu_tasks_rude, ""); | |
744 | } | |
27c0f144 PM |
745 | EXPORT_SYMBOL_GPL(show_rcu_tasks_rude_gp_kthread); |
746 | #endif // !defined(CONFIG_TINY_RCU) | |
747 | #endif /* #ifdef CONFIG_TASKS_RUDE_RCU */ | |
d5f177d3 PM |
748 | |
749 | //////////////////////////////////////////////////////////////////////// | |
750 | // | |
751 | // Tracing variant of Tasks RCU. This variant is designed to be used | |
752 | // to protect tracing hooks, including those of BPF. This variant | |
753 | // therefore: | |
754 | // | |
755 | // 1. Has explicit read-side markers to allow finite grace periods | |
756 | // in the face of in-kernel loops for PREEMPT=n builds. | |
757 | // | |
758 | // 2. Protects code in the idle loop, exception entry/exit, and | |
759 | // CPU-hotplug code paths, similar to the capabilities of SRCU. | |
760 | // | |
761 | // 3. Avoids expensive read-side instruction, having overhead similar | |
762 | // to that of Preemptible RCU. | |
763 | // | |
764 | // There are of course downsides. The grace-period code can send IPIs to | |
765 | // CPUs, even when those CPUs are in the idle loop or in nohz_full userspace. | |
766 | // It is necessary to scan the full tasklist, much as for Tasks RCU. There | |
767 | // is a single callback queue guarded by a single lock, again, much as for | |
768 | // Tasks RCU. If needed, these downsides can be at least partially remedied. | |
769 | // | |
770 | // Perhaps most important, this variant of RCU does not affect the vanilla | |
771 | // flavors, rcu_preempt and rcu_sched. The fact that RCU Tasks Trace | |
772 | // readers can operate from idle, offline, and exception entry/exit in no | |
773 | // way allows rcu_preempt and rcu_sched readers to also do so. | |
a434dd10 PM |
774 | // |
775 | // The implementation uses rcu_tasks_wait_gp(), which relies on function | |
776 | // pointers in the rcu_tasks structure. The rcu_spawn_tasks_trace_kthread() | |
777 | // function sets these function pointers up so that rcu_tasks_wait_gp() | |
778 | // invokes these functions in this order: | |
779 | // | |
780 | // rcu_tasks_trace_pregp_step(): | |
781 | // Initialize the count of readers and block CPU-hotplug operations. | |
782 | // rcu_tasks_trace_pertask(), invoked on every non-idle task: | |
783 | // Initialize per-task state and attempt to identify an immediate | |
784 | // quiescent state for that task, or, failing that, attempt to | |
785 | // set that task's .need_qs flag so that task's next outermost | |
786 | // rcu_read_unlock_trace() will report the quiescent state (in which | |
787 | // case the count of readers is incremented). If both attempts fail, | |
45f4b4a2 PM |
788 | // the task is added to a "holdout" list. Note that IPIs are used |
789 | // to invoke trc_read_check_handler() in the context of running tasks | |
790 | // in order to avoid ordering overhead on common-case shared-variable | |
791 | // accessses. | |
a434dd10 PM |
792 | // rcu_tasks_trace_postscan(): |
793 | // Initialize state and attempt to identify an immediate quiescent | |
794 | // state as above (but only for idle tasks), unblock CPU-hotplug | |
795 | // operations, and wait for an RCU grace period to avoid races with | |
796 | // tasks that are in the process of exiting. | |
797 | // check_all_holdout_tasks_trace(), repeatedly until holdout list is empty: | |
798 | // Scans the holdout list, attempting to identify a quiescent state | |
799 | // for each task on the list. If there is a quiescent state, the | |
800 | // corresponding task is removed from the holdout list. | |
801 | // rcu_tasks_trace_postgp(): | |
802 | // Wait for the count of readers do drop to zero, reporting any stalls. | |
803 | // Also execute full memory barriers to maintain ordering with code | |
804 | // executing after the grace period. | |
805 | // | |
806 | // The exit_tasks_rcu_finish_trace() synchronizes with exiting tasks. | |
807 | // | |
808 | // Pre-grace-period update-side code is ordered before the grace | |
809 | // period via the ->cbs_lock and barriers in rcu_tasks_kthread(). | |
810 | // Pre-grace-period read-side code is ordered before the grace period by | |
811 | // atomic_dec_and_test() of the count of readers (for IPIed readers) and by | |
812 | // scheduler context-switch ordering (for locked-down non-running readers). | |
d5f177d3 PM |
813 | |
814 | // The lockdep state must be outside of #ifdef to be useful. | |
815 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
816 | static struct lock_class_key rcu_lock_trace_key; | |
817 | struct lockdep_map rcu_trace_lock_map = | |
818 | STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_trace", &rcu_lock_trace_key); | |
819 | EXPORT_SYMBOL_GPL(rcu_trace_lock_map); | |
820 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
821 | ||
822 | #ifdef CONFIG_TASKS_TRACE_RCU | |
823 | ||
30d8aa51 PM |
824 | static atomic_t trc_n_readers_need_end; // Number of waited-for readers. |
825 | static DECLARE_WAIT_QUEUE_HEAD(trc_wait); // List of holdout tasks. | |
d5f177d3 PM |
826 | |
827 | // Record outstanding IPIs to each CPU. No point in sending two... | |
828 | static DEFINE_PER_CPU(bool, trc_ipi_to_cpu); | |
829 | ||
40471509 PM |
830 | // The number of detections of task quiescent state relying on |
831 | // heavyweight readers executing explicit memory barriers. | |
6731da9e PM |
832 | static unsigned long n_heavy_reader_attempts; |
833 | static unsigned long n_heavy_reader_updates; | |
834 | static unsigned long n_heavy_reader_ofl_updates; | |
40471509 | 835 | |
b0afa0f0 PM |
836 | void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func); |
837 | DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace, | |
838 | "RCU Tasks Trace"); | |
839 | ||
b38f57c1 PM |
840 | /* |
841 | * This irq_work handler allows rcu_read_unlock_trace() to be invoked | |
842 | * while the scheduler locks are held. | |
843 | */ | |
844 | static void rcu_read_unlock_iw(struct irq_work *iwp) | |
845 | { | |
846 | wake_up(&trc_wait); | |
847 | } | |
848 | static DEFINE_IRQ_WORK(rcu_tasks_trace_iw, rcu_read_unlock_iw); | |
849 | ||
d5f177d3 | 850 | /* If we are the last reader, wake up the grace-period kthread. */ |
276c4104 | 851 | void rcu_read_unlock_trace_special(struct task_struct *t, int nesting) |
d5f177d3 | 852 | { |
f8ab3fad | 853 | int nq = READ_ONCE(t->trc_reader_special.b.need_qs); |
276c4104 | 854 | |
9ae58d7b PM |
855 | if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && |
856 | t->trc_reader_special.b.need_mb) | |
276c4104 PM |
857 | smp_mb(); // Pairs with update-side barriers. |
858 | // Update .need_qs before ->trc_reader_nesting for irq/NMI handlers. | |
859 | if (nq) | |
860 | WRITE_ONCE(t->trc_reader_special.b.need_qs, false); | |
861 | WRITE_ONCE(t->trc_reader_nesting, nesting); | |
862 | if (nq && atomic_dec_and_test(&trc_n_readers_need_end)) | |
b38f57c1 | 863 | irq_work_queue(&rcu_tasks_trace_iw); |
d5f177d3 PM |
864 | } |
865 | EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special); | |
866 | ||
867 | /* Add a task to the holdout list, if it is not already on the list. */ | |
868 | static void trc_add_holdout(struct task_struct *t, struct list_head *bhp) | |
869 | { | |
870 | if (list_empty(&t->trc_holdout_list)) { | |
871 | get_task_struct(t); | |
872 | list_add(&t->trc_holdout_list, bhp); | |
873 | } | |
874 | } | |
875 | ||
876 | /* Remove a task from the holdout list, if it is in fact present. */ | |
877 | static void trc_del_holdout(struct task_struct *t) | |
878 | { | |
879 | if (!list_empty(&t->trc_holdout_list)) { | |
880 | list_del_init(&t->trc_holdout_list); | |
881 | put_task_struct(t); | |
882 | } | |
883 | } | |
884 | ||
885 | /* IPI handler to check task state. */ | |
886 | static void trc_read_check_handler(void *t_in) | |
887 | { | |
888 | struct task_struct *t = current; | |
889 | struct task_struct *texp = t_in; | |
890 | ||
891 | // If the task is no longer running on this CPU, leave. | |
892 | if (unlikely(texp != t)) { | |
d5f177d3 PM |
893 | goto reset_ipi; // Already on holdout list, so will check later. |
894 | } | |
895 | ||
896 | // If the task is not in a read-side critical section, and | |
897 | // if this is the last reader, awaken the grace-period kthread. | |
bdb0cca0 | 898 | if (likely(!READ_ONCE(t->trc_reader_nesting))) { |
d5f177d3 PM |
899 | WRITE_ONCE(t->trc_reader_checked, true); |
900 | goto reset_ipi; | |
901 | } | |
ba3a86e4 | 902 | // If we are racing with an rcu_read_unlock_trace(), try again later. |
96017bf9 | 903 | if (unlikely(READ_ONCE(t->trc_reader_nesting) < 0)) |
ba3a86e4 | 904 | goto reset_ipi; |
d5f177d3 PM |
905 | WRITE_ONCE(t->trc_reader_checked, true); |
906 | ||
907 | // Get here if the task is in a read-side critical section. Set | |
908 | // its state so that it will awaken the grace-period kthread upon | |
909 | // exit from that critical section. | |
96017bf9 | 910 | atomic_inc(&trc_n_readers_need_end); // One more to wait on. |
f8ab3fad | 911 | WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs)); |
276c4104 | 912 | WRITE_ONCE(t->trc_reader_special.b.need_qs, true); |
d5f177d3 PM |
913 | |
914 | reset_ipi: | |
915 | // Allow future IPIs to be sent on CPU and for task. | |
916 | // Also order this IPI handler against any later manipulations of | |
917 | // the intended task. | |
8211e922 | 918 | smp_store_release(per_cpu_ptr(&trc_ipi_to_cpu, smp_processor_id()), false); // ^^^ |
d5f177d3 PM |
919 | smp_store_release(&texp->trc_ipi_to_cpu, -1); // ^^^ |
920 | } | |
921 | ||
922 | /* Callback function for scheduler to check locked-down task. */ | |
923 | static bool trc_inspect_reader(struct task_struct *t, void *arg) | |
924 | { | |
7d0c9c50 PM |
925 | int cpu = task_cpu(t); |
926 | bool in_qs = false; | |
7e3b70e0 | 927 | bool ofl = cpu_is_offline(cpu); |
7d0c9c50 PM |
928 | |
929 | if (task_curr(t)) { | |
30d8aa51 | 930 | WARN_ON_ONCE(ofl && !is_idle_task(t)); |
7e3b70e0 | 931 | |
7d0c9c50 | 932 | // If no chance of heavyweight readers, do it the hard way. |
7e3b70e0 | 933 | if (!ofl && !IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) |
7d0c9c50 PM |
934 | return false; |
935 | ||
936 | // If heavyweight readers are enabled on the remote task, | |
937 | // we can inspect its state despite its currently running. | |
938 | // However, we cannot safely change its state. | |
40471509 | 939 | n_heavy_reader_attempts++; |
7e3b70e0 PM |
940 | if (!ofl && // Check for "running" idle tasks on offline CPUs. |
941 | !rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting)) | |
7d0c9c50 | 942 | return false; // No quiescent state, do it the hard way. |
40471509 | 943 | n_heavy_reader_updates++; |
edf3775f PM |
944 | if (ofl) |
945 | n_heavy_reader_ofl_updates++; | |
7d0c9c50 PM |
946 | in_qs = true; |
947 | } else { | |
bdb0cca0 | 948 | // The task is not running, so C-language access is safe. |
7d0c9c50 PM |
949 | in_qs = likely(!t->trc_reader_nesting); |
950 | } | |
d5f177d3 | 951 | |
1d10bf55 PM |
952 | // Mark as checked so that the grace-period kthread will |
953 | // remove it from the holdout list. | |
d5f177d3 | 954 | t->trc_reader_checked = true; |
d5f177d3 | 955 | |
7d0c9c50 PM |
956 | if (in_qs) |
957 | return true; // Already in quiescent state, done!!! | |
958 | ||
959 | // The task is in a read-side critical section, so set up its | |
960 | // state so that it will awaken the grace-period kthread upon exit | |
961 | // from that critical section. | |
962 | atomic_inc(&trc_n_readers_need_end); // One more to wait on. | |
f8ab3fad | 963 | WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs)); |
7d0c9c50 | 964 | WRITE_ONCE(t->trc_reader_special.b.need_qs, true); |
d5f177d3 PM |
965 | return true; |
966 | } | |
967 | ||
968 | /* Attempt to extract the state for the specified task. */ | |
969 | static void trc_wait_for_one_reader(struct task_struct *t, | |
970 | struct list_head *bhp) | |
971 | { | |
972 | int cpu; | |
973 | ||
974 | // If a previous IPI is still in flight, let it complete. | |
975 | if (smp_load_acquire(&t->trc_ipi_to_cpu) != -1) // Order IPI | |
976 | return; | |
977 | ||
978 | // The current task had better be in a quiescent state. | |
979 | if (t == current) { | |
980 | t->trc_reader_checked = true; | |
bdb0cca0 | 981 | WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting)); |
d5f177d3 PM |
982 | return; |
983 | } | |
984 | ||
985 | // Attempt to nail down the task for inspection. | |
986 | get_task_struct(t); | |
987 | if (try_invoke_on_locked_down_task(t, trc_inspect_reader, NULL)) { | |
988 | put_task_struct(t); | |
989 | return; | |
990 | } | |
991 | put_task_struct(t); | |
992 | ||
45f4b4a2 PM |
993 | // If this task is not yet on the holdout list, then we are in |
994 | // an RCU read-side critical section. Otherwise, the invocation of | |
995 | // rcu_add_holdout() that added it to the list did the necessary | |
996 | // get_task_struct(). Either way, the task cannot be freed out | |
997 | // from under this code. | |
998 | ||
d5f177d3 PM |
999 | // If currently running, send an IPI, either way, add to list. |
1000 | trc_add_holdout(t, bhp); | |
574de876 PM |
1001 | if (task_curr(t) && |
1002 | time_after(jiffies + 1, rcu_tasks_trace.gp_start + rcu_task_ipi_delay)) { | |
d5f177d3 PM |
1003 | // The task is currently running, so try IPIing it. |
1004 | cpu = task_cpu(t); | |
1005 | ||
1006 | // If there is already an IPI outstanding, let it happen. | |
1007 | if (per_cpu(trc_ipi_to_cpu, cpu) || t->trc_ipi_to_cpu >= 0) | |
1008 | return; | |
1009 | ||
d5f177d3 PM |
1010 | per_cpu(trc_ipi_to_cpu, cpu) = true; |
1011 | t->trc_ipi_to_cpu = cpu; | |
238dbce3 | 1012 | rcu_tasks_trace.n_ipis++; |
96017bf9 | 1013 | if (smp_call_function_single(cpu, trc_read_check_handler, t, 0)) { |
d5f177d3 PM |
1014 | // Just in case there is some other reason for |
1015 | // failure than the target CPU being offline. | |
7e0669c3 | 1016 | rcu_tasks_trace.n_ipis_fails++; |
d5f177d3 PM |
1017 | per_cpu(trc_ipi_to_cpu, cpu) = false; |
1018 | t->trc_ipi_to_cpu = cpu; | |
d5f177d3 PM |
1019 | } |
1020 | } | |
1021 | } | |
1022 | ||
1023 | /* Initialize for a new RCU-tasks-trace grace period. */ | |
1024 | static void rcu_tasks_trace_pregp_step(void) | |
1025 | { | |
1026 | int cpu; | |
1027 | ||
d5f177d3 PM |
1028 | // Allow for fast-acting IPIs. |
1029 | atomic_set(&trc_n_readers_need_end, 1); | |
1030 | ||
1031 | // There shouldn't be any old IPIs, but... | |
1032 | for_each_possible_cpu(cpu) | |
1033 | WARN_ON_ONCE(per_cpu(trc_ipi_to_cpu, cpu)); | |
81b4a7bc PM |
1034 | |
1035 | // Disable CPU hotplug across the tasklist scan. | |
1036 | // This also waits for all readers in CPU-hotplug code paths. | |
1037 | cpus_read_lock(); | |
d5f177d3 PM |
1038 | } |
1039 | ||
1040 | /* Do first-round processing for the specified task. */ | |
1041 | static void rcu_tasks_trace_pertask(struct task_struct *t, | |
1042 | struct list_head *hop) | |
1043 | { | |
1b04fa99 URS |
1044 | // During early boot when there is only the one boot CPU, there |
1045 | // is no idle task for the other CPUs. Just return. | |
1046 | if (unlikely(t == NULL)) | |
1047 | return; | |
1048 | ||
276c4104 | 1049 | WRITE_ONCE(t->trc_reader_special.b.need_qs, false); |
43766c3e | 1050 | WRITE_ONCE(t->trc_reader_checked, false); |
d5f177d3 PM |
1051 | t->trc_ipi_to_cpu = -1; |
1052 | trc_wait_for_one_reader(t, hop); | |
1053 | } | |
1054 | ||
9796e1ae PM |
1055 | /* |
1056 | * Do intermediate processing between task and holdout scans and | |
1057 | * pick up the idle tasks. | |
1058 | */ | |
1059 | static void rcu_tasks_trace_postscan(struct list_head *hop) | |
d5f177d3 | 1060 | { |
9796e1ae PM |
1061 | int cpu; |
1062 | ||
1063 | for_each_possible_cpu(cpu) | |
1064 | rcu_tasks_trace_pertask(idle_task(cpu), hop); | |
1065 | ||
81b4a7bc PM |
1066 | // Re-enable CPU hotplug now that the tasklist scan has completed. |
1067 | cpus_read_unlock(); | |
1068 | ||
d5f177d3 PM |
1069 | // Wait for late-stage exiting tasks to finish exiting. |
1070 | // These might have passed the call to exit_tasks_rcu_finish(). | |
1071 | synchronize_rcu(); | |
1072 | // Any tasks that exit after this point will set ->trc_reader_checked. | |
1073 | } | |
1074 | ||
4593e772 PM |
1075 | /* Show the state of a task stalling the current RCU tasks trace GP. */ |
1076 | static void show_stalled_task_trace(struct task_struct *t, bool *firstreport) | |
1077 | { | |
1078 | int cpu; | |
1079 | ||
1080 | if (*firstreport) { | |
1081 | pr_err("INFO: rcu_tasks_trace detected stalls on tasks:\n"); | |
1082 | *firstreport = false; | |
1083 | } | |
1084 | // FIXME: This should attempt to use try_invoke_on_nonrunning_task(). | |
1085 | cpu = task_cpu(t); | |
1086 | pr_alert("P%d: %c%c%c nesting: %d%c cpu: %d\n", | |
1087 | t->pid, | |
1088 | ".I"[READ_ONCE(t->trc_ipi_to_cpu) > 0], | |
1089 | ".i"[is_idle_task(t)], | |
1090 | ".N"[cpu > 0 && tick_nohz_full_cpu(cpu)], | |
bdb0cca0 | 1091 | READ_ONCE(t->trc_reader_nesting), |
f8ab3fad | 1092 | " N"[!!READ_ONCE(t->trc_reader_special.b.need_qs)], |
4593e772 PM |
1093 | cpu); |
1094 | sched_show_task(t); | |
1095 | } | |
1096 | ||
1097 | /* List stalled IPIs for RCU tasks trace. */ | |
1098 | static void show_stalled_ipi_trace(void) | |
1099 | { | |
1100 | int cpu; | |
1101 | ||
1102 | for_each_possible_cpu(cpu) | |
1103 | if (per_cpu(trc_ipi_to_cpu, cpu)) | |
1104 | pr_alert("\tIPI outstanding to CPU %d\n", cpu); | |
1105 | } | |
1106 | ||
d5f177d3 PM |
1107 | /* Do one scan of the holdout list. */ |
1108 | static void check_all_holdout_tasks_trace(struct list_head *hop, | |
4593e772 | 1109 | bool needreport, bool *firstreport) |
d5f177d3 PM |
1110 | { |
1111 | struct task_struct *g, *t; | |
1112 | ||
81b4a7bc PM |
1113 | // Disable CPU hotplug across the holdout list scan. |
1114 | cpus_read_lock(); | |
1115 | ||
d5f177d3 PM |
1116 | list_for_each_entry_safe(t, g, hop, trc_holdout_list) { |
1117 | // If safe and needed, try to check the current task. | |
1118 | if (READ_ONCE(t->trc_ipi_to_cpu) == -1 && | |
1119 | !READ_ONCE(t->trc_reader_checked)) | |
1120 | trc_wait_for_one_reader(t, hop); | |
1121 | ||
1122 | // If check succeeded, remove this task from the list. | |
1123 | if (READ_ONCE(t->trc_reader_checked)) | |
1124 | trc_del_holdout(t); | |
4593e772 PM |
1125 | else if (needreport) |
1126 | show_stalled_task_trace(t, firstreport); | |
1127 | } | |
81b4a7bc PM |
1128 | |
1129 | // Re-enable CPU hotplug now that the holdout list scan has completed. | |
1130 | cpus_read_unlock(); | |
1131 | ||
4593e772 PM |
1132 | if (needreport) { |
1133 | if (firstreport) | |
1134 | pr_err("INFO: rcu_tasks_trace detected stalls? (Late IPI?)\n"); | |
1135 | show_stalled_ipi_trace(); | |
d5f177d3 PM |
1136 | } |
1137 | } | |
1138 | ||
cbe0d8d9 PM |
1139 | static void rcu_tasks_trace_empty_fn(void *unused) |
1140 | { | |
1141 | } | |
1142 | ||
d5f177d3 | 1143 | /* Wait for grace period to complete and provide ordering. */ |
af051ca4 | 1144 | static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp) |
d5f177d3 | 1145 | { |
cbe0d8d9 | 1146 | int cpu; |
4593e772 PM |
1147 | bool firstreport; |
1148 | struct task_struct *g, *t; | |
1149 | LIST_HEAD(holdouts); | |
1150 | long ret; | |
1151 | ||
cbe0d8d9 PM |
1152 | // Wait for any lingering IPI handlers to complete. Note that |
1153 | // if a CPU has gone offline or transitioned to userspace in the | |
1154 | // meantime, all IPI handlers should have been drained beforehand. | |
1155 | // Yes, this assumes that CPUs process IPIs in order. If that ever | |
1156 | // changes, there will need to be a recheck and/or timed wait. | |
1157 | for_each_online_cpu(cpu) | |
1158 | if (smp_load_acquire(per_cpu_ptr(&trc_ipi_to_cpu, cpu))) | |
1159 | smp_call_function_single(cpu, rcu_tasks_trace_empty_fn, NULL, 1); | |
1160 | ||
d5f177d3 PM |
1161 | // Remove the safety count. |
1162 | smp_mb__before_atomic(); // Order vs. earlier atomics | |
1163 | atomic_dec(&trc_n_readers_need_end); | |
1164 | smp_mb__after_atomic(); // Order vs. later atomics | |
1165 | ||
1166 | // Wait for readers. | |
af051ca4 | 1167 | set_tasks_gp_state(rtp, RTGS_WAIT_READERS); |
4593e772 PM |
1168 | for (;;) { |
1169 | ret = wait_event_idle_exclusive_timeout( | |
1170 | trc_wait, | |
1171 | atomic_read(&trc_n_readers_need_end) == 0, | |
1172 | READ_ONCE(rcu_task_stall_timeout)); | |
1173 | if (ret) | |
1174 | break; // Count reached zero. | |
af051ca4 | 1175 | // Stall warning time, so make a list of the offenders. |
f747c7e1 | 1176 | rcu_read_lock(); |
4593e772 | 1177 | for_each_process_thread(g, t) |
276c4104 | 1178 | if (READ_ONCE(t->trc_reader_special.b.need_qs)) |
4593e772 | 1179 | trc_add_holdout(t, &holdouts); |
f747c7e1 | 1180 | rcu_read_unlock(); |
4593e772 | 1181 | firstreport = true; |
592031cc PM |
1182 | list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list) { |
1183 | if (READ_ONCE(t->trc_reader_special.b.need_qs)) | |
4593e772 | 1184 | show_stalled_task_trace(t, &firstreport); |
592031cc PM |
1185 | trc_del_holdout(t); // Release task_struct reference. |
1186 | } | |
4593e772 PM |
1187 | if (firstreport) |
1188 | pr_err("INFO: rcu_tasks_trace detected stalls? (Counter/taskslist mismatch?)\n"); | |
1189 | show_stalled_ipi_trace(); | |
1190 | pr_err("\t%d holdouts\n", atomic_read(&trc_n_readers_need_end)); | |
1191 | } | |
d5f177d3 | 1192 | smp_mb(); // Caller's code must be ordered after wakeup. |
43766c3e | 1193 | // Pairs with pretty much every ordering primitive. |
d5f177d3 PM |
1194 | } |
1195 | ||
1196 | /* Report any needed quiescent state for this exiting task. */ | |
25246fc8 | 1197 | static void exit_tasks_rcu_finish_trace(struct task_struct *t) |
d5f177d3 PM |
1198 | { |
1199 | WRITE_ONCE(t->trc_reader_checked, true); | |
bdb0cca0 | 1200 | WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting)); |
d5f177d3 | 1201 | WRITE_ONCE(t->trc_reader_nesting, 0); |
276c4104 PM |
1202 | if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs))) |
1203 | rcu_read_unlock_trace_special(t, 0); | |
d5f177d3 PM |
1204 | } |
1205 | ||
d5f177d3 PM |
1206 | /** |
1207 | * call_rcu_tasks_trace() - Queue a callback trace task-based grace period | |
1208 | * @rhp: structure to be used for queueing the RCU updates. | |
1209 | * @func: actual callback function to be invoked after the grace period | |
1210 | * | |
1211 | * The callback function will be invoked some time after a full grace | |
1212 | * period elapses, in other words after all currently executing RCU | |
1213 | * read-side critical sections have completed. call_rcu_tasks_trace() | |
1214 | * assumes that the read-side critical sections end at context switch, | |
1215 | * cond_resched_rcu_qs(), or transition to usermode execution. As such, | |
1216 | * there are no read-side primitives analogous to rcu_read_lock() and | |
1217 | * rcu_read_unlock() because this primitive is intended to determine | |
1218 | * that all tasks have passed through a safe state, not so much for | |
a616aec9 | 1219 | * data-structure synchronization. |
d5f177d3 PM |
1220 | * |
1221 | * See the description of call_rcu() for more detailed information on | |
1222 | * memory ordering guarantees. | |
1223 | */ | |
1224 | void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func) | |
1225 | { | |
1226 | call_rcu_tasks_generic(rhp, func, &rcu_tasks_trace); | |
1227 | } | |
1228 | EXPORT_SYMBOL_GPL(call_rcu_tasks_trace); | |
1229 | ||
1230 | /** | |
1231 | * synchronize_rcu_tasks_trace - wait for a trace rcu-tasks grace period | |
1232 | * | |
1233 | * Control will return to the caller some time after a trace rcu-tasks | |
c7dcf810 PM |
1234 | * grace period has elapsed, in other words after all currently executing |
1235 | * rcu-tasks read-side critical sections have elapsed. These read-side | |
1236 | * critical sections are delimited by calls to rcu_read_lock_trace() | |
1237 | * and rcu_read_unlock_trace(). | |
d5f177d3 PM |
1238 | * |
1239 | * This is a very specialized primitive, intended only for a few uses in | |
1240 | * tracing and other situations requiring manipulation of function preambles | |
1241 | * and profiling hooks. The synchronize_rcu_tasks_trace() function is not | |
1242 | * (yet) intended for heavy use from multiple CPUs. | |
1243 | * | |
1244 | * See the description of synchronize_rcu() for more detailed information | |
1245 | * on memory ordering guarantees. | |
1246 | */ | |
1247 | void synchronize_rcu_tasks_trace(void) | |
1248 | { | |
1249 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_trace_lock_map), "Illegal synchronize_rcu_tasks_trace() in RCU Tasks Trace read-side critical section"); | |
1250 | synchronize_rcu_tasks_generic(&rcu_tasks_trace); | |
1251 | } | |
1252 | EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_trace); | |
1253 | ||
1254 | /** | |
1255 | * rcu_barrier_tasks_trace - Wait for in-flight call_rcu_tasks_trace() callbacks. | |
1256 | * | |
1257 | * Although the current implementation is guaranteed to wait, it is not | |
1258 | * obligated to, for example, if there are no pending callbacks. | |
1259 | */ | |
1260 | void rcu_barrier_tasks_trace(void) | |
1261 | { | |
1262 | /* There is only one callback queue, so this is easy. ;-) */ | |
1263 | synchronize_rcu_tasks_trace(); | |
1264 | } | |
1265 | EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace); | |
1266 | ||
1267 | static int __init rcu_spawn_tasks_trace_kthread(void) | |
1268 | { | |
2393a613 | 1269 | if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) { |
4fe192df | 1270 | rcu_tasks_trace.gp_sleep = HZ / 10; |
75dc2da5 | 1271 | rcu_tasks_trace.init_fract = HZ / 10; |
2393a613 | 1272 | } else { |
4fe192df PM |
1273 | rcu_tasks_trace.gp_sleep = HZ / 200; |
1274 | if (rcu_tasks_trace.gp_sleep <= 0) | |
1275 | rcu_tasks_trace.gp_sleep = 1; | |
75dc2da5 | 1276 | rcu_tasks_trace.init_fract = HZ / 200; |
2393a613 PM |
1277 | if (rcu_tasks_trace.init_fract <= 0) |
1278 | rcu_tasks_trace.init_fract = 1; | |
1279 | } | |
d5f177d3 PM |
1280 | rcu_tasks_trace.pregp_func = rcu_tasks_trace_pregp_step; |
1281 | rcu_tasks_trace.pertask_func = rcu_tasks_trace_pertask; | |
1282 | rcu_tasks_trace.postscan_func = rcu_tasks_trace_postscan; | |
1283 | rcu_tasks_trace.holdouts_func = check_all_holdout_tasks_trace; | |
1284 | rcu_tasks_trace.postgp_func = rcu_tasks_trace_postgp; | |
1285 | rcu_spawn_tasks_kthread_generic(&rcu_tasks_trace); | |
1286 | return 0; | |
1287 | } | |
d5f177d3 | 1288 | |
27c0f144 PM |
1289 | #if !defined(CONFIG_TINY_RCU) |
1290 | void show_rcu_tasks_trace_gp_kthread(void) | |
e21408ce | 1291 | { |
40471509 | 1292 | char buf[64]; |
e21408ce | 1293 | |
edf3775f PM |
1294 | sprintf(buf, "N%d h:%lu/%lu/%lu", atomic_read(&trc_n_readers_need_end), |
1295 | data_race(n_heavy_reader_ofl_updates), | |
40471509 PM |
1296 | data_race(n_heavy_reader_updates), |
1297 | data_race(n_heavy_reader_attempts)); | |
e21408ce PM |
1298 | show_rcu_tasks_generic_gp_kthread(&rcu_tasks_trace, buf); |
1299 | } | |
27c0f144 PM |
1300 | EXPORT_SYMBOL_GPL(show_rcu_tasks_trace_gp_kthread); |
1301 | #endif // !defined(CONFIG_TINY_RCU) | |
e21408ce | 1302 | |
d5f177d3 | 1303 | #else /* #ifdef CONFIG_TASKS_TRACE_RCU */ |
25246fc8 | 1304 | static void exit_tasks_rcu_finish_trace(struct task_struct *t) { } |
d5f177d3 | 1305 | #endif /* #else #ifdef CONFIG_TASKS_TRACE_RCU */ |
8fd8ca38 | 1306 | |
8344496e | 1307 | #ifndef CONFIG_TINY_RCU |
e21408ce PM |
1308 | void show_rcu_tasks_gp_kthreads(void) |
1309 | { | |
1310 | show_rcu_tasks_classic_gp_kthread(); | |
1311 | show_rcu_tasks_rude_gp_kthread(); | |
1312 | show_rcu_tasks_trace_gp_kthread(); | |
1313 | } | |
8344496e | 1314 | #endif /* #ifndef CONFIG_TINY_RCU */ |
e21408ce | 1315 | |
bfba7ed0 URS |
1316 | #ifdef CONFIG_PROVE_RCU |
1317 | struct rcu_tasks_test_desc { | |
1318 | struct rcu_head rh; | |
1319 | const char *name; | |
1320 | bool notrun; | |
1321 | }; | |
1322 | ||
1323 | static struct rcu_tasks_test_desc tests[] = { | |
1324 | { | |
1325 | .name = "call_rcu_tasks()", | |
1326 | /* If not defined, the test is skipped. */ | |
1327 | .notrun = !IS_ENABLED(CONFIG_TASKS_RCU), | |
1328 | }, | |
1329 | { | |
1330 | .name = "call_rcu_tasks_rude()", | |
1331 | /* If not defined, the test is skipped. */ | |
1332 | .notrun = !IS_ENABLED(CONFIG_TASKS_RUDE_RCU), | |
1333 | }, | |
1334 | { | |
1335 | .name = "call_rcu_tasks_trace()", | |
1336 | /* If not defined, the test is skipped. */ | |
1337 | .notrun = !IS_ENABLED(CONFIG_TASKS_TRACE_RCU) | |
1338 | } | |
1339 | }; | |
1340 | ||
1341 | static void test_rcu_tasks_callback(struct rcu_head *rhp) | |
1342 | { | |
1343 | struct rcu_tasks_test_desc *rttd = | |
1344 | container_of(rhp, struct rcu_tasks_test_desc, rh); | |
1345 | ||
1346 | pr_info("Callback from %s invoked.\n", rttd->name); | |
1347 | ||
1348 | rttd->notrun = true; | |
1349 | } | |
1350 | ||
1351 | static void rcu_tasks_initiate_self_tests(void) | |
1352 | { | |
1353 | pr_info("Running RCU-tasks wait API self tests\n"); | |
1354 | #ifdef CONFIG_TASKS_RCU | |
1355 | synchronize_rcu_tasks(); | |
1356 | call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback); | |
1357 | #endif | |
1358 | ||
1359 | #ifdef CONFIG_TASKS_RUDE_RCU | |
1360 | synchronize_rcu_tasks_rude(); | |
1361 | call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback); | |
1362 | #endif | |
1363 | ||
1364 | #ifdef CONFIG_TASKS_TRACE_RCU | |
1365 | synchronize_rcu_tasks_trace(); | |
1366 | call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback); | |
1367 | #endif | |
1368 | } | |
1369 | ||
1370 | static int rcu_tasks_verify_self_tests(void) | |
1371 | { | |
1372 | int ret = 0; | |
1373 | int i; | |
1374 | ||
1375 | for (i = 0; i < ARRAY_SIZE(tests); i++) { | |
1376 | if (!tests[i].notrun) { // still hanging. | |
1377 | pr_err("%s has been failed.\n", tests[i].name); | |
1378 | ret = -1; | |
1379 | } | |
1380 | } | |
1381 | ||
1382 | if (ret) | |
1383 | WARN_ON(1); | |
1384 | ||
1385 | return ret; | |
1386 | } | |
1387 | late_initcall(rcu_tasks_verify_self_tests); | |
1388 | #else /* #ifdef CONFIG_PROVE_RCU */ | |
1389 | static void rcu_tasks_initiate_self_tests(void) { } | |
1390 | #endif /* #else #ifdef CONFIG_PROVE_RCU */ | |
1391 | ||
1b04fa99 URS |
1392 | void __init rcu_init_tasks_generic(void) |
1393 | { | |
1394 | #ifdef CONFIG_TASKS_RCU | |
1395 | rcu_spawn_tasks_kthread(); | |
1396 | #endif | |
1397 | ||
1398 | #ifdef CONFIG_TASKS_RUDE_RCU | |
1399 | rcu_spawn_tasks_rude_kthread(); | |
1400 | #endif | |
1401 | ||
1402 | #ifdef CONFIG_TASKS_TRACE_RCU | |
1403 | rcu_spawn_tasks_trace_kthread(); | |
1404 | #endif | |
bfba7ed0 URS |
1405 | |
1406 | // Run the self-tests. | |
1407 | rcu_tasks_initiate_self_tests(); | |
1b04fa99 URS |
1408 | } |
1409 | ||
8fd8ca38 PM |
1410 | #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ |
1411 | static inline void rcu_tasks_bootup_oddness(void) {} | |
1412 | #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ |