~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/kernel/rcu/update.c

Version: ~ [ linux-5.13-rc7 ] ~ [ linux-5.12.12 ] ~ [ linux-5.11.22 ] ~ [ linux-5.10.45 ] ~ [ linux-5.9.16 ] ~ [ linux-5.8.18 ] ~ [ linux-5.7.19 ] ~ [ linux-5.6.19 ] ~ [ linux-5.5.19 ] ~ [ linux-5.4.127 ] ~ [ linux-5.3.18 ] ~ [ linux-5.2.21 ] ~ [ linux-5.1.21 ] ~ [ linux-5.0.21 ] ~ [ linux-4.20.17 ] ~ [ linux-4.19.195 ] ~ [ linux-4.18.20 ] ~ [ linux-4.17.19 ] ~ [ linux-4.16.18 ] ~ [ linux-4.15.18 ] ~ [ linux-4.14.237 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.273 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.273 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.52 ] ~ [ linux-4.0.9 ] ~ [ linux-3.18.140 ] ~ [ linux-3.16.85 ] ~ [ linux-3.14.79 ] ~ [ linux-3.12.74 ] ~ [ linux-3.10.108 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  1 /*
  2  * Read-Copy Update mechanism for mutual exclusion
  3  *
  4  * This program is free software; you can redistribute it and/or modify
  5  * it under the terms of the GNU General Public License as published by
  6  * the Free Software Foundation; either version 2 of the License, or
  7  * (at your option) any later version.
  8  *
  9  * This program is distributed in the hope that it will be useful,
 10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 12  * GNU General Public License for more details.
 13  *
 14  * You should have received a copy of the GNU General Public License
 15  * along with this program; if not, you can access it online at
 16  * http://www.gnu.org/licenses/gpl-2.0.html.
 17  *
 18  * Copyright IBM Corporation, 2001
 19  *
 20  * Authors: Dipankar Sarma <dipankar@in.ibm.com>
 21  *          Manfred Spraul <manfred@colorfullife.com>
 22  *
 23  * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
 24  * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
 25  * Papers:
 26  * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
 27  * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
 28  *
 29  * For detailed explanation of Read-Copy Update mechanism see -
 30  *              http://lse.sourceforge.net/locking/rcupdate.html
 31  *
 32  */
 33 #include <linux/types.h>
 34 #include <linux/kernel.h>
 35 #include <linux/init.h>
 36 #include <linux/spinlock.h>
 37 #include <linux/smp.h>
 38 #include <linux/interrupt.h>
 39 #include <linux/sched/signal.h>
 40 #include <linux/sched/debug.h>
 41 #include <linux/atomic.h>
 42 #include <linux/bitops.h>
 43 #include <linux/percpu.h>
 44 #include <linux/notifier.h>
 45 #include <linux/cpu.h>
 46 #include <linux/mutex.h>
 47 #include <linux/export.h>
 48 #include <linux/hardirq.h>
 49 #include <linux/delay.h>
 50 #include <linux/moduleparam.h>
 51 #include <linux/kthread.h>
 52 #include <linux/tick.h>
 53 #include <linux/rcupdate_wait.h>
 54 #include <linux/sched/isolation.h>
 55 
 56 #define CREATE_TRACE_POINTS
 57 
 58 #include "rcu.h"
 59 
 60 #ifdef MODULE_PARAM_PREFIX
 61 #undef MODULE_PARAM_PREFIX
 62 #endif
 63 #define MODULE_PARAM_PREFIX "rcupdate."
 64 
 65 #ifndef CONFIG_TINY_RCU
 66 extern int rcu_expedited; /* from sysctl */
 67 module_param(rcu_expedited, int, 0);
 68 extern int rcu_normal; /* from sysctl */
 69 module_param(rcu_normal, int, 0);
 70 static int rcu_normal_after_boot;
 71 module_param(rcu_normal_after_boot, int, 0);
 72 #endif /* #ifndef CONFIG_TINY_RCU */
 73 
 74 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 75 /**
 76  * rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
 77  *
 78  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
 79  * RCU-sched read-side critical section.  In absence of
 80  * CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
 81  * critical section unless it can prove otherwise.  Note that disabling
 82  * of preemption (including disabling irqs) counts as an RCU-sched
 83  * read-side critical section.  This is useful for debug checks in functions
 84  * that required that they be called within an RCU-sched read-side
 85  * critical section.
 86  *
 87  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot
 88  * and while lockdep is disabled.
 89  *
 90  * Note that if the CPU is in the idle loop from an RCU point of
 91  * view (ie: that we are in the section between rcu_idle_enter() and
 92  * rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
 93  * did an rcu_read_lock().  The reason for this is that RCU ignores CPUs
 94  * that are in such a section, considering these as in extended quiescent
 95  * state, so such a CPU is effectively never in an RCU read-side critical
 96  * section regardless of what RCU primitives it invokes.  This state of
 97  * affairs is required --- we need to keep an RCU-free window in idle
 98  * where the CPU may possibly enter into low power mode. This way we can
 99  * notice an extended quiescent state to other CPUs that started a grace
100  * period. Otherwise we would delay any grace period as long as we run in
101  * the idle task.
102  *
103  * Similarly, we avoid claiming an SRCU read lock held if the current
104  * CPU is offline.
105  */
106 int rcu_read_lock_sched_held(void)
107 {
108         int lockdep_opinion = 0;
109 
110         if (!debug_lockdep_rcu_enabled())
111                 return 1;
112         if (!rcu_is_watching())
113                 return 0;
114         if (!rcu_lockdep_current_cpu_online())
115                 return 0;
116         if (debug_locks)
117                 lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
118         return lockdep_opinion || !preemptible();
119 }
120 EXPORT_SYMBOL(rcu_read_lock_sched_held);
121 #endif
122 
123 #ifndef CONFIG_TINY_RCU
124 
125 /*
126  * Should expedited grace-period primitives always fall back to their
127  * non-expedited counterparts?  Intended for use within RCU.  Note
128  * that if the user specifies both rcu_expedited and rcu_normal, then
129  * rcu_normal wins.  (Except during the time period during boot from
130  * when the first task is spawned until the rcu_set_runtime_mode()
131  * core_initcall() is invoked, at which point everything is expedited.)
132  */
133 bool rcu_gp_is_normal(void)
134 {
135         return READ_ONCE(rcu_normal) &&
136                rcu_scheduler_active != RCU_SCHEDULER_INIT;
137 }
138 EXPORT_SYMBOL_GPL(rcu_gp_is_normal);
139 
140 static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
141 
142 /*
143  * Should normal grace-period primitives be expedited?  Intended for
144  * use within RCU.  Note that this function takes the rcu_expedited
145  * sysfs/boot variable and rcu_scheduler_active into account as well
146  * as the rcu_expedite_gp() nesting.  So looping on rcu_unexpedite_gp()
147  * until rcu_gp_is_expedited() returns false is a -really- bad idea.
148  */
149 bool rcu_gp_is_expedited(void)
150 {
151         return rcu_expedited || atomic_read(&rcu_expedited_nesting) ||
152                rcu_scheduler_active == RCU_SCHEDULER_INIT;
153 }
154 EXPORT_SYMBOL_GPL(rcu_gp_is_expedited);
155 
156 /**
157  * rcu_expedite_gp - Expedite future RCU grace periods
158  *
159  * After a call to this function, future calls to synchronize_rcu() and
160  * friends act as the corresponding synchronize_rcu_expedited() function
161  * had instead been called.
162  */
163 void rcu_expedite_gp(void)
164 {
165         atomic_inc(&rcu_expedited_nesting);
166 }
167 EXPORT_SYMBOL_GPL(rcu_expedite_gp);
168 
169 /**
170  * rcu_unexpedite_gp - Cancel prior rcu_expedite_gp() invocation
171  *
172  * Undo a prior call to rcu_expedite_gp().  If all prior calls to
173  * rcu_expedite_gp() are undone by a subsequent call to rcu_unexpedite_gp(),
174  * and if the rcu_expedited sysfs/boot parameter is not set, then all
175  * subsequent calls to synchronize_rcu() and friends will return to
176  * their normal non-expedited behavior.
177  */
178 void rcu_unexpedite_gp(void)
179 {
180         atomic_dec(&rcu_expedited_nesting);
181 }
182 EXPORT_SYMBOL_GPL(rcu_unexpedite_gp);
183 
184 /*
185  * Inform RCU of the end of the in-kernel boot sequence.
186  */
187 void rcu_end_inkernel_boot(void)
188 {
189         rcu_unexpedite_gp();
190         if (rcu_normal_after_boot)
191                 WRITE_ONCE(rcu_normal, 1);
192 }
193 
194 #endif /* #ifndef CONFIG_TINY_RCU */
195 
196 /*
197  * Test each non-SRCU synchronous grace-period wait API.  This is
198  * useful just after a change in mode for these primitives, and
199  * during early boot.
200  */
201 void rcu_test_sync_prims(void)
202 {
203         if (!IS_ENABLED(CONFIG_PROVE_RCU))
204                 return;
205         synchronize_rcu();
206         synchronize_rcu_bh();
207         synchronize_sched();
208         synchronize_rcu_expedited();
209         synchronize_rcu_bh_expedited();
210         synchronize_sched_expedited();
211 }
212 
213 #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU)
214 
215 /*
216  * Switch to run-time mode once RCU has fully initialized.
217  */
218 static int __init rcu_set_runtime_mode(void)
219 {
220         rcu_test_sync_prims();
221         rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
222         rcu_test_sync_prims();
223         return 0;
224 }
225 core_initcall(rcu_set_runtime_mode);
226 
227 #endif /* #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) */
228 
229 #ifdef CONFIG_PREEMPT_RCU
230 
231 /*
232  * Preemptible RCU implementation for rcu_read_lock().
233  * Just increment ->rcu_read_lock_nesting, shared state will be updated
234  * if we block.
235  */
236 void __rcu_read_lock(void)
237 {
238         current->rcu_read_lock_nesting++;
239         barrier();  /* critical section after entry code. */
240 }
241 EXPORT_SYMBOL_GPL(__rcu_read_lock);
242 
243 /*
244  * Preemptible RCU implementation for rcu_read_unlock().
245  * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
246  * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
247  * invoke rcu_read_unlock_special() to clean up after a context switch
248  * in an RCU read-side critical section and other special cases.
249  */
250 void __rcu_read_unlock(void)
251 {
252         struct task_struct *t = current;
253 
254         if (t->rcu_read_lock_nesting != 1) {
255                 --t->rcu_read_lock_nesting;
256         } else {
257                 barrier();  /* critical section before exit code. */
258                 t->rcu_read_lock_nesting = INT_MIN;
259                 barrier();  /* assign before ->rcu_read_unlock_special load */
260                 if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s)))
261                         rcu_read_unlock_special(t);
262                 barrier();  /* ->rcu_read_unlock_special load before assign */
263                 t->rcu_read_lock_nesting = 0;
264         }
265 #ifdef CONFIG_PROVE_LOCKING
266         {
267                 int rrln = READ_ONCE(t->rcu_read_lock_nesting);
268 
269                 WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
270         }
271 #endif /* #ifdef CONFIG_PROVE_LOCKING */
272 }
273 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
274 
275 #endif /* #ifdef CONFIG_PREEMPT_RCU */
276 
277 #ifdef CONFIG_DEBUG_LOCK_ALLOC
278 static struct lock_class_key rcu_lock_key;
279 struct lockdep_map rcu_lock_map =
280         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
281 EXPORT_SYMBOL_GPL(rcu_lock_map);
282 
283 static struct lock_class_key rcu_bh_lock_key;
284 struct lockdep_map rcu_bh_lock_map =
285         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
286 EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
287 
288 static struct lock_class_key rcu_sched_lock_key;
289 struct lockdep_map rcu_sched_lock_map =
290         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
291 EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
292 
293 static struct lock_class_key rcu_callback_key;
294 struct lockdep_map rcu_callback_map =
295         STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
296 EXPORT_SYMBOL_GPL(rcu_callback_map);
297 
298 int notrace debug_lockdep_rcu_enabled(void)
299 {
300         return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && debug_locks &&
301                current->lockdep_recursion == 0;
302 }
303 EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
304 
305 /**
306  * rcu_read_lock_held() - might we be in RCU read-side critical section?
307  *
308  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
309  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
310  * this assumes we are in an RCU read-side critical section unless it can
311  * prove otherwise.  This is useful for debug checks in functions that
312  * require that they be called within an RCU read-side critical section.
313  *
314  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
315  * and while lockdep is disabled.
316  *
317  * Note that rcu_read_lock() and the matching rcu_read_unlock() must
318  * occur in the same context, for example, it is illegal to invoke
319  * rcu_read_unlock() in process context if the matching rcu_read_lock()
320  * was invoked from within an irq handler.
321  *
322  * Note that rcu_read_lock() is disallowed if the CPU is either idle or
323  * offline from an RCU perspective, so check for those as well.
324  */
325 int rcu_read_lock_held(void)
326 {
327         if (!debug_lockdep_rcu_enabled())
328                 return 1;
329         if (!rcu_is_watching())
330                 return 0;
331         if (!rcu_lockdep_current_cpu_online())
332                 return 0;
333         return lock_is_held(&rcu_lock_map);
334 }
335 EXPORT_SYMBOL_GPL(rcu_read_lock_held);
336 
337 /**
338  * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
339  *
340  * Check for bottom half being disabled, which covers both the
341  * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
342  * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
343  * will show the situation.  This is useful for debug checks in functions
344  * that require that they be called within an RCU read-side critical
345  * section.
346  *
347  * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
348  *
349  * Note that rcu_read_lock() is disallowed if the CPU is either idle or
350  * offline from an RCU perspective, so check for those as well.
351  */
352 int rcu_read_lock_bh_held(void)
353 {
354         if (!debug_lockdep_rcu_enabled())
355                 return 1;
356         if (!rcu_is_watching())
357                 return 0;
358         if (!rcu_lockdep_current_cpu_online())
359                 return 0;
360         return in_softirq() || irqs_disabled();
361 }
362 EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
363 
364 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
365 
366 /**
367  * wakeme_after_rcu() - Callback function to awaken a task after grace period
368  * @head: Pointer to rcu_head member within rcu_synchronize structure
369  *
370  * Awaken the corresponding task now that a grace period has elapsed.
371  */
372 void wakeme_after_rcu(struct rcu_head *head)
373 {
374         struct rcu_synchronize *rcu;
375 
376         rcu = container_of(head, struct rcu_synchronize, head);
377         complete(&rcu->completion);
378 }
379 EXPORT_SYMBOL_GPL(wakeme_after_rcu);
380 
381 void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array,
382                    struct rcu_synchronize *rs_array)
383 {
384         int i;
385         int j;
386 
387         /* Initialize and register callbacks for each flavor specified. */
388         for (i = 0; i < n; i++) {
389                 if (checktiny &&
390                     (crcu_array[i] == call_rcu ||
391                      crcu_array[i] == call_rcu_bh)) {
392                         might_sleep();
393                         continue;
394                 }
395                 init_rcu_head_on_stack(&rs_array[i].head);
396                 init_completion(&rs_array[i].completion);
397                 for (j = 0; j < i; j++)
398                         if (crcu_array[j] == crcu_array[i])
399                                 break;
400                 if (j == i)
401                         (crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
402         }
403 
404         /* Wait for all callbacks to be invoked. */
405         for (i = 0; i < n; i++) {
406                 if (checktiny &&
407                     (crcu_array[i] == call_rcu ||
408                      crcu_array[i] == call_rcu_bh))
409                         continue;
410                 for (j = 0; j < i; j++)
411                         if (crcu_array[j] == crcu_array[i])
412                                 break;
413                 if (j == i)
414                         wait_for_completion(&rs_array[i].completion);
415                 destroy_rcu_head_on_stack(&rs_array[i].head);
416         }
417 }
418 EXPORT_SYMBOL_GPL(__wait_rcu_gp);
419 
420 #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
421 void init_rcu_head(struct rcu_head *head)
422 {
423         debug_object_init(head, &rcuhead_debug_descr);
424 }
425 EXPORT_SYMBOL_GPL(init_rcu_head);
426 
427 void destroy_rcu_head(struct rcu_head *head)
428 {
429         debug_object_free(head, &rcuhead_debug_descr);
430 }
431 EXPORT_SYMBOL_GPL(destroy_rcu_head);
432 
433 static bool rcuhead_is_static_object(void *addr)
434 {
435         return true;
436 }
437 
438 /**
439  * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
440  * @head: pointer to rcu_head structure to be initialized
441  *
442  * This function informs debugobjects of a new rcu_head structure that
443  * has been allocated as an auto variable on the stack.  This function
444  * is not required for rcu_head structures that are statically defined or
445  * that are dynamically allocated on the heap.  This function has no
446  * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
447  */
448 void init_rcu_head_on_stack(struct rcu_head *head)
449 {
450         debug_object_init_on_stack(head, &rcuhead_debug_descr);
451 }
452 EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
453 
454 /**
455  * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
456  * @head: pointer to rcu_head structure to be initialized
457  *
458  * This function informs debugobjects that an on-stack rcu_head structure
459  * is about to go out of scope.  As with init_rcu_head_on_stack(), this
460  * function is not required for rcu_head structures that are statically
461  * defined or that are dynamically allocated on the heap.  Also as with
462  * init_rcu_head_on_stack(), this function has no effect for
463  * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
464  */
465 void destroy_rcu_head_on_stack(struct rcu_head *head)
466 {
467         debug_object_free(head, &rcuhead_debug_descr);
468 }
469 EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
470 
471 struct debug_obj_descr rcuhead_debug_descr = {
472         .name = "rcu_head",
473         .is_static_object = rcuhead_is_static_object,
474 };
475 EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
476 #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
477 
478 #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
479 void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
480                                unsigned long secs,
481                                unsigned long c_old, unsigned long c)
482 {
483         trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
484 }
485 EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
486 #else
487 #define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
488         do { } while (0)
489 #endif
490 
491 #ifdef CONFIG_RCU_STALL_COMMON
492 
493 #ifdef CONFIG_PROVE_RCU
494 #define RCU_STALL_DELAY_DELTA          (5 * HZ)
495 #else
496 #define RCU_STALL_DELAY_DELTA          0
497 #endif
498 
499 int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
500 EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress);
501 static int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
502 
503 module_param(rcu_cpu_stall_suppress, int, 0644);
504 module_param(rcu_cpu_stall_timeout, int, 0644);
505 
506 int rcu_jiffies_till_stall_check(void)
507 {
508         int till_stall_check = READ_ONCE(rcu_cpu_stall_timeout);
509 
510         /*
511          * Limit check must be consistent with the Kconfig limits
512          * for CONFIG_RCU_CPU_STALL_TIMEOUT.
513          */
514         if (till_stall_check < 3) {
515                 WRITE_ONCE(rcu_cpu_stall_timeout, 3);
516                 till_stall_check = 3;
517         } else if (till_stall_check > 300) {
518                 WRITE_ONCE(rcu_cpu_stall_timeout, 300);
519                 till_stall_check = 300;
520         }
521         return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
522 }
523 
524 void rcu_sysrq_start(void)
525 {
526         if (!rcu_cpu_stall_suppress)
527                 rcu_cpu_stall_suppress = 2;
528 }
529 
530 void rcu_sysrq_end(void)
531 {
532         if (rcu_cpu_stall_suppress == 2)
533                 rcu_cpu_stall_suppress = 0;
534 }
535 
536 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
537 {
538         rcu_cpu_stall_suppress = 1;
539         return NOTIFY_DONE;
540 }
541 
542 static struct notifier_block rcu_panic_block = {
543         .notifier_call = rcu_panic,
544 };
545 
546 static int __init check_cpu_stall_init(void)
547 {
548         atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
549         return 0;
550 }
551 early_initcall(check_cpu_stall_init);
552 
553 #endif /* #ifdef CONFIG_RCU_STALL_COMMON */
554 
555 #ifdef CONFIG_TASKS_RCU
556 
557 /*
558  * Simple variant of RCU whose quiescent states are voluntary context switch,
559  * user-space execution, and idle.  As such, grace periods can take one good
560  * long time.  There are no read-side primitives similar to rcu_read_lock()
561  * and rcu_read_unlock() because this implementation is intended to get
562  * the system into a safe state for some of the manipulations involved in
563  * tracing and the like.  Finally, this implementation does not support
564  * high call_rcu_tasks() rates from multiple CPUs.  If this is required,
565  * per-CPU callback lists will be needed.
566  */
567 
568 /* Global list of callbacks and associated lock. */
569 static struct rcu_head *rcu_tasks_cbs_head;
570 static struct rcu_head **rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
571 static DECLARE_WAIT_QUEUE_HEAD(rcu_tasks_cbs_wq);
572 static DEFINE_RAW_SPINLOCK(rcu_tasks_cbs_lock);
573 
574 /* Track exiting tasks in order to allow them to be waited for. */
575 DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu);
576 
577 /* Control stall timeouts.  Disable with <= 0, otherwise jiffies till stall. */
578 #define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10)
579 static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT;
580 module_param(rcu_task_stall_timeout, int, 0644);
581 
582 static struct task_struct *rcu_tasks_kthread_ptr;
583 
584 /**
585  * call_rcu_tasks() - Queue an RCU for invocation task-based grace period
586  * @rhp: structure to be used for queueing the RCU updates.
587  * @func: actual callback function to be invoked after the grace period
588  *
589  * The callback function will be invoked some time after a full grace
590  * period elapses, in other words after all currently executing RCU
591  * read-side critical sections have completed. call_rcu_tasks() assumes
592  * that the read-side critical sections end at a voluntary context
593  * switch (not a preemption!), entry into idle, or transition to usermode
594  * execution.  As such, there are no read-side primitives analogous to
595  * rcu_read_lock() and rcu_read_unlock() because this primitive is intended
596  * to determine that all tasks have passed through a safe state, not so
597  * much for data-strcuture synchronization.
598  *
599  * See the description of call_rcu() for more detailed information on
600  * memory ordering guarantees.
601  */
602 void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func)
603 {
604         unsigned long flags;
605         bool needwake;
606 
607         rhp->next = NULL;
608         rhp->func = func;
609         raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
610         needwake = !rcu_tasks_cbs_head;
611         *rcu_tasks_cbs_tail = rhp;
612         rcu_tasks_cbs_tail = &rhp->next;
613         raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
614         /* We can't create the thread unless interrupts are enabled. */
615         if (needwake && READ_ONCE(rcu_tasks_kthread_ptr))
616                 wake_up(&rcu_tasks_cbs_wq);
617 }
618 EXPORT_SYMBOL_GPL(call_rcu_tasks);
619 
620 /**
621  * synchronize_rcu_tasks - wait until an rcu-tasks grace period has elapsed.
622  *
623  * Control will return to the caller some time after a full rcu-tasks
624  * grace period has elapsed, in other words after all currently
625  * executing rcu-tasks read-side critical sections have elapsed.  These
626  * read-side critical sections are delimited by calls to schedule(),
627  * cond_resched_rcu_qs(), idle execution, userspace execution, calls
628  * to synchronize_rcu_tasks(), and (in theory, anyway) cond_resched().
629  *
630  * This is a very specialized primitive, intended only for a few uses in
631  * tracing and other situations requiring manipulation of function
632  * preambles and profiling hooks.  The synchronize_rcu_tasks() function
633  * is not (yet) intended for heavy use from multiple CPUs.
634  *
635  * Note that this guarantee implies further memory-ordering guarantees.
636  * On systems with more than one CPU, when synchronize_rcu_tasks() returns,
637  * each CPU is guaranteed to have executed a full memory barrier since the
638  * end of its last RCU-tasks read-side critical section whose beginning
639  * preceded the call to synchronize_rcu_tasks().  In addition, each CPU
640  * having an RCU-tasks read-side critical section that extends beyond
641  * the return from synchronize_rcu_tasks() is guaranteed to have executed
642  * a full memory barrier after the beginning of synchronize_rcu_tasks()
643  * and before the beginning of that RCU-tasks read-side critical section.
644  * Note that these guarantees include CPUs that are offline, idle, or
645  * executing in user mode, as well as CPUs that are executing in the kernel.
646  *
647  * Furthermore, if CPU A invoked synchronize_rcu_tasks(), which returned
648  * to its caller on CPU B, then both CPU A and CPU B are guaranteed
649  * to have executed a full memory barrier during the execution of
650  * synchronize_rcu_tasks() -- even if CPU A and CPU B are the same CPU
651  * (but again only if the system has more than one CPU).
652  */
653 void synchronize_rcu_tasks(void)
654 {
655         /* Complain if the scheduler has not started.  */
656         RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE,
657                          "synchronize_rcu_tasks called too soon");
658 
659         /* Wait for the grace period. */
660         wait_rcu_gp(call_rcu_tasks);
661 }
662 EXPORT_SYMBOL_GPL(synchronize_rcu_tasks);
663 
664 /**
665  * rcu_barrier_tasks - Wait for in-flight call_rcu_tasks() callbacks.
666  *
667  * Although the current implementation is guaranteed to wait, it is not
668  * obligated to, for example, if there are no pending callbacks.
669  */
670 void rcu_barrier_tasks(void)
671 {
672         /* There is only one callback queue, so this is easy.  ;-) */
673         synchronize_rcu_tasks();
674 }
675 EXPORT_SYMBOL_GPL(rcu_barrier_tasks);
676 
677 /* See if tasks are still holding out, complain if so. */
678 static void check_holdout_task(struct task_struct *t,
679                                bool needreport, bool *firstreport)
680 {
681         int cpu;
682 
683         if (!READ_ONCE(t->rcu_tasks_holdout) ||
684             t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) ||
685             !READ_ONCE(t->on_rq) ||
686             (IS_ENABLED(CONFIG_NO_HZ_FULL) &&
687              !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) {
688                 WRITE_ONCE(t->rcu_tasks_holdout, false);
689                 list_del_init(&t->rcu_tasks_holdout_list);
690                 put_task_struct(t);
691                 return;
692         }
693         rcu_request_urgent_qs_task(t);
694         if (!needreport)
695                 return;
696         if (*firstreport) {
697                 pr_err("INFO: rcu_tasks detected stalls on tasks:\n");
698                 *firstreport = false;
699         }
700         cpu = task_cpu(t);
701         pr_alert("%p: %c%c nvcsw: %lu/%lu holdout: %d idle_cpu: %d/%d\n",
702                  t, ".I"[is_idle_task(t)],
703                  "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)],
704                  t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout,
705                  t->rcu_tasks_idle_cpu, cpu);
706         sched_show_task(t);
707 }
708 
709 /* RCU-tasks kthread that detects grace periods and invokes callbacks. */
710 static int __noreturn rcu_tasks_kthread(void *arg)
711 {
712         unsigned long flags;
713         struct task_struct *g, *t;
714         unsigned long lastreport;
715         struct rcu_head *list;
716         struct rcu_head *next;
717         LIST_HEAD(rcu_tasks_holdouts);
718 
719         /* Run on housekeeping CPUs by default.  Sysadm can move if desired. */
720         housekeeping_affine(current, HK_FLAG_RCU);
721 
722         /*
723          * Each pass through the following loop makes one check for
724          * newly arrived callbacks, and, if there are some, waits for
725          * one RCU-tasks grace period and then invokes the callbacks.
726          * This loop is terminated by the system going down.  ;-)
727          */
728         for (;;) {
729 
730                 /* Pick up any new callbacks. */
731                 raw_spin_lock_irqsave(&rcu_tasks_cbs_lock, flags);
732                 list = rcu_tasks_cbs_head;
733                 rcu_tasks_cbs_head = NULL;
734                 rcu_tasks_cbs_tail = &rcu_tasks_cbs_head;
735                 raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags);
736 
737                 /* If there were none, wait a bit and start over. */
738                 if (!list) {
739                         wait_event_interruptible(rcu_tasks_cbs_wq,
740                                                  rcu_tasks_cbs_head);
741                         if (!rcu_tasks_cbs_head) {
742                                 WARN_ON(signal_pending(current));
743                                 schedule_timeout_interruptible(HZ/10);
744                         }
745                         continue;
746                 }
747 
748                 /*
749                  * Wait for all pre-existing t->on_rq and t->nvcsw
750                  * transitions to complete.  Invoking synchronize_sched()
751                  * suffices because all these transitions occur with
752                  * interrupts disabled.  Without this synchronize_sched(),
753                  * a read-side critical section that started before the
754                  * grace period might be incorrectly seen as having started
755                  * after the grace period.
756                  *
757                  * This synchronize_sched() also dispenses with the
758                  * need for a memory barrier on the first store to
759                  * ->rcu_tasks_holdout, as it forces the store to happen
760                  * after the beginning of the grace period.
761                  */
762                 synchronize_sched();
763 
764                 /*
765                  * There were callbacks, so we need to wait for an
766                  * RCU-tasks grace period.  Start off by scanning
767                  * the task list for tasks that are not already
768                  * voluntarily blocked.  Mark these tasks and make
769                  * a list of them in rcu_tasks_holdouts.
770                  */
771                 rcu_read_lock();
772                 for_each_process_thread(g, t) {
773                         if (t != current && READ_ONCE(t->on_rq) &&
774                             !is_idle_task(t)) {
775                                 get_task_struct(t);
776                                 t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw);
777                                 WRITE_ONCE(t->rcu_tasks_holdout, true);
778                                 list_add(&t->rcu_tasks_holdout_list,
779                                          &rcu_tasks_holdouts);
780                         }
781                 }
782                 rcu_read_unlock();
783 
784                 /*
785                  * Wait for tasks that are in the process of exiting.
786                  * This does only part of the job, ensuring that all
787                  * tasks that were previously exiting reach the point
788                  * where they have disabled preemption, allowing the
789                  * later synchronize_sched() to finish the job.
790                  */
791                 synchronize_srcu(&tasks_rcu_exit_srcu);
792 
793                 /*
794                  * Each pass through the following loop scans the list
795                  * of holdout tasks, removing any that are no longer
796                  * holdouts.  When the list is empty, we are done.
797                  */
798                 lastreport = jiffies;
799                 while (!list_empty(&rcu_tasks_holdouts)) {
800                         bool firstreport;
801                         bool needreport;
802                         int rtst;
803                         struct task_struct *t1;
804 
805                         schedule_timeout_interruptible(HZ);
806                         rtst = READ_ONCE(rcu_task_stall_timeout);
807                         needreport = rtst > 0 &&
808                                      time_after(jiffies, lastreport + rtst);
809                         if (needreport)
810                                 lastreport = jiffies;
811                         firstreport = true;
812                         WARN_ON(signal_pending(current));
813                         list_for_each_entry_safe(t, t1, &rcu_tasks_holdouts,
814                                                 rcu_tasks_holdout_list) {
815                                 check_holdout_task(t, needreport, &firstreport);
816                                 cond_resched();
817                         }
818                 }
819 
820                 /*
821                  * Because ->on_rq and ->nvcsw are not guaranteed
822                  * to have a full memory barriers prior to them in the
823                  * schedule() path, memory reordering on other CPUs could
824                  * cause their RCU-tasks read-side critical sections to
825                  * extend past the end of the grace period.  However,
826                  * because these ->nvcsw updates are carried out with
827                  * interrupts disabled, we can use synchronize_sched()
828                  * to force the needed ordering on all such CPUs.
829                  *
830                  * This synchronize_sched() also confines all
831                  * ->rcu_tasks_holdout accesses to be within the grace
832                  * period, avoiding the need for memory barriers for
833                  * ->rcu_tasks_holdout accesses.
834                  *
835                  * In addition, this synchronize_sched() waits for exiting
836                  * tasks to complete their final preempt_disable() region
837                  * of execution, cleaning up after the synchronize_srcu()
838                  * above.
839                  */
840                 synchronize_sched();
841 
842                 /* Invoke the callbacks. */
843                 while (list) {
844                         next = list->next;
845                         local_bh_disable();
846                         list->func(list);
847                         local_bh_enable();
848                         list = next;
849                         cond_resched();
850                 }
851                 schedule_timeout_uninterruptible(HZ/10);
852         }
853 }
854 
855 /* Spawn rcu_tasks_kthread() at core_initcall() time. */
856 static int __init rcu_spawn_tasks_kthread(void)
857 {
858         struct task_struct *t;
859 
860         t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread");
861         BUG_ON(IS_ERR(t));
862         smp_mb(); /* Ensure others see full kthread. */
863         WRITE_ONCE(rcu_tasks_kthread_ptr, t);
864         return 0;
865 }
866 core_initcall(rcu_spawn_tasks_kthread);
867 
868 /* Do the srcu_read_lock() for the above synchronize_srcu().  */
869 void exit_tasks_rcu_start(void)
870 {
871         preempt_disable();
872         current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu);
873         preempt_enable();
874 }
875 
876 /* Do the srcu_read_unlock() for the above synchronize_srcu().  */
877 void exit_tasks_rcu_finish(void)
878 {
879         preempt_disable();
880         __srcu_read_unlock(&tasks_rcu_exit_srcu, current->rcu_tasks_idx);
881         preempt_enable();
882 }
883 
884 #endif /* #ifdef CONFIG_TASKS_RCU */
885 
886 #ifndef CONFIG_TINY_RCU
887 
888 /*
889  * Print any non-default Tasks RCU settings.
890  */
891 static void __init rcu_tasks_bootup_oddness(void)
892 {
893 #ifdef CONFIG_TASKS_RCU
894         if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT)
895                 pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout);
896         else
897                 pr_info("\tTasks RCU enabled.\n");
898 #endif /* #ifdef CONFIG_TASKS_RCU */
899 }
900 
901 #endif /* #ifndef CONFIG_TINY_RCU */
902 
903 #ifdef CONFIG_PROVE_RCU
904 
905 /*
906  * Early boot self test parameters, one for each flavor
907  */
908 static bool rcu_self_test;
909 static bool rcu_self_test_bh;
910 static bool rcu_self_test_sched;
911 
912 module_param(rcu_self_test, bool, 0444);
913 module_param(rcu_self_test_bh, bool, 0444);
914 module_param(rcu_self_test_sched, bool, 0444);
915 
916 static int rcu_self_test_counter;
917 
918 static void test_callback(struct rcu_head *r)
919 {
920         rcu_self_test_counter++;
921         pr_info("RCU test callback executed %d\n", rcu_self_test_counter);
922 }
923 
924 static void early_boot_test_call_rcu(void)
925 {
926         static struct rcu_head head;
927 
928         call_rcu(&head, test_callback);
929 }
930 
931 static void early_boot_test_call_rcu_bh(void)
932 {
933         static struct rcu_head head;
934 
935         call_rcu_bh(&head, test_callback);
936 }
937 
938 static void early_boot_test_call_rcu_sched(void)
939 {
940         static struct rcu_head head;
941 
942         call_rcu_sched(&head, test_callback);
943 }
944 
945 void rcu_early_boot_tests(void)
946 {
947         pr_info("Running RCU self tests\n");
948 
949         if (rcu_self_test)
950                 early_boot_test_call_rcu();
951         if (rcu_self_test_bh)
952                 early_boot_test_call_rcu_bh();
953         if (rcu_self_test_sched)
954                 early_boot_test_call_rcu_sched();
955         rcu_test_sync_prims();
956 }
957 
958 static int rcu_verify_early_boot_tests(void)
959 {
960         int ret = 0;
961         int early_boot_test_counter = 0;
962 
963         if (rcu_self_test) {
964                 early_boot_test_counter++;
965                 rcu_barrier();
966         }
967         if (rcu_self_test_bh) {
968                 early_boot_test_counter++;
969                 rcu_barrier_bh();
970         }
971         if (rcu_self_test_sched) {
972                 early_boot_test_counter++;
973                 rcu_barrier_sched();
974         }
975 
976         if (rcu_self_test_counter != early_boot_test_counter) {
977                 WARN_ON(1);
978                 ret = -1;
979         }
980 
981         return ret;
982 }
983 late_initcall(rcu_verify_early_boot_tests);
984 #else
985 void rcu_early_boot_tests(void) {}
986 #endif /* CONFIG_PROVE_RCU */
987 
988 #ifndef CONFIG_TINY_RCU
989 
990 /*
991  * Print any significant non-default boot-time settings.
992  */
993 void __init rcupdate_announce_bootup_oddness(void)
994 {
995         if (rcu_normal)
996                 pr_info("\tNo expedited grace period (rcu_normal).\n");
997         else if (rcu_normal_after_boot)
998                 pr_info("\tNo expedited grace period (rcu_normal_after_boot).\n");
999         else if (rcu_expedited)
1000                 pr_info("\tAll grace periods are expedited (rcu_expedited).\n");
1001         if (rcu_cpu_stall_suppress)
1002                 pr_info("\tRCU CPU stall warnings suppressed (rcu_cpu_stall_suppress).\n");
1003         if (rcu_cpu_stall_timeout != CONFIG_RCU_CPU_STALL_TIMEOUT)
1004                 pr_info("\tRCU CPU stall warnings timeout set to %d (rcu_cpu_stall_timeout).\n", rcu_cpu_stall_timeout);
1005         rcu_tasks_bootup_oddness();
1006 }
1007 
1008 #endif /* #ifndef CONFIG_TINY_RCU */
1009 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp