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Ingo Molnar23f78d4a2006-06-27 02:54:53 -07001/*
2 * RT-Mutexes: simple blocking mutual exclusion locks with PI support
3 *
4 * started by Ingo Molnar and Thomas Gleixner.
5 *
6 * Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
7 * Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
8 * Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
9 * Copyright (C) 2006 Esben Nielsen
Steven Rostedtd07fe822006-07-30 03:04:03 -070010 *
11 * See Documentation/rt-mutex-design.txt for details.
Ingo Molnar23f78d4a2006-06-27 02:54:53 -070012 */
13#include <linux/spinlock.h>
14#include <linux/module.h>
15#include <linux/sched.h>
16#include <linux/timer.h>
17
18#include "rtmutex_common.h"
19
Ingo Molnar23f78d4a2006-06-27 02:54:53 -070020/*
21 * lock->owner state tracking:
22 *
23 * lock->owner holds the task_struct pointer of the owner. Bit 0 and 1
24 * are used to keep track of the "owner is pending" and "lock has
25 * waiters" state.
26 *
27 * owner bit1 bit0
28 * NULL 0 0 lock is free (fast acquire possible)
29 * NULL 0 1 invalid state
30 * NULL 1 0 Transitional State*
31 * NULL 1 1 invalid state
32 * taskpointer 0 0 lock is held (fast release possible)
33 * taskpointer 0 1 task is pending owner
34 * taskpointer 1 0 lock is held and has waiters
35 * taskpointer 1 1 task is pending owner and lock has more waiters
36 *
37 * Pending ownership is assigned to the top (highest priority)
38 * waiter of the lock, when the lock is released. The thread is woken
39 * up and can now take the lock. Until the lock is taken (bit 0
40 * cleared) a competing higher priority thread can steal the lock
41 * which puts the woken up thread back on the waiters list.
42 *
43 * The fast atomic compare exchange based acquire and release is only
44 * possible when bit 0 and 1 of lock->owner are 0.
45 *
46 * (*) There's a small time where the owner can be NULL and the
47 * "lock has waiters" bit is set. This can happen when grabbing the lock.
48 * To prevent a cmpxchg of the owner releasing the lock, we need to set this
49 * bit before looking at the lock, hence the reason this is a transitional
50 * state.
51 */
52
Thomas Gleixnerbd197232007-06-17 21:11:10 +020053static void
Ingo Molnar23f78d4a2006-06-27 02:54:53 -070054rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner,
55 unsigned long mask)
56{
57 unsigned long val = (unsigned long)owner | mask;
58
59 if (rt_mutex_has_waiters(lock))
60 val |= RT_MUTEX_HAS_WAITERS;
61
62 lock->owner = (struct task_struct *)val;
63}
64
65static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
66{
67 lock->owner = (struct task_struct *)
68 ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
69}
70
71static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
72{
73 if (!rt_mutex_has_waiters(lock))
74 clear_rt_mutex_waiters(lock);
75}
76
77/*
Thomas Gleixnerbd197232007-06-17 21:11:10 +020078 * We can speed up the acquire/release, if the architecture
79 * supports cmpxchg and if there's no debugging state to be set up
80 */
81#if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
82# define rt_mutex_cmpxchg(l,c,n) (cmpxchg(&l->owner, c, n) == c)
83static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
84{
85 unsigned long owner, *p = (unsigned long *) &lock->owner;
86
87 do {
88 owner = *p;
89 } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
90}
91#else
92# define rt_mutex_cmpxchg(l,c,n) (0)
93static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
94{
95 lock->owner = (struct task_struct *)
96 ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
97}
98#endif
99
100/*
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700101 * Calculate task priority from the waiter list priority
102 *
103 * Return task->normal_prio when the waiter list is empty or when
104 * the waiter is not allowed to do priority boosting
105 */
106int rt_mutex_getprio(struct task_struct *task)
107{
108 if (likely(!task_has_pi_waiters(task)))
109 return task->normal_prio;
110
111 return min(task_top_pi_waiter(task)->pi_list_entry.prio,
112 task->normal_prio);
113}
114
115/*
116 * Adjust the priority of a task, after its pi_waiters got modified.
117 *
118 * This can be both boosting and unboosting. task->pi_lock must be held.
119 */
Thomas Gleixnerbd197232007-06-17 21:11:10 +0200120static void __rt_mutex_adjust_prio(struct task_struct *task)
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700121{
122 int prio = rt_mutex_getprio(task);
123
124 if (task->prio != prio)
125 rt_mutex_setprio(task, prio);
126}
127
128/*
129 * Adjust task priority (undo boosting). Called from the exit path of
130 * rt_mutex_slowunlock() and rt_mutex_slowlock().
131 *
132 * (Note: We do this outside of the protection of lock->wait_lock to
133 * allow the lock to be taken while or before we readjust the priority
134 * of task. We do not use the spin_xx_mutex() variants here as we are
135 * outside of the debug path.)
136 */
137static void rt_mutex_adjust_prio(struct task_struct *task)
138{
139 unsigned long flags;
140
141 spin_lock_irqsave(&task->pi_lock, flags);
142 __rt_mutex_adjust_prio(task);
143 spin_unlock_irqrestore(&task->pi_lock, flags);
144}
145
146/*
147 * Max number of times we'll walk the boosting chain:
148 */
149int max_lock_depth = 1024;
150
151/*
152 * Adjust the priority chain. Also used for deadlock detection.
153 * Decreases task's usage by one - may thus free the task.
154 * Returns 0 or -EDEADLK.
155 */
Thomas Gleixnerbd197232007-06-17 21:11:10 +0200156static int rt_mutex_adjust_prio_chain(struct task_struct *task,
157 int deadlock_detect,
158 struct rt_mutex *orig_lock,
159 struct rt_mutex_waiter *orig_waiter,
160 struct task_struct *top_task)
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700161{
162 struct rt_mutex *lock;
163 struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
164 int detect_deadlock, ret = 0, depth = 0;
165 unsigned long flags;
166
167 detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
168 deadlock_detect);
169
170 /*
171 * The (de)boosting is a step by step approach with a lot of
172 * pitfalls. We want this to be preemptible and we want hold a
173 * maximum of two locks per step. So we have to check
174 * carefully whether things change under us.
175 */
176 again:
177 if (++depth > max_lock_depth) {
178 static int prev_max;
179
180 /*
181 * Print this only once. If the admin changes the limit,
182 * print a new message when reaching the limit again.
183 */
184 if (prev_max != max_lock_depth) {
185 prev_max = max_lock_depth;
186 printk(KERN_WARNING "Maximum lock depth %d reached "
187 "task: %s (%d)\n", max_lock_depth,
Pavel Emelyanovba25f9d2007-10-18 23:40:40 -0700188 top_task->comm, task_pid_nr(top_task));
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700189 }
190 put_task_struct(task);
191
192 return deadlock_detect ? -EDEADLK : 0;
193 }
194 retry:
195 /*
196 * Task can not go away as we did a get_task() before !
197 */
198 spin_lock_irqsave(&task->pi_lock, flags);
199
200 waiter = task->pi_blocked_on;
201 /*
202 * Check whether the end of the boosting chain has been
203 * reached or the state of the chain has changed while we
204 * dropped the locks.
205 */
206 if (!waiter || !waiter->task)
207 goto out_unlock_pi;
208
Thomas Gleixner1a539a82007-06-08 13:46:58 -0700209 /*
210 * Check the orig_waiter state. After we dropped the locks,
211 * the previous owner of the lock might have released the lock
212 * and made us the pending owner:
213 */
214 if (orig_waiter && !orig_waiter->task)
215 goto out_unlock_pi;
216
217 /*
218 * Drop out, when the task has no waiters. Note,
219 * top_waiter can be NULL, when we are in the deboosting
220 * mode!
221 */
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700222 if (top_waiter && (!task_has_pi_waiters(task) ||
223 top_waiter != task_top_pi_waiter(task)))
224 goto out_unlock_pi;
225
226 /*
227 * When deadlock detection is off then we check, if further
228 * priority adjustment is necessary.
229 */
230 if (!detect_deadlock && waiter->list_entry.prio == task->prio)
231 goto out_unlock_pi;
232
233 lock = waiter->lock;
234 if (!spin_trylock(&lock->wait_lock)) {
235 spin_unlock_irqrestore(&task->pi_lock, flags);
236 cpu_relax();
237 goto retry;
238 }
239
240 /* Deadlock detection */
Thomas Gleixner95e02ca2006-06-27 02:55:02 -0700241 if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700242 debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
243 spin_unlock(&lock->wait_lock);
244 ret = deadlock_detect ? -EDEADLK : 0;
245 goto out_unlock_pi;
246 }
247
248 top_waiter = rt_mutex_top_waiter(lock);
249
250 /* Requeue the waiter */
251 plist_del(&waiter->list_entry, &lock->wait_list);
252 waiter->list_entry.prio = task->prio;
253 plist_add(&waiter->list_entry, &lock->wait_list);
254
255 /* Release the task */
256 spin_unlock_irqrestore(&task->pi_lock, flags);
257 put_task_struct(task);
258
259 /* Grab the next task */
260 task = rt_mutex_owner(lock);
Steven Rostedtdb630632006-09-29 01:59:44 -0700261 get_task_struct(task);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700262 spin_lock_irqsave(&task->pi_lock, flags);
263
264 if (waiter == rt_mutex_top_waiter(lock)) {
265 /* Boost the owner */
266 plist_del(&top_waiter->pi_list_entry, &task->pi_waiters);
267 waiter->pi_list_entry.prio = waiter->list_entry.prio;
268 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
269 __rt_mutex_adjust_prio(task);
270
271 } else if (top_waiter == waiter) {
272 /* Deboost the owner */
273 plist_del(&waiter->pi_list_entry, &task->pi_waiters);
274 waiter = rt_mutex_top_waiter(lock);
275 waiter->pi_list_entry.prio = waiter->list_entry.prio;
276 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
277 __rt_mutex_adjust_prio(task);
278 }
279
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700280 spin_unlock_irqrestore(&task->pi_lock, flags);
281
282 top_waiter = rt_mutex_top_waiter(lock);
283 spin_unlock(&lock->wait_lock);
284
285 if (!detect_deadlock && waiter != top_waiter)
286 goto out_put_task;
287
288 goto again;
289
290 out_unlock_pi:
291 spin_unlock_irqrestore(&task->pi_lock, flags);
292 out_put_task:
293 put_task_struct(task);
Ingo Molnar36c8b582006-07-03 00:25:41 -0700294
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700295 return ret;
296}
297
298/*
299 * Optimization: check if we can steal the lock from the
300 * assigned pending owner [which might not have taken the
301 * lock yet]:
302 */
303static inline int try_to_steal_lock(struct rt_mutex *lock)
304{
305 struct task_struct *pendowner = rt_mutex_owner(lock);
306 struct rt_mutex_waiter *next;
307 unsigned long flags;
308
309 if (!rt_mutex_owner_pending(lock))
310 return 0;
311
312 if (pendowner == current)
313 return 1;
314
315 spin_lock_irqsave(&pendowner->pi_lock, flags);
316 if (current->prio >= pendowner->prio) {
317 spin_unlock_irqrestore(&pendowner->pi_lock, flags);
318 return 0;
319 }
320
321 /*
322 * Check if a waiter is enqueued on the pending owners
323 * pi_waiters list. Remove it and readjust pending owners
324 * priority.
325 */
326 if (likely(!rt_mutex_has_waiters(lock))) {
327 spin_unlock_irqrestore(&pendowner->pi_lock, flags);
328 return 1;
329 }
330
331 /* No chain handling, pending owner is not blocked on anything: */
332 next = rt_mutex_top_waiter(lock);
333 plist_del(&next->pi_list_entry, &pendowner->pi_waiters);
334 __rt_mutex_adjust_prio(pendowner);
335 spin_unlock_irqrestore(&pendowner->pi_lock, flags);
336
337 /*
338 * We are going to steal the lock and a waiter was
339 * enqueued on the pending owners pi_waiters queue. So
340 * we have to enqueue this waiter into
341 * current->pi_waiters list. This covers the case,
342 * where current is boosted because it holds another
343 * lock and gets unboosted because the booster is
344 * interrupted, so we would delay a waiter with higher
345 * priority as current->normal_prio.
346 *
347 * Note: in the rare case of a SCHED_OTHER task changing
348 * its priority and thus stealing the lock, next->task
349 * might be current:
350 */
351 if (likely(next->task != current)) {
352 spin_lock_irqsave(&current->pi_lock, flags);
353 plist_add(&next->pi_list_entry, &current->pi_waiters);
354 __rt_mutex_adjust_prio(current);
355 spin_unlock_irqrestore(&current->pi_lock, flags);
356 }
357 return 1;
358}
359
360/*
361 * Try to take an rt-mutex
362 *
363 * This fails
364 * - when the lock has a real owner
365 * - when a different pending owner exists and has higher priority than current
366 *
367 * Must be called with lock->wait_lock held.
368 */
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700369static int try_to_take_rt_mutex(struct rt_mutex *lock)
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700370{
371 /*
372 * We have to be careful here if the atomic speedups are
373 * enabled, such that, when
374 * - no other waiter is on the lock
375 * - the lock has been released since we did the cmpxchg
376 * the lock can be released or taken while we are doing the
377 * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
378 *
379 * The atomic acquire/release aware variant of
380 * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
381 * the WAITERS bit, the atomic release / acquire can not
382 * happen anymore and lock->wait_lock protects us from the
383 * non-atomic case.
384 *
385 * Note, that this might set lock->owner =
386 * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
387 * any more. This is fixed up when we take the ownership.
388 * This is the transitional state explained at the top of this file.
389 */
390 mark_rt_mutex_waiters(lock);
391
392 if (rt_mutex_owner(lock) && !try_to_steal_lock(lock))
393 return 0;
394
395 /* We got the lock. */
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700396 debug_rt_mutex_lock(lock);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700397
398 rt_mutex_set_owner(lock, current, 0);
399
400 rt_mutex_deadlock_account_lock(lock, current);
401
402 return 1;
403}
404
405/*
406 * Task blocks on lock.
407 *
408 * Prepare waiter and propagate pi chain
409 *
410 * This must be called with lock->wait_lock held.
411 */
412static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
413 struct rt_mutex_waiter *waiter,
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700414 int detect_deadlock)
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700415{
Ingo Molnar36c8b582006-07-03 00:25:41 -0700416 struct task_struct *owner = rt_mutex_owner(lock);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700417 struct rt_mutex_waiter *top_waiter = waiter;
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700418 unsigned long flags;
Steven Rostedtdb630632006-09-29 01:59:44 -0700419 int chain_walk = 0, res;
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700420
421 spin_lock_irqsave(&current->pi_lock, flags);
422 __rt_mutex_adjust_prio(current);
423 waiter->task = current;
424 waiter->lock = lock;
425 plist_node_init(&waiter->list_entry, current->prio);
426 plist_node_init(&waiter->pi_list_entry, current->prio);
427
428 /* Get the top priority waiter on the lock */
429 if (rt_mutex_has_waiters(lock))
430 top_waiter = rt_mutex_top_waiter(lock);
431 plist_add(&waiter->list_entry, &lock->wait_list);
432
433 current->pi_blocked_on = waiter;
434
435 spin_unlock_irqrestore(&current->pi_lock, flags);
436
437 if (waiter == rt_mutex_top_waiter(lock)) {
438 spin_lock_irqsave(&owner->pi_lock, flags);
439 plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
440 plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
441
442 __rt_mutex_adjust_prio(owner);
Steven Rostedtdb630632006-09-29 01:59:44 -0700443 if (owner->pi_blocked_on)
444 chain_walk = 1;
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700445 spin_unlock_irqrestore(&owner->pi_lock, flags);
446 }
Steven Rostedtdb630632006-09-29 01:59:44 -0700447 else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock))
448 chain_walk = 1;
449
450 if (!chain_walk)
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700451 return 0;
452
Steven Rostedtdb630632006-09-29 01:59:44 -0700453 /*
454 * The owner can't disappear while holding a lock,
455 * so the owner struct is protected by wait_lock.
456 * Gets dropped in rt_mutex_adjust_prio_chain()!
457 */
458 get_task_struct(owner);
459
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700460 spin_unlock(&lock->wait_lock);
461
Thomas Gleixner95e02ca2006-06-27 02:55:02 -0700462 res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700463 current);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700464
465 spin_lock(&lock->wait_lock);
466
467 return res;
468}
469
470/*
471 * Wake up the next waiter on the lock.
472 *
473 * Remove the top waiter from the current tasks waiter list and from
474 * the lock waiter list. Set it as pending owner. Then wake it up.
475 *
476 * Called with lock->wait_lock held.
477 */
478static void wakeup_next_waiter(struct rt_mutex *lock)
479{
480 struct rt_mutex_waiter *waiter;
481 struct task_struct *pendowner;
482 unsigned long flags;
483
484 spin_lock_irqsave(&current->pi_lock, flags);
485
486 waiter = rt_mutex_top_waiter(lock);
487 plist_del(&waiter->list_entry, &lock->wait_list);
488
489 /*
490 * Remove it from current->pi_waiters. We do not adjust a
491 * possible priority boost right now. We execute wakeup in the
492 * boosted mode and go back to normal after releasing
493 * lock->wait_lock.
494 */
495 plist_del(&waiter->pi_list_entry, &current->pi_waiters);
496 pendowner = waiter->task;
497 waiter->task = NULL;
498
499 rt_mutex_set_owner(lock, pendowner, RT_MUTEX_OWNER_PENDING);
500
501 spin_unlock_irqrestore(&current->pi_lock, flags);
502
503 /*
504 * Clear the pi_blocked_on variable and enqueue a possible
505 * waiter into the pi_waiters list of the pending owner. This
506 * prevents that in case the pending owner gets unboosted a
507 * waiter with higher priority than pending-owner->normal_prio
508 * is blocked on the unboosted (pending) owner.
509 */
510 spin_lock_irqsave(&pendowner->pi_lock, flags);
511
512 WARN_ON(!pendowner->pi_blocked_on);
513 WARN_ON(pendowner->pi_blocked_on != waiter);
514 WARN_ON(pendowner->pi_blocked_on->lock != lock);
515
516 pendowner->pi_blocked_on = NULL;
517
518 if (rt_mutex_has_waiters(lock)) {
519 struct rt_mutex_waiter *next;
520
521 next = rt_mutex_top_waiter(lock);
522 plist_add(&next->pi_list_entry, &pendowner->pi_waiters);
523 }
524 spin_unlock_irqrestore(&pendowner->pi_lock, flags);
525
526 wake_up_process(pendowner);
527}
528
529/*
530 * Remove a waiter from a lock
531 *
532 * Must be called with lock->wait_lock held
533 */
Thomas Gleixnerbd197232007-06-17 21:11:10 +0200534static void remove_waiter(struct rt_mutex *lock,
535 struct rt_mutex_waiter *waiter)
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700536{
537 int first = (waiter == rt_mutex_top_waiter(lock));
Ingo Molnar36c8b582006-07-03 00:25:41 -0700538 struct task_struct *owner = rt_mutex_owner(lock);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700539 unsigned long flags;
Steven Rostedtdb630632006-09-29 01:59:44 -0700540 int chain_walk = 0;
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700541
542 spin_lock_irqsave(&current->pi_lock, flags);
543 plist_del(&waiter->list_entry, &lock->wait_list);
544 waiter->task = NULL;
545 current->pi_blocked_on = NULL;
546 spin_unlock_irqrestore(&current->pi_lock, flags);
547
548 if (first && owner != current) {
549
550 spin_lock_irqsave(&owner->pi_lock, flags);
551
552 plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
553
554 if (rt_mutex_has_waiters(lock)) {
555 struct rt_mutex_waiter *next;
556
557 next = rt_mutex_top_waiter(lock);
558 plist_add(&next->pi_list_entry, &owner->pi_waiters);
559 }
560 __rt_mutex_adjust_prio(owner);
561
Steven Rostedtdb630632006-09-29 01:59:44 -0700562 if (owner->pi_blocked_on)
563 chain_walk = 1;
564
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700565 spin_unlock_irqrestore(&owner->pi_lock, flags);
566 }
567
568 WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
569
Steven Rostedtdb630632006-09-29 01:59:44 -0700570 if (!chain_walk)
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700571 return;
572
Steven Rostedtdb630632006-09-29 01:59:44 -0700573 /* gets dropped in rt_mutex_adjust_prio_chain()! */
574 get_task_struct(owner);
575
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700576 spin_unlock(&lock->wait_lock);
577
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700578 rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700579
580 spin_lock(&lock->wait_lock);
581}
582
583/*
Thomas Gleixner95e02ca2006-06-27 02:55:02 -0700584 * Recheck the pi chain, in case we got a priority setting
585 *
586 * Called from sched_setscheduler
587 */
588void rt_mutex_adjust_pi(struct task_struct *task)
589{
590 struct rt_mutex_waiter *waiter;
591 unsigned long flags;
592
593 spin_lock_irqsave(&task->pi_lock, flags);
594
595 waiter = task->pi_blocked_on;
596 if (!waiter || waiter->list_entry.prio == task->prio) {
597 spin_unlock_irqrestore(&task->pi_lock, flags);
598 return;
599 }
600
Thomas Gleixner95e02ca2006-06-27 02:55:02 -0700601 spin_unlock_irqrestore(&task->pi_lock, flags);
602
Steven Rostedtdb630632006-09-29 01:59:44 -0700603 /* gets dropped in rt_mutex_adjust_prio_chain()! */
604 get_task_struct(task);
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700605 rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
Thomas Gleixner95e02ca2006-06-27 02:55:02 -0700606}
607
608/*
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700609 * Slow path lock function:
610 */
611static int __sched
612rt_mutex_slowlock(struct rt_mutex *lock, int state,
613 struct hrtimer_sleeper *timeout,
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700614 int detect_deadlock)
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700615{
616 struct rt_mutex_waiter waiter;
617 int ret = 0;
618
619 debug_rt_mutex_init_waiter(&waiter);
620 waiter.task = NULL;
621
622 spin_lock(&lock->wait_lock);
623
624 /* Try to acquire the lock again: */
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700625 if (try_to_take_rt_mutex(lock)) {
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700626 spin_unlock(&lock->wait_lock);
627 return 0;
628 }
629
630 set_current_state(state);
631
632 /* Setup the timer, when timeout != NULL */
Peter Zijlstra720a2592008-02-13 15:45:36 +0100633 if (unlikely(timeout)) {
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700634 hrtimer_start(&timeout->timer, timeout->timer.expires,
Thomas Gleixnerc9cb2e32007-02-16 01:27:49 -0800635 HRTIMER_MODE_ABS);
Peter Zijlstra720a2592008-02-13 15:45:36 +0100636 if (!hrtimer_active(&timeout->timer))
637 timeout->task = NULL;
638 }
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700639
640 for (;;) {
641 /* Try to acquire the lock: */
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700642 if (try_to_take_rt_mutex(lock))
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700643 break;
644
645 /*
646 * TASK_INTERRUPTIBLE checks for signals and
647 * timeout. Ignored otherwise.
648 */
649 if (unlikely(state == TASK_INTERRUPTIBLE)) {
650 /* Signal pending? */
651 if (signal_pending(current))
652 ret = -EINTR;
653 if (timeout && !timeout->task)
654 ret = -ETIMEDOUT;
655 if (ret)
656 break;
657 }
658
659 /*
660 * waiter.task is NULL the first time we come here and
661 * when we have been woken up by the previous owner
662 * but the lock got stolen by a higher prio task.
663 */
664 if (!waiter.task) {
665 ret = task_blocks_on_rt_mutex(lock, &waiter,
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700666 detect_deadlock);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700667 /*
668 * If we got woken up by the owner then start loop
669 * all over without going into schedule to try
670 * to get the lock now:
671 */
Thomas Gleixnerc0d1d2b2007-06-08 13:46:57 -0700672 if (unlikely(!waiter.task)) {
673 /*
674 * Reset the return value. We might
675 * have returned with -EDEADLK and the
676 * owner released the lock while we
677 * were walking the pi chain.
678 */
679 ret = 0;
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700680 continue;
Thomas Gleixnerc0d1d2b2007-06-08 13:46:57 -0700681 }
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700682 if (unlikely(ret))
683 break;
684 }
Thomas Gleixner95e02ca2006-06-27 02:55:02 -0700685
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700686 spin_unlock(&lock->wait_lock);
687
688 debug_rt_mutex_print_deadlock(&waiter);
689
Thomas Gleixner61a87122006-06-27 02:54:56 -0700690 if (waiter.task)
691 schedule_rt_mutex(lock);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700692
693 spin_lock(&lock->wait_lock);
694 set_current_state(state);
695 }
696
697 set_current_state(TASK_RUNNING);
698
699 if (unlikely(waiter.task))
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700700 remove_waiter(lock, &waiter);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700701
702 /*
703 * try_to_take_rt_mutex() sets the waiter bit
704 * unconditionally. We might have to fix that up.
705 */
706 fixup_rt_mutex_waiters(lock);
707
708 spin_unlock(&lock->wait_lock);
709
710 /* Remove pending timer: */
711 if (unlikely(timeout))
712 hrtimer_cancel(&timeout->timer);
713
714 /*
715 * Readjust priority, when we did not get the lock. We might
716 * have been the pending owner and boosted. Since we did not
717 * take the lock, the PI boost has to go.
718 */
719 if (unlikely(ret))
720 rt_mutex_adjust_prio(current);
721
722 debug_rt_mutex_free_waiter(&waiter);
723
724 return ret;
725}
726
727/*
728 * Slow path try-lock function:
729 */
730static inline int
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700731rt_mutex_slowtrylock(struct rt_mutex *lock)
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700732{
733 int ret = 0;
734
735 spin_lock(&lock->wait_lock);
736
737 if (likely(rt_mutex_owner(lock) != current)) {
738
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700739 ret = try_to_take_rt_mutex(lock);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700740 /*
741 * try_to_take_rt_mutex() sets the lock waiters
742 * bit unconditionally. Clean this up.
743 */
744 fixup_rt_mutex_waiters(lock);
745 }
746
747 spin_unlock(&lock->wait_lock);
748
749 return ret;
750}
751
752/*
753 * Slow path to release a rt-mutex:
754 */
755static void __sched
756rt_mutex_slowunlock(struct rt_mutex *lock)
757{
758 spin_lock(&lock->wait_lock);
759
760 debug_rt_mutex_unlock(lock);
761
762 rt_mutex_deadlock_account_unlock(current);
763
764 if (!rt_mutex_has_waiters(lock)) {
765 lock->owner = NULL;
766 spin_unlock(&lock->wait_lock);
767 return;
768 }
769
770 wakeup_next_waiter(lock);
771
772 spin_unlock(&lock->wait_lock);
773
774 /* Undo pi boosting if necessary: */
775 rt_mutex_adjust_prio(current);
776}
777
778/*
779 * debug aware fast / slowpath lock,trylock,unlock
780 *
781 * The atomic acquire/release ops are compiled away, when either the
782 * architecture does not support cmpxchg or when debugging is enabled.
783 */
784static inline int
785rt_mutex_fastlock(struct rt_mutex *lock, int state,
786 int detect_deadlock,
787 int (*slowfn)(struct rt_mutex *lock, int state,
788 struct hrtimer_sleeper *timeout,
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700789 int detect_deadlock))
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700790{
791 if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
792 rt_mutex_deadlock_account_lock(lock, current);
793 return 0;
794 } else
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700795 return slowfn(lock, state, NULL, detect_deadlock);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700796}
797
798static inline int
799rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
800 struct hrtimer_sleeper *timeout, int detect_deadlock,
801 int (*slowfn)(struct rt_mutex *lock, int state,
802 struct hrtimer_sleeper *timeout,
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700803 int detect_deadlock))
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700804{
805 if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
806 rt_mutex_deadlock_account_lock(lock, current);
807 return 0;
808 } else
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700809 return slowfn(lock, state, timeout, detect_deadlock);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700810}
811
812static inline int
813rt_mutex_fasttrylock(struct rt_mutex *lock,
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700814 int (*slowfn)(struct rt_mutex *lock))
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700815{
816 if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
817 rt_mutex_deadlock_account_lock(lock, current);
818 return 1;
819 }
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700820 return slowfn(lock);
Ingo Molnar23f78d4a2006-06-27 02:54:53 -0700821}
822
823static inline void
824rt_mutex_fastunlock(struct rt_mutex *lock,
825 void (*slowfn)(struct rt_mutex *lock))
826{
827 if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
828 rt_mutex_deadlock_account_unlock(current);
829 else
830 slowfn(lock);
831}
832
833/**
834 * rt_mutex_lock - lock a rt_mutex
835 *
836 * @lock: the rt_mutex to be locked
837 */
838void __sched rt_mutex_lock(struct rt_mutex *lock)
839{
840 might_sleep();
841
842 rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
843}
844EXPORT_SYMBOL_GPL(rt_mutex_lock);
845
846/**
847 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
848 *
849 * @lock: the rt_mutex to be locked
850 * @detect_deadlock: deadlock detection on/off
851 *
852 * Returns:
853 * 0 on success
854 * -EINTR when interrupted by a signal
855 * -EDEADLK when the lock would deadlock (when deadlock detection is on)
856 */
857int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
858 int detect_deadlock)
859{
860 might_sleep();
861
862 return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
863 detect_deadlock, rt_mutex_slowlock);
864}
865EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
866
867/**
868 * rt_mutex_lock_interruptible_ktime - lock a rt_mutex interruptible
869 * the timeout structure is provided
870 * by the caller
871 *
872 * @lock: the rt_mutex to be locked
873 * @timeout: timeout structure or NULL (no timeout)
874 * @detect_deadlock: deadlock detection on/off
875 *
876 * Returns:
877 * 0 on success
878 * -EINTR when interrupted by a signal
879 * -ETIMEOUT when the timeout expired
880 * -EDEADLK when the lock would deadlock (when deadlock detection is on)
881 */
882int
883rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
884 int detect_deadlock)
885{
886 might_sleep();
887
888 return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
889 detect_deadlock, rt_mutex_slowlock);
890}
891EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
892
893/**
894 * rt_mutex_trylock - try to lock a rt_mutex
895 *
896 * @lock: the rt_mutex to be locked
897 *
898 * Returns 1 on success and 0 on contention
899 */
900int __sched rt_mutex_trylock(struct rt_mutex *lock)
901{
902 return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
903}
904EXPORT_SYMBOL_GPL(rt_mutex_trylock);
905
906/**
907 * rt_mutex_unlock - unlock a rt_mutex
908 *
909 * @lock: the rt_mutex to be unlocked
910 */
911void __sched rt_mutex_unlock(struct rt_mutex *lock)
912{
913 rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
914}
915EXPORT_SYMBOL_GPL(rt_mutex_unlock);
916
917/***
918 * rt_mutex_destroy - mark a mutex unusable
919 * @lock: the mutex to be destroyed
920 *
921 * This function marks the mutex uninitialized, and any subsequent
922 * use of the mutex is forbidden. The mutex must not be locked when
923 * this function is called.
924 */
925void rt_mutex_destroy(struct rt_mutex *lock)
926{
927 WARN_ON(rt_mutex_is_locked(lock));
928#ifdef CONFIG_DEBUG_RT_MUTEXES
929 lock->magic = NULL;
930#endif
931}
932
933EXPORT_SYMBOL_GPL(rt_mutex_destroy);
934
935/**
936 * __rt_mutex_init - initialize the rt lock
937 *
938 * @lock: the rt lock to be initialized
939 *
940 * Initialize the rt lock to unlocked state.
941 *
942 * Initializing of a locked rt lock is not allowed
943 */
944void __rt_mutex_init(struct rt_mutex *lock, const char *name)
945{
946 lock->owner = NULL;
947 spin_lock_init(&lock->wait_lock);
948 plist_head_init(&lock->wait_list, &lock->wait_lock);
949
950 debug_rt_mutex_init(lock, name);
951}
952EXPORT_SYMBOL_GPL(__rt_mutex_init);
Ingo Molnar0cdbee92006-06-27 02:54:57 -0700953
954/**
955 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
956 * proxy owner
957 *
958 * @lock: the rt_mutex to be locked
959 * @proxy_owner:the task to set as owner
960 *
961 * No locking. Caller has to do serializing itself
962 * Special API call for PI-futex support
963 */
964void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
965 struct task_struct *proxy_owner)
966{
967 __rt_mutex_init(lock, NULL);
Ingo Molnar9a11b49a2006-07-03 00:24:33 -0700968 debug_rt_mutex_proxy_lock(lock, proxy_owner);
Ingo Molnar0cdbee92006-06-27 02:54:57 -0700969 rt_mutex_set_owner(lock, proxy_owner, 0);
970 rt_mutex_deadlock_account_lock(lock, proxy_owner);
971}
972
973/**
974 * rt_mutex_proxy_unlock - release a lock on behalf of owner
975 *
976 * @lock: the rt_mutex to be locked
977 *
978 * No locking. Caller has to do serializing itself
979 * Special API call for PI-futex support
980 */
981void rt_mutex_proxy_unlock(struct rt_mutex *lock,
982 struct task_struct *proxy_owner)
983{
984 debug_rt_mutex_proxy_unlock(lock);
985 rt_mutex_set_owner(lock, NULL, 0);
986 rt_mutex_deadlock_account_unlock(proxy_owner);
987}
988
989/**
990 * rt_mutex_next_owner - return the next owner of the lock
991 *
992 * @lock: the rt lock query
993 *
994 * Returns the next owner of the lock or NULL
995 *
996 * Caller has to serialize against other accessors to the lock
997 * itself.
998 *
999 * Special API call for PI-futex support
1000 */
1001struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1002{
1003 if (!rt_mutex_has_waiters(lock))
1004 return NULL;
1005
1006 return rt_mutex_top_waiter(lock)->task;
1007}