[PATCH] pi-futex: rt mutex core
[linux-2.6.git] / kernel / rtmutex.c
1 /*
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
10  */
11 #include <linux/spinlock.h>
12 #include <linux/module.h>
13 #include <linux/sched.h>
14 #include <linux/timer.h>
15
16 #include "rtmutex_common.h"
17
18 #ifdef CONFIG_DEBUG_RT_MUTEXES
19 # include "rtmutex-debug.h"
20 #else
21 # include "rtmutex.h"
22 #endif
23
24 /*
25  * lock->owner state tracking:
26  *
27  * lock->owner holds the task_struct pointer of the owner. Bit 0 and 1
28  * are used to keep track of the "owner is pending" and "lock has
29  * waiters" state.
30  *
31  * owner        bit1    bit0
32  * NULL         0       0       lock is free (fast acquire possible)
33  * NULL         0       1       invalid state
34  * NULL         1       0       Transitional State*
35  * NULL         1       1       invalid state
36  * taskpointer  0       0       lock is held (fast release possible)
37  * taskpointer  0       1       task is pending owner
38  * taskpointer  1       0       lock is held and has waiters
39  * taskpointer  1       1       task is pending owner and lock has more waiters
40  *
41  * Pending ownership is assigned to the top (highest priority)
42  * waiter of the lock, when the lock is released. The thread is woken
43  * up and can now take the lock. Until the lock is taken (bit 0
44  * cleared) a competing higher priority thread can steal the lock
45  * which puts the woken up thread back on the waiters list.
46  *
47  * The fast atomic compare exchange based acquire and release is only
48  * possible when bit 0 and 1 of lock->owner are 0.
49  *
50  * (*) There's a small time where the owner can be NULL and the
51  * "lock has waiters" bit is set.  This can happen when grabbing the lock.
52  * To prevent a cmpxchg of the owner releasing the lock, we need to set this
53  * bit before looking at the lock, hence the reason this is a transitional
54  * state.
55  */
56
57 static void
58 rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner,
59                    unsigned long mask)
60 {
61         unsigned long val = (unsigned long)owner | mask;
62
63         if (rt_mutex_has_waiters(lock))
64                 val |= RT_MUTEX_HAS_WAITERS;
65
66         lock->owner = (struct task_struct *)val;
67 }
68
69 static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
70 {
71         lock->owner = (struct task_struct *)
72                         ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
73 }
74
75 static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
76 {
77         if (!rt_mutex_has_waiters(lock))
78                 clear_rt_mutex_waiters(lock);
79 }
80
81 /*
82  * We can speed up the acquire/release, if the architecture
83  * supports cmpxchg and if there's no debugging state to be set up
84  */
85 #if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
86 # define rt_mutex_cmpxchg(l,c,n)        (cmpxchg(&l->owner, c, n) == c)
87 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
88 {
89         unsigned long owner, *p = (unsigned long *) &lock->owner;
90
91         do {
92                 owner = *p;
93         } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
94 }
95 #else
96 # define rt_mutex_cmpxchg(l,c,n)        (0)
97 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
98 {
99         lock->owner = (struct task_struct *)
100                         ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
101 }
102 #endif
103
104 /*
105  * Calculate task priority from the waiter list priority
106  *
107  * Return task->normal_prio when the waiter list is empty or when
108  * the waiter is not allowed to do priority boosting
109  */
110 int rt_mutex_getprio(struct task_struct *task)
111 {
112         if (likely(!task_has_pi_waiters(task)))
113                 return task->normal_prio;
114
115         return min(task_top_pi_waiter(task)->pi_list_entry.prio,
116                    task->normal_prio);
117 }
118
119 /*
120  * Adjust the priority of a task, after its pi_waiters got modified.
121  *
122  * This can be both boosting and unboosting. task->pi_lock must be held.
123  */
124 static void __rt_mutex_adjust_prio(struct task_struct *task)
125 {
126         int prio = rt_mutex_getprio(task);
127
128         if (task->prio != prio)
129                 rt_mutex_setprio(task, prio);
130 }
131
132 /*
133  * Adjust task priority (undo boosting). Called from the exit path of
134  * rt_mutex_slowunlock() and rt_mutex_slowlock().
135  *
136  * (Note: We do this outside of the protection of lock->wait_lock to
137  * allow the lock to be taken while or before we readjust the priority
138  * of task. We do not use the spin_xx_mutex() variants here as we are
139  * outside of the debug path.)
140  */
141 static void rt_mutex_adjust_prio(struct task_struct *task)
142 {
143         unsigned long flags;
144
145         spin_lock_irqsave(&task->pi_lock, flags);
146         __rt_mutex_adjust_prio(task);
147         spin_unlock_irqrestore(&task->pi_lock, flags);
148 }
149
150 /*
151  * Max number of times we'll walk the boosting chain:
152  */
153 int max_lock_depth = 1024;
154
155 /*
156  * Adjust the priority chain. Also used for deadlock detection.
157  * Decreases task's usage by one - may thus free the task.
158  * Returns 0 or -EDEADLK.
159  */
160 static int rt_mutex_adjust_prio_chain(task_t *task,
161                                       int deadlock_detect,
162                                       struct rt_mutex *orig_lock,
163                                       struct rt_mutex_waiter *orig_waiter
164                                       __IP_DECL__)
165 {
166         struct rt_mutex *lock;
167         struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
168         int detect_deadlock, ret = 0, depth = 0;
169         unsigned long flags;
170
171         detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
172                                                          deadlock_detect);
173
174         /*
175          * The (de)boosting is a step by step approach with a lot of
176          * pitfalls. We want this to be preemptible and we want hold a
177          * maximum of two locks per step. So we have to check
178          * carefully whether things change under us.
179          */
180  again:
181         if (++depth > max_lock_depth) {
182                 static int prev_max;
183
184                 /*
185                  * Print this only once. If the admin changes the limit,
186                  * print a new message when reaching the limit again.
187                  */
188                 if (prev_max != max_lock_depth) {
189                         prev_max = max_lock_depth;
190                         printk(KERN_WARNING "Maximum lock depth %d reached "
191                                "task: %s (%d)\n", max_lock_depth,
192                                current->comm, current->pid);
193                 }
194                 put_task_struct(task);
195
196                 return deadlock_detect ? -EDEADLK : 0;
197         }
198  retry:
199         /*
200          * Task can not go away as we did a get_task() before !
201          */
202         spin_lock_irqsave(&task->pi_lock, flags);
203
204         waiter = task->pi_blocked_on;
205         /*
206          * Check whether the end of the boosting chain has been
207          * reached or the state of the chain has changed while we
208          * dropped the locks.
209          */
210         if (!waiter || !waiter->task)
211                 goto out_unlock_pi;
212
213         if (top_waiter && (!task_has_pi_waiters(task) ||
214                            top_waiter != task_top_pi_waiter(task)))
215                 goto out_unlock_pi;
216
217         /*
218          * When deadlock detection is off then we check, if further
219          * priority adjustment is necessary.
220          */
221         if (!detect_deadlock && waiter->list_entry.prio == task->prio)
222                 goto out_unlock_pi;
223
224         lock = waiter->lock;
225         if (!spin_trylock(&lock->wait_lock)) {
226                 spin_unlock_irqrestore(&task->pi_lock, flags);
227                 cpu_relax();
228                 goto retry;
229         }
230
231         /* Deadlock detection */
232         if (lock == orig_lock || rt_mutex_owner(lock) == current) {
233                 debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
234                 spin_unlock(&lock->wait_lock);
235                 ret = deadlock_detect ? -EDEADLK : 0;
236                 goto out_unlock_pi;
237         }
238
239         top_waiter = rt_mutex_top_waiter(lock);
240
241         /* Requeue the waiter */
242         plist_del(&waiter->list_entry, &lock->wait_list);
243         waiter->list_entry.prio = task->prio;
244         plist_add(&waiter->list_entry, &lock->wait_list);
245
246         /* Release the task */
247         spin_unlock_irqrestore(&task->pi_lock, flags);
248         put_task_struct(task);
249
250         /* Grab the next task */
251         task = rt_mutex_owner(lock);
252         spin_lock_irqsave(&task->pi_lock, flags);
253
254         if (waiter == rt_mutex_top_waiter(lock)) {
255                 /* Boost the owner */
256                 plist_del(&top_waiter->pi_list_entry, &task->pi_waiters);
257                 waiter->pi_list_entry.prio = waiter->list_entry.prio;
258                 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
259                 __rt_mutex_adjust_prio(task);
260
261         } else if (top_waiter == waiter) {
262                 /* Deboost the owner */
263                 plist_del(&waiter->pi_list_entry, &task->pi_waiters);
264                 waiter = rt_mutex_top_waiter(lock);
265                 waiter->pi_list_entry.prio = waiter->list_entry.prio;
266                 plist_add(&waiter->pi_list_entry, &task->pi_waiters);
267                 __rt_mutex_adjust_prio(task);
268         }
269
270         get_task_struct(task);
271         spin_unlock_irqrestore(&task->pi_lock, flags);
272
273         top_waiter = rt_mutex_top_waiter(lock);
274         spin_unlock(&lock->wait_lock);
275
276         if (!detect_deadlock && waiter != top_waiter)
277                 goto out_put_task;
278
279         goto again;
280
281  out_unlock_pi:
282         spin_unlock_irqrestore(&task->pi_lock, flags);
283  out_put_task:
284         put_task_struct(task);
285         return ret;
286 }
287
288 /*
289  * Optimization: check if we can steal the lock from the
290  * assigned pending owner [which might not have taken the
291  * lock yet]:
292  */
293 static inline int try_to_steal_lock(struct rt_mutex *lock)
294 {
295         struct task_struct *pendowner = rt_mutex_owner(lock);
296         struct rt_mutex_waiter *next;
297         unsigned long flags;
298
299         if (!rt_mutex_owner_pending(lock))
300                 return 0;
301
302         if (pendowner == current)
303                 return 1;
304
305         spin_lock_irqsave(&pendowner->pi_lock, flags);
306         if (current->prio >= pendowner->prio) {
307                 spin_unlock_irqrestore(&pendowner->pi_lock, flags);
308                 return 0;
309         }
310
311         /*
312          * Check if a waiter is enqueued on the pending owners
313          * pi_waiters list. Remove it and readjust pending owners
314          * priority.
315          */
316         if (likely(!rt_mutex_has_waiters(lock))) {
317                 spin_unlock_irqrestore(&pendowner->pi_lock, flags);
318                 return 1;
319         }
320
321         /* No chain handling, pending owner is not blocked on anything: */
322         next = rt_mutex_top_waiter(lock);
323         plist_del(&next->pi_list_entry, &pendowner->pi_waiters);
324         __rt_mutex_adjust_prio(pendowner);
325         spin_unlock_irqrestore(&pendowner->pi_lock, flags);
326
327         /*
328          * We are going to steal the lock and a waiter was
329          * enqueued on the pending owners pi_waiters queue. So
330          * we have to enqueue this waiter into
331          * current->pi_waiters list. This covers the case,
332          * where current is boosted because it holds another
333          * lock and gets unboosted because the booster is
334          * interrupted, so we would delay a waiter with higher
335          * priority as current->normal_prio.
336          *
337          * Note: in the rare case of a SCHED_OTHER task changing
338          * its priority and thus stealing the lock, next->task
339          * might be current:
340          */
341         if (likely(next->task != current)) {
342                 spin_lock_irqsave(&current->pi_lock, flags);
343                 plist_add(&next->pi_list_entry, &current->pi_waiters);
344                 __rt_mutex_adjust_prio(current);
345                 spin_unlock_irqrestore(&current->pi_lock, flags);
346         }
347         return 1;
348 }
349
350 /*
351  * Try to take an rt-mutex
352  *
353  * This fails
354  * - when the lock has a real owner
355  * - when a different pending owner exists and has higher priority than current
356  *
357  * Must be called with lock->wait_lock held.
358  */
359 static int try_to_take_rt_mutex(struct rt_mutex *lock __IP_DECL__)
360 {
361         /*
362          * We have to be careful here if the atomic speedups are
363          * enabled, such that, when
364          *  - no other waiter is on the lock
365          *  - the lock has been released since we did the cmpxchg
366          * the lock can be released or taken while we are doing the
367          * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
368          *
369          * The atomic acquire/release aware variant of
370          * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
371          * the WAITERS bit, the atomic release / acquire can not
372          * happen anymore and lock->wait_lock protects us from the
373          * non-atomic case.
374          *
375          * Note, that this might set lock->owner =
376          * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
377          * any more. This is fixed up when we take the ownership.
378          * This is the transitional state explained at the top of this file.
379          */
380         mark_rt_mutex_waiters(lock);
381
382         if (rt_mutex_owner(lock) && !try_to_steal_lock(lock))
383                 return 0;
384
385         /* We got the lock. */
386         debug_rt_mutex_lock(lock __IP__);
387
388         rt_mutex_set_owner(lock, current, 0);
389
390         rt_mutex_deadlock_account_lock(lock, current);
391
392         return 1;
393 }
394
395 /*
396  * Task blocks on lock.
397  *
398  * Prepare waiter and propagate pi chain
399  *
400  * This must be called with lock->wait_lock held.
401  */
402 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
403                                    struct rt_mutex_waiter *waiter,
404                                    int detect_deadlock
405                                    __IP_DECL__)
406 {
407         struct rt_mutex_waiter *top_waiter = waiter;
408         task_t *owner = rt_mutex_owner(lock);
409         int boost = 0, res;
410         unsigned long flags;
411
412         spin_lock_irqsave(&current->pi_lock, flags);
413         __rt_mutex_adjust_prio(current);
414         waiter->task = current;
415         waiter->lock = lock;
416         plist_node_init(&waiter->list_entry, current->prio);
417         plist_node_init(&waiter->pi_list_entry, current->prio);
418
419         /* Get the top priority waiter on the lock */
420         if (rt_mutex_has_waiters(lock))
421                 top_waiter = rt_mutex_top_waiter(lock);
422         plist_add(&waiter->list_entry, &lock->wait_list);
423
424         current->pi_blocked_on = waiter;
425
426         spin_unlock_irqrestore(&current->pi_lock, flags);
427
428         if (waiter == rt_mutex_top_waiter(lock)) {
429                 spin_lock_irqsave(&owner->pi_lock, flags);
430                 plist_del(&top_waiter->pi_list_entry, &owner->pi_waiters);
431                 plist_add(&waiter->pi_list_entry, &owner->pi_waiters);
432
433                 __rt_mutex_adjust_prio(owner);
434                 if (owner->pi_blocked_on) {
435                         boost = 1;
436                         get_task_struct(owner);
437                 }
438                 spin_unlock_irqrestore(&owner->pi_lock, flags);
439         }
440         else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
441                 spin_lock_irqsave(&owner->pi_lock, flags);
442                 if (owner->pi_blocked_on) {
443                         boost = 1;
444                         get_task_struct(owner);
445                 }
446                 spin_unlock_irqrestore(&owner->pi_lock, flags);
447         }
448         if (!boost)
449                 return 0;
450
451         spin_unlock(&lock->wait_lock);
452
453         res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock,
454                                          waiter __IP__);
455
456         spin_lock(&lock->wait_lock);
457
458         return res;
459 }
460
461 /*
462  * Wake up the next waiter on the lock.
463  *
464  * Remove the top waiter from the current tasks waiter list and from
465  * the lock waiter list. Set it as pending owner. Then wake it up.
466  *
467  * Called with lock->wait_lock held.
468  */
469 static void wakeup_next_waiter(struct rt_mutex *lock)
470 {
471         struct rt_mutex_waiter *waiter;
472         struct task_struct *pendowner;
473         unsigned long flags;
474
475         spin_lock_irqsave(&current->pi_lock, flags);
476
477         waiter = rt_mutex_top_waiter(lock);
478         plist_del(&waiter->list_entry, &lock->wait_list);
479
480         /*
481          * Remove it from current->pi_waiters. We do not adjust a
482          * possible priority boost right now. We execute wakeup in the
483          * boosted mode and go back to normal after releasing
484          * lock->wait_lock.
485          */
486         plist_del(&waiter->pi_list_entry, &current->pi_waiters);
487         pendowner = waiter->task;
488         waiter->task = NULL;
489
490         rt_mutex_set_owner(lock, pendowner, RT_MUTEX_OWNER_PENDING);
491
492         spin_unlock_irqrestore(&current->pi_lock, flags);
493
494         /*
495          * Clear the pi_blocked_on variable and enqueue a possible
496          * waiter into the pi_waiters list of the pending owner. This
497          * prevents that in case the pending owner gets unboosted a
498          * waiter with higher priority than pending-owner->normal_prio
499          * is blocked on the unboosted (pending) owner.
500          */
501         spin_lock_irqsave(&pendowner->pi_lock, flags);
502
503         WARN_ON(!pendowner->pi_blocked_on);
504         WARN_ON(pendowner->pi_blocked_on != waiter);
505         WARN_ON(pendowner->pi_blocked_on->lock != lock);
506
507         pendowner->pi_blocked_on = NULL;
508
509         if (rt_mutex_has_waiters(lock)) {
510                 struct rt_mutex_waiter *next;
511
512                 next = rt_mutex_top_waiter(lock);
513                 plist_add(&next->pi_list_entry, &pendowner->pi_waiters);
514         }
515         spin_unlock_irqrestore(&pendowner->pi_lock, flags);
516
517         wake_up_process(pendowner);
518 }
519
520 /*
521  * Remove a waiter from a lock
522  *
523  * Must be called with lock->wait_lock held
524  */
525 static void remove_waiter(struct rt_mutex *lock,
526                           struct rt_mutex_waiter *waiter  __IP_DECL__)
527 {
528         int first = (waiter == rt_mutex_top_waiter(lock));
529         int boost = 0;
530         task_t *owner = rt_mutex_owner(lock);
531         unsigned long flags;
532
533         spin_lock_irqsave(&current->pi_lock, flags);
534         plist_del(&waiter->list_entry, &lock->wait_list);
535         waiter->task = NULL;
536         current->pi_blocked_on = NULL;
537         spin_unlock_irqrestore(&current->pi_lock, flags);
538
539         if (first && owner != current) {
540
541                 spin_lock_irqsave(&owner->pi_lock, flags);
542
543                 plist_del(&waiter->pi_list_entry, &owner->pi_waiters);
544
545                 if (rt_mutex_has_waiters(lock)) {
546                         struct rt_mutex_waiter *next;
547
548                         next = rt_mutex_top_waiter(lock);
549                         plist_add(&next->pi_list_entry, &owner->pi_waiters);
550                 }
551                 __rt_mutex_adjust_prio(owner);
552
553                 if (owner->pi_blocked_on) {
554                         boost = 1;
555                         get_task_struct(owner);
556                 }
557                 spin_unlock_irqrestore(&owner->pi_lock, flags);
558         }
559
560         WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
561
562         if (!boost)
563                 return;
564
565         spin_unlock(&lock->wait_lock);
566
567         rt_mutex_adjust_prio_chain(owner, 0, lock, NULL __IP__);
568
569         spin_lock(&lock->wait_lock);
570 }
571
572 /*
573  * Slow path lock function:
574  */
575 static int __sched
576 rt_mutex_slowlock(struct rt_mutex *lock, int state,
577                   struct hrtimer_sleeper *timeout,
578                   int detect_deadlock __IP_DECL__)
579 {
580         struct rt_mutex_waiter waiter;
581         int ret = 0;
582
583         debug_rt_mutex_init_waiter(&waiter);
584         waiter.task = NULL;
585
586         spin_lock(&lock->wait_lock);
587
588         /* Try to acquire the lock again: */
589         if (try_to_take_rt_mutex(lock __IP__)) {
590                 spin_unlock(&lock->wait_lock);
591                 return 0;
592         }
593
594         set_current_state(state);
595
596         /* Setup the timer, when timeout != NULL */
597         if (unlikely(timeout))
598                 hrtimer_start(&timeout->timer, timeout->timer.expires,
599                               HRTIMER_ABS);
600
601         for (;;) {
602                 /* Try to acquire the lock: */
603                 if (try_to_take_rt_mutex(lock __IP__))
604                         break;
605
606                 /*
607                  * TASK_INTERRUPTIBLE checks for signals and
608                  * timeout. Ignored otherwise.
609                  */
610                 if (unlikely(state == TASK_INTERRUPTIBLE)) {
611                         /* Signal pending? */
612                         if (signal_pending(current))
613                                 ret = -EINTR;
614                         if (timeout && !timeout->task)
615                                 ret = -ETIMEDOUT;
616                         if (ret)
617                                 break;
618                 }
619
620                 /*
621                  * waiter.task is NULL the first time we come here and
622                  * when we have been woken up by the previous owner
623                  * but the lock got stolen by a higher prio task.
624                  */
625                 if (!waiter.task) {
626                         ret = task_blocks_on_rt_mutex(lock, &waiter,
627                                                       detect_deadlock __IP__);
628                         /*
629                          * If we got woken up by the owner then start loop
630                          * all over without going into schedule to try
631                          * to get the lock now:
632                          */
633                         if (unlikely(!waiter.task))
634                                 continue;
635
636                         if (unlikely(ret))
637                                 break;
638                 }
639                 spin_unlock(&lock->wait_lock);
640
641                 debug_rt_mutex_print_deadlock(&waiter);
642
643                 schedule();
644
645                 spin_lock(&lock->wait_lock);
646                 set_current_state(state);
647         }
648
649         set_current_state(TASK_RUNNING);
650
651         if (unlikely(waiter.task))
652                 remove_waiter(lock, &waiter __IP__);
653
654         /*
655          * try_to_take_rt_mutex() sets the waiter bit
656          * unconditionally. We might have to fix that up.
657          */
658         fixup_rt_mutex_waiters(lock);
659
660         spin_unlock(&lock->wait_lock);
661
662         /* Remove pending timer: */
663         if (unlikely(timeout))
664                 hrtimer_cancel(&timeout->timer);
665
666         /*
667          * Readjust priority, when we did not get the lock. We might
668          * have been the pending owner and boosted. Since we did not
669          * take the lock, the PI boost has to go.
670          */
671         if (unlikely(ret))
672                 rt_mutex_adjust_prio(current);
673
674         debug_rt_mutex_free_waiter(&waiter);
675
676         return ret;
677 }
678
679 /*
680  * Slow path try-lock function:
681  */
682 static inline int
683 rt_mutex_slowtrylock(struct rt_mutex *lock __IP_DECL__)
684 {
685         int ret = 0;
686
687         spin_lock(&lock->wait_lock);
688
689         if (likely(rt_mutex_owner(lock) != current)) {
690
691                 ret = try_to_take_rt_mutex(lock __IP__);
692                 /*
693                  * try_to_take_rt_mutex() sets the lock waiters
694                  * bit unconditionally. Clean this up.
695                  */
696                 fixup_rt_mutex_waiters(lock);
697         }
698
699         spin_unlock(&lock->wait_lock);
700
701         return ret;
702 }
703
704 /*
705  * Slow path to release a rt-mutex:
706  */
707 static void __sched
708 rt_mutex_slowunlock(struct rt_mutex *lock)
709 {
710         spin_lock(&lock->wait_lock);
711
712         debug_rt_mutex_unlock(lock);
713
714         rt_mutex_deadlock_account_unlock(current);
715
716         if (!rt_mutex_has_waiters(lock)) {
717                 lock->owner = NULL;
718                 spin_unlock(&lock->wait_lock);
719                 return;
720         }
721
722         wakeup_next_waiter(lock);
723
724         spin_unlock(&lock->wait_lock);
725
726         /* Undo pi boosting if necessary: */
727         rt_mutex_adjust_prio(current);
728 }
729
730 /*
731  * debug aware fast / slowpath lock,trylock,unlock
732  *
733  * The atomic acquire/release ops are compiled away, when either the
734  * architecture does not support cmpxchg or when debugging is enabled.
735  */
736 static inline int
737 rt_mutex_fastlock(struct rt_mutex *lock, int state,
738                   int detect_deadlock,
739                   int (*slowfn)(struct rt_mutex *lock, int state,
740                                 struct hrtimer_sleeper *timeout,
741                                 int detect_deadlock __IP_DECL__))
742 {
743         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
744                 rt_mutex_deadlock_account_lock(lock, current);
745                 return 0;
746         } else
747                 return slowfn(lock, state, NULL, detect_deadlock __RET_IP__);
748 }
749
750 static inline int
751 rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
752                         struct hrtimer_sleeper *timeout, int detect_deadlock,
753                         int (*slowfn)(struct rt_mutex *lock, int state,
754                                       struct hrtimer_sleeper *timeout,
755                                       int detect_deadlock __IP_DECL__))
756 {
757         if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
758                 rt_mutex_deadlock_account_lock(lock, current);
759                 return 0;
760         } else
761                 return slowfn(lock, state, timeout, detect_deadlock __RET_IP__);
762 }
763
764 static inline int
765 rt_mutex_fasttrylock(struct rt_mutex *lock,
766                      int (*slowfn)(struct rt_mutex *lock __IP_DECL__))
767 {
768         if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
769                 rt_mutex_deadlock_account_lock(lock, current);
770                 return 1;
771         }
772         return slowfn(lock __RET_IP__);
773 }
774
775 static inline void
776 rt_mutex_fastunlock(struct rt_mutex *lock,
777                     void (*slowfn)(struct rt_mutex *lock))
778 {
779         if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
780                 rt_mutex_deadlock_account_unlock(current);
781         else
782                 slowfn(lock);
783 }
784
785 /**
786  * rt_mutex_lock - lock a rt_mutex
787  *
788  * @lock: the rt_mutex to be locked
789  */
790 void __sched rt_mutex_lock(struct rt_mutex *lock)
791 {
792         might_sleep();
793
794         rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
795 }
796 EXPORT_SYMBOL_GPL(rt_mutex_lock);
797
798 /**
799  * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
800  *
801  * @lock:               the rt_mutex to be locked
802  * @detect_deadlock:    deadlock detection on/off
803  *
804  * Returns:
805  *  0           on success
806  * -EINTR       when interrupted by a signal
807  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
808  */
809 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
810                                                  int detect_deadlock)
811 {
812         might_sleep();
813
814         return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
815                                  detect_deadlock, rt_mutex_slowlock);
816 }
817 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
818
819 /**
820  * rt_mutex_lock_interruptible_ktime - lock a rt_mutex interruptible
821  *                                     the timeout structure is provided
822  *                                     by the caller
823  *
824  * @lock:               the rt_mutex to be locked
825  * @timeout:            timeout structure or NULL (no timeout)
826  * @detect_deadlock:    deadlock detection on/off
827  *
828  * Returns:
829  *  0           on success
830  * -EINTR       when interrupted by a signal
831  * -ETIMEOUT    when the timeout expired
832  * -EDEADLK     when the lock would deadlock (when deadlock detection is on)
833  */
834 int
835 rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
836                     int detect_deadlock)
837 {
838         might_sleep();
839
840         return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
841                                        detect_deadlock, rt_mutex_slowlock);
842 }
843 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
844
845 /**
846  * rt_mutex_trylock - try to lock a rt_mutex
847  *
848  * @lock:       the rt_mutex to be locked
849  *
850  * Returns 1 on success and 0 on contention
851  */
852 int __sched rt_mutex_trylock(struct rt_mutex *lock)
853 {
854         return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
855 }
856 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
857
858 /**
859  * rt_mutex_unlock - unlock a rt_mutex
860  *
861  * @lock: the rt_mutex to be unlocked
862  */
863 void __sched rt_mutex_unlock(struct rt_mutex *lock)
864 {
865         rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
866 }
867 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
868
869 /***
870  * rt_mutex_destroy - mark a mutex unusable
871  * @lock: the mutex to be destroyed
872  *
873  * This function marks the mutex uninitialized, and any subsequent
874  * use of the mutex is forbidden. The mutex must not be locked when
875  * this function is called.
876  */
877 void rt_mutex_destroy(struct rt_mutex *lock)
878 {
879         WARN_ON(rt_mutex_is_locked(lock));
880 #ifdef CONFIG_DEBUG_RT_MUTEXES
881         lock->magic = NULL;
882 #endif
883 }
884
885 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
886
887 /**
888  * __rt_mutex_init - initialize the rt lock
889  *
890  * @lock: the rt lock to be initialized
891  *
892  * Initialize the rt lock to unlocked state.
893  *
894  * Initializing of a locked rt lock is not allowed
895  */
896 void __rt_mutex_init(struct rt_mutex *lock, const char *name)
897 {
898         lock->owner = NULL;
899         spin_lock_init(&lock->wait_lock);
900         plist_head_init(&lock->wait_list, &lock->wait_lock);
901
902         debug_rt_mutex_init(lock, name);
903 }
904 EXPORT_SYMBOL_GPL(__rt_mutex_init);