1	// SPDX-License-Identifier: GPL-2.0-only
2	/*
3	* RT-Mutexes: simple blocking mutual exclusion locks with PI support
4	*
5	* started by Ingo Molnar and Thomas Gleixner.
6	*
7	* Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
8	* Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
9	* Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
10	* Copyright (C) 2006 Esben Nielsen
11	* Adaptive Spinlocks:
12	* Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich,
13	* and Peter Morreale,
14	* Adaptive Spinlocks simplification:
15	* Copyright (C) 2008 Red Hat, Inc., Steven Rostedt <srostedt@redhat.com>
16	*
17	* See Documentation/locking/rt-mutex-design.rst for details.
18	*/
19	#include <linux/sched.h>
20	#include <linux/sched/debug.h>
21	#include <linux/sched/deadline.h>
22	#include <linux/sched/signal.h>
23	#include <linux/sched/rt.h>
24	#include <linux/sched/wake_q.h>
25	#include <linux/ww_mutex.h>
26
27	#include <trace/events/lock.h>
28
29	#include "rtmutex_common.h"
30
31	#ifndef WW_RT
32	# define build_ww_mutex() (false)
33	# define ww_container_of(rtm) NULL
34
35	static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter,
36	struct rt_mutex *lock,
37	struct ww_acquire_ctx *ww_ctx)
38	{
39	return 0;
40	}
41
42	static inline void __ww_mutex_check_waiters(struct rt_mutex *lock,
43	struct ww_acquire_ctx *ww_ctx)
44	{
45	}
46
47	static inline void ww_mutex_lock_acquired(struct ww_mutex *lock,
48	struct ww_acquire_ctx *ww_ctx)
49	{
50	}
51
52	static inline int __ww_mutex_check_kill(struct rt_mutex *lock,
53	struct rt_mutex_waiter *waiter,
54	struct ww_acquire_ctx *ww_ctx)
55	{
56	return 0;
57	}
58
59	#else
60	# define build_ww_mutex() (true)
61	# define ww_container_of(rtm) container_of(rtm, struct ww_mutex, base)
62	# include "ww_mutex.h"
63	#endif
64
65	/*
66	* lock->owner state tracking:
67	*
68	* lock->owner holds the task_struct pointer of the owner. Bit 0
69	* is used to keep track of the "lock has waiters" state.
70	*
71	* owner bit0
72	* NULL 0 lock is free (fast acquire possible)
73	* NULL 1 lock is free and has waiters and the top waiter
74	* is going to take the lock*
75	* taskpointer 0 lock is held (fast release possible)
76	* taskpointer 1 lock is held and has waiters**
77	*
78	* The fast atomic compare exchange based acquire and release is only
79	* possible when bit 0 of lock->owner is 0.
80	*
81	* (*) It also can be a transitional state when grabbing the lock
82	* with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
83	* we need to set the bit0 before looking at the lock, and the owner may be
84	* NULL in this small time, hence this can be a transitional state.
85	*
86	* (**) There is a small time when bit 0 is set but there are no
87	* waiters. This can happen when grabbing the lock in the slow path.
88	* To prevent a cmpxchg of the owner releasing the lock, we need to
89	* set this bit before looking at the lock.
90	*/
91
92	static __always_inline struct task_struct *
93	rt_mutex_owner_encode(struct rt_mutex_base *lock, struct task_struct *owner)
94	{
95	unsigned long val = (unsigned long)owner;
96
97	if (rt_mutex_has_waiters(lock))
98	val |= RT_MUTEX_HAS_WAITERS;
99
100	return (struct task_struct *)val;
101	}
102
103	static __always_inline void
104	rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner)
105	{
106	/*
107	* lock->wait_lock is held but explicit acquire semantics are needed
108	* for a new lock owner so WRITE_ONCE is insufficient.
109	*/
110	xchg_acquire(&lock->owner, rt_mutex_owner_encode(lock, owner));
111	}
112
113	static __always_inline void rt_mutex_clear_owner(struct rt_mutex_base *lock)
114	{
115	/* lock->wait_lock is held so the unlock provides release semantics. */
116	WRITE_ONCE(lock->owner, rt_mutex_owner_encode(lock, NULL));
117	}
118
119	static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock)
120	{
121	lock->owner = (struct task_struct *)
122	((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
123	}
124
125	static __always_inline void
126	fixup_rt_mutex_waiters(struct rt_mutex_base *lock, bool acquire_lock)
127	{
128	unsigned long owner, *p = (unsigned long *) &lock->owner;
129
130	if (rt_mutex_has_waiters(lock))
131	return;
132
133	/*
134	* The rbtree has no waiters enqueued, now make sure that the
135	* lock->owner still has the waiters bit set, otherwise the
136	* following can happen:
137	*
138	* CPU 0 CPU 1 CPU2
139	* l->owner=T1
140	* rt_mutex_lock(l)
141	* lock(l->lock)
142	* l->owner = T1 | HAS_WAITERS;
143	* enqueue(T2)
144	* boost()
145	* unlock(l->lock)
146	* block()
147	*
148	* rt_mutex_lock(l)
149	* lock(l->lock)
150	* l->owner = T1 | HAS_WAITERS;
151	* enqueue(T3)
152	* boost()
153	* unlock(l->lock)
154	* block()
155	* signal(->T2) signal(->T3)
156	* lock(l->lock)
157	* dequeue(T2)
158	* deboost()
159	* unlock(l->lock)
160	* lock(l->lock)
161	* dequeue(T3)
162	* ==> wait list is empty
163	* deboost()
164	* unlock(l->lock)
165	* lock(l->lock)
166	* fixup_rt_mutex_waiters()
167	* if (wait_list_empty(l) {
168	* l->owner = owner
169	* owner = l->owner & ~HAS_WAITERS;
170	* ==> l->owner = T1
171	* }
172	* lock(l->lock)
173	* rt_mutex_unlock(l) fixup_rt_mutex_waiters()
174	* if (wait_list_empty(l) {
175	* owner = l->owner & ~HAS_WAITERS;
176	* cmpxchg(l->owner, T1, NULL)
177	* ===> Success (l->owner = NULL)
178	*
179	* l->owner = owner
180	* ==> l->owner = T1
181	* }
182	*
183	* With the check for the waiter bit in place T3 on CPU2 will not
184	* overwrite. All tasks fiddling with the waiters bit are
185	* serialized by l->lock, so nothing else can modify the waiters
186	* bit. If the bit is set then nothing can change l->owner either
187	* so the simple RMW is safe. The cmpxchg() will simply fail if it
188	* happens in the middle of the RMW because the waiters bit is
189	* still set.
190	*/
191	owner = READ_ONCE(*p);
192	if (owner & RT_MUTEX_HAS_WAITERS) {
193	/*
194	* See rt_mutex_set_owner() and rt_mutex_clear_owner() on
195	* why xchg_acquire() is used for updating owner for
196	* locking and WRITE_ONCE() for unlocking.
197	*
198	* WRITE_ONCE() would work for the acquire case too, but
199	* in case that the lock acquisition failed it might
200	* force other lockers into the slow path unnecessarily.
201	*/
202	if (acquire_lock)
203	xchg_acquire(p, owner & ~RT_MUTEX_HAS_WAITERS);
204	else
205	WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
206	}
207	}
208
209	/*
210	* We can speed up the acquire/release, if there's no debugging state to be
211	* set up.
212	*/
213	#ifndef CONFIG_DEBUG_RT_MUTEXES
214	static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
215	struct task_struct *old,
216	struct task_struct *new)
217	{
218	return try_cmpxchg_acquire(&lock->owner, &old, new);
219	}
220
221	static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock)
222	{
223	return rt_mutex_cmpxchg_acquire(lock, NULL, current);
224	}
225
226	static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
227	struct task_struct *old,
228	struct task_struct *new)
229	{
230	return try_cmpxchg_release(&lock->owner, &old, new);
231	}
232
233	/*
234	* Callers must hold the ->wait_lock -- which is the whole purpose as we force
235	* all future threads that attempt to [Rmw] the lock to the slowpath. As such
236	* relaxed semantics suffice.
237	*/
238	static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
239	{
240	unsigned long *p = (unsigned long *) &lock->owner;
241	unsigned long owner, new;
242
243	owner = READ_ONCE(*p);
244	do {
245	new = owner | RT_MUTEX_HAS_WAITERS;
246	} while (!try_cmpxchg_relaxed(p, &owner, new));
247
248	/*
249	* The cmpxchg loop above is relaxed to avoid back-to-back ACQUIRE
250	* operations in the event of contention. Ensure the successful
251	* cmpxchg is visible.
252	*/
253	smp_mb__after_atomic();
254	}
255
256	/*
257	* Safe fastpath aware unlock:
258	* 1) Clear the waiters bit
259	* 2) Drop lock->wait_lock
260	* 3) Try to unlock the lock with cmpxchg
261	*/
262	static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
263	unsigned long flags)
264	__releases(lock->wait_lock)
265	{
266	struct task_struct *owner = rt_mutex_owner(lock);
267
268	clear_rt_mutex_waiters(lock);
269	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
270	/*
271	* If a new waiter comes in between the unlock and the cmpxchg
272	* we have two situations:
273	*
274	* unlock(wait_lock);
275	* lock(wait_lock);
276	* cmpxchg(p, owner, 0) == owner
277	* mark_rt_mutex_waiters(lock);
278	* acquire(lock);
279	* or:
280	*
281	* unlock(wait_lock);
282	* lock(wait_lock);
283	* mark_rt_mutex_waiters(lock);
284	*
285	* cmpxchg(p, owner, 0) != owner
286	* enqueue_waiter();
287	* unlock(wait_lock);
288	* lock(wait_lock);
289	* wake waiter();
290	* unlock(wait_lock);
291	* lock(wait_lock);
292	* acquire(lock);
293	*/
294	return rt_mutex_cmpxchg_release(lock, owner, NULL);
295	}
296
297	#else
298	static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
299	struct task_struct *old,
300	struct task_struct *new)
301	{
302	return false;
303
304	}
305
306	static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock);
307
308	static __always_inline bool rt_mutex_try_acquire(struct rt_mutex_base *lock)
309	{
310	/*
311	* With debug enabled rt_mutex_cmpxchg trylock() will always fail.
312	*
313	* Avoid unconditionally taking the slow path by using
314	* rt_mutex_slow_trylock() which is covered by the debug code and can
315	* acquire a non-contended rtmutex.
316	*/
317	return rt_mutex_slowtrylock(lock);
318	}
319
320	static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
321	struct task_struct *old,
322	struct task_struct *new)
323	{
324	return false;
325	}
326
327	static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
328	{
329	lock->owner = (struct task_struct *)
330	((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
331	}
332
333	/*
334	* Simple slow path only version: lock->owner is protected by lock->wait_lock.
335	*/
336	static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
337	unsigned long flags)
338	__releases(lock->wait_lock)
339	{
340	lock->owner = NULL;
341	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
342	return true;
343	}
344	#endif
345
346	static __always_inline int __waiter_prio(struct task_struct *task)
347	{
348	int prio = task->prio;
349
350	if (!rt_prio(prio))
351	return DEFAULT_PRIO;
352
353	return prio;
354	}
355
356	/*
357	* Update the waiter->tree copy of the sort keys.
358	*/
359	static __always_inline void
360	waiter_update_prio(struct rt_mutex_waiter *waiter, struct task_struct *task)
361	{
362	lockdep_assert_held(&waiter->lock->wait_lock);
363	lockdep_assert(RB_EMPTY_NODE(&waiter->tree.entry));
364
365	waiter->tree.prio = __waiter_prio(task);
366	waiter->tree.deadline = task->dl.deadline;
367	}
368
369	/*
370	* Update the waiter->pi_tree copy of the sort keys (from the tree copy).
371	*/
372	static __always_inline void
373	waiter_clone_prio(struct rt_mutex_waiter *waiter, struct task_struct *task)
374	{
375	lockdep_assert_held(&waiter->lock->wait_lock);
376	lockdep_assert_held(&task->pi_lock);
377	lockdep_assert(RB_EMPTY_NODE(&waiter->pi_tree.entry));
378
379	waiter->pi_tree.prio = waiter->tree.prio;
380	waiter->pi_tree.deadline = waiter->tree.deadline;
381	}
382
383	/*
384	* Only use with rt_waiter_node_{less,equal}()
385	*/
386	#define task_to_waiter_node(p) \
387	&(struct rt_waiter_node){ .prio = __waiter_prio(p), .deadline = (p)->dl.deadline }
388	#define task_to_waiter(p) \
389	&(struct rt_mutex_waiter){ .tree = *task_to_waiter_node(p) }
390
391	static __always_inline int rt_waiter_node_less(struct rt_waiter_node *left,
392	struct rt_waiter_node *right)
393	{
394	if (left->prio < right->prio)
395	return 1;
396
397	/*
398	* If both waiters have dl_prio(), we check the deadlines of the
399	* associated tasks.
400	* If left waiter has a dl_prio(), and we didn't return 1 above,
401	* then right waiter has a dl_prio() too.
402	*/
403	if (dl_prio(prio: left->prio))
404	return dl_time_before(a: left->deadline, b: right->deadline);
405
406	return 0;
407	}
408
409	static __always_inline int rt_waiter_node_equal(struct rt_waiter_node *left,
410	struct rt_waiter_node *right)
411	{
412	if (left->prio != right->prio)
413	return 0;
414
415	/*
416	* If both waiters have dl_prio(), we check the deadlines of the
417	* associated tasks.
418	* If left waiter has a dl_prio(), and we didn't return 0 above,
419	* then right waiter has a dl_prio() too.
420	*/
421	if (dl_prio(prio: left->prio))
422	return left->deadline == right->deadline;
423
424	return 1;
425	}
426
427	static inline bool rt_mutex_steal(struct rt_mutex_waiter *waiter,
428	struct rt_mutex_waiter *top_waiter)
429	{
430	if (rt_waiter_node_less(left: &waiter->tree, right: &top_waiter->tree))
431	return true;
432
433	#ifdef RT_MUTEX_BUILD_SPINLOCKS
434	/*
435	* Note that RT tasks are excluded from same priority (lateral)
436	* steals to prevent the introduction of an unbounded latency.
437	*/
438	if (rt_prio(waiter->tree.prio) || dl_prio(waiter->tree.prio))
439	return false;
440
441	return rt_waiter_node_equal(&waiter->tree, &top_waiter->tree);
442	#else
443	return false;
444	#endif
445	}
446
447	#define __node_2_waiter(node) \
448	rb_entry((node), struct rt_mutex_waiter, tree.entry)
449
450	static __always_inline bool __waiter_less(struct rb_node *a, const struct rb_node *b)
451	{
452	struct rt_mutex_waiter *aw = __node_2_waiter(a);
453	struct rt_mutex_waiter *bw = __node_2_waiter(b);
454
455	if (rt_waiter_node_less(left: &aw->tree, right: &bw->tree))
456	return 1;
457
458	if (!build_ww_mutex())
459	return 0;
460
461	if (rt_waiter_node_less(left: &bw->tree, right: &aw->tree))
462	return 0;
463
464	/* NOTE: relies on waiter->ww_ctx being set before insertion */
465	if (aw->ww_ctx) {
466	if (!bw->ww_ctx)
467	return 1;
468
469	return (signed long)(aw->ww_ctx->stamp -
470	bw->ww_ctx->stamp) < 0;
471	}
472
473	return 0;
474	}
475
476	static __always_inline void
477	rt_mutex_enqueue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
478	{
479	lockdep_assert_held(&lock->wait_lock);
480
481	rb_add_cached(node: &waiter->tree.entry, tree: &lock->waiters, less: __waiter_less);
482	}
483
484	static __always_inline void
485	rt_mutex_dequeue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
486	{
487	lockdep_assert_held(&lock->wait_lock);
488
489	if (RB_EMPTY_NODE(&waiter->tree.entry))
490	return;
491
492	rb_erase_cached(node: &waiter->tree.entry, root: &lock->waiters);
493	RB_CLEAR_NODE(&waiter->tree.entry);
494	}
495
496	#define __node_2_rt_node(node) \
497	rb_entry((node), struct rt_waiter_node, entry)
498
499	static __always_inline bool __pi_waiter_less(struct rb_node *a, const struct rb_node *b)
500	{
501	return rt_waiter_node_less(__node_2_rt_node(a), __node_2_rt_node(b));
502	}
503
504	static __always_inline void
505	rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
506	{
507	lockdep_assert_held(&task->pi_lock);
508
509	rb_add_cached(node: &waiter->pi_tree.entry, tree: &task->pi_waiters, less: __pi_waiter_less);
510	}
511
512	static __always_inline void
513	rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
514	{
515	lockdep_assert_held(&task->pi_lock);
516
517	if (RB_EMPTY_NODE(&waiter->pi_tree.entry))
518	return;
519
520	rb_erase_cached(node: &waiter->pi_tree.entry, root: &task->pi_waiters);
521	RB_CLEAR_NODE(&waiter->pi_tree.entry);
522	}
523
524	static __always_inline void rt_mutex_adjust_prio(struct rt_mutex_base *lock,
525	struct task_struct *p)
526	{
527	struct task_struct *pi_task = NULL;
528
529	lockdep_assert_held(&lock->wait_lock);
530	lockdep_assert(rt_mutex_owner(lock) == p);
531	lockdep_assert_held(&p->pi_lock);
532
533	if (task_has_pi_waiters(p))
534	pi_task = task_top_pi_waiter(p)->task;
535
536	rt_mutex_setprio(p, pi_task);
537	}
538
539	/* RT mutex specific wake_q wrappers */
540	static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh,
541	struct task_struct *task,
542	unsigned int wake_state)
543	{
544	if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state == TASK_RTLOCK_WAIT) {
545	if (IS_ENABLED(CONFIG_PROVE_LOCKING))
546	WARN_ON_ONCE(wqh->rtlock_task);
547	get_task_struct(t: task);
548	wqh->rtlock_task = task;
549	} else {
550	wake_q_add(head: &wqh->head, task);
551	}
552	}
553
554	static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
555	struct rt_mutex_waiter *w)
556	{
557	rt_mutex_wake_q_add_task(wqh, task: w->task, wake_state: w->wake_state);
558	}
559
560	static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh)
561	{
562	if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task) {
563	wake_up_state(tsk: wqh->rtlock_task, TASK_RTLOCK_WAIT);
564	put_task_struct(t: wqh->rtlock_task);
565	wqh->rtlock_task = NULL;
566	}
567
568	if (!wake_q_empty(head: &wqh->head))
569	wake_up_q(head: &wqh->head);
570
571	/* Pairs with preempt_disable() in mark_wakeup_next_waiter() */
572	preempt_enable();
573	}
574
575	/*
576	* Deadlock detection is conditional:
577	*
578	* If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
579	* if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
580	*
581	* If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
582	* conducted independent of the detect argument.
583	*
584	* If the waiter argument is NULL this indicates the deboost path and
585	* deadlock detection is disabled independent of the detect argument
586	* and the config settings.
587	*/
588	static __always_inline bool
589	rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
590	enum rtmutex_chainwalk chwalk)
591	{
592	if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
593	return waiter != NULL;
594	return chwalk == RT_MUTEX_FULL_CHAINWALK;
595	}
596
597	static __always_inline struct rt_mutex_base *task_blocked_on_lock(struct task_struct *p)
598	{
599	return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
600	}
601
602	/*
603	* Adjust the priority chain. Also used for deadlock detection.
604	* Decreases task's usage by one - may thus free the task.
605	*
606	* @task: the task owning the mutex (owner) for which a chain walk is
607	* probably needed
608	* @chwalk: do we have to carry out deadlock detection?
609	* @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
610	* things for a task that has just got its priority adjusted, and
611	* is waiting on a mutex)
612	* @next_lock: the mutex on which the owner of @orig_lock was blocked before
613	* we dropped its pi_lock. Is never dereferenced, only used for
614	* comparison to detect lock chain changes.
615	* @orig_waiter: rt_mutex_waiter struct for the task that has just donated
616	* its priority to the mutex owner (can be NULL in the case
617	* depicted above or if the top waiter is gone away and we are
618	* actually deboosting the owner)
619	* @top_task: the current top waiter
620	*
621	* Returns 0 or -EDEADLK.
622	*
623	* Chain walk basics and protection scope
624	*
625	* [R] refcount on task
626	* [Pn] task->pi_lock held
627	* [L] rtmutex->wait_lock held
628	*
629	* Normal locking order:
630	*
631	* rtmutex->wait_lock
632	* task->pi_lock
633	*
634	* Step Description Protected by
635	* function arguments:
636	* @task [R]
637	* @orig_lock if != NULL @top_task is blocked on it
638	* @next_lock Unprotected. Cannot be
639	* dereferenced. Only used for
640	* comparison.
641	* @orig_waiter if != NULL @top_task is blocked on it
642	* @top_task current, or in case of proxy
643	* locking protected by calling
644	* code
645	* again:
646	* loop_sanity_check();
647	* retry:
648	* [1] lock(task->pi_lock); [R] acquire [P1]
649	* [2] waiter = task->pi_blocked_on; [P1]
650	* [3] check_exit_conditions_1(); [P1]
651	* [4] lock = waiter->lock; [P1]
652	* [5] if (!try_lock(lock->wait_lock)) { [P1] try to acquire [L]
653	* unlock(task->pi_lock); release [P1]
654	* goto retry;
655	* }
656	* [6] check_exit_conditions_2(); [P1] + [L]
657	* [7] requeue_lock_waiter(lock, waiter); [P1] + [L]
658	* [8] unlock(task->pi_lock); release [P1]
659	* put_task_struct(task); release [R]
660	* [9] check_exit_conditions_3(); [L]
661	* [10] task = owner(lock); [L]
662	* get_task_struct(task); [L] acquire [R]
663	* lock(task->pi_lock); [L] acquire [P2]
664	* [11] requeue_pi_waiter(tsk, waiters(lock));[P2] + [L]
665	* [12] check_exit_conditions_4(); [P2] + [L]
666	* [13] unlock(task->pi_lock); release [P2]
667	* unlock(lock->wait_lock); release [L]
668	* goto again;
669	*
670	* Where P1 is the blocking task and P2 is the lock owner; going up one step
671	* the owner becomes the next blocked task etc..
672	*
673	*
674	*/
675	static int __sched rt_mutex_adjust_prio_chain(struct task_struct *task,
676	enum rtmutex_chainwalk chwalk,
677	struct rt_mutex_base *orig_lock,
678	struct rt_mutex_base *next_lock,
679	struct rt_mutex_waiter *orig_waiter,
680	struct task_struct *top_task)
681	{
682	struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
683	struct rt_mutex_waiter *prerequeue_top_waiter;
684	int ret = 0, depth = 0;
685	struct rt_mutex_base *lock;
686	bool detect_deadlock;
687	bool requeue = true;
688
689	detect_deadlock = rt_mutex_cond_detect_deadlock(waiter: orig_waiter, chwalk);
690
691	/*
692	* The (de)boosting is a step by step approach with a lot of
693	* pitfalls. We want this to be preemptible and we want hold a
694	* maximum of two locks per step. So we have to check
695	* carefully whether things change under us.
696	*/
697	again:
698	/*
699	* We limit the lock chain length for each invocation.
700	*/
701	if (++depth > max_lock_depth) {
702	static int prev_max;
703
704	/*
705	* Print this only once. If the admin changes the limit,
706	* print a new message when reaching the limit again.
707	*/
708	if (prev_max != max_lock_depth) {
709	prev_max = max_lock_depth;
710	printk(KERN_WARNING "Maximum lock depth %d reached "
711	"task: %s (%d)\n", max_lock_depth,
712	top_task->comm, task_pid_nr(top_task));
713	}
714	put_task_struct(t: task);
715
716	return -EDEADLK;
717	}
718
719	/*
720	* We are fully preemptible here and only hold the refcount on
721	* @task. So everything can have changed under us since the
722	* caller or our own code below (goto retry/again) dropped all
723	* locks.
724	*/
725	retry:
726	/*
727	* [1] Task cannot go away as we did a get_task() before !
728	*/
729	raw_spin_lock_irq(&task->pi_lock);
730
731	/*
732	* [2] Get the waiter on which @task is blocked on.
733	*/
734	waiter = task->pi_blocked_on;
735
736	/*
737	* [3] check_exit_conditions_1() protected by task->pi_lock.
738	*/
739
740	/*
741	* Check whether the end of the boosting chain has been
742	* reached or the state of the chain has changed while we
743	* dropped the locks.
744	*/
745	if (!waiter)
746	goto out_unlock_pi;
747
748	/*
749	* Check the orig_waiter state. After we dropped the locks,
750	* the previous owner of the lock might have released the lock.
751	*/
752	if (orig_waiter && !rt_mutex_owner(lock: orig_lock))
753	goto out_unlock_pi;
754
755	/*
756	* We dropped all locks after taking a refcount on @task, so
757	* the task might have moved on in the lock chain or even left
758	* the chain completely and blocks now on an unrelated lock or
759	* on @orig_lock.
760	*
761	* We stored the lock on which @task was blocked in @next_lock,
762	* so we can detect the chain change.
763	*/
764	if (next_lock != waiter->lock)
765	goto out_unlock_pi;
766
767	/*
768	* There could be 'spurious' loops in the lock graph due to ww_mutex,
769	* consider:
770	*
771	* P1: A, ww_A, ww_B
772	* P2: ww_B, ww_A
773	* P3: A
774	*
775	* P3 should not return -EDEADLK because it gets trapped in the cycle
776	* created by P1 and P2 (which will resolve -- and runs into
777	* max_lock_depth above). Therefore disable detect_deadlock such that
778	* the below termination condition can trigger once all relevant tasks
779	* are boosted.
780	*
781	* Even when we start with ww_mutex we can disable deadlock detection,
782	* since we would supress a ww_mutex induced deadlock at [6] anyway.
783	* Supressing it here however is not sufficient since we might still
784	* hit [6] due to adjustment driven iteration.
785	*
786	* NOTE: if someone were to create a deadlock between 2 ww_classes we'd
787	* utterly fail to report it; lockdep should.
788	*/
789	if (IS_ENABLED(CONFIG_PREEMPT_RT) && waiter->ww_ctx && detect_deadlock)
790	detect_deadlock = false;
791
792	/*
793	* Drop out, when the task has no waiters. Note,
794	* top_waiter can be NULL, when we are in the deboosting
795	* mode!
796	*/
797	if (top_waiter) {
798	if (!task_has_pi_waiters(p: task))
799	goto out_unlock_pi;
800	/*
801	* If deadlock detection is off, we stop here if we
802	* are not the top pi waiter of the task. If deadlock
803	* detection is enabled we continue, but stop the
804	* requeueing in the chain walk.
805	*/
806	if (top_waiter != task_top_pi_waiter(p: task)) {
807	if (!detect_deadlock)
808	goto out_unlock_pi;
809	else
810	requeue = false;
811	}
812	}
813
814	/*
815	* If the waiter priority is the same as the task priority
816	* then there is no further priority adjustment necessary. If
817	* deadlock detection is off, we stop the chain walk. If its
818	* enabled we continue, but stop the requeueing in the chain
819	* walk.
820	*/
821	if (rt_waiter_node_equal(left: &waiter->tree, task_to_waiter_node(task))) {
822	if (!detect_deadlock)
823	goto out_unlock_pi;
824	else
825	requeue = false;
826	}
827
828	/*
829	* [4] Get the next lock; per holding task->pi_lock we can't unblock
830	* and guarantee @lock's existence.
831	*/
832	lock = waiter->lock;
833	/*
834	* [5] We need to trylock here as we are holding task->pi_lock,
835	* which is the reverse lock order versus the other rtmutex
836	* operations.
837	*
838	* Per the above, holding task->pi_lock guarantees lock exists, so
839	* inverting this lock order is infeasible from a life-time
840	* perspective.
841	*/
842	if (!raw_spin_trylock(&lock->wait_lock)) {
843	raw_spin_unlock_irq(&task->pi_lock);
844	cpu_relax();
845	goto retry;
846	}
847
848	/*
849	* [6] check_exit_conditions_2() protected by task->pi_lock and
850	* lock->wait_lock.
851	*
852	* Deadlock detection. If the lock is the same as the original
853	* lock which caused us to walk the lock chain or if the
854	* current lock is owned by the task which initiated the chain
855	* walk, we detected a deadlock.
856	*/
857	if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
858	ret = -EDEADLK;
859
860	/*
861	* When the deadlock is due to ww_mutex; also see above. Don't
862	* report the deadlock and instead let the ww_mutex wound/die
863	* logic pick which of the contending threads gets -EDEADLK.
864	*
865	* NOTE: assumes the cycle only contains a single ww_class; any
866	* other configuration and we fail to report; also, see
867	* lockdep.
868	*/
869	if (IS_ENABLED(CONFIG_PREEMPT_RT) && orig_waiter && orig_waiter->ww_ctx)
870	ret = 0;
871
872	raw_spin_unlock(&lock->wait_lock);
873	goto out_unlock_pi;
874	}
875
876	/*
877	* If we just follow the lock chain for deadlock detection, no
878	* need to do all the requeue operations. To avoid a truckload
879	* of conditionals around the various places below, just do the
880	* minimum chain walk checks.
881	*/
882	if (!requeue) {
883	/*
884	* No requeue[7] here. Just release @task [8]
885	*/
886	raw_spin_unlock(&task->pi_lock);
887	put_task_struct(t: task);
888
889	/*
890	* [9] check_exit_conditions_3 protected by lock->wait_lock.
891	* If there is no owner of the lock, end of chain.
892	*/
893	if (!rt_mutex_owner(lock)) {
894	raw_spin_unlock_irq(&lock->wait_lock);
895	return 0;
896	}
897
898	/* [10] Grab the next task, i.e. owner of @lock */
899	task = get_task_struct(t: rt_mutex_owner(lock));
900	raw_spin_lock(&task->pi_lock);
901
902	/*
903	* No requeue [11] here. We just do deadlock detection.
904	*
905	* [12] Store whether owner is blocked
906	* itself. Decision is made after dropping the locks
907	*/
908	next_lock = task_blocked_on_lock(p: task);
909	/*
910	* Get the top waiter for the next iteration
911	*/
912	top_waiter = rt_mutex_top_waiter(lock);
913
914	/* [13] Drop locks */
915	raw_spin_unlock(&task->pi_lock);
916	raw_spin_unlock_irq(&lock->wait_lock);
917
918	/* If owner is not blocked, end of chain. */
919	if (!next_lock)
920	goto out_put_task;
921	goto again;
922	}
923
924	/*
925	* Store the current top waiter before doing the requeue
926	* operation on @lock. We need it for the boost/deboost
927	* decision below.
928	*/
929	prerequeue_top_waiter = rt_mutex_top_waiter(lock);
930
931	/* [7] Requeue the waiter in the lock waiter tree. */
932	rt_mutex_dequeue(lock, waiter);
933
934	/*
935	* Update the waiter prio fields now that we're dequeued.
936	*
937	* These values can have changed through either:
938	*
939	* sys_sched_set_scheduler() / sys_sched_setattr()
940	*
941	* or
942	*
943	* DL CBS enforcement advancing the effective deadline.
944	*/
945	waiter_update_prio(waiter, task);
946
947	rt_mutex_enqueue(lock, waiter);
948
949	/*
950	* [8] Release the (blocking) task in preparation for
951	* taking the owner task in [10].
952	*
953	* Since we hold lock->waiter_lock, task cannot unblock, even if we
954	* release task->pi_lock.
955	*/
956	raw_spin_unlock(&task->pi_lock);
957	put_task_struct(t: task);
958
959	/*
960	* [9] check_exit_conditions_3 protected by lock->wait_lock.
961	*
962	* We must abort the chain walk if there is no lock owner even
963	* in the dead lock detection case, as we have nothing to
964	* follow here. This is the end of the chain we are walking.
965	*/
966	if (!rt_mutex_owner(lock)) {
967	/*
968	* If the requeue [7] above changed the top waiter,
969	* then we need to wake the new top waiter up to try
970	* to get the lock.
971	*/
972	top_waiter = rt_mutex_top_waiter(lock);
973	if (prerequeue_top_waiter != top_waiter)
974	wake_up_state(tsk: top_waiter->task, state: top_waiter->wake_state);
975	raw_spin_unlock_irq(&lock->wait_lock);
976	return 0;
977	}
978
979	/*
980	* [10] Grab the next task, i.e. the owner of @lock
981	*
982	* Per holding lock->wait_lock and checking for !owner above, there
983	* must be an owner and it cannot go away.
984	*/
985	task = get_task_struct(t: rt_mutex_owner(lock));
986	raw_spin_lock(&task->pi_lock);
987
988	/* [11] requeue the pi waiters if necessary */
989	if (waiter == rt_mutex_top_waiter(lock)) {
990	/*
991	* The waiter became the new top (highest priority)
992	* waiter on the lock. Replace the previous top waiter
993	* in the owner tasks pi waiters tree with this waiter
994	* and adjust the priority of the owner.
995	*/
996	rt_mutex_dequeue_pi(task, waiter: prerequeue_top_waiter);
997	waiter_clone_prio(waiter, task);
998	rt_mutex_enqueue_pi(task, waiter);
999	rt_mutex_adjust_prio(lock, p: task);
1000
1001	} else if (prerequeue_top_waiter == waiter) {
1002	/*
1003	* The waiter was the top waiter on the lock, but is
1004	* no longer the top priority waiter. Replace waiter in
1005	* the owner tasks pi waiters tree with the new top
1006	* (highest priority) waiter and adjust the priority
1007	* of the owner.
1008	* The new top waiter is stored in @waiter so that
1009	* @waiter == @top_waiter evaluates to true below and
1010	* we continue to deboost the rest of the chain.
1011	*/
1012	rt_mutex_dequeue_pi(task, waiter);
1013	waiter = rt_mutex_top_waiter(lock);
1014	waiter_clone_prio(waiter, task);
1015	rt_mutex_enqueue_pi(task, waiter);
1016	rt_mutex_adjust_prio(lock, p: task);
1017	} else {
1018	/*
1019	* Nothing changed. No need to do any priority
1020	* adjustment.
1021	*/
1022	}
1023
1024	/*
1025	* [12] check_exit_conditions_4() protected by task->pi_lock
1026	* and lock->wait_lock. The actual decisions are made after we
1027	* dropped the locks.
1028	*
1029	* Check whether the task which owns the current lock is pi
1030	* blocked itself. If yes we store a pointer to the lock for
1031	* the lock chain change detection above. After we dropped
1032	* task->pi_lock next_lock cannot be dereferenced anymore.
1033	*/
1034	next_lock = task_blocked_on_lock(p: task);
1035	/*
1036	* Store the top waiter of @lock for the end of chain walk
1037	* decision below.
1038	*/
1039	top_waiter = rt_mutex_top_waiter(lock);
1040
1041	/* [13] Drop the locks */
1042	raw_spin_unlock(&task->pi_lock);
1043	raw_spin_unlock_irq(&lock->wait_lock);
1044
1045	/*
1046	* Make the actual exit decisions [12], based on the stored
1047	* values.
1048	*
1049	* We reached the end of the lock chain. Stop right here. No
1050	* point to go back just to figure that out.
1051	*/
1052	if (!next_lock)
1053	goto out_put_task;
1054
1055	/*
1056	* If the current waiter is not the top waiter on the lock,
1057	* then we can stop the chain walk here if we are not in full
1058	* deadlock detection mode.
1059	*/
1060	if (!detect_deadlock && waiter != top_waiter)
1061	goto out_put_task;
1062
1063	goto again;
1064
1065	out_unlock_pi:
1066	raw_spin_unlock_irq(&task->pi_lock);
1067	out_put_task:
1068	put_task_struct(t: task);
1069
1070	return ret;
1071	}
1072
1073	/*
1074	* Try to take an rt-mutex
1075	*
1076	* Must be called with lock->wait_lock held and interrupts disabled
1077	*
1078	* @lock: The lock to be acquired.
1079	* @task: The task which wants to acquire the lock
1080	* @waiter: The waiter that is queued to the lock's wait tree if the
1081	* callsite called task_blocked_on_lock(), otherwise NULL
1082	*/
1083	static int __sched
1084	try_to_take_rt_mutex(struct rt_mutex_base *lock, struct task_struct *task,
1085	struct rt_mutex_waiter *waiter)
1086	{
1087	lockdep_assert_held(&lock->wait_lock);
1088
1089	/*
1090	* Before testing whether we can acquire @lock, we set the
1091	* RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
1092	* other tasks which try to modify @lock into the slow path
1093	* and they serialize on @lock->wait_lock.
1094	*
1095	* The RT_MUTEX_HAS_WAITERS bit can have a transitional state
1096	* as explained at the top of this file if and only if:
1097	*
1098	* - There is a lock owner. The caller must fixup the
1099	* transient state if it does a trylock or leaves the lock
1100	* function due to a signal or timeout.
1101	*
1102	* - @task acquires the lock and there are no other
1103	* waiters. This is undone in rt_mutex_set_owner(@task) at
1104	* the end of this function.
1105	*/
1106	mark_rt_mutex_waiters(lock);
1107
1108	/*
1109	* If @lock has an owner, give up.
1110	*/
1111	if (rt_mutex_owner(lock))
1112	return 0;
1113
1114	/*
1115	* If @waiter != NULL, @task has already enqueued the waiter
1116	* into @lock waiter tree. If @waiter == NULL then this is a
1117	* trylock attempt.
1118	*/
1119	if (waiter) {
1120	struct rt_mutex_waiter *top_waiter = rt_mutex_top_waiter(lock);
1121
1122	/*
1123	* If waiter is the highest priority waiter of @lock,
1124	* or allowed to steal it, take it over.
1125	*/
1126	if (waiter == top_waiter || rt_mutex_steal(waiter, top_waiter)) {
1127	/*
1128	* We can acquire the lock. Remove the waiter from the
1129	* lock waiters tree.
1130	*/
1131	rt_mutex_dequeue(lock, waiter);
1132	} else {
1133	return 0;
1134	}
1135	} else {
1136	/*
1137	* If the lock has waiters already we check whether @task is
1138	* eligible to take over the lock.
1139	*
1140	* If there are no other waiters, @task can acquire
1141	* the lock. @task->pi_blocked_on is NULL, so it does
1142	* not need to be dequeued.
1143	*/
1144	if (rt_mutex_has_waiters(lock)) {
1145	/* Check whether the trylock can steal it. */
1146	if (!rt_mutex_steal(task_to_waiter(task),
1147	top_waiter: rt_mutex_top_waiter(lock)))
1148	return 0;
1149
1150	/*
1151	* The current top waiter stays enqueued. We
1152	* don't have to change anything in the lock
1153	* waiters order.
1154	*/
1155	} else {
1156	/*
1157	* No waiters. Take the lock without the
1158	* pi_lock dance.@task->pi_blocked_on is NULL
1159	* and we have no waiters to enqueue in @task
1160	* pi waiters tree.
1161	*/
1162	goto takeit;
1163	}
1164	}
1165
1166	/*
1167	* Clear @task->pi_blocked_on. Requires protection by
1168	* @task->pi_lock. Redundant operation for the @waiter == NULL
1169	* case, but conditionals are more expensive than a redundant
1170	* store.
1171	*/
1172	raw_spin_lock(&task->pi_lock);
1173	task->pi_blocked_on = NULL;
1174	/*
1175	* Finish the lock acquisition. @task is the new owner. If
1176	* other waiters exist we have to insert the highest priority
1177	* waiter into @task->pi_waiters tree.
1178	*/
1179	if (rt_mutex_has_waiters(lock))
1180	rt_mutex_enqueue_pi(task, waiter: rt_mutex_top_waiter(lock));
1181	raw_spin_unlock(&task->pi_lock);
1182
1183	takeit:
1184	/*
1185	* This either preserves the RT_MUTEX_HAS_WAITERS bit if there
1186	* are still waiters or clears it.
1187	*/
1188	rt_mutex_set_owner(lock, owner: task);
1189
1190	return 1;
1191	}
1192
1193	/*
1194	* Task blocks on lock.
1195	*
1196	* Prepare waiter and propagate pi chain
1197	*
1198	* This must be called with lock->wait_lock held and interrupts disabled
1199	*/
1200	static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
1201	struct rt_mutex_waiter *waiter,
1202	struct task_struct *task,
1203	struct ww_acquire_ctx *ww_ctx,
1204	enum rtmutex_chainwalk chwalk)
1205	{
1206	struct task_struct *owner = rt_mutex_owner(lock);
1207	struct rt_mutex_waiter *top_waiter = waiter;
1208	struct rt_mutex_base *next_lock;
1209	int chain_walk = 0, res;
1210
1211	lockdep_assert_held(&lock->wait_lock);
1212
1213	/*
1214	* Early deadlock detection. We really don't want the task to
1215	* enqueue on itself just to untangle the mess later. It's not
1216	* only an optimization. We drop the locks, so another waiter
1217	* can come in before the chain walk detects the deadlock. So
1218	* the other will detect the deadlock and return -EDEADLOCK,
1219	* which is wrong, as the other waiter is not in a deadlock
1220	* situation.
1221	*
1222	* Except for ww_mutex, in that case the chain walk must already deal
1223	* with spurious cycles, see the comments at [3] and [6].
1224	*/
1225	if (owner == task && !(build_ww_mutex() && ww_ctx))
1226	return -EDEADLK;
1227
1228	raw_spin_lock(&task->pi_lock);
1229	waiter->task = task;
1230	waiter->lock = lock;
1231	waiter_update_prio(waiter, task);
1232	waiter_clone_prio(waiter, task);
1233
1234	/* Get the top priority waiter on the lock */
1235	if (rt_mutex_has_waiters(lock))
1236	top_waiter = rt_mutex_top_waiter(lock);
1237	rt_mutex_enqueue(lock, waiter);
1238
1239	task->pi_blocked_on = waiter;
1240
1241	raw_spin_unlock(&task->pi_lock);
1242
1243	if (build_ww_mutex() && ww_ctx) {
1244	struct rt_mutex *rtm;
1245
1246	/* Check whether the waiter should back out immediately */
1247	rtm = container_of(lock, struct rt_mutex, rtmutex);
1248	res = __ww_mutex_add_waiter(waiter, lock: rtm, ww_ctx);
1249	if (res) {
1250	raw_spin_lock(&task->pi_lock);
1251	rt_mutex_dequeue(lock, waiter);
1252	task->pi_blocked_on = NULL;
1253	raw_spin_unlock(&task->pi_lock);
1254	return res;
1255	}
1256	}
1257
1258	if (!owner)
1259	return 0;
1260
1261	raw_spin_lock(&owner->pi_lock);
1262	if (waiter == rt_mutex_top_waiter(lock)) {
1263	rt_mutex_dequeue_pi(task: owner, waiter: top_waiter);
1264	rt_mutex_enqueue_pi(task: owner, waiter);
1265
1266	rt_mutex_adjust_prio(lock, p: owner);
1267	if (owner->pi_blocked_on)
1268	chain_walk = 1;
1269	} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
1270	chain_walk = 1;
1271	}
1272
1273	/* Store the lock on which owner is blocked or NULL */
1274	next_lock = task_blocked_on_lock(p: owner);
1275
1276	raw_spin_unlock(&owner->pi_lock);
1277	/*
1278	* Even if full deadlock detection is on, if the owner is not
1279	* blocked itself, we can avoid finding this out in the chain
1280	* walk.
1281	*/
1282	if (!chain_walk || !next_lock)
1283	return 0;
1284
1285	/*
1286	* The owner can't disappear while holding a lock,
1287	* so the owner struct is protected by wait_lock.
1288	* Gets dropped in rt_mutex_adjust_prio_chain()!
1289	*/
1290	get_task_struct(t: owner);
1291
1292	raw_spin_unlock_irq(&lock->wait_lock);
1293
1294	res = rt_mutex_adjust_prio_chain(task: owner, chwalk, orig_lock: lock,
1295	next_lock, orig_waiter: waiter, top_task: task);
1296
1297	raw_spin_lock_irq(&lock->wait_lock);
1298
1299	return res;
1300	}
1301
1302	/*
1303	* Remove the top waiter from the current tasks pi waiter tree and
1304	* queue it up.
1305	*
1306	* Called with lock->wait_lock held and interrupts disabled.
1307	*/
1308	static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh,
1309	struct rt_mutex_base *lock)
1310	{
1311	struct rt_mutex_waiter *waiter;
1312
1313	lockdep_assert_held(&lock->wait_lock);
1314
1315	raw_spin_lock(&current->pi_lock);
1316
1317	waiter = rt_mutex_top_waiter(lock);
1318
1319	/*
1320	* Remove it from current->pi_waiters and deboost.
1321	*
1322	* We must in fact deboost here in order to ensure we call
1323	* rt_mutex_setprio() to update p->pi_top_task before the
1324	* task unblocks.
1325	*/
1326	rt_mutex_dequeue_pi(current, waiter);
1327	rt_mutex_adjust_prio(lock, current);
1328
1329	/*
1330	* As we are waking up the top waiter, and the waiter stays
1331	* queued on the lock until it gets the lock, this lock
1332	* obviously has waiters. Just set the bit here and this has
1333	* the added benefit of forcing all new tasks into the
1334	* slow path making sure no task of lower priority than
1335	* the top waiter can steal this lock.
1336	*/
1337	lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1338
1339	/*
1340	* We deboosted before waking the top waiter task such that we don't
1341	* run two tasks with the 'same' priority (and ensure the
1342	* p->pi_top_task pointer points to a blocked task). This however can
1343	* lead to priority inversion if we would get preempted after the
1344	* deboost but before waking our donor task, hence the preempt_disable()
1345	* before unlock.
1346	*
1347	* Pairs with preempt_enable() in rt_mutex_wake_up_q();
1348	*/
1349	preempt_disable();
1350	rt_mutex_wake_q_add(wqh, w: waiter);
1351	raw_spin_unlock(&current->pi_lock);
1352	}
1353
1354	static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock)
1355	{
1356	int ret = try_to_take_rt_mutex(lock, current, NULL);
1357
1358	/*
1359	* try_to_take_rt_mutex() sets the lock waiters bit
1360	* unconditionally. Clean this up.
1361	*/
1362	fixup_rt_mutex_waiters(lock, acquire_lock: true);
1363
1364	return ret;
1365	}
1366
1367	/*
1368	* Slow path try-lock function:
1369	*/
1370	static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock)
1371	{
1372	unsigned long flags;
1373	int ret;
1374
1375	/*
1376	* If the lock already has an owner we fail to get the lock.
1377	* This can be done without taking the @lock->wait_lock as
1378	* it is only being read, and this is a trylock anyway.
1379	*/
1380	if (rt_mutex_owner(lock))
1381	return 0;
1382
1383	/*
1384	* The mutex has currently no owner. Lock the wait lock and try to
1385	* acquire the lock. We use irqsave here to support early boot calls.
1386	*/
1387	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1388
1389	ret = __rt_mutex_slowtrylock(lock);
1390
1391	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1392
1393	return ret;
1394	}
1395
1396	static __always_inline int __rt_mutex_trylock(struct rt_mutex_base *lock)
1397	{
1398	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1399	return 1;
1400
1401	return rt_mutex_slowtrylock(lock);
1402	}
1403
1404	/*
1405	* Slow path to release a rt-mutex.
1406	*/
1407	static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
1408	{
1409	DEFINE_RT_WAKE_Q(wqh);
1410	unsigned long flags;
1411
1412	/* irqsave required to support early boot calls */
1413	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1414
1415	debug_rt_mutex_unlock(lock);
1416
1417	/*
1418	* We must be careful here if the fast path is enabled. If we
1419	* have no waiters queued we cannot set owner to NULL here
1420	* because of:
1421	*
1422	* foo->lock->owner = NULL;
1423	* rtmutex_lock(foo->lock); <- fast path
1424	* free = atomic_dec_and_test(foo->refcnt);
1425	* rtmutex_unlock(foo->lock); <- fast path
1426	* if (free)
1427	* kfree(foo);
1428	* raw_spin_unlock(foo->lock->wait_lock);
1429	*
1430	* So for the fastpath enabled kernel:
1431	*
1432	* Nothing can set the waiters bit as long as we hold
1433	* lock->wait_lock. So we do the following sequence:
1434	*
1435	* owner = rt_mutex_owner(lock);
1436	* clear_rt_mutex_waiters(lock);
1437	* raw_spin_unlock(&lock->wait_lock);
1438	* if (cmpxchg(&lock->owner, owner, 0) == owner)
1439	* return;
1440	* goto retry;
1441	*
1442	* The fastpath disabled variant is simple as all access to
1443	* lock->owner is serialized by lock->wait_lock:
1444	*
1445	* lock->owner = NULL;
1446	* raw_spin_unlock(&lock->wait_lock);
1447	*/
1448	while (!rt_mutex_has_waiters(lock)) {
1449	/* Drops lock->wait_lock ! */
1450	if (unlock_rt_mutex_safe(lock, flags) == true)
1451	return;
1452	/* Relock the rtmutex and try again */
1453	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1454	}
1455
1456	/*
1457	* The wakeup next waiter path does not suffer from the above
1458	* race. See the comments there.
1459	*
1460	* Queue the next waiter for wakeup once we release the wait_lock.
1461	*/
1462	mark_wakeup_next_waiter(wqh: &wqh, lock);
1463	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1464
1465	rt_mutex_wake_up_q(wqh: &wqh);
1466	}
1467
1468	static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock)
1469	{
1470	if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
1471	return;
1472
1473	rt_mutex_slowunlock(lock);
1474	}
1475
1476	#ifdef CONFIG_SMP
1477	static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
1478	struct rt_mutex_waiter *waiter,
1479	struct task_struct *owner)
1480	{
1481	bool res = true;
1482
1483	rcu_read_lock();
1484	for (;;) {
1485	/* If owner changed, trylock again. */
1486	if (owner != rt_mutex_owner(lock))
1487	break;
1488	/*
1489	* Ensure that @owner is dereferenced after checking that
1490	* the lock owner still matches @owner. If that fails,
1491	* @owner might point to freed memory. If it still matches,
1492	* the rcu_read_lock() ensures the memory stays valid.
1493	*/
1494	barrier();
1495	/*
1496	* Stop spinning when:
1497	* - the lock owner has been scheduled out
1498	* - current is not longer the top waiter
1499	* - current is requested to reschedule (redundant
1500	* for CONFIG_PREEMPT_RCU=y)
1501	* - the VCPU on which owner runs is preempted
1502	*/
1503	if (!owner_on_cpu(owner) || need_resched() ||
1504	!rt_mutex_waiter_is_top_waiter(lock, waiter)) {
1505	res = false;
1506	break;
1507	}
1508	cpu_relax();
1509	}
1510	rcu_read_unlock();
1511	return res;
1512	}
1513	#else
1514	static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
1515	struct rt_mutex_waiter *waiter,
1516	struct task_struct *owner)
1517	{
1518	return false;
1519	}
1520	#endif
1521
1522	#ifdef RT_MUTEX_BUILD_MUTEX
1523	/*
1524	* Functions required for:
1525	* - rtmutex, futex on all kernels
1526	* - mutex and rwsem substitutions on RT kernels
1527	*/
1528
1529	/*
1530	* Remove a waiter from a lock and give up
1531	*
1532	* Must be called with lock->wait_lock held and interrupts disabled. It must
1533	* have just failed to try_to_take_rt_mutex().
1534	*/
1535	static void __sched remove_waiter(struct rt_mutex_base *lock,
1536	struct rt_mutex_waiter *waiter)
1537	{
1538	bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1539	struct task_struct *owner = rt_mutex_owner(lock);
1540	struct rt_mutex_base *next_lock;
1541
1542	lockdep_assert_held(&lock->wait_lock);
1543
1544	raw_spin_lock(&current->pi_lock);
1545	rt_mutex_dequeue(lock, waiter);
1546	current->pi_blocked_on = NULL;
1547	raw_spin_unlock(&current->pi_lock);
1548
1549	/*
1550	* Only update priority if the waiter was the highest priority
1551	* waiter of the lock and there is an owner to update.
1552	*/
1553	if (!owner || !is_top_waiter)
1554	return;
1555
1556	raw_spin_lock(&owner->pi_lock);
1557
1558	rt_mutex_dequeue_pi(owner, waiter);
1559
1560	if (rt_mutex_has_waiters(lock))
1561	rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1562
1563	rt_mutex_adjust_prio(lock, owner);
1564
1565	/* Store the lock on which owner is blocked or NULL */
1566	next_lock = task_blocked_on_lock(owner);
1567
1568	raw_spin_unlock(&owner->pi_lock);
1569
1570	/*
1571	* Don't walk the chain, if the owner task is not blocked
1572	* itself.
1573	*/
1574	if (!next_lock)
1575	return;
1576
1577	/* gets dropped in rt_mutex_adjust_prio_chain()! */
1578	get_task_struct(owner);
1579
1580	raw_spin_unlock_irq(&lock->wait_lock);
1581
1582	rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1583	next_lock, NULL, current);
1584
1585	raw_spin_lock_irq(&lock->wait_lock);
1586	}
1587
1588	/**
1589	* rt_mutex_slowlock_block() - Perform the wait-wake-try-to-take loop
1590	* @lock: the rt_mutex to take
1591	* @ww_ctx: WW mutex context pointer
1592	* @state: the state the task should block in (TASK_INTERRUPTIBLE
1593	* or TASK_UNINTERRUPTIBLE)
1594	* @timeout: the pre-initialized and started timer, or NULL for none
1595	* @waiter: the pre-initialized rt_mutex_waiter
1596	*
1597	* Must be called with lock->wait_lock held and interrupts disabled
1598	*/
1599	static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
1600	struct ww_acquire_ctx *ww_ctx,
1601	unsigned int state,
1602	struct hrtimer_sleeper *timeout,
1603	struct rt_mutex_waiter *waiter)
1604	{
1605	struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
1606	struct task_struct *owner;
1607	int ret = 0;
1608
1609	for (;;) {
1610	/* Try to acquire the lock: */
1611	if (try_to_take_rt_mutex(lock, current, waiter))
1612	break;
1613
1614	if (timeout && !timeout->task) {
1615	ret = -ETIMEDOUT;
1616	break;
1617	}
1618	if (signal_pending_state(state, current)) {
1619	ret = -EINTR;
1620	break;
1621	}
1622
1623	if (build_ww_mutex() && ww_ctx) {
1624	ret = __ww_mutex_check_kill(rtm, waiter, ww_ctx);
1625	if (ret)
1626	break;
1627	}
1628
1629	if (waiter == rt_mutex_top_waiter(lock))
1630	owner = rt_mutex_owner(lock);
1631	else
1632	owner = NULL;
1633	raw_spin_unlock_irq(&lock->wait_lock);
1634
1635	if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner))
1636	rt_mutex_schedule();
1637
1638	raw_spin_lock_irq(&lock->wait_lock);
1639	set_current_state(state);
1640	}
1641
1642	__set_current_state(TASK_RUNNING);
1643	return ret;
1644	}
1645
1646	static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
1647	struct rt_mutex_waiter *w)
1648	{
1649	/*
1650	* If the result is not -EDEADLOCK or the caller requested
1651	* deadlock detection, nothing to do here.
1652	*/
1653	if (res != -EDEADLOCK || detect_deadlock)
1654	return;
1655
1656	if (build_ww_mutex() && w->ww_ctx)
1657	return;
1658
1659	/*
1660	* Yell loudly and stop the task right here.
1661	*/
1662	WARN(1, "rtmutex deadlock detected\n");
1663	while (1) {
1664	set_current_state(TASK_INTERRUPTIBLE);
1665	rt_mutex_schedule();
1666	}
1667	}
1668
1669	/**
1670	* __rt_mutex_slowlock - Locking slowpath invoked with lock::wait_lock held
1671	* @lock: The rtmutex to block lock
1672	* @ww_ctx: WW mutex context pointer
1673	* @state: The task state for sleeping
1674	* @chwalk: Indicator whether full or partial chainwalk is requested
1675	* @waiter: Initializer waiter for blocking
1676	*/
1677	static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
1678	struct ww_acquire_ctx *ww_ctx,
1679	unsigned int state,
1680	enum rtmutex_chainwalk chwalk,
1681	struct rt_mutex_waiter *waiter)
1682	{
1683	struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
1684	struct ww_mutex *ww = ww_container_of(rtm);
1685	int ret;
1686
1687	lockdep_assert_held(&lock->wait_lock);
1688
1689	/* Try to acquire the lock again: */
1690	if (try_to_take_rt_mutex(lock, current, NULL)) {
1691	if (build_ww_mutex() && ww_ctx) {
1692	__ww_mutex_check_waiters(rtm, ww_ctx);
1693	ww_mutex_lock_acquired(ww, ww_ctx);
1694	}
1695	return 0;
1696	}
1697
1698	set_current_state(state);
1699
1700	trace_contention_begin(lock, LCB_F_RT);
1701
1702	ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk);
1703	if (likely(!ret))
1704	ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter);
1705
1706	if (likely(!ret)) {
1707	/* acquired the lock */
1708	if (build_ww_mutex() && ww_ctx) {
1709	if (!ww_ctx->is_wait_die)
1710	__ww_mutex_check_waiters(rtm, ww_ctx);
1711	ww_mutex_lock_acquired(ww, ww_ctx);
1712	}
1713	} else {
1714	__set_current_state(TASK_RUNNING);
1715	remove_waiter(lock, waiter);
1716	rt_mutex_handle_deadlock(ret, chwalk, waiter);
1717	}
1718
1719	/*
1720	* try_to_take_rt_mutex() sets the waiter bit
1721	* unconditionally. We might have to fix that up.
1722	*/
1723	fixup_rt_mutex_waiters(lock, true);
1724
1725	trace_contention_end(lock, ret);
1726
1727	return ret;
1728	}
1729
1730	static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
1731	struct ww_acquire_ctx *ww_ctx,
1732	unsigned int state)
1733	{
1734	struct rt_mutex_waiter waiter;
1735	int ret;
1736
1737	rt_mutex_init_waiter(&waiter);
1738	waiter.ww_ctx = ww_ctx;
1739
1740	ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK,
1741	&waiter);
1742
1743	debug_rt_mutex_free_waiter(&waiter);
1744	return ret;
1745	}
1746
1747	/*
1748	* rt_mutex_slowlock - Locking slowpath invoked when fast path fails
1749	* @lock: The rtmutex to block lock
1750	* @ww_ctx: WW mutex context pointer
1751	* @state: The task state for sleeping
1752	*/
1753	static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
1754	struct ww_acquire_ctx *ww_ctx,
1755	unsigned int state)
1756	{
1757	unsigned long flags;
1758	int ret;
1759
1760	/*
1761	* Do all pre-schedule work here, before we queue a waiter and invoke
1762	* PI -- any such work that trips on rtlock (PREEMPT_RT spinlock) would
1763	* otherwise recurse back into task_blocks_on_rt_mutex() through
1764	* rtlock_slowlock() and will then enqueue a second waiter for this
1765	* same task and things get really confusing real fast.
1766	*/
1767	rt_mutex_pre_schedule();
1768
1769	/*
1770	* Technically we could use raw_spin_[un]lock_irq() here, but this can
1771	* be called in early boot if the cmpxchg() fast path is disabled
1772	* (debug, no architecture support). In this case we will acquire the
1773	* rtmutex with lock->wait_lock held. But we cannot unconditionally
1774	* enable interrupts in that early boot case. So we need to use the
1775	* irqsave/restore variants.
1776	*/
1777	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1778	ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state);
1779	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1780	rt_mutex_post_schedule();
1781
1782	return ret;
1783	}
1784
1785	static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,
1786	unsigned int state)
1787	{
1788	lockdep_assert(!current->pi_blocked_on);
1789
1790	if (likely(rt_mutex_try_acquire(lock)))
1791	return 0;
1792
1793	return rt_mutex_slowlock(lock, NULL, state);
1794	}
1795	#endif /* RT_MUTEX_BUILD_MUTEX */
1796
1797	#ifdef RT_MUTEX_BUILD_SPINLOCKS
1798	/*
1799	* Functions required for spin/rw_lock substitution on RT kernels
1800	*/
1801
1802	/**
1803	* rtlock_slowlock_locked - Slow path lock acquisition for RT locks
1804	* @lock: The underlying RT mutex
1805	*/
1806	static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
1807	{
1808	struct rt_mutex_waiter waiter;
1809	struct task_struct *owner;
1810
1811	lockdep_assert_held(&lock->wait_lock);
1812
1813	if (try_to_take_rt_mutex(lock, current, NULL))
1814	return;
1815
1816	rt_mutex_init_rtlock_waiter(&waiter);
1817
1818	/* Save current state and set state to TASK_RTLOCK_WAIT */
1819	current_save_and_set_rtlock_wait_state();
1820
1821	trace_contention_begin(lock, LCB_F_RT);
1822
1823	task_blocks_on_rt_mutex(lock, &waiter, current, NULL, RT_MUTEX_MIN_CHAINWALK);
1824
1825	for (;;) {
1826	/* Try to acquire the lock again */
1827	if (try_to_take_rt_mutex(lock, current, &waiter))
1828	break;
1829
1830	if (&waiter == rt_mutex_top_waiter(lock))
1831	owner = rt_mutex_owner(lock);
1832	else
1833	owner = NULL;
1834	raw_spin_unlock_irq(&lock->wait_lock);
1835
1836	if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner))
1837	schedule_rtlock();
1838
1839	raw_spin_lock_irq(&lock->wait_lock);
1840	set_current_state(TASK_RTLOCK_WAIT);
1841	}
1842
1843	/* Restore the task state */
1844	current_restore_rtlock_saved_state();
1845
1846	/*
1847	* try_to_take_rt_mutex() sets the waiter bit unconditionally.
1848	* We might have to fix that up:
1849	*/
1850	fixup_rt_mutex_waiters(lock, true);
1851	debug_rt_mutex_free_waiter(&waiter);
1852
1853	trace_contention_end(lock, 0);
1854	}
1855
1856	static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock)
1857	{
1858	unsigned long flags;
1859
1860	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1861	rtlock_slowlock_locked(lock);
1862	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1863	}
1864
1865	#endif /* RT_MUTEX_BUILD_SPINLOCKS */
1866