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 *
  12 *  See Documentation/locking/rt-mutex-design.rst for details.
  13 */
  14#include <linux/spinlock.h>
  15#include <linux/export.h>
  16#include <linux/sched/signal.h>
  17#include <linux/sched/rt.h>
  18#include <linux/sched/deadline.h>
  19#include <linux/sched/wake_q.h>
  20#include <linux/sched/debug.h>
  21#include <linux/timer.h>
  22
  23#include "rtmutex_common.h"
  24
  25/*
  26 * lock->owner state tracking:
  27 *
  28 * lock->owner holds the task_struct pointer of the owner. Bit 0
  29 * is used to keep track of the "lock has waiters" state.
  30 *
  31 * owner	bit0
  32 * NULL		0	lock is free (fast acquire possible)
  33 * NULL		1	lock is free and has waiters and the top waiter
  34 *				is going to take the lock*
  35 * taskpointer	0	lock is held (fast release possible)
  36 * taskpointer	1	lock is held and has waiters**
  37 *
  38 * The fast atomic compare exchange based acquire and release is only
  39 * possible when bit 0 of lock->owner is 0.
  40 *
  41 * (*) It also can be a transitional state when grabbing the lock
  42 * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
  43 * we need to set the bit0 before looking at the lock, and the owner may be
  44 * NULL in this small time, hence this can be a transitional state.
  45 *
  46 * (**) There is a small time when bit 0 is set but there are no
  47 * waiters. This can happen when grabbing the lock in the slow path.
  48 * To prevent a cmpxchg of the owner releasing the lock, we need to
  49 * set this bit before looking at the lock.
  50 */
  51
  52static void
  53rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
  54{
  55	unsigned long val = (unsigned long)owner;
  56
  57	if (rt_mutex_has_waiters(lock))
  58		val |= RT_MUTEX_HAS_WAITERS;
  59
  60	lock->owner = (struct task_struct *)val;
  61}
  62
  63static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
  64{
  65	lock->owner = (struct task_struct *)
  66			((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
  67}
  68
  69static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
  70{
  71	unsigned long owner, *p = (unsigned long *) &lock->owner;
  72
  73	if (rt_mutex_has_waiters(lock))
  74		return;
  75
  76	/*
  77	 * The rbtree has no waiters enqueued, now make sure that the
  78	 * lock->owner still has the waiters bit set, otherwise the
  79	 * following can happen:
  80	 *
  81	 * CPU 0	CPU 1		CPU2
  82	 * l->owner=T1
  83	 *		rt_mutex_lock(l)
  84	 *		lock(l->lock)
  85	 *		l->owner = T1 | HAS_WAITERS;
  86	 *		enqueue(T2)
  87	 *		boost()
  88	 *		  unlock(l->lock)
  89	 *		block()
  90	 *
  91	 *				rt_mutex_lock(l)
  92	 *				lock(l->lock)
  93	 *				l->owner = T1 | HAS_WAITERS;
  94	 *				enqueue(T3)
  95	 *				boost()
  96	 *				  unlock(l->lock)
  97	 *				block()
  98	 *		signal(->T2)	signal(->T3)
  99	 *		lock(l->lock)
 100	 *		dequeue(T2)
 101	 *		deboost()
 102	 *		  unlock(l->lock)
 103	 *				lock(l->lock)
 104	 *				dequeue(T3)
 105	 *				 ==> wait list is empty
 106	 *				deboost()
 107	 *				 unlock(l->lock)
 108	 *		lock(l->lock)
 109	 *		fixup_rt_mutex_waiters()
 110	 *		  if (wait_list_empty(l) {
 111	 *		    l->owner = owner
 112	 *		    owner = l->owner & ~HAS_WAITERS;
 113	 *		      ==> l->owner = T1
 114	 *		  }
 115	 *				lock(l->lock)
 116	 * rt_mutex_unlock(l)		fixup_rt_mutex_waiters()
 117	 *				  if (wait_list_empty(l) {
 118	 *				    owner = l->owner & ~HAS_WAITERS;
 119	 * cmpxchg(l->owner, T1, NULL)
 120	 *  ===> Success (l->owner = NULL)
 121	 *
 122	 *				    l->owner = owner
 123	 *				      ==> l->owner = T1
 124	 *				  }
 125	 *
 126	 * With the check for the waiter bit in place T3 on CPU2 will not
 127	 * overwrite. All tasks fiddling with the waiters bit are
 128	 * serialized by l->lock, so nothing else can modify the waiters
 129	 * bit. If the bit is set then nothing can change l->owner either
 130	 * so the simple RMW is safe. The cmpxchg() will simply fail if it
 131	 * happens in the middle of the RMW because the waiters bit is
 132	 * still set.
 133	 */
 134	owner = READ_ONCE(*p);
 135	if (owner & RT_MUTEX_HAS_WAITERS)
 136		WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
 137}
 138
 139/*
 140 * We can speed up the acquire/release, if there's no debugging state to be
 141 * set up.
 142 */
 143#ifndef CONFIG_DEBUG_RT_MUTEXES
 144# define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
 145# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
 146# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
 147
 148/*
 149 * Callers must hold the ->wait_lock -- which is the whole purpose as we force
 150 * all future threads that attempt to [Rmw] the lock to the slowpath. As such
 151 * relaxed semantics suffice.
 152 */
 153static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
 154{
 155	unsigned long owner, *p = (unsigned long *) &lock->owner;
 156
 157	do {
 158		owner = *p;
 159	} while (cmpxchg_relaxed(p, owner,
 160				 owner | RT_MUTEX_HAS_WAITERS) != owner);
 161}
 162
 163/*
 164 * Safe fastpath aware unlock:
 165 * 1) Clear the waiters bit
 166 * 2) Drop lock->wait_lock
 167 * 3) Try to unlock the lock with cmpxchg
 168 */
 169static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
 170					unsigned long flags)
 171	__releases(lock->wait_lock)
 172{
 173	struct task_struct *owner = rt_mutex_owner(lock);
 174
 175	clear_rt_mutex_waiters(lock);
 176	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 177	/*
 178	 * If a new waiter comes in between the unlock and the cmpxchg
 179	 * we have two situations:
 180	 *
 181	 * unlock(wait_lock);
 182	 *					lock(wait_lock);
 183	 * cmpxchg(p, owner, 0) == owner
 184	 *					mark_rt_mutex_waiters(lock);
 185	 *					acquire(lock);
 186	 * or:
 187	 *
 188	 * unlock(wait_lock);
 189	 *					lock(wait_lock);
 190	 *					mark_rt_mutex_waiters(lock);
 191	 *
 192	 * cmpxchg(p, owner, 0) != owner
 193	 *					enqueue_waiter();
 194	 *					unlock(wait_lock);
 195	 * lock(wait_lock);
 196	 * wake waiter();
 197	 * unlock(wait_lock);
 198	 *					lock(wait_lock);
 199	 *					acquire(lock);
 200	 */
 201	return rt_mutex_cmpxchg_release(lock, owner, NULL);
 202}
 203
 204#else
 205# define rt_mutex_cmpxchg_relaxed(l,c,n)	(0)
 206# define rt_mutex_cmpxchg_acquire(l,c,n)	(0)
 207# define rt_mutex_cmpxchg_release(l,c,n)	(0)
 208
 209static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
 210{
 211	lock->owner = (struct task_struct *)
 212			((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
 213}
 214
 215/*
 216 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
 217 */
 218static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
 219					unsigned long flags)
 220	__releases(lock->wait_lock)
 221{
 222	lock->owner = NULL;
 223	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 224	return true;
 225}
 226#endif
 227
 228/*
 229 * Only use with rt_mutex_waiter_{less,equal}()
 230 */
 231#define task_to_waiter(p)	\
 232	&(struct rt_mutex_waiter){ .prio = (p)->prio, .deadline = (p)->dl.deadline }
 233
 234static inline int
 235rt_mutex_waiter_less(struct rt_mutex_waiter *left,
 236		     struct rt_mutex_waiter *right)
 237{
 238	if (left->prio < right->prio)
 239		return 1;
 240
 241	/*
 242	 * If both waiters have dl_prio(), we check the deadlines of the
 243	 * associated tasks.
 244	 * If left waiter has a dl_prio(), and we didn't return 1 above,
 245	 * then right waiter has a dl_prio() too.
 246	 */
 247	if (dl_prio(left->prio))
 248		return dl_time_before(left->deadline, right->deadline);
 249
 250	return 0;
 251}
 252
 253static inline int
 254rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
 255		      struct rt_mutex_waiter *right)
 256{
 257	if (left->prio != right->prio)
 258		return 0;
 259
 260	/*
 261	 * If both waiters have dl_prio(), we check the deadlines of the
 262	 * associated tasks.
 263	 * If left waiter has a dl_prio(), and we didn't return 0 above,
 264	 * then right waiter has a dl_prio() too.
 265	 */
 266	if (dl_prio(left->prio))
 267		return left->deadline == right->deadline;
 268
 269	return 1;
 270}
 271
 272static void
 273rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
 274{
 275	struct rb_node **link = &lock->waiters.rb_root.rb_node;
 276	struct rb_node *parent = NULL;
 277	struct rt_mutex_waiter *entry;
 278	bool leftmost = true;
 279
 280	while (*link) {
 281		parent = *link;
 282		entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
 283		if (rt_mutex_waiter_less(waiter, entry)) {
 284			link = &parent->rb_left;
 285		} else {
 286			link = &parent->rb_right;
 287			leftmost = false;
 288		}
 289	}
 290
 291	rb_link_node(&waiter->tree_entry, parent, link);
 292	rb_insert_color_cached(&waiter->tree_entry, &lock->waiters, leftmost);
 293}
 294
 295static void
 296rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
 297{
 298	if (RB_EMPTY_NODE(&waiter->tree_entry))
 299		return;
 300
 301	rb_erase_cached(&waiter->tree_entry, &lock->waiters);
 302	RB_CLEAR_NODE(&waiter->tree_entry);
 303}
 304
 305static void
 306rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 307{
 308	struct rb_node **link = &task->pi_waiters.rb_root.rb_node;
 309	struct rb_node *parent = NULL;
 310	struct rt_mutex_waiter *entry;
 311	bool leftmost = true;
 312
 313	while (*link) {
 314		parent = *link;
 315		entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
 316		if (rt_mutex_waiter_less(waiter, entry)) {
 317			link = &parent->rb_left;
 318		} else {
 319			link = &parent->rb_right;
 320			leftmost = false;
 321		}
 322	}
 323
 324	rb_link_node(&waiter->pi_tree_entry, parent, link);
 325	rb_insert_color_cached(&waiter->pi_tree_entry, &task->pi_waiters, leftmost);
 326}
 327
 328static void
 329rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 330{
 331	if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
 332		return;
 333
 334	rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
 335	RB_CLEAR_NODE(&waiter->pi_tree_entry);
 336}
 337
 338static void rt_mutex_adjust_prio(struct task_struct *p)
 339{
 340	struct task_struct *pi_task = NULL;
 341
 342	lockdep_assert_held(&p->pi_lock);
 343
 344	if (task_has_pi_waiters(p))
 345		pi_task = task_top_pi_waiter(p)->task;
 346
 347	rt_mutex_setprio(p, pi_task);
 348}
 349
 350/*
 351 * Deadlock detection is conditional:
 352 *
 353 * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
 354 * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
 355 *
 356 * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
 357 * conducted independent of the detect argument.
 358 *
 359 * If the waiter argument is NULL this indicates the deboost path and
 360 * deadlock detection is disabled independent of the detect argument
 361 * and the config settings.
 362 */
 363static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
 364					  enum rtmutex_chainwalk chwalk)
 365{
 366	/*
 367	 * This is just a wrapper function for the following call,
 368	 * because debug_rt_mutex_detect_deadlock() smells like a magic
 369	 * debug feature and I wanted to keep the cond function in the
 370	 * main source file along with the comments instead of having
 371	 * two of the same in the headers.
 372	 */
 373	return debug_rt_mutex_detect_deadlock(waiter, chwalk);
 374}
 375
 376/*
 377 * Max number of times we'll walk the boosting chain:
 378 */
 379int max_lock_depth = 1024;
 380
 381static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
 382{
 383	return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
 384}
 385
 386/*
 387 * Adjust the priority chain. Also used for deadlock detection.
 388 * Decreases task's usage by one - may thus free the task.
 389 *
 390 * @task:	the task owning the mutex (owner) for which a chain walk is
 391 *		probably needed
 392 * @chwalk:	do we have to carry out deadlock detection?
 393 * @orig_lock:	the mutex (can be NULL if we are walking the chain to recheck
 394 *		things for a task that has just got its priority adjusted, and
 395 *		is waiting on a mutex)
 396 * @next_lock:	the mutex on which the owner of @orig_lock was blocked before
 397 *		we dropped its pi_lock. Is never dereferenced, only used for
 398 *		comparison to detect lock chain changes.
 399 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
 400 *		its priority to the mutex owner (can be NULL in the case
 401 *		depicted above or if the top waiter is gone away and we are
 402 *		actually deboosting the owner)
 403 * @top_task:	the current top waiter
 404 *
 405 * Returns 0 or -EDEADLK.
 406 *
 407 * Chain walk basics and protection scope
 408 *
 409 * [R] refcount on task
 410 * [P] task->pi_lock held
 411 * [L] rtmutex->wait_lock held
 412 *
 413 * Step	Description				Protected by
 414 *	function arguments:
 415 *	@task					[R]
 416 *	@orig_lock if != NULL			@top_task is blocked on it
 417 *	@next_lock				Unprotected. Cannot be
 418 *						dereferenced. Only used for
 419 *						comparison.
 420 *	@orig_waiter if != NULL			@top_task is blocked on it
 421 *	@top_task				current, or in case of proxy
 422 *						locking protected by calling
 423 *						code
 424 *	again:
 425 *	  loop_sanity_check();
 426 *	retry:
 427 * [1]	  lock(task->pi_lock);			[R] acquire [P]
 428 * [2]	  waiter = task->pi_blocked_on;		[P]
 429 * [3]	  check_exit_conditions_1();		[P]
 430 * [4]	  lock = waiter->lock;			[P]
 431 * [5]	  if (!try_lock(lock->wait_lock)) {	[P] try to acquire [L]
 432 *	    unlock(task->pi_lock);		release [P]
 433 *	    goto retry;
 434 *	  }
 435 * [6]	  check_exit_conditions_2();		[P] + [L]
 436 * [7]	  requeue_lock_waiter(lock, waiter);	[P] + [L]
 437 * [8]	  unlock(task->pi_lock);		release [P]
 438 *	  put_task_struct(task);		release [R]
 439 * [9]	  check_exit_conditions_3();		[L]
 440 * [10]	  task = owner(lock);			[L]
 441 *	  get_task_struct(task);		[L] acquire [R]
 442 *	  lock(task->pi_lock);			[L] acquire [P]
 443 * [11]	  requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
 444 * [12]	  check_exit_conditions_4();		[P] + [L]
 445 * [13]	  unlock(task->pi_lock);		release [P]
 446 *	  unlock(lock->wait_lock);		release [L]
 447 *	  goto again;
 448 */
 449static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 450				      enum rtmutex_chainwalk chwalk,
 451				      struct rt_mutex *orig_lock,
 452				      struct rt_mutex *next_lock,
 453				      struct rt_mutex_waiter *orig_waiter,
 454				      struct task_struct *top_task)
 455{
 456	struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 457	struct rt_mutex_waiter *prerequeue_top_waiter;
 458	int ret = 0, depth = 0;
 459	struct rt_mutex *lock;
 460	bool detect_deadlock;
 461	bool requeue = true;
 462
 463	detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
 464
 465	/*
 466	 * The (de)boosting is a step by step approach with a lot of
 467	 * pitfalls. We want this to be preemptible and we want hold a
 468	 * maximum of two locks per step. So we have to check
 469	 * carefully whether things change under us.
 470	 */
 471 again:
 472	/*
 473	 * We limit the lock chain length for each invocation.
 474	 */
 475	if (++depth > max_lock_depth) {
 476		static int prev_max;
 477
 478		/*
 479		 * Print this only once. If the admin changes the limit,
 480		 * print a new message when reaching the limit again.
 481		 */
 482		if (prev_max != max_lock_depth) {
 483			prev_max = max_lock_depth;
 484			printk(KERN_WARNING "Maximum lock depth %d reached "
 485			       "task: %s (%d)\n", max_lock_depth,
 486			       top_task->comm, task_pid_nr(top_task));
 487		}
 488		put_task_struct(task);
 489
 490		return -EDEADLK;
 491	}
 492
 493	/*
 494	 * We are fully preemptible here and only hold the refcount on
 495	 * @task. So everything can have changed under us since the
 496	 * caller or our own code below (goto retry/again) dropped all
 497	 * locks.
 498	 */
 499 retry:
 500	/*
 501	 * [1] Task cannot go away as we did a get_task() before !
 502	 */
 503	raw_spin_lock_irq(&task->pi_lock);
 504
 505	/*
 506	 * [2] Get the waiter on which @task is blocked on.
 507	 */
 508	waiter = task->pi_blocked_on;
 509
 510	/*
 511	 * [3] check_exit_conditions_1() protected by task->pi_lock.
 512	 */
 513
 514	/*
 515	 * Check whether the end of the boosting chain has been
 516	 * reached or the state of the chain has changed while we
 517	 * dropped the locks.
 518	 */
 519	if (!waiter)
 520		goto out_unlock_pi;
 521
 522	/*
 523	 * Check the orig_waiter state. After we dropped the locks,
 524	 * the previous owner of the lock might have released the lock.
 525	 */
 526	if (orig_waiter && !rt_mutex_owner(orig_lock))
 527		goto out_unlock_pi;
 528
 529	/*
 530	 * We dropped all locks after taking a refcount on @task, so
 531	 * the task might have moved on in the lock chain or even left
 532	 * the chain completely and blocks now on an unrelated lock or
 533	 * on @orig_lock.
 534	 *
 535	 * We stored the lock on which @task was blocked in @next_lock,
 536	 * so we can detect the chain change.
 537	 */
 538	if (next_lock != waiter->lock)
 539		goto out_unlock_pi;
 540
 541	/*
 542	 * Drop out, when the task has no waiters. Note,
 543	 * top_waiter can be NULL, when we are in the deboosting
 544	 * mode!
 545	 */
 546	if (top_waiter) {
 547		if (!task_has_pi_waiters(task))
 548			goto out_unlock_pi;
 549		/*
 550		 * If deadlock detection is off, we stop here if we
 551		 * are not the top pi waiter of the task. If deadlock
 552		 * detection is enabled we continue, but stop the
 553		 * requeueing in the chain walk.
 554		 */
 555		if (top_waiter != task_top_pi_waiter(task)) {
 556			if (!detect_deadlock)
 557				goto out_unlock_pi;
 558			else
 559				requeue = false;
 560		}
 561	}
 562
 563	/*
 564	 * If the waiter priority is the same as the task priority
 565	 * then there is no further priority adjustment necessary.  If
 566	 * deadlock detection is off, we stop the chain walk. If its
 567	 * enabled we continue, but stop the requeueing in the chain
 568	 * walk.
 569	 */
 570	if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
 571		if (!detect_deadlock)
 572			goto out_unlock_pi;
 573		else
 574			requeue = false;
 575	}
 576
 577	/*
 578	 * [4] Get the next lock
 579	 */
 580	lock = waiter->lock;
 581	/*
 582	 * [5] We need to trylock here as we are holding task->pi_lock,
 583	 * which is the reverse lock order versus the other rtmutex
 584	 * operations.
 585	 */
 586	if (!raw_spin_trylock(&lock->wait_lock)) {
 587		raw_spin_unlock_irq(&task->pi_lock);
 588		cpu_relax();
 589		goto retry;
 590	}
 591
 592	/*
 593	 * [6] check_exit_conditions_2() protected by task->pi_lock and
 594	 * lock->wait_lock.
 595	 *
 596	 * Deadlock detection. If the lock is the same as the original
 597	 * lock which caused us to walk the lock chain or if the
 598	 * current lock is owned by the task which initiated the chain
 599	 * walk, we detected a deadlock.
 600	 */
 601	if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 602		debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
 603		raw_spin_unlock(&lock->wait_lock);
 604		ret = -EDEADLK;
 605		goto out_unlock_pi;
 606	}
 607
 608	/*
 609	 * If we just follow the lock chain for deadlock detection, no
 610	 * need to do all the requeue operations. To avoid a truckload
 611	 * of conditionals around the various places below, just do the
 612	 * minimum chain walk checks.
 613	 */
 614	if (!requeue) {
 615		/*
 616		 * No requeue[7] here. Just release @task [8]
 617		 */
 618		raw_spin_unlock(&task->pi_lock);
 619		put_task_struct(task);
 620
 621		/*
 622		 * [9] check_exit_conditions_3 protected by lock->wait_lock.
 623		 * If there is no owner of the lock, end of chain.
 624		 */
 625		if (!rt_mutex_owner(lock)) {
 626			raw_spin_unlock_irq(&lock->wait_lock);
 627			return 0;
 628		}
 629
 630		/* [10] Grab the next task, i.e. owner of @lock */
 631		task = get_task_struct(rt_mutex_owner(lock));
 632		raw_spin_lock(&task->pi_lock);
 633
 634		/*
 635		 * No requeue [11] here. We just do deadlock detection.
 636		 *
 637		 * [12] Store whether owner is blocked
 638		 * itself. Decision is made after dropping the locks
 639		 */
 640		next_lock = task_blocked_on_lock(task);
 641		/*
 642		 * Get the top waiter for the next iteration
 643		 */
 644		top_waiter = rt_mutex_top_waiter(lock);
 645
 646		/* [13] Drop locks */
 647		raw_spin_unlock(&task->pi_lock);
 648		raw_spin_unlock_irq(&lock->wait_lock);
 649
 650		/* If owner is not blocked, end of chain. */
 651		if (!next_lock)
 652			goto out_put_task;
 653		goto again;
 654	}
 655
 656	/*
 657	 * Store the current top waiter before doing the requeue
 658	 * operation on @lock. We need it for the boost/deboost
 659	 * decision below.
 660	 */
 661	prerequeue_top_waiter = rt_mutex_top_waiter(lock);
 662
 663	/* [7] Requeue the waiter in the lock waiter tree. */
 664	rt_mutex_dequeue(lock, waiter);
 665
 666	/*
 667	 * Update the waiter prio fields now that we're dequeued.
 668	 *
 669	 * These values can have changed through either:
 670	 *
 671	 *   sys_sched_set_scheduler() / sys_sched_setattr()
 672	 *
 673	 * or
 674	 *
 675	 *   DL CBS enforcement advancing the effective deadline.
 676	 *
 677	 * Even though pi_waiters also uses these fields, and that tree is only
 678	 * updated in [11], we can do this here, since we hold [L], which
 679	 * serializes all pi_waiters access and rb_erase() does not care about
 680	 * the values of the node being removed.
 681	 */
 682	waiter->prio = task->prio;
 683	waiter->deadline = task->dl.deadline;
 684
 685	rt_mutex_enqueue(lock, waiter);
 686
 687	/* [8] Release the task */
 688	raw_spin_unlock(&task->pi_lock);
 689	put_task_struct(task);
 690
 691	/*
 692	 * [9] check_exit_conditions_3 protected by lock->wait_lock.
 693	 *
 694	 * We must abort the chain walk if there is no lock owner even
 695	 * in the dead lock detection case, as we have nothing to
 696	 * follow here. This is the end of the chain we are walking.
 697	 */
 698	if (!rt_mutex_owner(lock)) {
 699		/*
 700		 * If the requeue [7] above changed the top waiter,
 701		 * then we need to wake the new top waiter up to try
 702		 * to get the lock.
 703		 */
 704		if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))
 705			wake_up_process(rt_mutex_top_waiter(lock)->task);
 706		raw_spin_unlock_irq(&lock->wait_lock);
 707		return 0;
 708	}
 709
 710	/* [10] Grab the next task, i.e. the owner of @lock */
 711	task = get_task_struct(rt_mutex_owner(lock));
 712	raw_spin_lock(&task->pi_lock);
 713
 714	/* [11] requeue the pi waiters if necessary */
 715	if (waiter == rt_mutex_top_waiter(lock)) {
 716		/*
 717		 * The waiter became the new top (highest priority)
 718		 * waiter on the lock. Replace the previous top waiter
 719		 * in the owner tasks pi waiters tree with this waiter
 720		 * and adjust the priority of the owner.
 721		 */
 722		rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
 723		rt_mutex_enqueue_pi(task, waiter);
 724		rt_mutex_adjust_prio(task);
 725
 726	} else if (prerequeue_top_waiter == waiter) {
 727		/*
 728		 * The waiter was the top waiter on the lock, but is
 729		 * no longer the top prority waiter. Replace waiter in
 730		 * the owner tasks pi waiters tree with the new top
 731		 * (highest priority) waiter and adjust the priority
 732		 * of the owner.
 733		 * The new top waiter is stored in @waiter so that
 734		 * @waiter == @top_waiter evaluates to true below and
 735		 * we continue to deboost the rest of the chain.
 736		 */
 737		rt_mutex_dequeue_pi(task, waiter);
 738		waiter = rt_mutex_top_waiter(lock);
 739		rt_mutex_enqueue_pi(task, waiter);
 740		rt_mutex_adjust_prio(task);
 741	} else {
 742		/*
 743		 * Nothing changed. No need to do any priority
 744		 * adjustment.
 745		 */
 746	}
 747
 748	/*
 749	 * [12] check_exit_conditions_4() protected by task->pi_lock
 750	 * and lock->wait_lock. The actual decisions are made after we
 751	 * dropped the locks.
 752	 *
 753	 * Check whether the task which owns the current lock is pi
 754	 * blocked itself. If yes we store a pointer to the lock for
 755	 * the lock chain change detection above. After we dropped
 756	 * task->pi_lock next_lock cannot be dereferenced anymore.
 757	 */
 758	next_lock = task_blocked_on_lock(task);
 759	/*
 760	 * Store the top waiter of @lock for the end of chain walk
 761	 * decision below.
 762	 */
 763	top_waiter = rt_mutex_top_waiter(lock);
 764
 765	/* [13] Drop the locks */
 766	raw_spin_unlock(&task->pi_lock);
 767	raw_spin_unlock_irq(&lock->wait_lock);
 768
 769	/*
 770	 * Make the actual exit decisions [12], based on the stored
 771	 * values.
 772	 *
 773	 * We reached the end of the lock chain. Stop right here. No
 774	 * point to go back just to figure that out.
 775	 */
 776	if (!next_lock)
 777		goto out_put_task;
 778
 779	/*
 780	 * If the current waiter is not the top waiter on the lock,
 781	 * then we can stop the chain walk here if we are not in full
 782	 * deadlock detection mode.
 783	 */
 784	if (!detect_deadlock && waiter != top_waiter)
 785		goto out_put_task;
 786
 787	goto again;
 788
 789 out_unlock_pi:
 790	raw_spin_unlock_irq(&task->pi_lock);
 791 out_put_task:
 792	put_task_struct(task);
 793
 794	return ret;
 795}
 796
 797/*
 798 * Try to take an rt-mutex
 799 *
 800 * Must be called with lock->wait_lock held and interrupts disabled
 801 *
 802 * @lock:   The lock to be acquired.
 803 * @task:   The task which wants to acquire the lock
 804 * @waiter: The waiter that is queued to the lock's wait tree if the
 805 *	    callsite called task_blocked_on_lock(), otherwise NULL
 806 */
 807static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
 808				struct rt_mutex_waiter *waiter)
 809{
 810	lockdep_assert_held(&lock->wait_lock);
 811
 812	/*
 813	 * Before testing whether we can acquire @lock, we set the
 814	 * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
 815	 * other tasks which try to modify @lock into the slow path
 816	 * and they serialize on @lock->wait_lock.
 817	 *
 818	 * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
 819	 * as explained at the top of this file if and only if:
 820	 *
 821	 * - There is a lock owner. The caller must fixup the
 822	 *   transient state if it does a trylock or leaves the lock
 823	 *   function due to a signal or timeout.
 824	 *
 825	 * - @task acquires the lock and there are no other
 826	 *   waiters. This is undone in rt_mutex_set_owner(@task) at
 827	 *   the end of this function.
 828	 */
 829	mark_rt_mutex_waiters(lock);
 830
 831	/*
 832	 * If @lock has an owner, give up.
 833	 */
 834	if (rt_mutex_owner(lock))
 835		return 0;
 836
 837	/*
 838	 * If @waiter != NULL, @task has already enqueued the waiter
 839	 * into @lock waiter tree. If @waiter == NULL then this is a
 840	 * trylock attempt.
 841	 */
 842	if (waiter) {
 843		/*
 844		 * If waiter is not the highest priority waiter of
 845		 * @lock, give up.
 846		 */
 847		if (waiter != rt_mutex_top_waiter(lock))
 848			return 0;
 849
 850		/*
 851		 * We can acquire the lock. Remove the waiter from the
 852		 * lock waiters tree.
 853		 */
 854		rt_mutex_dequeue(lock, waiter);
 855
 856	} else {
 857		/*
 858		 * If the lock has waiters already we check whether @task is
 859		 * eligible to take over the lock.
 860		 *
 861		 * If there are no other waiters, @task can acquire
 862		 * the lock.  @task->pi_blocked_on is NULL, so it does
 863		 * not need to be dequeued.
 864		 */
 865		if (rt_mutex_has_waiters(lock)) {
 866			/*
 867			 * If @task->prio is greater than or equal to
 868			 * the top waiter priority (kernel view),
 869			 * @task lost.
 870			 */
 871			if (!rt_mutex_waiter_less(task_to_waiter(task),
 872						  rt_mutex_top_waiter(lock)))
 873				return 0;
 874
 875			/*
 876			 * The current top waiter stays enqueued. We
 877			 * don't have to change anything in the lock
 878			 * waiters order.
 879			 */
 880		} else {
 881			/*
 882			 * No waiters. Take the lock without the
 883			 * pi_lock dance.@task->pi_blocked_on is NULL
 884			 * and we have no waiters to enqueue in @task
 885			 * pi waiters tree.
 886			 */
 887			goto takeit;
 888		}
 889	}
 890
 891	/*
 892	 * Clear @task->pi_blocked_on. Requires protection by
 893	 * @task->pi_lock. Redundant operation for the @waiter == NULL
 894	 * case, but conditionals are more expensive than a redundant
 895	 * store.
 896	 */
 897	raw_spin_lock(&task->pi_lock);
 898	task->pi_blocked_on = NULL;
 899	/*
 900	 * Finish the lock acquisition. @task is the new owner. If
 901	 * other waiters exist we have to insert the highest priority
 902	 * waiter into @task->pi_waiters tree.
 903	 */
 904	if (rt_mutex_has_waiters(lock))
 905		rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
 906	raw_spin_unlock(&task->pi_lock);
 907
 908takeit:
 909	/* We got the lock. */
 910	debug_rt_mutex_lock(lock);
 911
 912	/*
 913	 * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
 914	 * are still waiters or clears it.
 915	 */
 916	rt_mutex_set_owner(lock, task);
 917
 918	return 1;
 919}
 920
 921/*
 922 * Task blocks on lock.
 923 *
 924 * Prepare waiter and propagate pi chain
 925 *
 926 * This must be called with lock->wait_lock held and interrupts disabled
 927 */
 928static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 929				   struct rt_mutex_waiter *waiter,
 930				   struct task_struct *task,
 931				   enum rtmutex_chainwalk chwalk)
 932{
 933	struct task_struct *owner = rt_mutex_owner(lock);
 934	struct rt_mutex_waiter *top_waiter = waiter;
 935	struct rt_mutex *next_lock;
 936	int chain_walk = 0, res;
 937
 938	lockdep_assert_held(&lock->wait_lock);
 939
 940	/*
 941	 * Early deadlock detection. We really don't want the task to
 942	 * enqueue on itself just to untangle the mess later. It's not
 943	 * only an optimization. We drop the locks, so another waiter
 944	 * can come in before the chain walk detects the deadlock. So
 945	 * the other will detect the deadlock and return -EDEADLOCK,
 946	 * which is wrong, as the other waiter is not in a deadlock
 947	 * situation.
 948	 */
 949	if (owner == task)
 950		return -EDEADLK;
 951
 952	raw_spin_lock(&task->pi_lock);
 953	waiter->task = task;
 954	waiter->lock = lock;
 955	waiter->prio = task->prio;
 956	waiter->deadline = task->dl.deadline;
 957
 958	/* Get the top priority waiter on the lock */
 959	if (rt_mutex_has_waiters(lock))
 960		top_waiter = rt_mutex_top_waiter(lock);
 961	rt_mutex_enqueue(lock, waiter);
 962
 963	task->pi_blocked_on = waiter;
 964
 965	raw_spin_unlock(&task->pi_lock);
 966
 967	if (!owner)
 968		return 0;
 969
 970	raw_spin_lock(&owner->pi_lock);
 971	if (waiter == rt_mutex_top_waiter(lock)) {
 972		rt_mutex_dequeue_pi(owner, top_waiter);
 973		rt_mutex_enqueue_pi(owner, waiter);
 974
 975		rt_mutex_adjust_prio(owner);
 976		if (owner->pi_blocked_on)
 977			chain_walk = 1;
 978	} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
 979		chain_walk = 1;
 980	}
 981
 982	/* Store the lock on which owner is blocked or NULL */
 983	next_lock = task_blocked_on_lock(owner);
 984
 985	raw_spin_unlock(&owner->pi_lock);
 986	/*
 987	 * Even if full deadlock detection is on, if the owner is not
 988	 * blocked itself, we can avoid finding this out in the chain
 989	 * walk.
 990	 */
 991	if (!chain_walk || !next_lock)
 992		return 0;
 993
 994	/*
 995	 * The owner can't disappear while holding a lock,
 996	 * so the owner struct is protected by wait_lock.
 997	 * Gets dropped in rt_mutex_adjust_prio_chain()!
 998	 */
 999	get_task_struct(owner);
1000
1001	raw_spin_unlock_irq(&lock->wait_lock);
1002
1003	res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
1004					 next_lock, waiter, task);
1005
1006	raw_spin_lock_irq(&lock->wait_lock);
1007
1008	return res;
1009}
1010
1011/*
1012 * Remove the top waiter from the current tasks pi waiter tree and
1013 * queue it up.
1014 *
1015 * Called with lock->wait_lock held and interrupts disabled.
1016 */
1017static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
1018				    struct rt_mutex *lock)
1019{
1020	struct rt_mutex_waiter *waiter;
1021
1022	raw_spin_lock(&current->pi_lock);
1023
1024	waiter = rt_mutex_top_waiter(lock);
1025
1026	/*
1027	 * Remove it from current->pi_waiters and deboost.
1028	 *
1029	 * We must in fact deboost here in order to ensure we call
1030	 * rt_mutex_setprio() to update p->pi_top_task before the
1031	 * task unblocks.
1032	 */
1033	rt_mutex_dequeue_pi(current, waiter);
1034	rt_mutex_adjust_prio(current);
1035
1036	/*
1037	 * As we are waking up the top waiter, and the waiter stays
1038	 * queued on the lock until it gets the lock, this lock
1039	 * obviously has waiters. Just set the bit here and this has
1040	 * the added benefit of forcing all new tasks into the
1041	 * slow path making sure no task of lower priority than
1042	 * the top waiter can steal this lock.
1043	 */
1044	lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1045
1046	/*
1047	 * We deboosted before waking the top waiter task such that we don't
1048	 * run two tasks with the 'same' priority (and ensure the
1049	 * p->pi_top_task pointer points to a blocked task). This however can
1050	 * lead to priority inversion if we would get preempted after the
1051	 * deboost but before waking our donor task, hence the preempt_disable()
1052	 * before unlock.
1053	 *
1054	 * Pairs with preempt_enable() in rt_mutex_postunlock();
1055	 */
1056	preempt_disable();
1057	wake_q_add(wake_q, waiter->task);
1058	raw_spin_unlock(&current->pi_lock);
1059}
1060
1061/*
1062 * Remove a waiter from a lock and give up
1063 *
1064 * Must be called with lock->wait_lock held and interrupts disabled. I must
1065 * have just failed to try_to_take_rt_mutex().
1066 */
1067static void remove_waiter(struct rt_mutex *lock,
1068			  struct rt_mutex_waiter *waiter)
1069{
1070	bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1071	struct task_struct *owner = rt_mutex_owner(lock);
1072	struct rt_mutex *next_lock;
1073
1074	lockdep_assert_held(&lock->wait_lock);
1075
1076	raw_spin_lock(&current->pi_lock);
1077	rt_mutex_dequeue(lock, waiter);
1078	current->pi_blocked_on = NULL;
1079	raw_spin_unlock(&current->pi_lock);
1080
1081	/*
1082	 * Only update priority if the waiter was the highest priority
1083	 * waiter of the lock and there is an owner to update.
1084	 */
1085	if (!owner || !is_top_waiter)
1086		return;
1087
1088	raw_spin_lock(&owner->pi_lock);
1089
1090	rt_mutex_dequeue_pi(owner, waiter);
1091
1092	if (rt_mutex_has_waiters(lock))
1093		rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1094
1095	rt_mutex_adjust_prio(owner);
1096
1097	/* Store the lock on which owner is blocked or NULL */
1098	next_lock = task_blocked_on_lock(owner);
1099
1100	raw_spin_unlock(&owner->pi_lock);
1101
1102	/*
1103	 * Don't walk the chain, if the owner task is not blocked
1104	 * itself.
1105	 */
1106	if (!next_lock)
1107		return;
1108
1109	/* gets dropped in rt_mutex_adjust_prio_chain()! */
1110	get_task_struct(owner);
1111
1112	raw_spin_unlock_irq(&lock->wait_lock);
1113
1114	rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1115				   next_lock, NULL, current);
1116
1117	raw_spin_lock_irq(&lock->wait_lock);
1118}
1119
1120/*
1121 * Recheck the pi chain, in case we got a priority setting
1122 *
1123 * Called from sched_setscheduler
1124 */
1125void rt_mutex_adjust_pi(struct task_struct *task)
1126{
1127	struct rt_mutex_waiter *waiter;
1128	struct rt_mutex *next_lock;
1129	unsigned long flags;
1130
1131	raw_spin_lock_irqsave(&task->pi_lock, flags);
1132
1133	waiter = task->pi_blocked_on;
1134	if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
1135		raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1136		return;
1137	}
1138	next_lock = waiter->lock;
1139	raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1140
1141	/* gets dropped in rt_mutex_adjust_prio_chain()! */
1142	get_task_struct(task);
1143
1144	rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
1145				   next_lock, NULL, task);
1146}
1147
1148void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
1149{
1150	debug_rt_mutex_init_waiter(waiter);
1151	RB_CLEAR_NODE(&waiter->pi_tree_entry);
1152	RB_CLEAR_NODE(&waiter->tree_entry);
1153	waiter->task = NULL;
1154}
1155
1156/**
1157 * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
1158 * @lock:		 the rt_mutex to take
1159 * @state:		 the state the task should block in (TASK_INTERRUPTIBLE
1160 *			 or TASK_UNINTERRUPTIBLE)
1161 * @timeout:		 the pre-initialized and started timer, or NULL for none
1162 * @waiter:		 the pre-initialized rt_mutex_waiter
1163 *
1164 * Must be called with lock->wait_lock held and interrupts disabled
1165 */
1166static int __sched
1167__rt_mutex_slowlock(struct rt_mutex *lock, int state,
1168		    struct hrtimer_sleeper *timeout,
1169		    struct rt_mutex_waiter *waiter)
1170{
1171	int ret = 0;
1172
1173	for (;;) {
1174		/* Try to acquire the lock: */
1175		if (try_to_take_rt_mutex(lock, current, waiter))
1176			break;
1177
1178		/*
1179		 * TASK_INTERRUPTIBLE checks for signals and
1180		 * timeout. Ignored otherwise.
1181		 */
1182		if (likely(state == TASK_INTERRUPTIBLE)) {
1183			/* Signal pending? */
1184			if (signal_pending(current))
1185				ret = -EINTR;
1186			if (timeout && !timeout->task)
1187				ret = -ETIMEDOUT;
1188			if (ret)
1189				break;
1190		}
1191
1192		raw_spin_unlock_irq(&lock->wait_lock);
1193
1194		debug_rt_mutex_print_deadlock(waiter);
1195
1196		schedule();
1197
1198		raw_spin_lock_irq(&lock->wait_lock);
1199		set_current_state(state);
1200	}
1201
1202	__set_current_state(TASK_RUNNING);
1203	return ret;
1204}
1205
1206static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
1207				     struct rt_mutex_waiter *w)
1208{
1209	/*
1210	 * If the result is not -EDEADLOCK or the caller requested
1211	 * deadlock detection, nothing to do here.
1212	 */
1213	if (res != -EDEADLOCK || detect_deadlock)
1214		return;
1215
1216	/*
1217	 * Yell lowdly and stop the task right here.
1218	 */
1219	rt_mutex_print_deadlock(w);
1220	while (1) {
1221		set_current_state(TASK_INTERRUPTIBLE);
1222		schedule();
1223	}
1224}
1225
1226/*
1227 * Slow path lock function:
1228 */
1229static int __sched
1230rt_mutex_slowlock(struct rt_mutex *lock, int state,
1231		  struct hrtimer_sleeper *timeout,
1232		  enum rtmutex_chainwalk chwalk)
1233{
1234	struct rt_mutex_waiter waiter;
1235	unsigned long flags;
1236	int ret = 0;
1237
1238	rt_mutex_init_waiter(&waiter);
1239
1240	/*
1241	 * Technically we could use raw_spin_[un]lock_irq() here, but this can
1242	 * be called in early boot if the cmpxchg() fast path is disabled
1243	 * (debug, no architecture support). In this case we will acquire the
1244	 * rtmutex with lock->wait_lock held. But we cannot unconditionally
1245	 * enable interrupts in that early boot case. So we need to use the
1246	 * irqsave/restore variants.
1247	 */
1248	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1249
1250	/* Try to acquire the lock again: */
1251	if (try_to_take_rt_mutex(lock, current, NULL)) {
1252		raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1253		return 0;
1254	}
1255
1256	set_current_state(state);
1257
1258	/* Setup the timer, when timeout != NULL */
1259	if (unlikely(timeout))
1260		hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1261
1262	ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
1263
1264	if (likely(!ret))
1265		/* sleep on the mutex */
1266		ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
1267
1268	if (unlikely(ret)) {
1269		__set_current_state(TASK_RUNNING);
1270		remove_waiter(lock, &waiter);
1271		rt_mutex_handle_deadlock(ret, chwalk, &waiter);
1272	}
1273
1274	/*
1275	 * try_to_take_rt_mutex() sets the waiter bit
1276	 * unconditionally. We might have to fix that up.
1277	 */
1278	fixup_rt_mutex_waiters(lock);
1279
1280	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1281
1282	/* Remove pending timer: */
1283	if (unlikely(timeout))
1284		hrtimer_cancel(&timeout->timer);
1285
1286	debug_rt_mutex_free_waiter(&waiter);
1287
1288	return ret;
1289}
1290
1291static inline int __rt_mutex_slowtrylock(struct rt_mutex *lock)
1292{
1293	int ret = try_to_take_rt_mutex(lock, current, NULL);
1294
1295	/*
1296	 * try_to_take_rt_mutex() sets the lock waiters bit
1297	 * unconditionally. Clean this up.
1298	 */
1299	fixup_rt_mutex_waiters(lock);
1300
1301	return ret;
1302}
1303
1304/*
1305 * Slow path try-lock function:
1306 */
1307static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
1308{
1309	unsigned long flags;
1310	int ret;
1311
1312	/*
1313	 * If the lock already has an owner we fail to get the lock.
1314	 * This can be done without taking the @lock->wait_lock as
1315	 * it is only being read, and this is a trylock anyway.
1316	 */
1317	if (rt_mutex_owner(lock))
1318		return 0;
1319
1320	/*
1321	 * The mutex has currently no owner. Lock the wait lock and try to
1322	 * acquire the lock. We use irqsave here to support early boot calls.
1323	 */
1324	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1325
1326	ret = __rt_mutex_slowtrylock(lock);
1327
1328	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1329
1330	return ret;
1331}
1332
1333/*
1334 * Slow path to release a rt-mutex.
1335 *
1336 * Return whether the current task needs to call rt_mutex_postunlock().
1337 */
1338static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
1339					struct wake_q_head *wake_q)
1340{
1341	unsigned long flags;
1342
1343	/* irqsave required to support early boot calls */
1344	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1345
1346	debug_rt_mutex_unlock(lock);
1347
1348	/*
1349	 * We must be careful here if the fast path is enabled. If we
1350	 * have no waiters queued we cannot set owner to NULL here
1351	 * because of:
1352	 *
1353	 * foo->lock->owner = NULL;
1354	 *			rtmutex_lock(foo->lock);   <- fast path
1355	 *			free = atomic_dec_and_test(foo->refcnt);
1356	 *			rtmutex_unlock(foo->lock); <- fast path
1357	 *			if (free)
1358	 *				kfree(foo);
1359	 * raw_spin_unlock(foo->lock->wait_lock);
1360	 *
1361	 * So for the fastpath enabled kernel:
1362	 *
1363	 * Nothing can set the waiters bit as long as we hold
1364	 * lock->wait_lock. So we do the following sequence:
1365	 *
1366	 *	owner = rt_mutex_owner(lock);
1367	 *	clear_rt_mutex_waiters(lock);
1368	 *	raw_spin_unlock(&lock->wait_lock);
1369	 *	if (cmpxchg(&lock->owner, owner, 0) == owner)
1370	 *		return;
1371	 *	goto retry;
1372	 *
1373	 * The fastpath disabled variant is simple as all access to
1374	 * lock->owner is serialized by lock->wait_lock:
1375	 *
1376	 *	lock->owner = NULL;
1377	 *	raw_spin_unlock(&lock->wait_lock);
1378	 */
1379	while (!rt_mutex_has_waiters(lock)) {
1380		/* Drops lock->wait_lock ! */
1381		if (unlock_rt_mutex_safe(lock, flags) == true)
1382			return false;
1383		/* Relock the rtmutex and try again */
1384		raw_spin_lock_irqsave(&lock->wait_lock, flags);
1385	}
1386
1387	/*
1388	 * The wakeup next waiter path does not suffer from the above
1389	 * race. See the comments there.
1390	 *
1391	 * Queue the next waiter for wakeup once we release the wait_lock.
1392	 */
1393	mark_wakeup_next_waiter(wake_q, lock);
1394	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1395
1396	return true; /* call rt_mutex_postunlock() */
1397}
1398
1399/*
1400 * debug aware fast / slowpath lock,trylock,unlock
1401 *
1402 * The atomic acquire/release ops are compiled away, when either the
1403 * architecture does not support cmpxchg or when debugging is enabled.
1404 */
1405static inline int
1406rt_mutex_fastlock(struct rt_mutex *lock, int state,
1407		  int (*slowfn)(struct rt_mutex *lock, int state,
1408				struct hrtimer_sleeper *timeout,
1409				enum rtmutex_chainwalk chwalk))
1410{
1411	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1412		return 0;
1413
1414	return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
1415}
1416
1417static inline int
1418rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1419			struct hrtimer_sleeper *timeout,
1420			enum rtmutex_chainwalk chwalk,
1421			int (*slowfn)(struct rt_mutex *lock, int state,
1422				      struct hrtimer_sleeper *timeout,
1423				      enum rtmutex_chainwalk chwalk))
1424{
1425	if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
1426	    likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1427		return 0;
1428
1429	return slowfn(lock, state, timeout, chwalk);
1430}
1431
1432static inline int
1433rt_mutex_fasttrylock(struct rt_mutex *lock,
1434		     int (*slowfn)(struct rt_mutex *lock))
1435{
1436	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1437		return 1;
1438
1439	return slowfn(lock);
1440}
1441
1442/*
1443 * Performs the wakeup of the the top-waiter and re-enables preemption.
1444 */
1445void rt_mutex_postunlock(struct wake_q_head *wake_q)
1446{
1447	wake_up_q(wake_q);
1448
1449	/* Pairs with preempt_disable() in rt_mutex_slowunlock() */
1450	preempt_enable();
1451}
1452
1453static inline void
1454rt_mutex_fastunlock(struct rt_mutex *lock,
1455		    bool (*slowfn)(struct rt_mutex *lock,
1456				   struct wake_q_head *wqh))
1457{
1458	DEFINE_WAKE_Q(wake_q);
1459
1460	if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
1461		return;
1462
1463	if (slowfn(lock, &wake_q))
1464		rt_mutex_postunlock(&wake_q);
1465}
1466
1467static inline void __rt_mutex_lock(struct rt_mutex *lock, unsigned int subclass)
1468{
1469	might_sleep();
1470
1471	mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
1472	rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
1473}
1474
1475#ifdef CONFIG_DEBUG_LOCK_ALLOC
1476/**
1477 * rt_mutex_lock_nested - lock a rt_mutex
1478 *
1479 * @lock: the rt_mutex to be locked
1480 * @subclass: the lockdep subclass
1481 */
1482void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
1483{
1484	__rt_mutex_lock(lock, subclass);
1485}
1486EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
1487
1488#else /* !CONFIG_DEBUG_LOCK_ALLOC */
1489
1490/**
1491 * rt_mutex_lock - lock a rt_mutex
1492 *
1493 * @lock: the rt_mutex to be locked
1494 */
1495void __sched rt_mutex_lock(struct rt_mutex *lock)
1496{
1497	__rt_mutex_lock(lock, 0);
1498}
1499EXPORT_SYMBOL_GPL(rt_mutex_lock);
1500#endif
1501
1502/**
1503 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1504 *
1505 * @lock:		the rt_mutex to be locked
1506 *
1507 * Returns:
1508 *  0		on success
1509 * -EINTR	when interrupted by a signal
1510 */
1511int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
1512{
1513	int ret;
1514
1515	might_sleep();
1516
1517	mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1518	ret = rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
1519	if (ret)
1520		mutex_release(&lock->dep_map, 1, _RET_IP_);
1521
1522	return ret;
1523}
1524EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1525
1526/*
1527 * Futex variant, must not use fastpath.
1528 */
1529int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
1530{
1531	return rt_mutex_slowtrylock(lock);
1532}
1533
1534int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
1535{
1536	return __rt_mutex_slowtrylock(lock);
1537}
1538
1539/**
1540 * rt_mutex_timed_lock - lock a rt_mutex interruptible
1541 *			the timeout structure is provided
1542 *			by the caller
1543 *
1544 * @lock:		the rt_mutex to be locked
1545 * @timeout:		timeout structure or NULL (no timeout)
1546 *
1547 * Returns:
1548 *  0		on success
1549 * -EINTR	when interrupted by a signal
1550 * -ETIMEDOUT	when the timeout expired
1551 */
1552int
1553rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
1554{
1555	int ret;
1556
1557	might_sleep();
1558
1559	mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1560	ret = rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1561				       RT_MUTEX_MIN_CHAINWALK,
1562				       rt_mutex_slowlock);
1563	if (ret)
1564		mutex_release(&lock->dep_map, 1, _RET_IP_);
1565
1566	return ret;
1567}
1568EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1569
1570/**
1571 * rt_mutex_trylock - try to lock a rt_mutex
1572 *
1573 * @lock:	the rt_mutex to be locked
1574 *
1575 * This function can only be called in thread context. It's safe to
1576 * call it from atomic regions, but not from hard interrupt or soft
1577 * interrupt context.
1578 *
1579 * Returns 1 on success and 0 on contention
1580 */
1581int __sched rt_mutex_trylock(struct rt_mutex *lock)
1582{
1583	int ret;
1584
1585	if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
1586		return 0;
1587
1588	ret = rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1589	if (ret)
1590		mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1591
1592	return ret;
1593}
1594EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1595
1596/**
1597 * rt_mutex_unlock - unlock a rt_mutex
1598 *
1599 * @lock: the rt_mutex to be unlocked
1600 */
1601void __sched rt_mutex_unlock(struct rt_mutex *lock)
1602{
1603	mutex_release(&lock->dep_map, 1, _RET_IP_);
1604	rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1605}
1606EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1607
1608/**
1609 * Futex variant, that since futex variants do not use the fast-path, can be
1610 * simple and will not need to retry.
1611 */
1612bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
1613				    struct wake_q_head *wake_q)
1614{
1615	lockdep_assert_held(&lock->wait_lock);
1616
1617	debug_rt_mutex_unlock(lock);
1618
1619	if (!rt_mutex_has_waiters(lock)) {
1620		lock->owner = NULL;
1621		return false; /* done */
1622	}
1623
1624	/*
1625	 * We've already deboosted, mark_wakeup_next_waiter() will
1626	 * retain preempt_disabled when we drop the wait_lock, to
1627	 * avoid inversion prior to the wakeup.  preempt_disable()
1628	 * therein pairs with rt_mutex_postunlock().
1629	 */
1630	mark_wakeup_next_waiter(wake_q, lock);
1631
1632	return true; /* call postunlock() */
1633}
1634
1635void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
1636{
1637	DEFINE_WAKE_Q(wake_q);
1638	unsigned long flags;
1639	bool postunlock;
1640
1641	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1642	postunlock = __rt_mutex_futex_unlock(lock, &wake_q);
1643	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1644
1645	if (postunlock)
1646		rt_mutex_postunlock(&wake_q);
1647}
1648
1649/**
1650 * rt_mutex_destroy - mark a mutex unusable
1651 * @lock: the mutex to be destroyed
1652 *
1653 * This function marks the mutex uninitialized, and any subsequent
1654 * use of the mutex is forbidden. The mutex must not be locked when
1655 * this function is called.
1656 */
1657void rt_mutex_destroy(struct rt_mutex *lock)
1658{
1659	WARN_ON(rt_mutex_is_locked(lock));
1660#ifdef CONFIG_DEBUG_RT_MUTEXES
1661	lock->magic = NULL;
1662#endif
1663}
1664EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1665
1666/**
1667 * __rt_mutex_init - initialize the rt lock
1668 *
1669 * @lock: the rt lock to be initialized
1670 *
1671 * Initialize the rt lock to unlocked state.
1672 *
1673 * Initializing of a locked rt lock is not allowed
1674 */
1675void __rt_mutex_init(struct rt_mutex *lock, const char *name,
1676		     struct lock_class_key *key)
1677{
1678	lock->owner = NULL;
1679	raw_spin_lock_init(&lock->wait_lock);
1680	lock->waiters = RB_ROOT_CACHED;
1681
1682	if (name && key)
1683		debug_rt_mutex_init(lock, name, key);
1684}
1685EXPORT_SYMBOL_GPL(__rt_mutex_init);
1686
1687/**
1688 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1689 *				proxy owner
1690 *
1691 * @lock:	the rt_mutex to be locked
1692 * @proxy_owner:the task to set as owner
1693 *
1694 * No locking. Caller has to do serializing itself
1695 *
1696 * Special API call for PI-futex support. This initializes the rtmutex and
1697 * assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
1698 * possible at this point because the pi_state which contains the rtmutex
1699 * is not yet visible to other tasks.
1700 */
1701void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1702				struct task_struct *proxy_owner)
1703{
1704	__rt_mutex_init(lock, NULL, NULL);
1705	debug_rt_mutex_proxy_lock(lock, proxy_owner);
1706	rt_mutex_set_owner(lock, proxy_owner);
1707}
1708
1709/**
1710 * rt_mutex_proxy_unlock - release a lock on behalf of owner
1711 *
1712 * @lock:	the rt_mutex to be locked
1713 *
1714 * No locking. Caller has to do serializing itself
1715 *
1716 * Special API call for PI-futex support. This merrily cleans up the rtmutex
1717 * (debugging) state. Concurrent operations on this rt_mutex are not
1718 * possible because it belongs to the pi_state which is about to be freed
1719 * and it is not longer visible to other tasks.
1720 */
1721void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1722			   struct task_struct *proxy_owner)
1723{
1724	debug_rt_mutex_proxy_unlock(lock);
1725	rt_mutex_set_owner(lock, NULL);
1726}
1727
1728/**
1729 * __rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1730 * @lock:		the rt_mutex to take
1731 * @waiter:		the pre-initialized rt_mutex_waiter
1732 * @task:		the task to prepare
1733 *
1734 * Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
1735 * detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
1736 *
1737 * NOTE: does _NOT_ remove the @waiter on failure; must either call
1738 * rt_mutex_wait_proxy_lock() or rt_mutex_cleanup_proxy_lock() after this.
1739 *
1740 * Returns:
1741 *  0 - task blocked on lock
1742 *  1 - acquired the lock for task, caller should wake it up
1743 * <0 - error
1744 *
1745 * Special API call for PI-futex support.
1746 */
1747int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1748			      struct rt_mutex_waiter *waiter,
1749			      struct task_struct *task)
1750{
1751	int ret;
1752
1753	lockdep_assert_held(&lock->wait_lock);
1754
1755	if (try_to_take_rt_mutex(lock, task, NULL))
1756		return 1;
1757
1758	/* We enforce deadlock detection for futexes */
1759	ret = task_blocks_on_rt_mutex(lock, waiter, task,
1760				      RT_MUTEX_FULL_CHAINWALK);
1761
1762	if (ret && !rt_mutex_owner(lock)) {
1763		/*
1764		 * Reset the return value. We might have
1765		 * returned with -EDEADLK and the owner
1766		 * released the lock while we were walking the
1767		 * pi chain.  Let the waiter sort it out.
1768		 */
1769		ret = 0;
1770	}
1771
1772	debug_rt_mutex_print_deadlock(waiter);
1773
1774	return ret;
1775}
1776
1777/**
1778 * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1779 * @lock:		the rt_mutex to take
1780 * @waiter:		the pre-initialized rt_mutex_waiter
1781 * @task:		the task to prepare
1782 *
1783 * Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
1784 * detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
1785 *
1786 * NOTE: unlike __rt_mutex_start_proxy_lock this _DOES_ remove the @waiter
1787 * on failure.
1788 *
1789 * Returns:
1790 *  0 - task blocked on lock
1791 *  1 - acquired the lock for task, caller should wake it up
1792 * <0 - error
1793 *
1794 * Special API call for PI-futex support.
1795 */
1796int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1797			      struct rt_mutex_waiter *waiter,
1798			      struct task_struct *task)
1799{
1800	int ret;
1801
1802	raw_spin_lock_irq(&lock->wait_lock);
1803	ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
1804	if (unlikely(ret))
1805		remove_waiter(lock, waiter);
1806	raw_spin_unlock_irq(&lock->wait_lock);
1807
1808	return ret;
1809}
1810
1811/**
1812 * rt_mutex_next_owner - return the next owner of the lock
1813 *
1814 * @lock: the rt lock query
1815 *
1816 * Returns the next owner of the lock or NULL
1817 *
1818 * Caller has to serialize against other accessors to the lock
1819 * itself.
1820 *
1821 * Special API call for PI-futex support
1822 */
1823struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1824{
1825	if (!rt_mutex_has_waiters(lock))
1826		return NULL;
1827
1828	return rt_mutex_top_waiter(lock)->task;
1829}
1830
1831/**
1832 * rt_mutex_wait_proxy_lock() - Wait for lock acquisition
1833 * @lock:		the rt_mutex we were woken on
1834 * @to:			the timeout, null if none. hrtimer should already have
1835 *			been started.
1836 * @waiter:		the pre-initialized rt_mutex_waiter
1837 *
1838 * Wait for the the lock acquisition started on our behalf by
1839 * rt_mutex_start_proxy_lock(). Upon failure, the caller must call
1840 * rt_mutex_cleanup_proxy_lock().
1841 *
1842 * Returns:
1843 *  0 - success
1844 * <0 - error, one of -EINTR, -ETIMEDOUT
1845 *
1846 * Special API call for PI-futex support
1847 */
1848int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
1849			       struct hrtimer_sleeper *to,
1850			       struct rt_mutex_waiter *waiter)
1851{
1852	int ret;
1853
1854	raw_spin_lock_irq(&lock->wait_lock);
1855	/* sleep on the mutex */
1856	set_current_state(TASK_INTERRUPTIBLE);
1857	ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1858	/*
1859	 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1860	 * have to fix that up.
1861	 */
1862	fixup_rt_mutex_waiters(lock);
1863	raw_spin_unlock_irq(&lock->wait_lock);
1864
1865	return ret;
1866}
1867
1868/**
1869 * rt_mutex_cleanup_proxy_lock() - Cleanup failed lock acquisition
1870 * @lock:		the rt_mutex we were woken on
1871 * @waiter:		the pre-initialized rt_mutex_waiter
1872 *
1873 * Attempt to clean up after a failed __rt_mutex_start_proxy_lock() or
1874 * rt_mutex_wait_proxy_lock().
1875 *
1876 * Unless we acquired the lock; we're still enqueued on the wait-list and can
1877 * in fact still be granted ownership until we're removed. Therefore we can
1878 * find we are in fact the owner and must disregard the
1879 * rt_mutex_wait_proxy_lock() failure.
1880 *
1881 * Returns:
1882 *  true  - did the cleanup, we done.
1883 *  false - we acquired the lock after rt_mutex_wait_proxy_lock() returned,
1884 *          caller should disregards its return value.
1885 *
1886 * Special API call for PI-futex support
1887 */
1888bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
1889				 struct rt_mutex_waiter *waiter)
1890{
1891	bool cleanup = false;
1892
1893	raw_spin_lock_irq(&lock->wait_lock);
1894	/*
1895	 * Do an unconditional try-lock, this deals with the lock stealing
1896	 * state where __rt_mutex_futex_unlock() -> mark_wakeup_next_waiter()
1897	 * sets a NULL owner.
1898	 *
1899	 * We're not interested in the return value, because the subsequent
1900	 * test on rt_mutex_owner() will infer that. If the trylock succeeded,
1901	 * we will own the lock and it will have removed the waiter. If we
1902	 * failed the trylock, we're still not owner and we need to remove
1903	 * ourselves.
1904	 */
1905	try_to_take_rt_mutex(lock, current, waiter);
1906	/*
1907	 * Unless we're the owner; we're still enqueued on the wait_list.
1908	 * So check if we became owner, if not, take us off the wait_list.
1909	 */
1910	if (rt_mutex_owner(lock) != current) {
1911		remove_waiter(lock, waiter);
1912		cleanup = true;
1913	}
1914	/*
1915	 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1916	 * have to fix that up.
1917	 */
1918	fixup_rt_mutex_waiters(lock);
1919
1920	raw_spin_unlock_irq(&lock->wait_lock);
1921
1922	return cleanup;
1923}