1/*
   2 * RT-Mutexes: simple blocking mutual exclusion locks with PI support
   3 *
   4 * started by Ingo Molnar and Thomas Gleixner.
   5 *
   6 *  Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   7 *  Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
   8 *  Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
   9 *  Copyright (C) 2006 Esben Nielsen
  10 *
  11 *  See Documentation/locking/rt-mutex-design.txt for details.
  12 */
  13#include <linux/spinlock.h>
  14#include <linux/export.h>
  15#include <linux/sched/signal.h>
  16#include <linux/sched/rt.h>
  17#include <linux/sched/deadline.h>
  18#include <linux/sched/wake_q.h>
  19#include <linux/sched/debug.h>
  20#include <linux/timer.h>
  21
  22#include "rtmutex_common.h"
  23
  24/*
  25 * lock->owner state tracking:
  26 *
  27 * lock->owner holds the task_struct pointer of the owner. Bit 0
  28 * is used to keep track of the "lock has waiters" state.
  29 *
  30 * owner	bit0
  31 * NULL		0	lock is free (fast acquire possible)
  32 * NULL		1	lock is free and has waiters and the top waiter
  33 *				is going to take the lock*
  34 * taskpointer	0	lock is held (fast release possible)
  35 * taskpointer	1	lock is held and has waiters**
  36 *
  37 * The fast atomic compare exchange based acquire and release is only
  38 * possible when bit 0 of lock->owner is 0.
  39 *
  40 * (*) It also can be a transitional state when grabbing the lock
  41 * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
  42 * we need to set the bit0 before looking at the lock, and the owner may be
  43 * NULL in this small time, hence this can be a transitional state.
  44 *
  45 * (**) There is a small time when bit 0 is set but there are no
  46 * waiters. This can happen when grabbing the lock in the slow path.
  47 * To prevent a cmpxchg of the owner releasing the lock, we need to
  48 * set this bit before looking at the lock.
  49 */
  50
  51static void
  52rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
  53{
  54	unsigned long val = (unsigned long)owner;
  55
  56	if (rt_mutex_has_waiters(lock))
  57		val |= RT_MUTEX_HAS_WAITERS;
  58
  59	lock->owner = (struct task_struct *)val;
  60}
  61
  62static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
  63{
  64	lock->owner = (struct task_struct *)
  65			((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
  66}
  67
  68static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
  69{
  70	unsigned long owner, *p = (unsigned long *) &lock->owner;
  71
  72	if (rt_mutex_has_waiters(lock))
  73		return;
  74
  75	/*
  76	 * The rbtree has no waiters enqueued, now make sure that the
  77	 * lock->owner still has the waiters bit set, otherwise the
  78	 * following can happen:
  79	 *
  80	 * CPU 0	CPU 1		CPU2
  81	 * l->owner=T1
  82	 *		rt_mutex_lock(l)
  83	 *		lock(l->lock)
  84	 *		l->owner = T1 | HAS_WAITERS;
  85	 *		enqueue(T2)
  86	 *		boost()
  87	 *		  unlock(l->lock)
  88	 *		block()
  89	 *
  90	 *				rt_mutex_lock(l)
  91	 *				lock(l->lock)
  92	 *				l->owner = T1 | HAS_WAITERS;
  93	 *				enqueue(T3)
  94	 *				boost()
  95	 *				  unlock(l->lock)
  96	 *				block()
  97	 *		signal(->T2)	signal(->T3)
  98	 *		lock(l->lock)
  99	 *		dequeue(T2)
 100	 *		deboost()
 101	 *		  unlock(l->lock)
 102	 *				lock(l->lock)
 103	 *				dequeue(T3)
 104	 *				 ==> wait list is empty
 105	 *				deboost()
 106	 *				 unlock(l->lock)
 107	 *		lock(l->lock)
 108	 *		fixup_rt_mutex_waiters()
 109	 *		  if (wait_list_empty(l) {
 110	 *		    l->owner = owner
 111	 *		    owner = l->owner & ~HAS_WAITERS;
 112	 *		      ==> l->owner = T1
 113	 *		  }
 114	 *				lock(l->lock)
 115	 * rt_mutex_unlock(l)		fixup_rt_mutex_waiters()
 116	 *				  if (wait_list_empty(l) {
 117	 *				    owner = l->owner & ~HAS_WAITERS;
 118	 * cmpxchg(l->owner, T1, NULL)
 119	 *  ===> Success (l->owner = NULL)
 120	 *
 121	 *				    l->owner = owner
 122	 *				      ==> l->owner = T1
 123	 *				  }
 124	 *
 125	 * With the check for the waiter bit in place T3 on CPU2 will not
 126	 * overwrite. All tasks fiddling with the waiters bit are
 127	 * serialized by l->lock, so nothing else can modify the waiters
 128	 * bit. If the bit is set then nothing can change l->owner either
 129	 * so the simple RMW is safe. The cmpxchg() will simply fail if it
 130	 * happens in the middle of the RMW because the waiters bit is
 131	 * still set.
 132	 */
 133	owner = READ_ONCE(*p);
 134	if (owner & RT_MUTEX_HAS_WAITERS)
 135		WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
 136}
 137
 138/*
 139 * We can speed up the acquire/release, if there's no debugging state to be
 140 * set up.
 141 */
 142#ifndef CONFIG_DEBUG_RT_MUTEXES
 143# define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
 144# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
 145# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
 146
 147/*
 148 * Callers must hold the ->wait_lock -- which is the whole purpose as we force
 149 * all future threads that attempt to [Rmw] the lock to the slowpath. As such
 150 * relaxed semantics suffice.
 151 */
 152static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
 153{
 154	unsigned long owner, *p = (unsigned long *) &lock->owner;
 155
 156	do {
 157		owner = *p;
 158	} while (cmpxchg_relaxed(p, owner,
 159				 owner | RT_MUTEX_HAS_WAITERS) != owner);
 160}
 161
 162/*
 163 * Safe fastpath aware unlock:
 164 * 1) Clear the waiters bit
 165 * 2) Drop lock->wait_lock
 166 * 3) Try to unlock the lock with cmpxchg
 167 */
 168static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
 169					unsigned long flags)
 170	__releases(lock->wait_lock)
 171{
 172	struct task_struct *owner = rt_mutex_owner(lock);
 173
 174	clear_rt_mutex_waiters(lock);
 175	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 176	/*
 177	 * If a new waiter comes in between the unlock and the cmpxchg
 178	 * we have two situations:
 179	 *
 180	 * unlock(wait_lock);
 181	 *					lock(wait_lock);
 182	 * cmpxchg(p, owner, 0) == owner
 183	 *					mark_rt_mutex_waiters(lock);
 184	 *					acquire(lock);
 185	 * or:
 186	 *
 187	 * unlock(wait_lock);
 188	 *					lock(wait_lock);
 189	 *					mark_rt_mutex_waiters(lock);
 190	 *
 191	 * cmpxchg(p, owner, 0) != owner
 192	 *					enqueue_waiter();
 193	 *					unlock(wait_lock);
 194	 * lock(wait_lock);
 195	 * wake waiter();
 196	 * unlock(wait_lock);
 197	 *					lock(wait_lock);
 198	 *					acquire(lock);
 199	 */
 200	return rt_mutex_cmpxchg_release(lock, owner, NULL);
 201}
 202
 203#else
 204# define rt_mutex_cmpxchg_relaxed(l,c,n)	(0)
 205# define rt_mutex_cmpxchg_acquire(l,c,n)	(0)
 206# define rt_mutex_cmpxchg_release(l,c,n)	(0)
 207
 208static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
 209{
 210	lock->owner = (struct task_struct *)
 211			((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
 212}
 213
 214/*
 215 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
 216 */
 217static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
 218					unsigned long flags)
 219	__releases(lock->wait_lock)
 220{
 221	lock->owner = NULL;
 222	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 223	return true;
 224}
 225#endif
 226
 227/*
 228 * Only use with rt_mutex_waiter_{less,equal}()
 229 */
 230#define task_to_waiter(p)	\
 231	&(struct rt_mutex_waiter){ .prio = (p)->prio, .deadline = (p)->dl.deadline }
 232
 233static inline int
 234rt_mutex_waiter_less(struct rt_mutex_waiter *left,
 235		     struct rt_mutex_waiter *right)
 236{
 237	if (left->prio < right->prio)
 238		return 1;
 239
 240	/*
 241	 * If both waiters have dl_prio(), we check the deadlines of the
 242	 * associated tasks.
 243	 * If left waiter has a dl_prio(), and we didn't return 1 above,
 244	 * then right waiter has a dl_prio() too.
 245	 */
 246	if (dl_prio(left->prio))
 247		return dl_time_before(left->deadline, right->deadline);
 248
 249	return 0;
 250}
 251
 252static inline int
 253rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
 254		      struct rt_mutex_waiter *right)
 255{
 256	if (left->prio != right->prio)
 257		return 0;
 258
 259	/*
 260	 * If both waiters have dl_prio(), we check the deadlines of the
 261	 * associated tasks.
 262	 * If left waiter has a dl_prio(), and we didn't return 0 above,
 263	 * then right waiter has a dl_prio() too.
 264	 */
 265	if (dl_prio(left->prio))
 266		return left->deadline == right->deadline;
 267
 268	return 1;
 269}
 270
 271static void
 272rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
 
 
 273{
 274	struct rb_node **link = &lock->waiters.rb_root.rb_node;
 275	struct rb_node *parent = NULL;
 276	struct rt_mutex_waiter *entry;
 277	bool leftmost = true;
 278
 279	while (*link) {
 280		parent = *link;
 281		entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
 282		if (rt_mutex_waiter_less(waiter, entry)) {
 283			link = &parent->rb_left;
 284		} else {
 285			link = &parent->rb_right;
 286			leftmost = false;
 287		}
 288	}
 289
 290	rb_link_node(&waiter->tree_entry, parent, link);
 291	rb_insert_color_cached(&waiter->tree_entry, &lock->waiters, leftmost);
 
 
 292}
 293
 294static void
 295rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
 296{
 297	if (RB_EMPTY_NODE(&waiter->tree_entry))
 298		return;
 299
 300	rb_erase_cached(&waiter->tree_entry, &lock->waiters);
 301	RB_CLEAR_NODE(&waiter->tree_entry);
 302}
 303
 304static void
 305rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 
 
 
 306{
 307	struct rb_node **link = &task->pi_waiters.rb_root.rb_node;
 308	struct rb_node *parent = NULL;
 309	struct rt_mutex_waiter *entry;
 310	bool leftmost = true;
 311
 312	while (*link) {
 313		parent = *link;
 314		entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
 315		if (rt_mutex_waiter_less(waiter, entry)) {
 316			link = &parent->rb_left;
 317		} else {
 318			link = &parent->rb_right;
 319			leftmost = false;
 320		}
 321	}
 322
 323	rb_link_node(&waiter->pi_tree_entry, parent, link);
 324	rb_insert_color_cached(&waiter->pi_tree_entry, &task->pi_waiters, leftmost);
 
 
 325}
 326
 327static void
 328rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 329{
 330	if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
 331		return;
 332
 333	rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
 334	RB_CLEAR_NODE(&waiter->pi_tree_entry);
 335}
 336
 337static void rt_mutex_adjust_prio(struct task_struct *p)
 338{
 339	struct task_struct *pi_task = NULL;
 340
 341	lockdep_assert_held(&p->pi_lock);
 342
 343	if (task_has_pi_waiters(p))
 344		pi_task = task_top_pi_waiter(p)->task;
 345
 346	rt_mutex_setprio(p, pi_task);
 347}
 348
 349/*
 350 * Deadlock detection is conditional:
 351 *
 352 * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
 353 * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
 354 *
 355 * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
 356 * conducted independent of the detect argument.
 357 *
 358 * If the waiter argument is NULL this indicates the deboost path and
 359 * deadlock detection is disabled independent of the detect argument
 360 * and the config settings.
 361 */
 362static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
 363					  enum rtmutex_chainwalk chwalk)
 364{
 365	/*
 366	 * This is just a wrapper function for the following call,
 367	 * because debug_rt_mutex_detect_deadlock() smells like a magic
 368	 * debug feature and I wanted to keep the cond function in the
 369	 * main source file along with the comments instead of having
 370	 * two of the same in the headers.
 371	 */
 372	return debug_rt_mutex_detect_deadlock(waiter, chwalk);
 373}
 374
 375/*
 376 * Max number of times we'll walk the boosting chain:
 377 */
 378int max_lock_depth = 1024;
 379
 380static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
 381{
 382	return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
 383}
 384
 385/*
 386 * Adjust the priority chain. Also used for deadlock detection.
 387 * Decreases task's usage by one - may thus free the task.
 388 *
 389 * @task:	the task owning the mutex (owner) for which a chain walk is
 390 *		probably needed
 391 * @chwalk:	do we have to carry out deadlock detection?
 392 * @orig_lock:	the mutex (can be NULL if we are walking the chain to recheck
 393 *		things for a task that has just got its priority adjusted, and
 394 *		is waiting on a mutex)
 395 * @next_lock:	the mutex on which the owner of @orig_lock was blocked before
 396 *		we dropped its pi_lock. Is never dereferenced, only used for
 397 *		comparison to detect lock chain changes.
 398 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
 399 *		its priority to the mutex owner (can be NULL in the case
 400 *		depicted above or if the top waiter is gone away and we are
 401 *		actually deboosting the owner)
 402 * @top_task:	the current top waiter
 403 *
 404 * Returns 0 or -EDEADLK.
 405 *
 406 * Chain walk basics and protection scope
 407 *
 408 * [R] refcount on task
 409 * [P] task->pi_lock held
 410 * [L] rtmutex->wait_lock held
 411 *
 412 * Step	Description				Protected by
 413 *	function arguments:
 414 *	@task					[R]
 415 *	@orig_lock if != NULL			@top_task is blocked on it
 416 *	@next_lock				Unprotected. Cannot be
 417 *						dereferenced. Only used for
 418 *						comparison.
 419 *	@orig_waiter if != NULL			@top_task is blocked on it
 420 *	@top_task				current, or in case of proxy
 421 *						locking protected by calling
 422 *						code
 423 *	again:
 424 *	  loop_sanity_check();
 425 *	retry:
 426 * [1]	  lock(task->pi_lock);			[R] acquire [P]
 427 * [2]	  waiter = task->pi_blocked_on;		[P]
 428 * [3]	  check_exit_conditions_1();		[P]
 429 * [4]	  lock = waiter->lock;			[P]
 430 * [5]	  if (!try_lock(lock->wait_lock)) {	[P] try to acquire [L]
 431 *	    unlock(task->pi_lock);		release [P]
 432 *	    goto retry;
 433 *	  }
 434 * [6]	  check_exit_conditions_2();		[P] + [L]
 435 * [7]	  requeue_lock_waiter(lock, waiter);	[P] + [L]
 436 * [8]	  unlock(task->pi_lock);		release [P]
 437 *	  put_task_struct(task);		release [R]
 438 * [9]	  check_exit_conditions_3();		[L]
 439 * [10]	  task = owner(lock);			[L]
 440 *	  get_task_struct(task);		[L] acquire [R]
 441 *	  lock(task->pi_lock);			[L] acquire [P]
 442 * [11]	  requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
 443 * [12]	  check_exit_conditions_4();		[P] + [L]
 444 * [13]	  unlock(task->pi_lock);		release [P]
 445 *	  unlock(lock->wait_lock);		release [L]
 446 *	  goto again;
 447 */
 448static int rt_mutex_adjust_prio_chain(struct task_struct *task,
 449				      enum rtmutex_chainwalk chwalk,
 450				      struct rt_mutex *orig_lock,
 451				      struct rt_mutex *next_lock,
 452				      struct rt_mutex_waiter *orig_waiter,
 453				      struct task_struct *top_task)
 454{
 455	struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 456	struct rt_mutex_waiter *prerequeue_top_waiter;
 457	int ret = 0, depth = 0;
 458	struct rt_mutex *lock;
 459	bool detect_deadlock;
 460	bool requeue = true;
 461
 462	detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
 463
 464	/*
 465	 * The (de)boosting is a step by step approach with a lot of
 466	 * pitfalls. We want this to be preemptible and we want hold a
 467	 * maximum of two locks per step. So we have to check
 468	 * carefully whether things change under us.
 469	 */
 470 again:
 471	/*
 472	 * We limit the lock chain length for each invocation.
 473	 */
 474	if (++depth > max_lock_depth) {
 475		static int prev_max;
 476
 477		/*
 478		 * Print this only once. If the admin changes the limit,
 479		 * print a new message when reaching the limit again.
 480		 */
 481		if (prev_max != max_lock_depth) {
 482			prev_max = max_lock_depth;
 483			printk(KERN_WARNING "Maximum lock depth %d reached "
 484			       "task: %s (%d)\n", max_lock_depth,
 485			       top_task->comm, task_pid_nr(top_task));
 486		}
 487		put_task_struct(task);
 488
 489		return -EDEADLK;
 490	}
 491
 492	/*
 493	 * We are fully preemptible here and only hold the refcount on
 494	 * @task. So everything can have changed under us since the
 495	 * caller or our own code below (goto retry/again) dropped all
 496	 * locks.
 497	 */
 498 retry:
 499	/*
 500	 * [1] Task cannot go away as we did a get_task() before !
 501	 */
 502	raw_spin_lock_irq(&task->pi_lock);
 503
 504	/*
 505	 * [2] Get the waiter on which @task is blocked on.
 506	 */
 507	waiter = task->pi_blocked_on;
 508
 509	/*
 510	 * [3] check_exit_conditions_1() protected by task->pi_lock.
 511	 */
 512
 513	/*
 514	 * Check whether the end of the boosting chain has been
 515	 * reached or the state of the chain has changed while we
 516	 * dropped the locks.
 517	 */
 518	if (!waiter)
 519		goto out_unlock_pi;
 520
 521	/*
 522	 * Check the orig_waiter state. After we dropped the locks,
 523	 * the previous owner of the lock might have released the lock.
 524	 */
 525	if (orig_waiter && !rt_mutex_owner(orig_lock))
 526		goto out_unlock_pi;
 527
 528	/*
 529	 * We dropped all locks after taking a refcount on @task, so
 530	 * the task might have moved on in the lock chain or even left
 531	 * the chain completely and blocks now on an unrelated lock or
 532	 * on @orig_lock.
 533	 *
 534	 * We stored the lock on which @task was blocked in @next_lock,
 535	 * so we can detect the chain change.
 536	 */
 537	if (next_lock != waiter->lock)
 538		goto out_unlock_pi;
 539
 540	/*
 541	 * Drop out, when the task has no waiters. Note,
 542	 * top_waiter can be NULL, when we are in the deboosting
 543	 * mode!
 544	 */
 545	if (top_waiter) {
 546		if (!task_has_pi_waiters(task))
 547			goto out_unlock_pi;
 548		/*
 549		 * If deadlock detection is off, we stop here if we
 550		 * are not the top pi waiter of the task. If deadlock
 551		 * detection is enabled we continue, but stop the
 552		 * requeueing in the chain walk.
 553		 */
 554		if (top_waiter != task_top_pi_waiter(task)) {
 555			if (!detect_deadlock)
 556				goto out_unlock_pi;
 557			else
 558				requeue = false;
 559		}
 560	}
 561
 562	/*
 563	 * If the waiter priority is the same as the task priority
 564	 * then there is no further priority adjustment necessary.  If
 565	 * deadlock detection is off, we stop the chain walk. If its
 566	 * enabled we continue, but stop the requeueing in the chain
 567	 * walk.
 568	 */
 569	if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
 570		if (!detect_deadlock)
 571			goto out_unlock_pi;
 572		else
 573			requeue = false;
 574	}
 575
 576	/*
 577	 * [4] Get the next lock
 578	 */
 579	lock = waiter->lock;
 580	/*
 581	 * [5] We need to trylock here as we are holding task->pi_lock,
 582	 * which is the reverse lock order versus the other rtmutex
 583	 * operations.
 584	 */
 585	if (!raw_spin_trylock(&lock->wait_lock)) {
 586		raw_spin_unlock_irq(&task->pi_lock);
 587		cpu_relax();
 588		goto retry;
 589	}
 590
 591	/*
 592	 * [6] check_exit_conditions_2() protected by task->pi_lock and
 593	 * lock->wait_lock.
 594	 *
 595	 * Deadlock detection. If the lock is the same as the original
 596	 * lock which caused us to walk the lock chain or if the
 597	 * current lock is owned by the task which initiated the chain
 598	 * walk, we detected a deadlock.
 599	 */
 600	if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 601		debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
 602		raw_spin_unlock(&lock->wait_lock);
 603		ret = -EDEADLK;
 604		goto out_unlock_pi;
 605	}
 606
 607	/*
 608	 * If we just follow the lock chain for deadlock detection, no
 609	 * need to do all the requeue operations. To avoid a truckload
 610	 * of conditionals around the various places below, just do the
 611	 * minimum chain walk checks.
 612	 */
 613	if (!requeue) {
 614		/*
 615		 * No requeue[7] here. Just release @task [8]
 616		 */
 617		raw_spin_unlock(&task->pi_lock);
 618		put_task_struct(task);
 619
 620		/*
 621		 * [9] check_exit_conditions_3 protected by lock->wait_lock.
 622		 * If there is no owner of the lock, end of chain.
 623		 */
 624		if (!rt_mutex_owner(lock)) {
 625			raw_spin_unlock_irq(&lock->wait_lock);
 626			return 0;
 627		}
 628
 629		/* [10] Grab the next task, i.e. owner of @lock */
 630		task = rt_mutex_owner(lock);
 631		get_task_struct(task);
 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 = rt_mutex_owner(lock);
 712	get_task_struct(task);
 713	raw_spin_lock(&task->pi_lock);
 714
 715	/* [11] requeue the pi waiters if necessary */
 716	if (waiter == rt_mutex_top_waiter(lock)) {
 717		/*
 718		 * The waiter became the new top (highest priority)
 719		 * waiter on the lock. Replace the previous top waiter
 720		 * in the owner tasks pi waiters tree with this waiter
 721		 * and adjust the priority of the owner.
 722		 */
 723		rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
 724		rt_mutex_enqueue_pi(task, waiter);
 725		rt_mutex_adjust_prio(task);
 726
 727	} else if (prerequeue_top_waiter == waiter) {
 728		/*
 729		 * The waiter was the top waiter on the lock, but is
 730		 * no longer the top prority waiter. Replace waiter in
 731		 * the owner tasks pi waiters tree with the new top
 732		 * (highest priority) waiter and adjust the priority
 733		 * of the owner.
 734		 * The new top waiter is stored in @waiter so that
 735		 * @waiter == @top_waiter evaluates to true below and
 736		 * we continue to deboost the rest of the chain.
 737		 */
 738		rt_mutex_dequeue_pi(task, waiter);
 739		waiter = rt_mutex_top_waiter(lock);
 740		rt_mutex_enqueue_pi(task, waiter);
 741		rt_mutex_adjust_prio(task);
 742	} else {
 743		/*
 744		 * Nothing changed. No need to do any priority
 745		 * adjustment.
 746		 */
 747	}
 748
 749	/*
 750	 * [12] check_exit_conditions_4() protected by task->pi_lock
 751	 * and lock->wait_lock. The actual decisions are made after we
 752	 * dropped the locks.
 753	 *
 754	 * Check whether the task which owns the current lock is pi
 755	 * blocked itself. If yes we store a pointer to the lock for
 756	 * the lock chain change detection above. After we dropped
 757	 * task->pi_lock next_lock cannot be dereferenced anymore.
 758	 */
 759	next_lock = task_blocked_on_lock(task);
 760	/*
 761	 * Store the top waiter of @lock for the end of chain walk
 762	 * decision below.
 763	 */
 764	top_waiter = rt_mutex_top_waiter(lock);
 765
 766	/* [13] Drop the locks */
 767	raw_spin_unlock(&task->pi_lock);
 768	raw_spin_unlock_irq(&lock->wait_lock);
 769
 770	/*
 771	 * Make the actual exit decisions [12], based on the stored
 772	 * values.
 773	 *
 774	 * We reached the end of the lock chain. Stop right here. No
 775	 * point to go back just to figure that out.
 776	 */
 777	if (!next_lock)
 778		goto out_put_task;
 779
 780	/*
 781	 * If the current waiter is not the top waiter on the lock,
 782	 * then we can stop the chain walk here if we are not in full
 783	 * deadlock detection mode.
 784	 */
 785	if (!detect_deadlock && waiter != top_waiter)
 786		goto out_put_task;
 787
 788	goto again;
 789
 790 out_unlock_pi:
 791	raw_spin_unlock_irq(&task->pi_lock);
 792 out_put_task:
 793	put_task_struct(task);
 794
 795	return ret;
 796}
 797
 798/*
 799 * Try to take an rt-mutex
 800 *
 801 * Must be called with lock->wait_lock held and interrupts disabled
 802 *
 803 * @lock:   The lock to be acquired.
 804 * @task:   The task which wants to acquire the lock
 805 * @waiter: The waiter that is queued to the lock's wait tree if the
 806 *	    callsite called task_blocked_on_lock(), otherwise NULL
 807 */
 808static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
 809				struct rt_mutex_waiter *waiter)
 
 810{
 811	lockdep_assert_held(&lock->wait_lock);
 812
 813	/*
 814	 * Before testing whether we can acquire @lock, we set the
 815	 * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
 816	 * other tasks which try to modify @lock into the slow path
 817	 * and they serialize on @lock->wait_lock.
 818	 *
 819	 * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
 820	 * as explained at the top of this file if and only if:
 821	 *
 822	 * - There is a lock owner. The caller must fixup the
 823	 *   transient state if it does a trylock or leaves the lock
 824	 *   function due to a signal or timeout.
 825	 *
 826	 * - @task acquires the lock and there are no other
 827	 *   waiters. This is undone in rt_mutex_set_owner(@task) at
 828	 *   the end of this function.
 829	 */
 830	mark_rt_mutex_waiters(lock);
 831
 832	/*
 833	 * If @lock has an owner, give up.
 834	 */
 835	if (rt_mutex_owner(lock))
 836		return 0;
 837
 838	/*
 839	 * If @waiter != NULL, @task has already enqueued the waiter
 840	 * into @lock waiter tree. If @waiter == NULL then this is a
 841	 * trylock attempt.
 842	 */
 843	if (waiter) {
 844		/*
 845		 * If waiter is not the highest priority waiter of
 846		 * @lock, give up.
 847		 */
 848		if (waiter != rt_mutex_top_waiter(lock))
 849			return 0;
 850
 851		/*
 852		 * We can acquire the lock. Remove the waiter from the
 853		 * lock waiters tree.
 854		 */
 855		rt_mutex_dequeue(lock, waiter);
 856
 857	} else {
 858		/*
 859		 * If the lock has waiters already we check whether @task is
 860		 * eligible to take over the lock.
 861		 *
 862		 * If there are no other waiters, @task can acquire
 863		 * the lock.  @task->pi_blocked_on is NULL, so it does
 864		 * not need to be dequeued.
 865		 */
 866		if (rt_mutex_has_waiters(lock)) {
 867			/*
 868			 * If @task->prio is greater than or equal to
 869			 * the top waiter priority (kernel view),
 870			 * @task lost.
 871			 */
 872			if (!rt_mutex_waiter_less(task_to_waiter(task),
 873						  rt_mutex_top_waiter(lock)))
 874				return 0;
 875
 876			/*
 877			 * The current top waiter stays enqueued. We
 878			 * don't have to change anything in the lock
 879			 * waiters order.
 880			 */
 881		} else {
 882			/*
 883			 * No waiters. Take the lock without the
 884			 * pi_lock dance.@task->pi_blocked_on is NULL
 885			 * and we have no waiters to enqueue in @task
 886			 * pi waiters tree.
 887			 */
 888			goto takeit;
 889		}
 890	}
 891
 892	/*
 893	 * Clear @task->pi_blocked_on. Requires protection by
 894	 * @task->pi_lock. Redundant operation for the @waiter == NULL
 895	 * case, but conditionals are more expensive than a redundant
 896	 * store.
 897	 */
 898	raw_spin_lock(&task->pi_lock);
 899	task->pi_blocked_on = NULL;
 900	/*
 901	 * Finish the lock acquisition. @task is the new owner. If
 902	 * other waiters exist we have to insert the highest priority
 903	 * waiter into @task->pi_waiters tree.
 904	 */
 905	if (rt_mutex_has_waiters(lock))
 906		rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
 907	raw_spin_unlock(&task->pi_lock);
 908
 909takeit:
 910	/* We got the lock. */
 911	debug_rt_mutex_lock(lock);
 912
 913	/*
 914	 * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
 915	 * are still waiters or clears it.
 916	 */
 917	rt_mutex_set_owner(lock, task);
 918
 919	return 1;
 920}
 921
 922/*
 923 * Task blocks on lock.
 924 *
 925 * Prepare waiter and propagate pi chain
 926 *
 927 * This must be called with lock->wait_lock held and interrupts disabled
 928 */
 929static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 930				   struct rt_mutex_waiter *waiter,
 931				   struct task_struct *task,
 932				   enum rtmutex_chainwalk chwalk)
 933{
 934	struct task_struct *owner = rt_mutex_owner(lock);
 935	struct rt_mutex_waiter *top_waiter = waiter;
 936	struct rt_mutex *next_lock;
 937	int chain_walk = 0, res;
 938
 939	lockdep_assert_held(&lock->wait_lock);
 940
 941	/*
 942	 * Early deadlock detection. We really don't want the task to
 943	 * enqueue on itself just to untangle the mess later. It's not
 944	 * only an optimization. We drop the locks, so another waiter
 945	 * can come in before the chain walk detects the deadlock. So
 946	 * the other will detect the deadlock and return -EDEADLOCK,
 947	 * which is wrong, as the other waiter is not in a deadlock
 948	 * situation.
 949	 */
 950	if (owner == task)
 951		return -EDEADLK;
 952
 953	raw_spin_lock(&task->pi_lock);
 954	waiter->task = task;
 955	waiter->lock = lock;
 956	waiter->prio = task->prio;
 957	waiter->deadline = task->dl.deadline;
 958
 959	/* Get the top priority waiter on the lock */
 960	if (rt_mutex_has_waiters(lock))
 961		top_waiter = rt_mutex_top_waiter(lock);
 962	rt_mutex_enqueue(lock, waiter);
 963
 964	task->pi_blocked_on = waiter;
 965
 966	raw_spin_unlock(&task->pi_lock);
 967
 968	if (!owner)
 969		return 0;
 970
 971	raw_spin_lock(&owner->pi_lock);
 972	if (waiter == rt_mutex_top_waiter(lock)) {
 973		rt_mutex_dequeue_pi(owner, top_waiter);
 974		rt_mutex_enqueue_pi(owner, waiter);
 975
 976		rt_mutex_adjust_prio(owner);
 977		if (owner->pi_blocked_on)
 978			chain_walk = 1;
 979	} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
 980		chain_walk = 1;
 981	}
 982
 983	/* Store the lock on which owner is blocked or NULL */
 984	next_lock = task_blocked_on_lock(owner);
 985
 986	raw_spin_unlock(&owner->pi_lock);
 987	/*
 988	 * Even if full deadlock detection is on, if the owner is not
 989	 * blocked itself, we can avoid finding this out in the chain
 990	 * walk.
 991	 */
 992	if (!chain_walk || !next_lock)
 993		return 0;
 994
 995	/*
 996	 * The owner can't disappear while holding a lock,
 997	 * so the owner struct is protected by wait_lock.
 998	 * Gets dropped in rt_mutex_adjust_prio_chain()!
 999	 */
1000	get_task_struct(owner);
1001
1002	raw_spin_unlock_irq(&lock->wait_lock);
1003
1004	res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
1005					 next_lock, waiter, task);
1006
1007	raw_spin_lock_irq(&lock->wait_lock);
1008
1009	return res;
1010}
1011
1012/*
1013 * Remove the top waiter from the current tasks pi waiter tree and
1014 * queue it up.
1015 *
1016 * Called with lock->wait_lock held and interrupts disabled.
1017 */
1018static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
1019				    struct rt_mutex *lock)
1020{
1021	struct rt_mutex_waiter *waiter;
1022
1023	raw_spin_lock(&current->pi_lock);
1024
1025	waiter = rt_mutex_top_waiter(lock);
1026
1027	/*
1028	 * Remove it from current->pi_waiters and deboost.
1029	 *
1030	 * We must in fact deboost here in order to ensure we call
1031	 * rt_mutex_setprio() to update p->pi_top_task before the
1032	 * task unblocks.
1033	 */
1034	rt_mutex_dequeue_pi(current, waiter);
1035	rt_mutex_adjust_prio(current);
1036
1037	/*
1038	 * As we are waking up the top waiter, and the waiter stays
1039	 * queued on the lock until it gets the lock, this lock
1040	 * obviously has waiters. Just set the bit here and this has
1041	 * the added benefit of forcing all new tasks into the
1042	 * slow path making sure no task of lower priority than
1043	 * the top waiter can steal this lock.
1044	 */
1045	lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1046
1047	/*
1048	 * We deboosted before waking the top waiter task such that we don't
1049	 * run two tasks with the 'same' priority (and ensure the
1050	 * p->pi_top_task pointer points to a blocked task). This however can
1051	 * lead to priority inversion if we would get preempted after the
1052	 * deboost but before waking our donor task, hence the preempt_disable()
1053	 * before unlock.
1054	 *
1055	 * Pairs with preempt_enable() in rt_mutex_postunlock();
1056	 */
1057	preempt_disable();
1058	wake_q_add(wake_q, waiter->task);
1059	raw_spin_unlock(&current->pi_lock);
1060}
1061
1062/*
1063 * Remove a waiter from a lock and give up
1064 *
1065 * Must be called with lock->wait_lock held and interrupts disabled. I must
1066 * have just failed to try_to_take_rt_mutex().
1067 */
1068static void remove_waiter(struct rt_mutex *lock,
1069			  struct rt_mutex_waiter *waiter)
1070{
1071	bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1072	struct task_struct *owner = rt_mutex_owner(lock);
1073	struct rt_mutex *next_lock;
1074
1075	lockdep_assert_held(&lock->wait_lock);
1076
1077	raw_spin_lock(&current->pi_lock);
1078	rt_mutex_dequeue(lock, waiter);
1079	current->pi_blocked_on = NULL;
1080	raw_spin_unlock(&current->pi_lock);
1081
1082	/*
1083	 * Only update priority if the waiter was the highest priority
1084	 * waiter of the lock and there is an owner to update.
1085	 */
1086	if (!owner || !is_top_waiter)
1087		return;
1088
1089	raw_spin_lock(&owner->pi_lock);
1090
1091	rt_mutex_dequeue_pi(owner, waiter);
1092
1093	if (rt_mutex_has_waiters(lock))
1094		rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1095
1096	rt_mutex_adjust_prio(owner);
1097
1098	/* Store the lock on which owner is blocked or NULL */
1099	next_lock = task_blocked_on_lock(owner);
1100
1101	raw_spin_unlock(&owner->pi_lock);
1102
1103	/*
1104	 * Don't walk the chain, if the owner task is not blocked
1105	 * itself.
1106	 */
1107	if (!next_lock)
1108		return;
1109
1110	/* gets dropped in rt_mutex_adjust_prio_chain()! */
1111	get_task_struct(owner);
1112
1113	raw_spin_unlock_irq(&lock->wait_lock);
1114
1115	rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1116				   next_lock, NULL, current);
1117
1118	raw_spin_lock_irq(&lock->wait_lock);
1119}
1120
1121/*
1122 * Recheck the pi chain, in case we got a priority setting
1123 *
1124 * Called from sched_setscheduler
1125 */
1126void rt_mutex_adjust_pi(struct task_struct *task)
1127{
1128	struct rt_mutex_waiter *waiter;
1129	struct rt_mutex *next_lock;
1130	unsigned long flags;
1131
1132	raw_spin_lock_irqsave(&task->pi_lock, flags);
1133
1134	waiter = task->pi_blocked_on;
1135	if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
1136		raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1137		return;
1138	}
1139	next_lock = waiter->lock;
1140	raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1141
1142	/* gets dropped in rt_mutex_adjust_prio_chain()! */
1143	get_task_struct(task);
1144
1145	rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
1146				   next_lock, NULL, task);
1147}
1148
1149void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
1150{
1151	debug_rt_mutex_init_waiter(waiter);
1152	RB_CLEAR_NODE(&waiter->pi_tree_entry);
1153	RB_CLEAR_NODE(&waiter->tree_entry);
1154	waiter->task = NULL;
1155}
1156
1157/**
1158 * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
1159 * @lock:		 the rt_mutex to take
1160 * @state:		 the state the task should block in (TASK_INTERRUPTIBLE
1161 *			 or TASK_UNINTERRUPTIBLE)
1162 * @timeout:		 the pre-initialized and started timer, or NULL for none
1163 * @waiter:		 the pre-initialized rt_mutex_waiter
1164 *
1165 * Must be called with lock->wait_lock held and interrupts disabled
1166 */
1167static int __sched
1168__rt_mutex_slowlock(struct rt_mutex *lock, int state,
1169		    struct hrtimer_sleeper *timeout,
1170		    struct rt_mutex_waiter *waiter)
1171{
1172	int ret = 0;
1173
1174	for (;;) {
1175		/* Try to acquire the lock: */
1176		if (try_to_take_rt_mutex(lock, current, waiter))
1177			break;
1178
1179		/*
1180		 * TASK_INTERRUPTIBLE checks for signals and
1181		 * timeout. Ignored otherwise.
1182		 */
1183		if (likely(state == TASK_INTERRUPTIBLE)) {
1184			/* Signal pending? */
1185			if (signal_pending(current))
1186				ret = -EINTR;
1187			if (timeout && !timeout->task)
1188				ret = -ETIMEDOUT;
1189			if (ret)
1190				break;
1191		}
1192
1193		raw_spin_unlock_irq(&lock->wait_lock);
1194
1195		debug_rt_mutex_print_deadlock(waiter);
1196
1197		schedule();
1198
1199		raw_spin_lock_irq(&lock->wait_lock);
1200		set_current_state(state);
1201	}
1202
1203	__set_current_state(TASK_RUNNING);
1204	return ret;
1205}
1206
1207static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
1208				     struct rt_mutex_waiter *w)
1209{
1210	/*
1211	 * If the result is not -EDEADLOCK or the caller requested
1212	 * deadlock detection, nothing to do here.
1213	 */
1214	if (res != -EDEADLOCK || detect_deadlock)
1215		return;
1216
1217	/*
1218	 * Yell lowdly and stop the task right here.
1219	 */
1220	rt_mutex_print_deadlock(w);
1221	while (1) {
1222		set_current_state(TASK_INTERRUPTIBLE);
1223		schedule();
1224	}
1225}
1226
1227/*
1228 * Slow path lock function:
1229 */
1230static int __sched
1231rt_mutex_slowlock(struct rt_mutex *lock, int state,
1232		  struct hrtimer_sleeper *timeout,
1233		  enum rtmutex_chainwalk chwalk)
1234{
1235	struct rt_mutex_waiter waiter;
1236	unsigned long flags;
1237	int ret = 0;
1238
1239	rt_mutex_init_waiter(&waiter);
1240
1241	/*
1242	 * Technically we could use raw_spin_[un]lock_irq() here, but this can
1243	 * be called in early boot if the cmpxchg() fast path is disabled
1244	 * (debug, no architecture support). In this case we will acquire the
1245	 * rtmutex with lock->wait_lock held. But we cannot unconditionally
1246	 * enable interrupts in that early boot case. So we need to use the
1247	 * irqsave/restore variants.
1248	 */
1249	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1250
1251	/* Try to acquire the lock again: */
1252	if (try_to_take_rt_mutex(lock, current, NULL)) {
1253		raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1254		return 0;
1255	}
1256
1257	set_current_state(state);
1258
1259	/* Setup the timer, when timeout != NULL */
1260	if (unlikely(timeout))
1261		hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1262
1263	ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
1264
1265	if (likely(!ret))
1266		/* sleep on the mutex */
1267		ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
1268
1269	if (unlikely(ret)) {
1270		__set_current_state(TASK_RUNNING);
1271		remove_waiter(lock, &waiter);
1272		rt_mutex_handle_deadlock(ret, chwalk, &waiter);
1273	}
1274
1275	/*
1276	 * try_to_take_rt_mutex() sets the waiter bit
1277	 * unconditionally. We might have to fix that up.
1278	 */
1279	fixup_rt_mutex_waiters(lock);
1280
1281	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1282
1283	/* Remove pending timer: */
1284	if (unlikely(timeout))
1285		hrtimer_cancel(&timeout->timer);
1286
1287	debug_rt_mutex_free_waiter(&waiter);
1288
1289	return ret;
1290}
1291
1292static inline int __rt_mutex_slowtrylock(struct rt_mutex *lock)
1293{
1294	int ret = try_to_take_rt_mutex(lock, current, NULL);
1295
1296	/*
1297	 * try_to_take_rt_mutex() sets the lock waiters bit
1298	 * unconditionally. Clean this up.
1299	 */
1300	fixup_rt_mutex_waiters(lock);
1301
1302	return ret;
1303}
1304
1305/*
1306 * Slow path try-lock function:
1307 */
1308static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
1309{
1310	unsigned long flags;
1311	int ret;
1312
1313	/*
1314	 * If the lock already has an owner we fail to get the lock.
1315	 * This can be done without taking the @lock->wait_lock as
1316	 * it is only being read, and this is a trylock anyway.
1317	 */
1318	if (rt_mutex_owner(lock))
1319		return 0;
1320
1321	/*
1322	 * The mutex has currently no owner. Lock the wait lock and try to
1323	 * acquire the lock. We use irqsave here to support early boot calls.
1324	 */
1325	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1326
1327	ret = __rt_mutex_slowtrylock(lock);
1328
1329	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1330
1331	return ret;
1332}
1333
1334/*
 
 
 
 
 
 
 
 
 
 
 
1335 * Slow path to release a rt-mutex.
1336 *
1337 * Return whether the current task needs to call rt_mutex_postunlock().
1338 */
1339static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
1340					struct wake_q_head *wake_q)
1341{
 
1342	unsigned long flags;
1343
1344	/* irqsave required to support early boot calls */
1345	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1346
1347	debug_rt_mutex_unlock(lock);
1348
1349	/*
1350	 * We must be careful here if the fast path is enabled. If we
1351	 * have no waiters queued we cannot set owner to NULL here
1352	 * because of:
1353	 *
1354	 * foo->lock->owner = NULL;
1355	 *			rtmutex_lock(foo->lock);   <- fast path
1356	 *			free = atomic_dec_and_test(foo->refcnt);
1357	 *			rtmutex_unlock(foo->lock); <- fast path
1358	 *			if (free)
1359	 *				kfree(foo);
1360	 * raw_spin_unlock(foo->lock->wait_lock);
1361	 *
1362	 * So for the fastpath enabled kernel:
1363	 *
1364	 * Nothing can set the waiters bit as long as we hold
1365	 * lock->wait_lock. So we do the following sequence:
1366	 *
1367	 *	owner = rt_mutex_owner(lock);
1368	 *	clear_rt_mutex_waiters(lock);
1369	 *	raw_spin_unlock(&lock->wait_lock);
1370	 *	if (cmpxchg(&lock->owner, owner, 0) == owner)
1371	 *		return;
1372	 *	goto retry;
1373	 *
1374	 * The fastpath disabled variant is simple as all access to
1375	 * lock->owner is serialized by lock->wait_lock:
1376	 *
1377	 *	lock->owner = NULL;
1378	 *	raw_spin_unlock(&lock->wait_lock);
1379	 */
1380	while (!rt_mutex_has_waiters(lock)) {
1381		/* Drops lock->wait_lock ! */
1382		if (unlock_rt_mutex_safe(lock, flags) == true)
1383			return false;
1384		/* Relock the rtmutex and try again */
1385		raw_spin_lock_irqsave(&lock->wait_lock, flags);
1386	}
1387
1388	/*
1389	 * The wakeup next waiter path does not suffer from the above
1390	 * race. See the comments there.
1391	 *
1392	 * Queue the next waiter for wakeup once we release the wait_lock.
1393	 */
1394	mark_wakeup_next_waiter(wake_q, lock);
1395	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1396
1397	return true; /* call rt_mutex_postunlock() */
1398}
1399
1400/*
1401 * debug aware fast / slowpath lock,trylock,unlock
1402 *
1403 * The atomic acquire/release ops are compiled away, when either the
1404 * architecture does not support cmpxchg or when debugging is enabled.
1405 */
1406static inline int
1407rt_mutex_fastlock(struct rt_mutex *lock, int state,
1408		  int (*slowfn)(struct rt_mutex *lock, int state,
1409				struct hrtimer_sleeper *timeout,
1410				enum rtmutex_chainwalk chwalk))
1411{
1412	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1413		return 0;
1414
1415	return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
1416}
1417
1418static inline int
1419rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1420			struct hrtimer_sleeper *timeout,
1421			enum rtmutex_chainwalk chwalk,
1422			int (*slowfn)(struct rt_mutex *lock, int state,
1423				      struct hrtimer_sleeper *timeout,
1424				      enum rtmutex_chainwalk chwalk))
1425{
1426	if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
1427	    likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1428		return 0;
1429
1430	return slowfn(lock, state, timeout, chwalk);
1431}
1432
1433static inline int
1434rt_mutex_fasttrylock(struct rt_mutex *lock,
1435		     int (*slowfn)(struct rt_mutex *lock))
1436{
1437	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1438		return 1;
1439
1440	return slowfn(lock);
 
 
 
1441}
1442
1443/*
1444 * Performs the wakeup of the the top-waiter and re-enables preemption.
 
 
 
 
1445 */
1446void rt_mutex_postunlock(struct wake_q_head *wake_q)
1447{
1448	wake_up_q(wake_q);
1449
1450	/* Pairs with preempt_disable() in rt_mutex_slowunlock() */
1451	preempt_enable();
1452}
 
1453
1454static inline void
1455rt_mutex_fastunlock(struct rt_mutex *lock,
1456		    bool (*slowfn)(struct rt_mutex *lock,
1457				   struct wake_q_head *wqh))
1458{
1459	DEFINE_WAKE_Q(wake_q);
1460
1461	if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
1462		return;
1463
1464	if (slowfn(lock, &wake_q))
1465		rt_mutex_postunlock(&wake_q);
1466}
1467
1468/**
1469 * rt_mutex_lock - lock a rt_mutex
1470 *
1471 * @lock: the rt_mutex to be locked
1472 */
1473void __sched rt_mutex_lock(struct rt_mutex *lock)
1474{
1475	might_sleep();
1476
1477	mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1478	rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
1479}
1480EXPORT_SYMBOL_GPL(rt_mutex_lock);
 
1481
1482/**
1483 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1484 *
1485 * @lock:		the rt_mutex to be locked
1486 *
1487 * Returns:
1488 *  0		on success
1489 * -EINTR	when interrupted by a signal
1490 */
1491int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
1492{
1493	int ret;
1494
1495	might_sleep();
1496
1497	mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1498	ret = rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
1499	if (ret)
1500		mutex_release(&lock->dep_map, 1, _RET_IP_);
1501
1502	return ret;
1503}
1504EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1505
1506/*
1507 * Futex variant, must not use fastpath.
1508 */
1509int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
1510{
1511	return rt_mutex_slowtrylock(lock);
1512}
1513
1514int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
1515{
1516	return __rt_mutex_slowtrylock(lock);
1517}
1518
1519/**
1520 * rt_mutex_timed_lock - lock a rt_mutex interruptible
1521 *			the timeout structure is provided
1522 *			by the caller
1523 *
1524 * @lock:		the rt_mutex to be locked
1525 * @timeout:		timeout structure or NULL (no timeout)
1526 *
1527 * Returns:
1528 *  0		on success
1529 * -EINTR	when interrupted by a signal
1530 * -ETIMEDOUT	when the timeout expired
1531 */
1532int
1533rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
1534{
1535	int ret;
1536
1537	might_sleep();
1538
1539	mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1540	ret = rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1541				       RT_MUTEX_MIN_CHAINWALK,
1542				       rt_mutex_slowlock);
1543	if (ret)
1544		mutex_release(&lock->dep_map, 1, _RET_IP_);
1545
1546	return ret;
1547}
1548EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1549
1550/**
1551 * rt_mutex_trylock - try to lock a rt_mutex
1552 *
1553 * @lock:	the rt_mutex to be locked
1554 *
1555 * This function can only be called in thread context. It's safe to
1556 * call it from atomic regions, but not from hard interrupt or soft
1557 * interrupt context.
1558 *
1559 * Returns 1 on success and 0 on contention
 
 
1560 */
1561int __sched rt_mutex_trylock(struct rt_mutex *lock)
1562{
1563	int ret;
1564
1565	if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
1566		return 0;
1567
1568	ret = rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
 
 
 
 
 
 
 
1569	if (ret)
1570		mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1571
1572	return ret;
1573}
1574EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1575
1576/**
1577 * rt_mutex_unlock - unlock a rt_mutex
1578 *
1579 * @lock: the rt_mutex to be unlocked
1580 */
1581void __sched rt_mutex_unlock(struct rt_mutex *lock)
1582{
1583	mutex_release(&lock->dep_map, 1, _RET_IP_);
1584	rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
 
 
 
1585}
1586EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1587
 
 
 
 
 
 
 
 
 
 
 
 
 
1588/**
1589 * Futex variant, that since futex variants do not use the fast-path, can be
1590 * simple and will not need to retry.
 
 
 
1591 */
1592bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
1593				    struct wake_q_head *wake_q)
1594{
1595	lockdep_assert_held(&lock->wait_lock);
1596
1597	debug_rt_mutex_unlock(lock);
1598
1599	if (!rt_mutex_has_waiters(lock)) {
1600		lock->owner = NULL;
1601		return false; /* done */
1602	}
1603
1604	/*
1605	 * We've already deboosted, mark_wakeup_next_waiter() will
1606	 * retain preempt_disabled when we drop the wait_lock, to
1607	 * avoid inversion prior to the wakeup.  preempt_disable()
1608	 * therein pairs with rt_mutex_postunlock().
1609	 */
1610	mark_wakeup_next_waiter(wake_q, lock);
1611
1612	return true; /* call postunlock() */
1613}
1614
1615void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
1616{
1617	DEFINE_WAKE_Q(wake_q);
1618	unsigned long flags;
1619	bool postunlock;
1620
1621	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1622	postunlock = __rt_mutex_futex_unlock(lock, &wake_q);
1623	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1624
1625	if (postunlock)
1626		rt_mutex_postunlock(&wake_q);
1627}
1628
1629/**
1630 * rt_mutex_destroy - mark a mutex unusable
1631 * @lock: the mutex to be destroyed
1632 *
1633 * This function marks the mutex uninitialized, and any subsequent
1634 * use of the mutex is forbidden. The mutex must not be locked when
1635 * this function is called.
1636 */
1637void rt_mutex_destroy(struct rt_mutex *lock)
1638{
1639	WARN_ON(rt_mutex_is_locked(lock));
1640#ifdef CONFIG_DEBUG_RT_MUTEXES
1641	lock->magic = NULL;
1642#endif
1643}
1644EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1645
1646/**
1647 * __rt_mutex_init - initialize the rt lock
1648 *
1649 * @lock: the rt lock to be initialized
 
 
1650 *
1651 * Initialize the rt lock to unlocked state.
1652 *
1653 * Initializing of a locked rt lock is not allowed
1654 */
1655void __rt_mutex_init(struct rt_mutex *lock, const char *name,
1656		     struct lock_class_key *key)
1657{
1658	lock->owner = NULL;
1659	raw_spin_lock_init(&lock->wait_lock);
1660	lock->waiters = RB_ROOT_CACHED;
1661
1662	if (name && key)
1663		debug_rt_mutex_init(lock, name, key);
1664}
1665EXPORT_SYMBOL_GPL(__rt_mutex_init);
1666
1667/**
1668 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1669 *				proxy owner
1670 *
1671 * @lock:	the rt_mutex to be locked
1672 * @proxy_owner:the task to set as owner
1673 *
1674 * No locking. Caller has to do serializing itself
1675 *
1676 * Special API call for PI-futex support. This initializes the rtmutex and
1677 * assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
1678 * possible at this point because the pi_state which contains the rtmutex
1679 * is not yet visible to other tasks.
1680 */
1681void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1682				struct task_struct *proxy_owner)
1683{
1684	__rt_mutex_init(lock, NULL, NULL);
1685	debug_rt_mutex_proxy_lock(lock, proxy_owner);
1686	rt_mutex_set_owner(lock, proxy_owner);
1687}
1688
1689/**
1690 * rt_mutex_proxy_unlock - release a lock on behalf of owner
1691 *
1692 * @lock:	the rt_mutex to be locked
1693 *
1694 * No locking. Caller has to do serializing itself
1695 *
1696 * Special API call for PI-futex support. This merrily cleans up the rtmutex
1697 * (debugging) state. Concurrent operations on this rt_mutex are not
1698 * possible because it belongs to the pi_state which is about to be freed
1699 * and it is not longer visible to other tasks.
1700 */
1701void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1702			   struct task_struct *proxy_owner)
1703{
1704	debug_rt_mutex_proxy_unlock(lock);
1705	rt_mutex_set_owner(lock, NULL);
1706}
1707
1708int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1709			      struct rt_mutex_waiter *waiter,
1710			      struct task_struct *task)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1711{
1712	int ret;
1713
 
 
1714	if (try_to_take_rt_mutex(lock, task, NULL))
1715		return 1;
1716
1717	/* We enforce deadlock detection for futexes */
1718	ret = task_blocks_on_rt_mutex(lock, waiter, task,
1719				      RT_MUTEX_FULL_CHAINWALK);
1720
1721	if (ret && !rt_mutex_owner(lock)) {
1722		/*
1723		 * Reset the return value. We might have
1724		 * returned with -EDEADLK and the owner
1725		 * released the lock while we were walking the
1726		 * pi chain.  Let the waiter sort it out.
1727		 */
1728		ret = 0;
1729	}
1730
1731	if (unlikely(ret))
1732		remove_waiter(lock, waiter);
1733
1734	debug_rt_mutex_print_deadlock(waiter);
1735
1736	return ret;
1737}
1738
1739/**
1740 * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1741 * @lock:		the rt_mutex to take
1742 * @waiter:		the pre-initialized rt_mutex_waiter
1743 * @task:		the task to prepare
1744 *
 
 
 
 
 
 
1745 * Returns:
1746 *  0 - task blocked on lock
1747 *  1 - acquired the lock for task, caller should wake it up
1748 * <0 - error
1749 *
1750 * Special API call for FUTEX_REQUEUE_PI support.
1751 */
1752int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1753			      struct rt_mutex_waiter *waiter,
1754			      struct task_struct *task)
1755{
1756	int ret;
1757
1758	raw_spin_lock_irq(&lock->wait_lock);
1759	ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
 
 
1760	raw_spin_unlock_irq(&lock->wait_lock);
1761
1762	return ret;
1763}
1764
1765/**
1766 * rt_mutex_next_owner - return the next owner of the lock
1767 *
1768 * @lock: the rt lock query
1769 *
1770 * Returns the next owner of the lock or NULL
1771 *
1772 * Caller has to serialize against other accessors to the lock
1773 * itself.
1774 *
1775 * Special API call for PI-futex support
1776 */
1777struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1778{
1779	if (!rt_mutex_has_waiters(lock))
1780		return NULL;
1781
1782	return rt_mutex_top_waiter(lock)->task;
1783}
1784
1785/**
1786 * rt_mutex_wait_proxy_lock() - Wait for lock acquisition
1787 * @lock:		the rt_mutex we were woken on
1788 * @to:			the timeout, null if none. hrtimer should already have
1789 *			been started.
1790 * @waiter:		the pre-initialized rt_mutex_waiter
1791 *
1792 * Wait for the the lock acquisition started on our behalf by
1793 * rt_mutex_start_proxy_lock(). Upon failure, the caller must call
1794 * rt_mutex_cleanup_proxy_lock().
1795 *
1796 * Returns:
1797 *  0 - success
1798 * <0 - error, one of -EINTR, -ETIMEDOUT
1799 *
1800 * Special API call for PI-futex support
1801 */
1802int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
1803			       struct hrtimer_sleeper *to,
1804			       struct rt_mutex_waiter *waiter)
1805{
1806	int ret;
1807
1808	raw_spin_lock_irq(&lock->wait_lock);
1809	/* sleep on the mutex */
1810	set_current_state(TASK_INTERRUPTIBLE);
1811	ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1812	/*
1813	 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1814	 * have to fix that up.
1815	 */
1816	fixup_rt_mutex_waiters(lock);
1817	raw_spin_unlock_irq(&lock->wait_lock);
1818
1819	return ret;
1820}
1821
1822/**
1823 * rt_mutex_cleanup_proxy_lock() - Cleanup failed lock acquisition
1824 * @lock:		the rt_mutex we were woken on
1825 * @waiter:		the pre-initialized rt_mutex_waiter
1826 *
1827 * Attempt to clean up after a failed rt_mutex_wait_proxy_lock().
 
1828 *
1829 * Unless we acquired the lock; we're still enqueued on the wait-list and can
1830 * in fact still be granted ownership until we're removed. Therefore we can
1831 * find we are in fact the owner and must disregard the
1832 * rt_mutex_wait_proxy_lock() failure.
1833 *
1834 * Returns:
1835 *  true  - did the cleanup, we done.
1836 *  false - we acquired the lock after rt_mutex_wait_proxy_lock() returned,
1837 *          caller should disregards its return value.
1838 *
1839 * Special API call for PI-futex support
1840 */
1841bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
1842				 struct rt_mutex_waiter *waiter)
1843{
1844	bool cleanup = false;
1845
1846	raw_spin_lock_irq(&lock->wait_lock);
1847	/*
1848	 * Do an unconditional try-lock, this deals with the lock stealing
1849	 * state where __rt_mutex_futex_unlock() -> mark_wakeup_next_waiter()
1850	 * sets a NULL owner.
1851	 *
1852	 * We're not interested in the return value, because the subsequent
1853	 * test on rt_mutex_owner() will infer that. If the trylock succeeded,
1854	 * we will own the lock and it will have removed the waiter. If we
1855	 * failed the trylock, we're still not owner and we need to remove
1856	 * ourselves.
1857	 */
1858	try_to_take_rt_mutex(lock, current, waiter);
1859	/*
1860	 * Unless we're the owner; we're still enqueued on the wait_list.
1861	 * So check if we became owner, if not, take us off the wait_list.
1862	 */
1863	if (rt_mutex_owner(lock) != current) {
1864		remove_waiter(lock, waiter);
1865		cleanup = true;
1866	}
1867	/*
1868	 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1869	 * have to fix that up.
1870	 */
1871	fixup_rt_mutex_waiters(lock);
1872
1873	raw_spin_unlock_irq(&lock->wait_lock);
1874
1875	return cleanup;
1876}