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