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