1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * RT-Mutexes: simple blocking mutual exclusion locks with PI support
   4 *
   5 * started by Ingo Molnar and Thomas Gleixner.
   6 *
   7 *  Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   8 *  Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
   9 *  Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
  10 *  Copyright (C) 2006 Esben Nielsen
  11 * Adaptive Spinlocks:
  12 *  Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich,
  13 *				     and Peter Morreale,
  14 * Adaptive Spinlocks simplification:
  15 *  Copyright (C) 2008 Red Hat, Inc., Steven Rostedt <srostedt@redhat.com>
  16 *
  17 *  See Documentation/locking/rt-mutex-design.rst for details.
  18 */
  19#include <linux/sched.h>
  20#include <linux/sched/debug.h>
  21#include <linux/sched/deadline.h>
  22#include <linux/sched/signal.h>
  23#include <linux/sched/rt.h>
 
  24#include <linux/sched/wake_q.h>
  25#include <linux/ww_mutex.h>
  26
  27#include <trace/events/lock.h>
  28
  29#include "rtmutex_common.h"
  30
  31#ifndef WW_RT
  32# define build_ww_mutex()	(false)
  33# define ww_container_of(rtm)	NULL
  34
  35static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter,
  36					struct rt_mutex *lock,
  37					struct ww_acquire_ctx *ww_ctx)
  38{
  39	return 0;
  40}
  41
  42static inline void __ww_mutex_check_waiters(struct rt_mutex *lock,
  43					    struct ww_acquire_ctx *ww_ctx)
  44{
  45}
  46
  47static inline void ww_mutex_lock_acquired(struct ww_mutex *lock,
  48					  struct ww_acquire_ctx *ww_ctx)
  49{
  50}
  51
  52static inline int __ww_mutex_check_kill(struct rt_mutex *lock,
  53					struct rt_mutex_waiter *waiter,
  54					struct ww_acquire_ctx *ww_ctx)
  55{
  56	return 0;
  57}
  58
  59#else
  60# define build_ww_mutex()	(true)
  61# define ww_container_of(rtm)	container_of(rtm, struct ww_mutex, base)
  62# include "ww_mutex.h"
  63#endif
  64
  65/*
  66 * lock->owner state tracking:
  67 *
  68 * lock->owner holds the task_struct pointer of the owner. Bit 0
  69 * is used to keep track of the "lock has waiters" state.
  70 *
  71 * owner	bit0
  72 * NULL		0	lock is free (fast acquire possible)
  73 * NULL		1	lock is free and has waiters and the top waiter
  74 *				is going to take the lock*
  75 * taskpointer	0	lock is held (fast release possible)
  76 * taskpointer	1	lock is held and has waiters**
  77 *
  78 * The fast atomic compare exchange based acquire and release is only
  79 * possible when bit 0 of lock->owner is 0.
  80 *
  81 * (*) It also can be a transitional state when grabbing the lock
  82 * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
  83 * we need to set the bit0 before looking at the lock, and the owner may be
  84 * NULL in this small time, hence this can be a transitional state.
  85 *
  86 * (**) There is a small time when bit 0 is set but there are no
  87 * waiters. This can happen when grabbing the lock in the slow path.
  88 * To prevent a cmpxchg of the owner releasing the lock, we need to
  89 * set this bit before looking at the lock.
  90 */
  91
  92static __always_inline struct task_struct *
  93rt_mutex_owner_encode(struct rt_mutex_base *lock, struct task_struct *owner)
  94{
  95	unsigned long val = (unsigned long)owner;
  96
  97	if (rt_mutex_has_waiters(lock))
  98		val |= RT_MUTEX_HAS_WAITERS;
  99
 100	return (struct task_struct *)val;
 101}
 102
 103static __always_inline void
 104rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner)
 105{
 106	/*
 107	 * lock->wait_lock is held but explicit acquire semantics are needed
 108	 * for a new lock owner so WRITE_ONCE is insufficient.
 109	 */
 110	xchg_acquire(&lock->owner, rt_mutex_owner_encode(lock, owner));
 111}
 112
 113static __always_inline void rt_mutex_clear_owner(struct rt_mutex_base *lock)
 114{
 115	/* lock->wait_lock is held so the unlock provides release semantics. */
 116	WRITE_ONCE(lock->owner, rt_mutex_owner_encode(lock, NULL));
 117}
 118
 119static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock)
 120{
 121	lock->owner = (struct task_struct *)
 122			((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
 123}
 124
 125static __always_inline void
 126fixup_rt_mutex_waiters(struct rt_mutex_base *lock, bool acquire_lock)
 127{
 128	unsigned long owner, *p = (unsigned long *) &lock->owner;
 129
 130	if (rt_mutex_has_waiters(lock))
 131		return;
 132
 133	/*
 134	 * The rbtree has no waiters enqueued, now make sure that the
 135	 * lock->owner still has the waiters bit set, otherwise the
 136	 * following can happen:
 137	 *
 138	 * CPU 0	CPU 1		CPU2
 139	 * l->owner=T1
 140	 *		rt_mutex_lock(l)
 141	 *		lock(l->lock)
 142	 *		l->owner = T1 | HAS_WAITERS;
 143	 *		enqueue(T2)
 144	 *		boost()
 145	 *		  unlock(l->lock)
 146	 *		block()
 147	 *
 148	 *				rt_mutex_lock(l)
 149	 *				lock(l->lock)
 150	 *				l->owner = T1 | HAS_WAITERS;
 151	 *				enqueue(T3)
 152	 *				boost()
 153	 *				  unlock(l->lock)
 154	 *				block()
 155	 *		signal(->T2)	signal(->T3)
 156	 *		lock(l->lock)
 157	 *		dequeue(T2)
 158	 *		deboost()
 159	 *		  unlock(l->lock)
 160	 *				lock(l->lock)
 161	 *				dequeue(T3)
 162	 *				 ==> wait list is empty
 163	 *				deboost()
 164	 *				 unlock(l->lock)
 165	 *		lock(l->lock)
 166	 *		fixup_rt_mutex_waiters()
 167	 *		  if (wait_list_empty(l) {
 168	 *		    l->owner = owner
 169	 *		    owner = l->owner & ~HAS_WAITERS;
 170	 *		      ==> l->owner = T1
 171	 *		  }
 172	 *				lock(l->lock)
 173	 * rt_mutex_unlock(l)		fixup_rt_mutex_waiters()
 174	 *				  if (wait_list_empty(l) {
 175	 *				    owner = l->owner & ~HAS_WAITERS;
 176	 * cmpxchg(l->owner, T1, NULL)
 177	 *  ===> Success (l->owner = NULL)
 178	 *
 179	 *				    l->owner = owner
 180	 *				      ==> l->owner = T1
 181	 *				  }
 182	 *
 183	 * With the check for the waiter bit in place T3 on CPU2 will not
 184	 * overwrite. All tasks fiddling with the waiters bit are
 185	 * serialized by l->lock, so nothing else can modify the waiters
 186	 * bit. If the bit is set then nothing can change l->owner either
 187	 * so the simple RMW is safe. The cmpxchg() will simply fail if it
 188	 * happens in the middle of the RMW because the waiters bit is
 189	 * still set.
 190	 */
 191	owner = READ_ONCE(*p);
 192	if (owner & RT_MUTEX_HAS_WAITERS) {
 193		/*
 194		 * See rt_mutex_set_owner() and rt_mutex_clear_owner() on
 195		 * why xchg_acquire() is used for updating owner for
 196		 * locking and WRITE_ONCE() for unlocking.
 197		 *
 198		 * WRITE_ONCE() would work for the acquire case too, but
 199		 * in case that the lock acquisition failed it might
 200		 * force other lockers into the slow path unnecessarily.
 201		 */
 202		if (acquire_lock)
 203			xchg_acquire(p, owner & ~RT_MUTEX_HAS_WAITERS);
 204		else
 205			WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
 206	}
 207}
 208
 209/*
 210 * We can speed up the acquire/release, if there's no debugging state to be
 211 * set up.
 212 */
 213#ifndef CONFIG_DEBUG_RT_MUTEXES
 214static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
 215						     struct task_struct *old,
 216						     struct task_struct *new)
 217{
 218	return try_cmpxchg_acquire(&lock->owner, &old, new);
 219}
 220
 221static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
 222						     struct task_struct *old,
 223						     struct task_struct *new)
 224{
 225	return try_cmpxchg_release(&lock->owner, &old, new);
 226}
 227
 228/*
 229 * Callers must hold the ->wait_lock -- which is the whole purpose as we force
 230 * all future threads that attempt to [Rmw] the lock to the slowpath. As such
 231 * relaxed semantics suffice.
 232 */
 233static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
 234{
 235	unsigned long owner, *p = (unsigned long *) &lock->owner;
 236
 237	do {
 238		owner = *p;
 239	} while (cmpxchg_relaxed(p, owner,
 240				 owner | RT_MUTEX_HAS_WAITERS) != owner);
 241
 242	/*
 243	 * The cmpxchg loop above is relaxed to avoid back-to-back ACQUIRE
 244	 * operations in the event of contention. Ensure the successful
 245	 * cmpxchg is visible.
 246	 */
 247	smp_mb__after_atomic();
 248}
 249
 250/*
 251 * Safe fastpath aware unlock:
 252 * 1) Clear the waiters bit
 253 * 2) Drop lock->wait_lock
 254 * 3) Try to unlock the lock with cmpxchg
 255 */
 256static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
 257						 unsigned long flags)
 258	__releases(lock->wait_lock)
 259{
 260	struct task_struct *owner = rt_mutex_owner(lock);
 261
 262	clear_rt_mutex_waiters(lock);
 263	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 264	/*
 265	 * If a new waiter comes in between the unlock and the cmpxchg
 266	 * we have two situations:
 267	 *
 268	 * unlock(wait_lock);
 269	 *					lock(wait_lock);
 270	 * cmpxchg(p, owner, 0) == owner
 271	 *					mark_rt_mutex_waiters(lock);
 272	 *					acquire(lock);
 273	 * or:
 274	 *
 275	 * unlock(wait_lock);
 276	 *					lock(wait_lock);
 277	 *					mark_rt_mutex_waiters(lock);
 278	 *
 279	 * cmpxchg(p, owner, 0) != owner
 280	 *					enqueue_waiter();
 281	 *					unlock(wait_lock);
 282	 * lock(wait_lock);
 283	 * wake waiter();
 284	 * unlock(wait_lock);
 285	 *					lock(wait_lock);
 286	 *					acquire(lock);
 287	 */
 288	return rt_mutex_cmpxchg_release(lock, owner, NULL);
 289}
 290
 291#else
 292static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
 293						     struct task_struct *old,
 294						     struct task_struct *new)
 295{
 296	return false;
 297
 298}
 299
 300static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
 301						     struct task_struct *old,
 302						     struct task_struct *new)
 303{
 304	return false;
 305}
 306
 307static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
 308{
 309	lock->owner = (struct task_struct *)
 310			((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
 311}
 312
 313/*
 314 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
 315 */
 316static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
 317						 unsigned long flags)
 318	__releases(lock->wait_lock)
 319{
 320	lock->owner = NULL;
 321	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
 322	return true;
 323}
 324#endif
 325
 326static __always_inline int __waiter_prio(struct task_struct *task)
 327{
 328	int prio = task->prio;
 329
 330	if (!rt_prio(prio))
 331		return DEFAULT_PRIO;
 332
 333	return prio;
 334}
 335
 336static __always_inline void
 337waiter_update_prio(struct rt_mutex_waiter *waiter, struct task_struct *task)
 338{
 339	waiter->prio = __waiter_prio(task);
 340	waiter->deadline = task->dl.deadline;
 341}
 342
 343/*
 344 * Only use with rt_mutex_waiter_{less,equal}()
 345 */
 346#define task_to_waiter(p)	\
 347	&(struct rt_mutex_waiter){ .prio = __waiter_prio(p), .deadline = (p)->dl.deadline }
 348
 349static __always_inline int rt_mutex_waiter_less(struct rt_mutex_waiter *left,
 350						struct rt_mutex_waiter *right)
 
 351{
 352	if (left->prio < right->prio)
 353		return 1;
 354
 355	/*
 356	 * If both waiters have dl_prio(), we check the deadlines of the
 357	 * associated tasks.
 358	 * If left waiter has a dl_prio(), and we didn't return 1 above,
 359	 * then right waiter has a dl_prio() too.
 360	 */
 361	if (dl_prio(left->prio))
 362		return dl_time_before(left->deadline, right->deadline);
 363
 364	return 0;
 365}
 366
 367static __always_inline int rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
 368						 struct rt_mutex_waiter *right)
 
 369{
 370	if (left->prio != right->prio)
 371		return 0;
 372
 373	/*
 374	 * If both waiters have dl_prio(), we check the deadlines of the
 375	 * associated tasks.
 376	 * If left waiter has a dl_prio(), and we didn't return 0 above,
 377	 * then right waiter has a dl_prio() too.
 378	 */
 379	if (dl_prio(left->prio))
 380		return left->deadline == right->deadline;
 381
 382	return 1;
 383}
 384
 385static inline bool rt_mutex_steal(struct rt_mutex_waiter *waiter,
 386				  struct rt_mutex_waiter *top_waiter)
 387{
 388	if (rt_mutex_waiter_less(waiter, top_waiter))
 389		return true;
 390
 391#ifdef RT_MUTEX_BUILD_SPINLOCKS
 392	/*
 393	 * Note that RT tasks are excluded from same priority (lateral)
 394	 * steals to prevent the introduction of an unbounded latency.
 395	 */
 396	if (rt_prio(waiter->prio) || dl_prio(waiter->prio))
 397		return false;
 398
 399	return rt_mutex_waiter_equal(waiter, top_waiter);
 400#else
 401	return false;
 402#endif
 403}
 404
 405#define __node_2_waiter(node) \
 406	rb_entry((node), struct rt_mutex_waiter, tree_entry)
 407
 408static __always_inline bool __waiter_less(struct rb_node *a, const struct rb_node *b)
 409{
 410	struct rt_mutex_waiter *aw = __node_2_waiter(a);
 411	struct rt_mutex_waiter *bw = __node_2_waiter(b);
 412
 413	if (rt_mutex_waiter_less(aw, bw))
 414		return 1;
 415
 416	if (!build_ww_mutex())
 417		return 0;
 418
 419	if (rt_mutex_waiter_less(bw, aw))
 420		return 0;
 421
 422	/* NOTE: relies on waiter->ww_ctx being set before insertion */
 423	if (aw->ww_ctx) {
 424		if (!bw->ww_ctx)
 425			return 1;
 426
 427		return (signed long)(aw->ww_ctx->stamp -
 428				     bw->ww_ctx->stamp) < 0;
 429	}
 430
 431	return 0;
 432}
 433
 434static __always_inline void
 435rt_mutex_enqueue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
 436{
 437	rb_add_cached(&waiter->tree_entry, &lock->waiters, __waiter_less);
 438}
 439
 440static __always_inline void
 441rt_mutex_dequeue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
 442{
 443	if (RB_EMPTY_NODE(&waiter->tree_entry))
 444		return;
 445
 446	rb_erase_cached(&waiter->tree_entry, &lock->waiters);
 447	RB_CLEAR_NODE(&waiter->tree_entry);
 448}
 449
 450#define __node_2_pi_waiter(node) \
 451	rb_entry((node), struct rt_mutex_waiter, pi_tree_entry)
 452
 453static __always_inline bool
 454__pi_waiter_less(struct rb_node *a, const struct rb_node *b)
 455{
 456	return rt_mutex_waiter_less(__node_2_pi_waiter(a), __node_2_pi_waiter(b));
 457}
 458
 459static __always_inline void
 460rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 461{
 462	rb_add_cached(&waiter->pi_tree_entry, &task->pi_waiters, __pi_waiter_less);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 463}
 464
 465static __always_inline void
 466rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 467{
 468	if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
 469		return;
 470
 471	rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
 472	RB_CLEAR_NODE(&waiter->pi_tree_entry);
 473}
 474
 475static __always_inline void rt_mutex_adjust_prio(struct task_struct *p)
 476{
 477	struct task_struct *pi_task = NULL;
 478
 479	lockdep_assert_held(&p->pi_lock);
 480
 481	if (task_has_pi_waiters(p))
 482		pi_task = task_top_pi_waiter(p)->task;
 483
 484	rt_mutex_setprio(p, pi_task);
 485}
 486
 487/* RT mutex specific wake_q wrappers */
 488static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh,
 489						     struct task_struct *task,
 490						     unsigned int wake_state)
 491{
 492	if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state == TASK_RTLOCK_WAIT) {
 493		if (IS_ENABLED(CONFIG_PROVE_LOCKING))
 494			WARN_ON_ONCE(wqh->rtlock_task);
 495		get_task_struct(task);
 496		wqh->rtlock_task = task;
 497	} else {
 498		wake_q_add(&wqh->head, task);
 499	}
 500}
 501
 502static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
 503						struct rt_mutex_waiter *w)
 504{
 505	rt_mutex_wake_q_add_task(wqh, w->task, w->wake_state);
 506}
 507
 508static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh)
 509{
 510	if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task) {
 511		wake_up_state(wqh->rtlock_task, TASK_RTLOCK_WAIT);
 512		put_task_struct(wqh->rtlock_task);
 513		wqh->rtlock_task = NULL;
 514	}
 515
 516	if (!wake_q_empty(&wqh->head))
 517		wake_up_q(&wqh->head);
 518
 519	/* Pairs with preempt_disable() in mark_wakeup_next_waiter() */
 520	preempt_enable();
 521}
 522
 523/*
 524 * Deadlock detection is conditional:
 525 *
 526 * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
 527 * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
 528 *
 529 * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
 530 * conducted independent of the detect argument.
 531 *
 532 * If the waiter argument is NULL this indicates the deboost path and
 533 * deadlock detection is disabled independent of the detect argument
 534 * and the config settings.
 535 */
 536static __always_inline bool
 537rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
 538			      enum rtmutex_chainwalk chwalk)
 539{
 540	if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
 541		return waiter != NULL;
 542	return chwalk == RT_MUTEX_FULL_CHAINWALK;
 
 
 
 
 
 543}
 544
 545static __always_inline struct rt_mutex_base *task_blocked_on_lock(struct task_struct *p)
 
 
 
 
 
 546{
 547	return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
 548}
 549
 550/*
 551 * Adjust the priority chain. Also used for deadlock detection.
 552 * Decreases task's usage by one - may thus free the task.
 553 *
 554 * @task:	the task owning the mutex (owner) for which a chain walk is
 555 *		probably needed
 556 * @chwalk:	do we have to carry out deadlock detection?
 557 * @orig_lock:	the mutex (can be NULL if we are walking the chain to recheck
 558 *		things for a task that has just got its priority adjusted, and
 559 *		is waiting on a mutex)
 560 * @next_lock:	the mutex on which the owner of @orig_lock was blocked before
 561 *		we dropped its pi_lock. Is never dereferenced, only used for
 562 *		comparison to detect lock chain changes.
 563 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
 564 *		its priority to the mutex owner (can be NULL in the case
 565 *		depicted above or if the top waiter is gone away and we are
 566 *		actually deboosting the owner)
 567 * @top_task:	the current top waiter
 568 *
 569 * Returns 0 or -EDEADLK.
 570 *
 571 * Chain walk basics and protection scope
 572 *
 573 * [R] refcount on task
 574 * [P] task->pi_lock held
 575 * [L] rtmutex->wait_lock held
 576 *
 577 * Step	Description				Protected by
 578 *	function arguments:
 579 *	@task					[R]
 580 *	@orig_lock if != NULL			@top_task is blocked on it
 581 *	@next_lock				Unprotected. Cannot be
 582 *						dereferenced. Only used for
 583 *						comparison.
 584 *	@orig_waiter if != NULL			@top_task is blocked on it
 585 *	@top_task				current, or in case of proxy
 586 *						locking protected by calling
 587 *						code
 588 *	again:
 589 *	  loop_sanity_check();
 590 *	retry:
 591 * [1]	  lock(task->pi_lock);			[R] acquire [P]
 592 * [2]	  waiter = task->pi_blocked_on;		[P]
 593 * [3]	  check_exit_conditions_1();		[P]
 594 * [4]	  lock = waiter->lock;			[P]
 595 * [5]	  if (!try_lock(lock->wait_lock)) {	[P] try to acquire [L]
 596 *	    unlock(task->pi_lock);		release [P]
 597 *	    goto retry;
 598 *	  }
 599 * [6]	  check_exit_conditions_2();		[P] + [L]
 600 * [7]	  requeue_lock_waiter(lock, waiter);	[P] + [L]
 601 * [8]	  unlock(task->pi_lock);		release [P]
 602 *	  put_task_struct(task);		release [R]
 603 * [9]	  check_exit_conditions_3();		[L]
 604 * [10]	  task = owner(lock);			[L]
 605 *	  get_task_struct(task);		[L] acquire [R]
 606 *	  lock(task->pi_lock);			[L] acquire [P]
 607 * [11]	  requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
 608 * [12]	  check_exit_conditions_4();		[P] + [L]
 609 * [13]	  unlock(task->pi_lock);		release [P]
 610 *	  unlock(lock->wait_lock);		release [L]
 611 *	  goto again;
 612 */
 613static int __sched rt_mutex_adjust_prio_chain(struct task_struct *task,
 614					      enum rtmutex_chainwalk chwalk,
 615					      struct rt_mutex_base *orig_lock,
 616					      struct rt_mutex_base *next_lock,
 617					      struct rt_mutex_waiter *orig_waiter,
 618					      struct task_struct *top_task)
 619{
 620	struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 621	struct rt_mutex_waiter *prerequeue_top_waiter;
 622	int ret = 0, depth = 0;
 623	struct rt_mutex_base *lock;
 624	bool detect_deadlock;
 625	bool requeue = true;
 626
 627	detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
 628
 629	/*
 630	 * The (de)boosting is a step by step approach with a lot of
 631	 * pitfalls. We want this to be preemptible and we want hold a
 632	 * maximum of two locks per step. So we have to check
 633	 * carefully whether things change under us.
 634	 */
 635 again:
 636	/*
 637	 * We limit the lock chain length for each invocation.
 638	 */
 639	if (++depth > max_lock_depth) {
 640		static int prev_max;
 641
 642		/*
 643		 * Print this only once. If the admin changes the limit,
 644		 * print a new message when reaching the limit again.
 645		 */
 646		if (prev_max != max_lock_depth) {
 647			prev_max = max_lock_depth;
 648			printk(KERN_WARNING "Maximum lock depth %d reached "
 649			       "task: %s (%d)\n", max_lock_depth,
 650			       top_task->comm, task_pid_nr(top_task));
 651		}
 652		put_task_struct(task);
 653
 654		return -EDEADLK;
 655	}
 656
 657	/*
 658	 * We are fully preemptible here and only hold the refcount on
 659	 * @task. So everything can have changed under us since the
 660	 * caller or our own code below (goto retry/again) dropped all
 661	 * locks.
 662	 */
 663 retry:
 664	/*
 665	 * [1] Task cannot go away as we did a get_task() before !
 666	 */
 667	raw_spin_lock_irq(&task->pi_lock);
 668
 669	/*
 670	 * [2] Get the waiter on which @task is blocked on.
 671	 */
 672	waiter = task->pi_blocked_on;
 673
 674	/*
 675	 * [3] check_exit_conditions_1() protected by task->pi_lock.
 676	 */
 677
 678	/*
 679	 * Check whether the end of the boosting chain has been
 680	 * reached or the state of the chain has changed while we
 681	 * dropped the locks.
 682	 */
 683	if (!waiter)
 684		goto out_unlock_pi;
 685
 686	/*
 687	 * Check the orig_waiter state. After we dropped the locks,
 688	 * the previous owner of the lock might have released the lock.
 689	 */
 690	if (orig_waiter && !rt_mutex_owner(orig_lock))
 691		goto out_unlock_pi;
 692
 693	/*
 694	 * We dropped all locks after taking a refcount on @task, so
 695	 * the task might have moved on in the lock chain or even left
 696	 * the chain completely and blocks now on an unrelated lock or
 697	 * on @orig_lock.
 698	 *
 699	 * We stored the lock on which @task was blocked in @next_lock,
 700	 * so we can detect the chain change.
 701	 */
 702	if (next_lock != waiter->lock)
 703		goto out_unlock_pi;
 704
 705	/*
 706	 * There could be 'spurious' loops in the lock graph due to ww_mutex,
 707	 * consider:
 708	 *
 709	 *   P1: A, ww_A, ww_B
 710	 *   P2: ww_B, ww_A
 711	 *   P3: A
 712	 *
 713	 * P3 should not return -EDEADLK because it gets trapped in the cycle
 714	 * created by P1 and P2 (which will resolve -- and runs into
 715	 * max_lock_depth above). Therefore disable detect_deadlock such that
 716	 * the below termination condition can trigger once all relevant tasks
 717	 * are boosted.
 718	 *
 719	 * Even when we start with ww_mutex we can disable deadlock detection,
 720	 * since we would supress a ww_mutex induced deadlock at [6] anyway.
 721	 * Supressing it here however is not sufficient since we might still
 722	 * hit [6] due to adjustment driven iteration.
 723	 *
 724	 * NOTE: if someone were to create a deadlock between 2 ww_classes we'd
 725	 * utterly fail to report it; lockdep should.
 726	 */
 727	if (IS_ENABLED(CONFIG_PREEMPT_RT) && waiter->ww_ctx && detect_deadlock)
 728		detect_deadlock = false;
 729
 730	/*
 731	 * Drop out, when the task has no waiters. Note,
 732	 * top_waiter can be NULL, when we are in the deboosting
 733	 * mode!
 734	 */
 735	if (top_waiter) {
 736		if (!task_has_pi_waiters(task))
 737			goto out_unlock_pi;
 738		/*
 739		 * If deadlock detection is off, we stop here if we
 740		 * are not the top pi waiter of the task. If deadlock
 741		 * detection is enabled we continue, but stop the
 742		 * requeueing in the chain walk.
 743		 */
 744		if (top_waiter != task_top_pi_waiter(task)) {
 745			if (!detect_deadlock)
 746				goto out_unlock_pi;
 747			else
 748				requeue = false;
 749		}
 750	}
 751
 752	/*
 753	 * If the waiter priority is the same as the task priority
 754	 * then there is no further priority adjustment necessary.  If
 755	 * deadlock detection is off, we stop the chain walk. If its
 756	 * enabled we continue, but stop the requeueing in the chain
 757	 * walk.
 758	 */
 759	if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
 760		if (!detect_deadlock)
 761			goto out_unlock_pi;
 762		else
 763			requeue = false;
 764	}
 765
 766	/*
 767	 * [4] Get the next lock
 768	 */
 769	lock = waiter->lock;
 770	/*
 771	 * [5] We need to trylock here as we are holding task->pi_lock,
 772	 * which is the reverse lock order versus the other rtmutex
 773	 * operations.
 774	 */
 775	if (!raw_spin_trylock(&lock->wait_lock)) {
 776		raw_spin_unlock_irq(&task->pi_lock);
 777		cpu_relax();
 778		goto retry;
 779	}
 780
 781	/*
 782	 * [6] check_exit_conditions_2() protected by task->pi_lock and
 783	 * lock->wait_lock.
 784	 *
 785	 * Deadlock detection. If the lock is the same as the original
 786	 * lock which caused us to walk the lock chain or if the
 787	 * current lock is owned by the task which initiated the chain
 788	 * walk, we detected a deadlock.
 789	 */
 790	if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 791		ret = -EDEADLK;
 792
 793		/*
 794		 * When the deadlock is due to ww_mutex; also see above. Don't
 795		 * report the deadlock and instead let the ww_mutex wound/die
 796		 * logic pick which of the contending threads gets -EDEADLK.
 797		 *
 798		 * NOTE: assumes the cycle only contains a single ww_class; any
 799		 * other configuration and we fail to report; also, see
 800		 * lockdep.
 801		 */
 802		if (IS_ENABLED(CONFIG_PREEMPT_RT) && orig_waiter && orig_waiter->ww_ctx)
 803			ret = 0;
 804
 805		raw_spin_unlock(&lock->wait_lock);
 
 806		goto out_unlock_pi;
 807	}
 808
 809	/*
 810	 * If we just follow the lock chain for deadlock detection, no
 811	 * need to do all the requeue operations. To avoid a truckload
 812	 * of conditionals around the various places below, just do the
 813	 * minimum chain walk checks.
 814	 */
 815	if (!requeue) {
 816		/*
 817		 * No requeue[7] here. Just release @task [8]
 818		 */
 819		raw_spin_unlock(&task->pi_lock);
 820		put_task_struct(task);
 821
 822		/*
 823		 * [9] check_exit_conditions_3 protected by lock->wait_lock.
 824		 * If there is no owner of the lock, end of chain.
 825		 */
 826		if (!rt_mutex_owner(lock)) {
 827			raw_spin_unlock_irq(&lock->wait_lock);
 828			return 0;
 829		}
 830
 831		/* [10] Grab the next task, i.e. owner of @lock */
 832		task = get_task_struct(rt_mutex_owner(lock));
 833		raw_spin_lock(&task->pi_lock);
 834
 835		/*
 836		 * No requeue [11] here. We just do deadlock detection.
 837		 *
 838		 * [12] Store whether owner is blocked
 839		 * itself. Decision is made after dropping the locks
 840		 */
 841		next_lock = task_blocked_on_lock(task);
 842		/*
 843		 * Get the top waiter for the next iteration
 844		 */
 845		top_waiter = rt_mutex_top_waiter(lock);
 846
 847		/* [13] Drop locks */
 848		raw_spin_unlock(&task->pi_lock);
 849		raw_spin_unlock_irq(&lock->wait_lock);
 850
 851		/* If owner is not blocked, end of chain. */
 852		if (!next_lock)
 853			goto out_put_task;
 854		goto again;
 855	}
 856
 857	/*
 858	 * Store the current top waiter before doing the requeue
 859	 * operation on @lock. We need it for the boost/deboost
 860	 * decision below.
 861	 */
 862	prerequeue_top_waiter = rt_mutex_top_waiter(lock);
 863
 864	/* [7] Requeue the waiter in the lock waiter tree. */
 865	rt_mutex_dequeue(lock, waiter);
 866
 867	/*
 868	 * Update the waiter prio fields now that we're dequeued.
 869	 *
 870	 * These values can have changed through either:
 871	 *
 872	 *   sys_sched_set_scheduler() / sys_sched_setattr()
 873	 *
 874	 * or
 875	 *
 876	 *   DL CBS enforcement advancing the effective deadline.
 877	 *
 878	 * Even though pi_waiters also uses these fields, and that tree is only
 879	 * updated in [11], we can do this here, since we hold [L], which
 880	 * serializes all pi_waiters access and rb_erase() does not care about
 881	 * the values of the node being removed.
 882	 */
 883	waiter_update_prio(waiter, task);
 
 884
 885	rt_mutex_enqueue(lock, waiter);
 886
 887	/* [8] Release the task */
 888	raw_spin_unlock(&task->pi_lock);
 889	put_task_struct(task);
 890
 891	/*
 892	 * [9] check_exit_conditions_3 protected by lock->wait_lock.
 893	 *
 894	 * We must abort the chain walk if there is no lock owner even
 895	 * in the dead lock detection case, as we have nothing to
 896	 * follow here. This is the end of the chain we are walking.
 897	 */
 898	if (!rt_mutex_owner(lock)) {
 899		/*
 900		 * If the requeue [7] above changed the top waiter,
 901		 * then we need to wake the new top waiter up to try
 902		 * to get the lock.
 903		 */
 904		top_waiter = rt_mutex_top_waiter(lock);
 905		if (prerequeue_top_waiter != top_waiter)
 906			wake_up_state(top_waiter->task, top_waiter->wake_state);
 907		raw_spin_unlock_irq(&lock->wait_lock);
 908		return 0;
 909	}
 910
 911	/* [10] Grab the next task, i.e. the owner of @lock */
 912	task = get_task_struct(rt_mutex_owner(lock));
 913	raw_spin_lock(&task->pi_lock);
 914
 915	/* [11] requeue the pi waiters if necessary */
 916	if (waiter == rt_mutex_top_waiter(lock)) {
 917		/*
 918		 * The waiter became the new top (highest priority)
 919		 * waiter on the lock. Replace the previous top waiter
 920		 * in the owner tasks pi waiters tree with this waiter
 921		 * and adjust the priority of the owner.
 922		 */
 923		rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
 924		rt_mutex_enqueue_pi(task, waiter);
 925		rt_mutex_adjust_prio(task);
 926
 927	} else if (prerequeue_top_waiter == waiter) {
 928		/*
 929		 * The waiter was the top waiter on the lock, but is
 930		 * no longer the top priority waiter. Replace waiter in
 931		 * the owner tasks pi waiters tree with the new top
 932		 * (highest priority) waiter and adjust the priority
 933		 * of the owner.
 934		 * The new top waiter is stored in @waiter so that
 935		 * @waiter == @top_waiter evaluates to true below and
 936		 * we continue to deboost the rest of the chain.
 937		 */
 938		rt_mutex_dequeue_pi(task, waiter);
 939		waiter = rt_mutex_top_waiter(lock);
 940		rt_mutex_enqueue_pi(task, waiter);
 941		rt_mutex_adjust_prio(task);
 942	} else {
 943		/*
 944		 * Nothing changed. No need to do any priority
 945		 * adjustment.
 946		 */
 947	}
 948
 949	/*
 950	 * [12] check_exit_conditions_4() protected by task->pi_lock
 951	 * and lock->wait_lock. The actual decisions are made after we
 952	 * dropped the locks.
 953	 *
 954	 * Check whether the task which owns the current lock is pi
 955	 * blocked itself. If yes we store a pointer to the lock for
 956	 * the lock chain change detection above. After we dropped
 957	 * task->pi_lock next_lock cannot be dereferenced anymore.
 958	 */
 959	next_lock = task_blocked_on_lock(task);
 960	/*
 961	 * Store the top waiter of @lock for the end of chain walk
 962	 * decision below.
 963	 */
 964	top_waiter = rt_mutex_top_waiter(lock);
 965
 966	/* [13] Drop the locks */
 967	raw_spin_unlock(&task->pi_lock);
 968	raw_spin_unlock_irq(&lock->wait_lock);
 969
 970	/*
 971	 * Make the actual exit decisions [12], based on the stored
 972	 * values.
 973	 *
 974	 * We reached the end of the lock chain. Stop right here. No
 975	 * point to go back just to figure that out.
 976	 */
 977	if (!next_lock)
 978		goto out_put_task;
 979
 980	/*
 981	 * If the current waiter is not the top waiter on the lock,
 982	 * then we can stop the chain walk here if we are not in full
 983	 * deadlock detection mode.
 984	 */
 985	if (!detect_deadlock && waiter != top_waiter)
 986		goto out_put_task;
 987
 988	goto again;
 989
 990 out_unlock_pi:
 991	raw_spin_unlock_irq(&task->pi_lock);
 992 out_put_task:
 993	put_task_struct(task);
 994
 995	return ret;
 996}
 997
 998/*
 999 * Try to take an rt-mutex
1000 *
1001 * Must be called with lock->wait_lock held and interrupts disabled
1002 *
1003 * @lock:   The lock to be acquired.
1004 * @task:   The task which wants to acquire the lock
1005 * @waiter: The waiter that is queued to the lock's wait tree if the
1006 *	    callsite called task_blocked_on_lock(), otherwise NULL
1007 */
1008static int __sched
1009try_to_take_rt_mutex(struct rt_mutex_base *lock, struct task_struct *task,
1010		     struct rt_mutex_waiter *waiter)
1011{
1012	lockdep_assert_held(&lock->wait_lock);
1013
1014	/*
1015	 * Before testing whether we can acquire @lock, we set the
1016	 * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
1017	 * other tasks which try to modify @lock into the slow path
1018	 * and they serialize on @lock->wait_lock.
1019	 *
1020	 * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
1021	 * as explained at the top of this file if and only if:
1022	 *
1023	 * - There is a lock owner. The caller must fixup the
1024	 *   transient state if it does a trylock or leaves the lock
1025	 *   function due to a signal or timeout.
1026	 *
1027	 * - @task acquires the lock and there are no other
1028	 *   waiters. This is undone in rt_mutex_set_owner(@task) at
1029	 *   the end of this function.
1030	 */
1031	mark_rt_mutex_waiters(lock);
1032
1033	/*
1034	 * If @lock has an owner, give up.
1035	 */
1036	if (rt_mutex_owner(lock))
1037		return 0;
1038
1039	/*
1040	 * If @waiter != NULL, @task has already enqueued the waiter
1041	 * into @lock waiter tree. If @waiter == NULL then this is a
1042	 * trylock attempt.
1043	 */
1044	if (waiter) {
1045		struct rt_mutex_waiter *top_waiter = rt_mutex_top_waiter(lock);
1046
1047		/*
1048		 * If waiter is the highest priority waiter of @lock,
1049		 * or allowed to steal it, take it over.
1050		 */
1051		if (waiter == top_waiter || rt_mutex_steal(waiter, top_waiter)) {
1052			/*
1053			 * We can acquire the lock. Remove the waiter from the
1054			 * lock waiters tree.
1055			 */
1056			rt_mutex_dequeue(lock, waiter);
1057		} else {
1058			return 0;
1059		}
 
 
 
 
 
 
1060	} else {
1061		/*
1062		 * If the lock has waiters already we check whether @task is
1063		 * eligible to take over the lock.
1064		 *
1065		 * If there are no other waiters, @task can acquire
1066		 * the lock.  @task->pi_blocked_on is NULL, so it does
1067		 * not need to be dequeued.
1068		 */
1069		if (rt_mutex_has_waiters(lock)) {
1070			/* Check whether the trylock can steal it. */
1071			if (!rt_mutex_steal(task_to_waiter(task),
1072					    rt_mutex_top_waiter(lock)))
 
 
 
 
1073				return 0;
1074
1075			/*
1076			 * The current top waiter stays enqueued. We
1077			 * don't have to change anything in the lock
1078			 * waiters order.
1079			 */
1080		} else {
1081			/*
1082			 * No waiters. Take the lock without the
1083			 * pi_lock dance.@task->pi_blocked_on is NULL
1084			 * and we have no waiters to enqueue in @task
1085			 * pi waiters tree.
1086			 */
1087			goto takeit;
1088		}
1089	}
1090
1091	/*
1092	 * Clear @task->pi_blocked_on. Requires protection by
1093	 * @task->pi_lock. Redundant operation for the @waiter == NULL
1094	 * case, but conditionals are more expensive than a redundant
1095	 * store.
1096	 */
1097	raw_spin_lock(&task->pi_lock);
1098	task->pi_blocked_on = NULL;
1099	/*
1100	 * Finish the lock acquisition. @task is the new owner. If
1101	 * other waiters exist we have to insert the highest priority
1102	 * waiter into @task->pi_waiters tree.
1103	 */
1104	if (rt_mutex_has_waiters(lock))
1105		rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
1106	raw_spin_unlock(&task->pi_lock);
1107
1108takeit:
 
 
 
1109	/*
1110	 * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
1111	 * are still waiters or clears it.
1112	 */
1113	rt_mutex_set_owner(lock, task);
1114
1115	return 1;
1116}
1117
1118/*
1119 * Task blocks on lock.
1120 *
1121 * Prepare waiter and propagate pi chain
1122 *
1123 * This must be called with lock->wait_lock held and interrupts disabled
1124 */
1125static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
1126					   struct rt_mutex_waiter *waiter,
1127					   struct task_struct *task,
1128					   struct ww_acquire_ctx *ww_ctx,
1129					   enum rtmutex_chainwalk chwalk)
1130{
1131	struct task_struct *owner = rt_mutex_owner(lock);
1132	struct rt_mutex_waiter *top_waiter = waiter;
1133	struct rt_mutex_base *next_lock;
1134	int chain_walk = 0, res;
1135
1136	lockdep_assert_held(&lock->wait_lock);
1137
1138	/*
1139	 * Early deadlock detection. We really don't want the task to
1140	 * enqueue on itself just to untangle the mess later. It's not
1141	 * only an optimization. We drop the locks, so another waiter
1142	 * can come in before the chain walk detects the deadlock. So
1143	 * the other will detect the deadlock and return -EDEADLOCK,
1144	 * which is wrong, as the other waiter is not in a deadlock
1145	 * situation.
1146	 *
1147	 * Except for ww_mutex, in that case the chain walk must already deal
1148	 * with spurious cycles, see the comments at [3] and [6].
1149	 */
1150	if (owner == task && !(build_ww_mutex() && ww_ctx))
1151		return -EDEADLK;
1152
1153	raw_spin_lock(&task->pi_lock);
1154	waiter->task = task;
1155	waiter->lock = lock;
1156	waiter_update_prio(waiter, task);
 
1157
1158	/* Get the top priority waiter on the lock */
1159	if (rt_mutex_has_waiters(lock))
1160		top_waiter = rt_mutex_top_waiter(lock);
1161	rt_mutex_enqueue(lock, waiter);
1162
1163	task->pi_blocked_on = waiter;
1164
1165	raw_spin_unlock(&task->pi_lock);
1166
1167	if (build_ww_mutex() && ww_ctx) {
1168		struct rt_mutex *rtm;
1169
1170		/* Check whether the waiter should back out immediately */
1171		rtm = container_of(lock, struct rt_mutex, rtmutex);
1172		res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx);
1173		if (res) {
1174			raw_spin_lock(&task->pi_lock);
1175			rt_mutex_dequeue(lock, waiter);
1176			task->pi_blocked_on = NULL;
1177			raw_spin_unlock(&task->pi_lock);
1178			return res;
1179		}
1180	}
1181
1182	if (!owner)
1183		return 0;
1184
1185	raw_spin_lock(&owner->pi_lock);
1186	if (waiter == rt_mutex_top_waiter(lock)) {
1187		rt_mutex_dequeue_pi(owner, top_waiter);
1188		rt_mutex_enqueue_pi(owner, waiter);
1189
1190		rt_mutex_adjust_prio(owner);
1191		if (owner->pi_blocked_on)
1192			chain_walk = 1;
1193	} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
1194		chain_walk = 1;
1195	}
1196
1197	/* Store the lock on which owner is blocked or NULL */
1198	next_lock = task_blocked_on_lock(owner);
1199
1200	raw_spin_unlock(&owner->pi_lock);
1201	/*
1202	 * Even if full deadlock detection is on, if the owner is not
1203	 * blocked itself, we can avoid finding this out in the chain
1204	 * walk.
1205	 */
1206	if (!chain_walk || !next_lock)
1207		return 0;
1208
1209	/*
1210	 * The owner can't disappear while holding a lock,
1211	 * so the owner struct is protected by wait_lock.
1212	 * Gets dropped in rt_mutex_adjust_prio_chain()!
1213	 */
1214	get_task_struct(owner);
1215
1216	raw_spin_unlock_irq(&lock->wait_lock);
1217
1218	res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
1219					 next_lock, waiter, task);
1220
1221	raw_spin_lock_irq(&lock->wait_lock);
1222
1223	return res;
1224}
1225
1226/*
1227 * Remove the top waiter from the current tasks pi waiter tree and
1228 * queue it up.
1229 *
1230 * Called with lock->wait_lock held and interrupts disabled.
1231 */
1232static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh,
1233					    struct rt_mutex_base *lock)
1234{
1235	struct rt_mutex_waiter *waiter;
1236
1237	raw_spin_lock(&current->pi_lock);
1238
1239	waiter = rt_mutex_top_waiter(lock);
1240
1241	/*
1242	 * Remove it from current->pi_waiters and deboost.
1243	 *
1244	 * We must in fact deboost here in order to ensure we call
1245	 * rt_mutex_setprio() to update p->pi_top_task before the
1246	 * task unblocks.
1247	 */
1248	rt_mutex_dequeue_pi(current, waiter);
1249	rt_mutex_adjust_prio(current);
1250
1251	/*
1252	 * As we are waking up the top waiter, and the waiter stays
1253	 * queued on the lock until it gets the lock, this lock
1254	 * obviously has waiters. Just set the bit here and this has
1255	 * the added benefit of forcing all new tasks into the
1256	 * slow path making sure no task of lower priority than
1257	 * the top waiter can steal this lock.
1258	 */
1259	lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1260
1261	/*
1262	 * We deboosted before waking the top waiter task such that we don't
1263	 * run two tasks with the 'same' priority (and ensure the
1264	 * p->pi_top_task pointer points to a blocked task). This however can
1265	 * lead to priority inversion if we would get preempted after the
1266	 * deboost but before waking our donor task, hence the preempt_disable()
1267	 * before unlock.
1268	 *
1269	 * Pairs with preempt_enable() in rt_mutex_wake_up_q();
1270	 */
1271	preempt_disable();
1272	rt_mutex_wake_q_add(wqh, waiter);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1273	raw_spin_unlock(&current->pi_lock);
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1274}
1275
1276static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock)
1277{
1278	int ret = try_to_take_rt_mutex(lock, current, NULL);
1279
1280	/*
1281	 * try_to_take_rt_mutex() sets the lock waiters bit
1282	 * unconditionally. Clean this up.
1283	 */
1284	fixup_rt_mutex_waiters(lock, true);
1285
1286	return ret;
1287}
1288
1289/*
1290 * Slow path try-lock function:
1291 */
1292static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock)
1293{
1294	unsigned long flags;
1295	int ret;
1296
1297	/*
1298	 * If the lock already has an owner we fail to get the lock.
1299	 * This can be done without taking the @lock->wait_lock as
1300	 * it is only being read, and this is a trylock anyway.
1301	 */
1302	if (rt_mutex_owner(lock))
1303		return 0;
1304
1305	/*
1306	 * The mutex has currently no owner. Lock the wait lock and try to
1307	 * acquire the lock. We use irqsave here to support early boot calls.
1308	 */
1309	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1310
1311	ret = __rt_mutex_slowtrylock(lock);
1312
1313	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1314
1315	return ret;
1316}
1317
1318static __always_inline int __rt_mutex_trylock(struct rt_mutex_base *lock)
1319{
1320	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1321		return 1;
1322
1323	return rt_mutex_slowtrylock(lock);
1324}
1325
1326/*
1327 * Slow path to release a rt-mutex.
 
 
1328 */
1329static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
 
1330{
1331	DEFINE_RT_WAKE_Q(wqh);
1332	unsigned long flags;
1333
1334	/* irqsave required to support early boot calls */
1335	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1336
1337	debug_rt_mutex_unlock(lock);
1338
1339	/*
1340	 * We must be careful here if the fast path is enabled. If we
1341	 * have no waiters queued we cannot set owner to NULL here
1342	 * because of:
1343	 *
1344	 * foo->lock->owner = NULL;
1345	 *			rtmutex_lock(foo->lock);   <- fast path
1346	 *			free = atomic_dec_and_test(foo->refcnt);
1347	 *			rtmutex_unlock(foo->lock); <- fast path
1348	 *			if (free)
1349	 *				kfree(foo);
1350	 * raw_spin_unlock(foo->lock->wait_lock);
1351	 *
1352	 * So for the fastpath enabled kernel:
1353	 *
1354	 * Nothing can set the waiters bit as long as we hold
1355	 * lock->wait_lock. So we do the following sequence:
1356	 *
1357	 *	owner = rt_mutex_owner(lock);
1358	 *	clear_rt_mutex_waiters(lock);
1359	 *	raw_spin_unlock(&lock->wait_lock);
1360	 *	if (cmpxchg(&lock->owner, owner, 0) == owner)
1361	 *		return;
1362	 *	goto retry;
1363	 *
1364	 * The fastpath disabled variant is simple as all access to
1365	 * lock->owner is serialized by lock->wait_lock:
1366	 *
1367	 *	lock->owner = NULL;
1368	 *	raw_spin_unlock(&lock->wait_lock);
1369	 */
1370	while (!rt_mutex_has_waiters(lock)) {
1371		/* Drops lock->wait_lock ! */
1372		if (unlock_rt_mutex_safe(lock, flags) == true)
1373			return;
1374		/* Relock the rtmutex and try again */
1375		raw_spin_lock_irqsave(&lock->wait_lock, flags);
1376	}
1377
1378	/*
1379	 * The wakeup next waiter path does not suffer from the above
1380	 * race. See the comments there.
1381	 *
1382	 * Queue the next waiter for wakeup once we release the wait_lock.
1383	 */
1384	mark_wakeup_next_waiter(&wqh, lock);
1385	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1386
1387	rt_mutex_wake_up_q(&wqh);
1388}
1389
1390static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock)
 
 
 
 
 
 
 
 
 
 
1391{
1392	if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
1393		return;
1394
1395	rt_mutex_slowunlock(lock);
1396}
1397
1398#ifdef CONFIG_SMP
1399static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
1400				  struct rt_mutex_waiter *waiter,
1401				  struct task_struct *owner)
 
 
 
1402{
1403	bool res = true;
 
 
1404
1405	rcu_read_lock();
1406	for (;;) {
1407		/* If owner changed, trylock again. */
1408		if (owner != rt_mutex_owner(lock))
1409			break;
1410		/*
1411		 * Ensure that @owner is dereferenced after checking that
1412		 * the lock owner still matches @owner. If that fails,
1413		 * @owner might point to freed memory. If it still matches,
1414		 * the rcu_read_lock() ensures the memory stays valid.
1415		 */
1416		barrier();
1417		/*
1418		 * Stop spinning when:
1419		 *  - the lock owner has been scheduled out
1420		 *  - current is not longer the top waiter
1421		 *  - current is requested to reschedule (redundant
1422		 *    for CONFIG_PREEMPT_RCU=y)
1423		 *  - the VCPU on which owner runs is preempted
1424		 */
1425		if (!owner_on_cpu(owner) || need_resched() ||
1426		    !rt_mutex_waiter_is_top_waiter(lock, waiter)) {
1427			res = false;
1428			break;
1429		}
1430		cpu_relax();
1431	}
1432	rcu_read_unlock();
1433	return res;
1434}
1435#else
1436static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
1437				  struct rt_mutex_waiter *waiter,
1438				  struct task_struct *owner)
1439{
1440	return false;
1441}
1442#endif
1443
1444#ifdef RT_MUTEX_BUILD_MUTEX
1445/*
1446 * Functions required for:
1447 *	- rtmutex, futex on all kernels
1448 *	- mutex and rwsem substitutions on RT kernels
1449 */
1450
1451/*
1452 * Remove a waiter from a lock and give up
1453 *
1454 * Must be called with lock->wait_lock held and interrupts disabled. It must
1455 * have just failed to try_to_take_rt_mutex().
1456 */
1457static void __sched remove_waiter(struct rt_mutex_base *lock,
1458				  struct rt_mutex_waiter *waiter)
1459{
1460	bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1461	struct task_struct *owner = rt_mutex_owner(lock);
1462	struct rt_mutex_base *next_lock;
1463
1464	lockdep_assert_held(&lock->wait_lock);
1465
1466	raw_spin_lock(&current->pi_lock);
1467	rt_mutex_dequeue(lock, waiter);
1468	current->pi_blocked_on = NULL;
1469	raw_spin_unlock(&current->pi_lock);
1470
1471	/*
1472	 * Only update priority if the waiter was the highest priority
1473	 * waiter of the lock and there is an owner to update.
1474	 */
1475	if (!owner || !is_top_waiter)
1476		return;
1477
1478	raw_spin_lock(&owner->pi_lock);
1479
1480	rt_mutex_dequeue_pi(owner, waiter);
1481
1482	if (rt_mutex_has_waiters(lock))
1483		rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1484
1485	rt_mutex_adjust_prio(owner);
1486
1487	/* Store the lock on which owner is blocked or NULL */
1488	next_lock = task_blocked_on_lock(owner);
1489
1490	raw_spin_unlock(&owner->pi_lock);
 
 
 
 
 
1491
1492	/*
1493	 * Don't walk the chain, if the owner task is not blocked
1494	 * itself.
1495	 */
1496	if (!next_lock)
1497		return;
1498
1499	/* gets dropped in rt_mutex_adjust_prio_chain()! */
1500	get_task_struct(owner);
1501
1502	raw_spin_unlock_irq(&lock->wait_lock);
1503
1504	rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1505				   next_lock, NULL, current);
 
1506
1507	raw_spin_lock_irq(&lock->wait_lock);
 
1508}
1509
 
1510/**
1511 * rt_mutex_slowlock_block() - Perform the wait-wake-try-to-take loop
1512 * @lock:		 the rt_mutex to take
1513 * @ww_ctx:		 WW mutex context pointer
1514 * @state:		 the state the task should block in (TASK_INTERRUPTIBLE
1515 *			 or TASK_UNINTERRUPTIBLE)
1516 * @timeout:		 the pre-initialized and started timer, or NULL for none
1517 * @waiter:		 the pre-initialized rt_mutex_waiter
1518 *
1519 * Must be called with lock->wait_lock held and interrupts disabled
 
1520 */
1521static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
1522					   struct ww_acquire_ctx *ww_ctx,
1523					   unsigned int state,
1524					   struct hrtimer_sleeper *timeout,
1525					   struct rt_mutex_waiter *waiter)
1526{
1527	struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
1528	struct task_struct *owner;
1529	int ret = 0;
1530
1531	for (;;) {
1532		/* Try to acquire the lock: */
1533		if (try_to_take_rt_mutex(lock, current, waiter))
1534			break;
1535
1536		if (timeout && !timeout->task) {
1537			ret = -ETIMEDOUT;
1538			break;
1539		}
1540		if (signal_pending_state(state, current)) {
1541			ret = -EINTR;
1542			break;
1543		}
1544
1545		if (build_ww_mutex() && ww_ctx) {
1546			ret = __ww_mutex_check_kill(rtm, waiter, ww_ctx);
1547			if (ret)
1548				break;
1549		}
 
 
 
 
 
 
1550
1551		if (waiter == rt_mutex_top_waiter(lock))
1552			owner = rt_mutex_owner(lock);
1553		else
1554			owner = NULL;
1555		raw_spin_unlock_irq(&lock->wait_lock);
 
 
 
 
 
 
 
1556
1557		if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner))
1558			schedule();
1559
1560		raw_spin_lock_irq(&lock->wait_lock);
1561		set_current_state(state);
1562	}
 
1563
1564	__set_current_state(TASK_RUNNING);
1565	return ret;
1566}
 
1567
1568static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
1569					     struct rt_mutex_waiter *w)
 
 
1570{
1571	/*
1572	 * If the result is not -EDEADLOCK or the caller requested
1573	 * deadlock detection, nothing to do here.
1574	 */
1575	if (res != -EDEADLOCK || detect_deadlock)
1576		return;
1577
1578	if (build_ww_mutex() && w->ww_ctx)
1579		return;
1580
1581	/*
1582	 * Yell loudly and stop the task right here.
1583	 */
1584	WARN(1, "rtmutex deadlock detected\n");
1585	while (1) {
1586		set_current_state(TASK_INTERRUPTIBLE);
1587		schedule();
1588	}
1589}
1590
1591/**
1592 * __rt_mutex_slowlock - Locking slowpath invoked with lock::wait_lock held
1593 * @lock:	The rtmutex to block lock
1594 * @ww_ctx:	WW mutex context pointer
1595 * @state:	The task state for sleeping
1596 * @chwalk:	Indicator whether full or partial chainwalk is requested
1597 * @waiter:	Initializer waiter for blocking
1598 */
1599static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
1600				       struct ww_acquire_ctx *ww_ctx,
1601				       unsigned int state,
1602				       enum rtmutex_chainwalk chwalk,
1603				       struct rt_mutex_waiter *waiter)
 
 
1604{
1605	struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
1606	struct ww_mutex *ww = ww_container_of(rtm);
1607	int ret;
1608
1609	lockdep_assert_held(&lock->wait_lock);
1610
1611	/* Try to acquire the lock again: */
1612	if (try_to_take_rt_mutex(lock, current, NULL)) {
1613		if (build_ww_mutex() && ww_ctx) {
1614			__ww_mutex_check_waiters(rtm, ww_ctx);
1615			ww_mutex_lock_acquired(ww, ww_ctx);
1616		}
1617		return 0;
1618	}
1619
1620	set_current_state(state);
1621
1622	trace_contention_begin(lock, LCB_F_RT);
1623
1624	ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk);
1625	if (likely(!ret))
1626		ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter);
1627
1628	if (likely(!ret)) {
1629		/* acquired the lock */
1630		if (build_ww_mutex() && ww_ctx) {
1631			if (!ww_ctx->is_wait_die)
1632				__ww_mutex_check_waiters(rtm, ww_ctx);
1633			ww_mutex_lock_acquired(ww, ww_ctx);
1634		}
1635	} else {
1636		__set_current_state(TASK_RUNNING);
1637		remove_waiter(lock, waiter);
1638		rt_mutex_handle_deadlock(ret, chwalk, waiter);
1639	}
 
 
1640
1641	/*
1642	 * try_to_take_rt_mutex() sets the waiter bit
1643	 * unconditionally. We might have to fix that up.
1644	 */
1645	fixup_rt_mutex_waiters(lock, true);
1646
1647	trace_contention_end(lock, ret);
 
 
1648
1649	return ret;
1650}
 
1651
1652static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
1653					     struct ww_acquire_ctx *ww_ctx,
1654					     unsigned int state)
 
 
 
1655{
1656	struct rt_mutex_waiter waiter;
1657	int ret;
 
 
1658
1659	rt_mutex_init_waiter(&waiter);
1660	waiter.ww_ctx = ww_ctx;
 
 
 
 
 
 
1661
1662	ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK,
1663				  &waiter);
1664
1665	debug_rt_mutex_free_waiter(&waiter);
1666	return ret;
 
 
 
 
 
 
 
 
 
 
 
 
1667}
1668
1669/*
1670 * rt_mutex_slowlock - Locking slowpath invoked when fast path fails
1671 * @lock:	The rtmutex to block lock
1672 * @ww_ctx:	WW mutex context pointer
1673 * @state:	The task state for sleeping
1674 */
1675static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
1676				     struct ww_acquire_ctx *ww_ctx,
1677				     unsigned int state)
1678{
 
1679	unsigned long flags;
1680	int ret;
1681
1682	/*
1683	 * Technically we could use raw_spin_[un]lock_irq() here, but this can
1684	 * be called in early boot if the cmpxchg() fast path is disabled
1685	 * (debug, no architecture support). In this case we will acquire the
1686	 * rtmutex with lock->wait_lock held. But we cannot unconditionally
1687	 * enable interrupts in that early boot case. So we need to use the
1688	 * irqsave/restore variants.
1689	 */
1690	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1691	ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state);
1692	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1693
1694	return ret;
 
1695}
1696
1697static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,
1698					   unsigned int state)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1699{
1700	if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1701		return 0;
 
1702
1703	return rt_mutex_slowlock(lock, NULL, state);
 
1704}
1705#endif /* RT_MUTEX_BUILD_MUTEX */
1706
1707#ifdef RT_MUTEX_BUILD_SPINLOCKS
1708/*
1709 * Functions required for spin/rw_lock substitution on RT kernels
 
 
 
 
 
 
 
 
 
 
1710 */
 
 
 
 
 
 
 
1711
1712/**
1713 * rtlock_slowlock_locked - Slow path lock acquisition for RT locks
1714 * @lock:	The underlying RT mutex
 
 
 
 
 
 
 
 
1715 */
1716static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
 
1717{
1718	struct rt_mutex_waiter waiter;
1719	struct task_struct *owner;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1720
1721	lockdep_assert_held(&lock->wait_lock);
1722
1723	if (try_to_take_rt_mutex(lock, current, NULL))
1724		return;
1725
1726	rt_mutex_init_rtlock_waiter(&waiter);
 
 
1727
1728	/* Save current state and set state to TASK_RTLOCK_WAIT */
1729	current_save_and_set_rtlock_wait_state();
 
 
 
 
 
 
 
1730
1731	trace_contention_begin(lock, LCB_F_RT);
1732
1733	task_blocks_on_rt_mutex(lock, &waiter, current, NULL, RT_MUTEX_MIN_CHAINWALK);
 
1734
1735	for (;;) {
1736		/* Try to acquire the lock again */
1737		if (try_to_take_rt_mutex(lock, current, &waiter))
1738			break;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1739
1740		if (&waiter == rt_mutex_top_waiter(lock))
1741			owner = rt_mutex_owner(lock);
1742		else
1743			owner = NULL;
1744		raw_spin_unlock_irq(&lock->wait_lock);
1745
1746		if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner))
1747			schedule_rtlock();
1748
1749		raw_spin_lock_irq(&lock->wait_lock);
1750		set_current_state(TASK_RTLOCK_WAIT);
1751	}
 
 
 
 
 
 
 
 
 
 
 
 
 
1752
1753	/* Restore the task state */
1754	current_restore_rtlock_saved_state();
1755
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1756	/*
1757	 * try_to_take_rt_mutex() sets the waiter bit unconditionally.
1758	 * We might have to fix that up:
1759	 */
1760	fixup_rt_mutex_waiters(lock, true);
1761	debug_rt_mutex_free_waiter(&waiter);
1762
1763	trace_contention_end(lock, 0);
1764}
1765
1766static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock)
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1767{
1768	unsigned long flags;
1769
1770	raw_spin_lock_irqsave(&lock->wait_lock, flags);
1771	rtlock_slowlock_locked(lock);
1772	raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1773}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1774
1775#endif /* RT_MUTEX_BUILD_SPINLOCKS */