1/*
   2 * kernel/locking/mutex.c
   3 *
   4 * Mutexes: blocking mutual exclusion locks
   5 *
   6 * Started by Ingo Molnar:
   7 *
   8 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
   9 *
  10 * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
  11 * David Howells for suggestions and improvements.
  12 *
  13 *  - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
  14 *    from the -rt tree, where it was originally implemented for rtmutexes
  15 *    by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
  16 *    and Sven Dietrich.
  17 *
  18 * Also see Documentation/locking/mutex-design.txt.
  19 */
  20#include <linux/mutex.h>
  21#include <linux/ww_mutex.h>
  22#include <linux/sched/signal.h>
  23#include <linux/sched/rt.h>
  24#include <linux/sched/wake_q.h>
  25#include <linux/sched/debug.h>
  26#include <linux/export.h>
  27#include <linux/spinlock.h>
  28#include <linux/interrupt.h>
  29#include <linux/debug_locks.h>
  30#include <linux/osq_lock.h>
  31
 
 
 
 
  32#ifdef CONFIG_DEBUG_MUTEXES
  33# include "mutex-debug.h"
 
 
 
 
 
 
 
 
  34#else
  35# include "mutex.h"
 
  36#endif
  37
 
 
 
 
 
 
  38void
  39__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
  40{
  41	atomic_long_set(&lock->owner, 0);
  42	spin_lock_init(&lock->wait_lock);
  43	INIT_LIST_HEAD(&lock->wait_list);
 
  44#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
  45	osq_lock_init(&lock->osq);
  46#endif
  47
  48	debug_mutex_init(lock, name, key);
  49}
  50EXPORT_SYMBOL(__mutex_init);
  51
  52/*
  53 * @owner: contains: 'struct task_struct *' to the current lock owner,
  54 * NULL means not owned. Since task_struct pointers are aligned at
  55 * at least L1_CACHE_BYTES, we have low bits to store extra state.
  56 *
  57 * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
  58 * Bit1 indicates unlock needs to hand the lock to the top-waiter
  59 * Bit2 indicates handoff has been done and we're waiting for pickup.
  60 */
  61#define MUTEX_FLAG_WAITERS	0x01
  62#define MUTEX_FLAG_HANDOFF	0x02
  63#define MUTEX_FLAG_PICKUP	0x04
  64
  65#define MUTEX_FLAGS		0x07
  66
  67static inline struct task_struct *__owner_task(unsigned long owner)
  68{
  69	return (struct task_struct *)(owner & ~MUTEX_FLAGS);
  70}
  71
  72static inline unsigned long __owner_flags(unsigned long owner)
  73{
  74	return owner & MUTEX_FLAGS;
  75}
  76
  77/*
  78 * Trylock variant that retuns the owning task on failure.
  79 */
  80static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
  81{
  82	unsigned long owner, curr = (unsigned long)current;
  83
  84	owner = atomic_long_read(&lock->owner);
  85	for (;;) { /* must loop, can race against a flag */
  86		unsigned long old, flags = __owner_flags(owner);
  87		unsigned long task = owner & ~MUTEX_FLAGS;
  88
  89		if (task) {
  90			if (likely(task != curr))
  91				break;
  92
  93			if (likely(!(flags & MUTEX_FLAG_PICKUP)))
  94				break;
  95
  96			flags &= ~MUTEX_FLAG_PICKUP;
  97		} else {
  98#ifdef CONFIG_DEBUG_MUTEXES
  99			DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP);
 100#endif
 101		}
 102
 103		/*
 104		 * We set the HANDOFF bit, we must make sure it doesn't live
 105		 * past the point where we acquire it. This would be possible
 106		 * if we (accidentally) set the bit on an unlocked mutex.
 107		 */
 108		flags &= ~MUTEX_FLAG_HANDOFF;
 109
 110		old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
 111		if (old == owner)
 112			return NULL;
 113
 114		owner = old;
 115	}
 116
 117	return __owner_task(owner);
 118}
 119
 120/*
 121 * Actual trylock that will work on any unlocked state.
 122 */
 123static inline bool __mutex_trylock(struct mutex *lock)
 124{
 125	return !__mutex_trylock_or_owner(lock);
 126}
 127
 128#ifndef CONFIG_DEBUG_LOCK_ALLOC
 129/*
 130 * Lockdep annotations are contained to the slow paths for simplicity.
 131 * There is nothing that would stop spreading the lockdep annotations outwards
 132 * except more code.
 133 */
 134
 135/*
 136 * Optimistic trylock that only works in the uncontended case. Make sure to
 137 * follow with a __mutex_trylock() before failing.
 138 */
 139static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
 140{
 141	unsigned long curr = (unsigned long)current;
 142
 143	if (!atomic_long_cmpxchg_acquire(&lock->owner, 0UL, curr))
 144		return true;
 145
 146	return false;
 147}
 148
 149static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
 150{
 151	unsigned long curr = (unsigned long)current;
 152
 153	if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
 154		return true;
 155
 156	return false;
 157}
 158#endif
 159
 160static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
 161{
 162	atomic_long_or(flag, &lock->owner);
 163}
 164
 165static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
 166{
 167	atomic_long_andnot(flag, &lock->owner);
 168}
 169
 170static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
 171{
 172	return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
 173}
 174
 175/*
 176 * Give up ownership to a specific task, when @task = NULL, this is equivalent
 177 * to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves
 178 * WAITERS. Provides RELEASE semantics like a regular unlock, the
 179 * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
 180 */
 181static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
 182{
 183	unsigned long owner = atomic_long_read(&lock->owner);
 184
 185	for (;;) {
 186		unsigned long old, new;
 187
 188#ifdef CONFIG_DEBUG_MUTEXES
 189		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
 190		DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
 191#endif
 192
 193		new = (owner & MUTEX_FLAG_WAITERS);
 194		new |= (unsigned long)task;
 195		if (task)
 196			new |= MUTEX_FLAG_PICKUP;
 197
 198		old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
 199		if (old == owner)
 200			break;
 201
 202		owner = old;
 203	}
 204}
 205
 206#ifndef CONFIG_DEBUG_LOCK_ALLOC
 207/*
 208 * We split the mutex lock/unlock logic into separate fastpath and
 209 * slowpath functions, to reduce the register pressure on the fastpath.
 210 * We also put the fastpath first in the kernel image, to make sure the
 211 * branch is predicted by the CPU as default-untaken.
 212 */
 213static void __sched __mutex_lock_slowpath(struct mutex *lock);
 214
 215/**
 216 * mutex_lock - acquire the mutex
 217 * @lock: the mutex to be acquired
 218 *
 219 * Lock the mutex exclusively for this task. If the mutex is not
 220 * available right now, it will sleep until it can get it.
 221 *
 222 * The mutex must later on be released by the same task that
 223 * acquired it. Recursive locking is not allowed. The task
 224 * may not exit without first unlocking the mutex. Also, kernel
 225 * memory where the mutex resides must not be freed with
 226 * the mutex still locked. The mutex must first be initialized
 227 * (or statically defined) before it can be locked. memset()-ing
 228 * the mutex to 0 is not allowed.
 229 *
 230 * (The CONFIG_DEBUG_MUTEXES .config option turns on debugging
 231 * checks that will enforce the restrictions and will also do
 232 * deadlock debugging)
 233 *
 234 * This function is similar to (but not equivalent to) down().
 235 */
 236void __sched mutex_lock(struct mutex *lock)
 237{
 238	might_sleep();
 239
 240	if (!__mutex_trylock_fast(lock))
 241		__mutex_lock_slowpath(lock);
 242}
 243EXPORT_SYMBOL(mutex_lock);
 244#endif
 245
 246static __always_inline void
 247ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
 248{
 249#ifdef CONFIG_DEBUG_MUTEXES
 250	/*
 251	 * If this WARN_ON triggers, you used ww_mutex_lock to acquire,
 252	 * but released with a normal mutex_unlock in this call.
 253	 *
 254	 * This should never happen, always use ww_mutex_unlock.
 255	 */
 256	DEBUG_LOCKS_WARN_ON(ww->ctx);
 257
 258	/*
 259	 * Not quite done after calling ww_acquire_done() ?
 
 260	 */
 261	DEBUG_LOCKS_WARN_ON(ww_ctx->done_acquire);
 262
 263	if (ww_ctx->contending_lock) {
 264		/*
 265		 * After -EDEADLK you tried to
 266		 * acquire a different ww_mutex? Bad!
 267		 */
 268		DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock != ww);
 269
 270		/*
 271		 * You called ww_mutex_lock after receiving -EDEADLK,
 272		 * but 'forgot' to unlock everything else first?
 273		 */
 274		DEBUG_LOCKS_WARN_ON(ww_ctx->acquired > 0);
 275		ww_ctx->contending_lock = NULL;
 276	}
 277
 278	/*
 279	 * Naughty, using a different class will lead to undefined behavior!
 280	 */
 281	DEBUG_LOCKS_WARN_ON(ww_ctx->ww_class != ww->ww_class);
 282#endif
 283	ww_ctx->acquired++;
 284}
 285
 286static inline bool __sched
 287__ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
 288{
 289	return a->stamp - b->stamp <= LONG_MAX &&
 290	       (a->stamp != b->stamp || a > b);
 291}
 292
 
 293/*
 294 * Wake up any waiters that may have to back off when the lock is held by the
 295 * given context.
 296 *
 297 * Due to the invariants on the wait list, this can only affect the first
 298 * waiter with a context.
 299 *
 300 * The current task must not be on the wait list.
 301 */
 302static void __sched
 303__ww_mutex_wakeup_for_backoff(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
 304{
 305	struct mutex_waiter *cur;
 306
 307	lockdep_assert_held(&lock->wait_lock);
 308
 309	list_for_each_entry(cur, &lock->wait_list, list) {
 310		if (!cur->ww_ctx)
 311			continue;
 312
 313		if (cur->ww_ctx->acquired > 0 &&
 314		    __ww_ctx_stamp_after(cur->ww_ctx, ww_ctx)) {
 315			debug_mutex_wake_waiter(lock, cur);
 316			wake_up_process(cur->task);
 317		}
 318
 319		break;
 320	}
 321}
 322
 323/*
 324 * After acquiring lock with fastpath or when we lost out in contested
 325 * slowpath, set ctx and wake up any waiters so they can recheck.
 326 */
 327static __always_inline void
 328ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 329{
 330	ww_mutex_lock_acquired(lock, ctx);
 331
 332	lock->ctx = ctx;
 333
 334	/*
 335	 * The lock->ctx update should be visible on all cores before
 336	 * the atomic read is done, otherwise contended waiters might be
 337	 * missed. The contended waiters will either see ww_ctx == NULL
 338	 * and keep spinning, or it will acquire wait_lock, add itself
 339	 * to waiter list and sleep.
 340	 */
 341	smp_mb(); /* ^^^ */
 342
 343	/*
 344	 * Check if lock is contended, if not there is nobody to wake up
 345	 */
 346	if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
 347		return;
 348
 349	/*
 350	 * Uh oh, we raced in fastpath, wake up everyone in this case,
 351	 * so they can see the new lock->ctx.
 352	 */
 353	spin_lock(&lock->base.wait_lock);
 354	__ww_mutex_wakeup_for_backoff(&lock->base, ctx);
 355	spin_unlock(&lock->base.wait_lock);
 356}
 357
 358/*
 359 * After acquiring lock in the slowpath set ctx.
 360 *
 361 * Unlike for the fast path, the caller ensures that waiters are woken up where
 362 * necessary.
 363 *
 364 * Callers must hold the mutex wait_lock.
 365 */
 366static __always_inline void
 367ww_mutex_set_context_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 368{
 369	ww_mutex_lock_acquired(lock, ctx);
 370	lock->ctx = ctx;
 371}
 372
 373#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
 374
 375static inline
 376bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
 377			    struct mutex_waiter *waiter)
 378{
 379	struct ww_mutex *ww;
 380
 381	ww = container_of(lock, struct ww_mutex, base);
 382
 383	/*
 384	 * If ww->ctx is set the contents are undefined, only
 385	 * by acquiring wait_lock there is a guarantee that
 386	 * they are not invalid when reading.
 387	 *
 388	 * As such, when deadlock detection needs to be
 389	 * performed the optimistic spinning cannot be done.
 390	 *
 391	 * Check this in every inner iteration because we may
 392	 * be racing against another thread's ww_mutex_lock.
 393	 */
 394	if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
 395		return false;
 396
 397	/*
 398	 * If we aren't on the wait list yet, cancel the spin
 399	 * if there are waiters. We want  to avoid stealing the
 400	 * lock from a waiter with an earlier stamp, since the
 401	 * other thread may already own a lock that we also
 402	 * need.
 403	 */
 404	if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
 405		return false;
 406
 407	/*
 408	 * Similarly, stop spinning if we are no longer the
 409	 * first waiter.
 
 
 410	 */
 411	if (waiter && !__mutex_waiter_is_first(lock, waiter))
 412		return false;
 413
 414	return true;
 415}
 416
 417/*
 418 * Look out! "owner" is an entirely speculative pointer access and not
 419 * reliable.
 420 *
 421 * "noinline" so that this function shows up on perf profiles.
 422 */
 423static noinline
 424bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
 425			 struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
 426{
 427	bool ret = true;
 428
 429	rcu_read_lock();
 430	while (__mutex_owner(lock) == owner) {
 431		/*
 432		 * Ensure we emit the owner->on_cpu, dereference _after_
 433		 * checking lock->owner still matches owner. If that fails,
 434		 * owner might point to freed memory. If it still matches,
 435		 * the rcu_read_lock() ensures the memory stays valid.
 436		 */
 437		barrier();
 438
 439		/*
 440		 * Use vcpu_is_preempted to detect lock holder preemption issue.
 441		 */
 442		if (!owner->on_cpu || need_resched() ||
 443				vcpu_is_preempted(task_cpu(owner))) {
 444			ret = false;
 445			break;
 446		}
 447
 448		if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
 449			ret = false;
 450			break;
 451		}
 452
 453		cpu_relax();
 454	}
 455	rcu_read_unlock();
 456
 457	return ret;
 
 
 
 
 
 458}
 459
 460/*
 461 * Initial check for entering the mutex spinning loop
 462 */
 463static inline int mutex_can_spin_on_owner(struct mutex *lock)
 464{
 465	struct task_struct *owner;
 466	int retval = 1;
 467
 468	if (need_resched())
 469		return 0;
 470
 471	rcu_read_lock();
 472	owner = __mutex_owner(lock);
 473
 474	/*
 475	 * As lock holder preemption issue, we both skip spinning if task is not
 476	 * on cpu or its cpu is preempted
 477	 */
 478	if (owner)
 479		retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
 480	rcu_read_unlock();
 481
 482	/*
 483	 * If lock->owner is not set, the mutex has been released. Return true
 484	 * such that we'll trylock in the spin path, which is a faster option
 485	 * than the blocking slow path.
 486	 */
 487	return retval;
 488}
 489
 490/*
 491 * Optimistic spinning.
 492 *
 493 * We try to spin for acquisition when we find that the lock owner
 494 * is currently running on a (different) CPU and while we don't
 495 * need to reschedule. The rationale is that if the lock owner is
 496 * running, it is likely to release the lock soon.
 497 *
 498 * The mutex spinners are queued up using MCS lock so that only one
 499 * spinner can compete for the mutex. However, if mutex spinning isn't
 500 * going to happen, there is no point in going through the lock/unlock
 501 * overhead.
 502 *
 503 * Returns true when the lock was taken, otherwise false, indicating
 504 * that we need to jump to the slowpath and sleep.
 505 *
 506 * The waiter flag is set to true if the spinner is a waiter in the wait
 507 * queue. The waiter-spinner will spin on the lock directly and concurrently
 508 * with the spinner at the head of the OSQ, if present, until the owner is
 509 * changed to itself.
 510 */
 511static __always_inline bool
 512mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
 513		      const bool use_ww_ctx, struct mutex_waiter *waiter)
 514{
 515	if (!waiter) {
 516		/*
 517		 * The purpose of the mutex_can_spin_on_owner() function is
 518		 * to eliminate the overhead of osq_lock() and osq_unlock()
 519		 * in case spinning isn't possible. As a waiter-spinner
 520		 * is not going to take OSQ lock anyway, there is no need
 521		 * to call mutex_can_spin_on_owner().
 522		 */
 523		if (!mutex_can_spin_on_owner(lock))
 524			goto fail;
 525
 526		/*
 527		 * In order to avoid a stampede of mutex spinners trying to
 528		 * acquire the mutex all at once, the spinners need to take a
 529		 * MCS (queued) lock first before spinning on the owner field.
 530		 */
 531		if (!osq_lock(&lock->osq))
 532			goto fail;
 533	}
 534
 535	for (;;) {
 536		struct task_struct *owner;
 537
 538		/* Try to acquire the mutex... */
 539		owner = __mutex_trylock_or_owner(lock);
 540		if (!owner)
 541			break;
 542
 543		/*
 544		 * There's an owner, wait for it to either
 545		 * release the lock or go to sleep.
 546		 */
 547		if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
 548			goto fail_unlock;
 549
 550		/*
 551		 * The cpu_relax() call is a compiler barrier which forces
 552		 * everything in this loop to be re-loaded. We don't need
 553		 * memory barriers as we'll eventually observe the right
 554		 * values at the cost of a few extra spins.
 555		 */
 556		cpu_relax();
 557	}
 558
 559	if (!waiter)
 560		osq_unlock(&lock->osq);
 561
 562	return true;
 563
 564
 565fail_unlock:
 566	if (!waiter)
 567		osq_unlock(&lock->osq);
 568
 569fail:
 570	/*
 571	 * If we fell out of the spin path because of need_resched(),
 572	 * reschedule now, before we try-lock the mutex. This avoids getting
 573	 * scheduled out right after we obtained the mutex.
 574	 */
 575	if (need_resched()) {
 576		/*
 577		 * We _should_ have TASK_RUNNING here, but just in case
 578		 * we do not, make it so, otherwise we might get stuck.
 579		 */
 580		__set_current_state(TASK_RUNNING);
 581		schedule_preempt_disabled();
 582	}
 583
 584	return false;
 585}
 586#else
 587static __always_inline bool
 588mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
 589		      const bool use_ww_ctx, struct mutex_waiter *waiter)
 590{
 591	return false;
 592}
 593#endif
 594
 595static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
 
 596
 597/**
 598 * mutex_unlock - release the mutex
 599 * @lock: the mutex to be released
 600 *
 601 * Unlock a mutex that has been locked by this task previously.
 602 *
 603 * This function must not be used in interrupt context. Unlocking
 604 * of a not locked mutex is not allowed.
 605 *
 606 * This function is similar to (but not equivalent to) up().
 607 */
 608void __sched mutex_unlock(struct mutex *lock)
 609{
 610#ifndef CONFIG_DEBUG_LOCK_ALLOC
 611	if (__mutex_unlock_fast(lock))
 612		return;
 
 
 
 
 
 
 
 
 613#endif
 614	__mutex_unlock_slowpath(lock, _RET_IP_);
 615}
 
 616EXPORT_SYMBOL(mutex_unlock);
 617
 618/**
 619 * ww_mutex_unlock - release the w/w mutex
 620 * @lock: the mutex to be released
 621 *
 622 * Unlock a mutex that has been locked by this task previously with any of the
 623 * ww_mutex_lock* functions (with or without an acquire context). It is
 624 * forbidden to release the locks after releasing the acquire context.
 625 *
 626 * This function must not be used in interrupt context. Unlocking
 627 * of a unlocked mutex is not allowed.
 628 */
 629void __sched ww_mutex_unlock(struct ww_mutex *lock)
 630{
 631	/*
 632	 * The unlocking fastpath is the 0->1 transition from 'locked'
 633	 * into 'unlocked' state:
 634	 */
 635	if (lock->ctx) {
 636#ifdef CONFIG_DEBUG_MUTEXES
 637		DEBUG_LOCKS_WARN_ON(!lock->ctx->acquired);
 638#endif
 639		if (lock->ctx->acquired > 0)
 640			lock->ctx->acquired--;
 641		lock->ctx = NULL;
 642	}
 643
 644	mutex_unlock(&lock->base);
 
 
 
 
 
 
 
 
 645}
 646EXPORT_SYMBOL(ww_mutex_unlock);
 647
 648static inline int __sched
 649__ww_mutex_lock_check_stamp(struct mutex *lock, struct mutex_waiter *waiter,
 650			    struct ww_acquire_ctx *ctx)
 651{
 652	struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
 653	struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
 654	struct mutex_waiter *cur;
 655
 656	if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx))
 657		goto deadlock;
 658
 659	/*
 660	 * If there is a waiter in front of us that has a context, then its
 661	 * stamp is earlier than ours and we must back off.
 662	 */
 663	cur = waiter;
 664	list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
 665		if (cur->ww_ctx)
 666			goto deadlock;
 
 
 667	}
 668
 669	return 0;
 
 670
 671deadlock:
 
 
 672#ifdef CONFIG_DEBUG_MUTEXES
 673	DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
 674	ctx->contending_lock = ww;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 675#endif
 676	return -EDEADLK;
 677}
 678
 679static inline int __sched
 680__ww_mutex_add_waiter(struct mutex_waiter *waiter,
 681		      struct mutex *lock,
 682		      struct ww_acquire_ctx *ww_ctx)
 
 
 
 
 
 
 683{
 
 684	struct mutex_waiter *cur;
 685	struct list_head *pos;
 686
 687	if (!ww_ctx) {
 688		list_add_tail(&waiter->list, &lock->wait_list);
 689		return 0;
 690	}
 691
 692	/*
 693	 * Add the waiter before the first waiter with a higher stamp.
 694	 * Waiters without a context are skipped to avoid starving
 695	 * them.
 
 
 696	 */
 697	pos = &lock->wait_list;
 698	list_for_each_entry_reverse(cur, &lock->wait_list, list) {
 699		if (!cur->ww_ctx)
 700			continue;
 701
 702		if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {
 703			/* Back off immediately if necessary. */
 704			if (ww_ctx->acquired > 0) {
 705#ifdef CONFIG_DEBUG_MUTEXES
 706				struct ww_mutex *ww;
 707
 708				ww = container_of(lock, struct ww_mutex, base);
 709				DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
 710				ww_ctx->contending_lock = ww;
 711#endif
 712				return -EDEADLK;
 713			}
 714
 715			break;
 716		}
 717
 718		pos = &cur->list;
 
 
 
 
 719
 720		/*
 721		 * Wake up the waiter so that it gets a chance to back
 722		 * off.
 723		 */
 724		if (cur->ww_ctx->acquired > 0) {
 725			debug_mutex_wake_waiter(lock, cur);
 726			wake_up_process(cur->task);
 727		}
 728	}
 729
 730	list_add_tail(&waiter->list, pos);
 731	return 0;
 732}
 733
 734/*
 735 * Lock a mutex (possibly interruptible), slowpath:
 736 */
 737static __always_inline int __sched
 738__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 739		    struct lockdep_map *nest_lock, unsigned long ip,
 740		    struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
 741{
 
 742	struct mutex_waiter waiter;
 743	bool first = false;
 744	struct ww_mutex *ww;
 745	int ret;
 746
 747	might_sleep();
 748
 749	ww = container_of(lock, struct ww_mutex, base);
 750	if (use_ww_ctx && ww_ctx) {
 751		if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
 752			return -EALREADY;
 753	}
 754
 755	preempt_disable();
 756	mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
 757
 758	if (__mutex_trylock(lock) ||
 759	    mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {
 760		/* got the lock, yay! */
 761		lock_acquired(&lock->dep_map, ip);
 762		if (use_ww_ctx && ww_ctx)
 763			ww_mutex_set_context_fastpath(ww, ww_ctx);
 764		preempt_enable();
 765		return 0;
 766	}
 767
 768	spin_lock(&lock->wait_lock);
 769	/*
 770	 * After waiting to acquire the wait_lock, try again.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 771	 */
 772	if (__mutex_trylock(lock)) {
 773		if (use_ww_ctx && ww_ctx)
 774			__ww_mutex_wakeup_for_backoff(lock, ww_ctx);
 775
 776		goto skip_wait;
 777	}
 778
 779	debug_mutex_lock_common(lock, &waiter);
 780	debug_mutex_add_waiter(lock, &waiter, current);
 781
 782	lock_contended(&lock->dep_map, ip);
 
 783
 784	if (!use_ww_ctx) {
 785		/* add waiting tasks to the end of the waitqueue (FIFO): */
 786		list_add_tail(&waiter.list, &lock->wait_list);
 
 
 
 
 
 
 
 
 
 787
 788#ifdef CONFIG_DEBUG_MUTEXES
 789		waiter.ww_ctx = MUTEX_POISON_WW_CTX;
 790#endif
 791	} else {
 792		/* Add in stamp order, waking up waiters that must back off. */
 793		ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
 794		if (ret)
 795			goto err_early_backoff;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 796
 797		waiter.ww_ctx = ww_ctx;
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 798	}
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 799
 800	waiter.task = current;
 
 
 801
 802	if (__mutex_waiter_is_first(lock, &waiter))
 803		__mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
 804
 805	set_current_state(state);
 806	for (;;) {
 807		/*
 808		 * Once we hold wait_lock, we're serialized against
 809		 * mutex_unlock() handing the lock off to us, do a trylock
 810		 * before testing the error conditions to make sure we pick up
 811		 * the handoff.
 
 
 
 812		 */
 813		if (__mutex_trylock(lock))
 814			goto acquired;
 
 815
 816		/*
 817		 * Check for signals and wound conditions while holding
 818		 * wait_lock. This ensures the lock cancellation is ordered
 819		 * against mutex_unlock() and wake-ups do not go missing.
 820		 */
 821		if (unlikely(signal_pending_state(state, current))) {
 822			ret = -EINTR;
 823			goto err;
 824		}
 825
 826		if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) {
 827			ret = __ww_mutex_lock_check_stamp(lock, &waiter, ww_ctx);
 828			if (ret)
 829				goto err;
 830		}
 831
 832		spin_unlock(&lock->wait_lock);
 833		schedule_preempt_disabled();
 834
 835		/*
 836		 * ww_mutex needs to always recheck its position since its waiter
 837		 * list is not FIFO ordered.
 838		 */
 839		if ((use_ww_ctx && ww_ctx) || !first) {
 840			first = __mutex_waiter_is_first(lock, &waiter);
 841			if (first)
 842				__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
 843		}
 844
 845		set_current_state(state);
 846		/*
 847		 * Here we order against unlock; we must either see it change
 848		 * state back to RUNNING and fall through the next schedule(),
 849		 * or we must see its unlock and acquire.
 850		 */
 851		if (__mutex_trylock(lock) ||
 852		    (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
 853			break;
 854
 855		spin_lock(&lock->wait_lock);
 
 
 
 856	}
 857	spin_lock(&lock->wait_lock);
 858acquired:
 859	__set_current_state(TASK_RUNNING);
 860
 861	mutex_remove_waiter(lock, &waiter, current);
 862	if (likely(list_empty(&lock->wait_list)))
 863		__mutex_clear_flag(lock, MUTEX_FLAGS);
 864
 865	debug_mutex_free_waiter(&waiter);
 866
 867skip_wait:
 868	/* got the lock - cleanup and rejoice! */
 869	lock_acquired(&lock->dep_map, ip);
 
 870
 871	if (use_ww_ctx && ww_ctx)
 872		ww_mutex_set_context_slowpath(ww, ww_ctx);
 
 
 
 
 
 
 
 
 873
 874	spin_unlock(&lock->wait_lock);
 
 
 
 
 
 
 
 
 
 
 875	preempt_enable();
 876	return 0;
 877
 878err:
 879	__set_current_state(TASK_RUNNING);
 880	mutex_remove_waiter(lock, &waiter, current);
 881err_early_backoff:
 882	spin_unlock(&lock->wait_lock);
 883	debug_mutex_free_waiter(&waiter);
 884	mutex_release(&lock->dep_map, 1, ip);
 885	preempt_enable();
 886	return ret;
 887}
 888
 889static int __sched
 890__mutex_lock(struct mutex *lock, long state, unsigned int subclass,
 891	     struct lockdep_map *nest_lock, unsigned long ip)
 892{
 893	return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
 894}
 895
 896static int __sched
 897__ww_mutex_lock(struct mutex *lock, long state, unsigned int subclass,
 898		struct lockdep_map *nest_lock, unsigned long ip,
 899		struct ww_acquire_ctx *ww_ctx)
 900{
 901	return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true);
 902}
 903
 904#ifdef CONFIG_DEBUG_LOCK_ALLOC
 905void __sched
 906mutex_lock_nested(struct mutex *lock, unsigned int subclass)
 907{
 908	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
 
 
 909}
 910
 911EXPORT_SYMBOL_GPL(mutex_lock_nested);
 912
 913void __sched
 914_mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
 915{
 916	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
 
 
 917}
 
 918EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
 919
 920int __sched
 921mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
 922{
 923	return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
 
 
 924}
 925EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
 926
 927int __sched
 928mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
 929{
 930	return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
 931}
 932EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
 933
 934void __sched
 935mutex_lock_io_nested(struct mutex *lock, unsigned int subclass)
 936{
 937	int token;
 938
 939	might_sleep();
 940
 941	token = io_schedule_prepare();
 942	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
 943			    subclass, NULL, _RET_IP_, NULL, 0);
 944	io_schedule_finish(token);
 945}
 946EXPORT_SYMBOL_GPL(mutex_lock_io_nested);
 
 947
 948static inline int
 949ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 950{
 951#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
 952	unsigned tmp;
 953
 954	if (ctx->deadlock_inject_countdown-- == 0) {
 955		tmp = ctx->deadlock_inject_interval;
 956		if (tmp > UINT_MAX/4)
 957			tmp = UINT_MAX;
 958		else
 959			tmp = tmp*2 + tmp + tmp/2;
 960
 961		ctx->deadlock_inject_interval = tmp;
 962		ctx->deadlock_inject_countdown = tmp;
 963		ctx->contending_lock = lock;
 964
 965		ww_mutex_unlock(lock);
 966
 967		return -EDEADLK;
 968	}
 969#endif
 970
 971	return 0;
 972}
 973
 974int __sched
 975ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 976{
 977	int ret;
 978
 979	might_sleep();
 980	ret =  __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
 981			       0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
 982			       ctx);
 983	if (!ret && ctx && ctx->acquired > 1)
 984		return ww_mutex_deadlock_injection(lock, ctx);
 985
 986	return ret;
 987}
 988EXPORT_SYMBOL_GPL(ww_mutex_lock);
 989
 990int __sched
 991ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 992{
 993	int ret;
 994
 995	might_sleep();
 996	ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
 997			      0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
 998			      ctx);
 999
1000	if (!ret && ctx && ctx->acquired > 1)
1001		return ww_mutex_deadlock_injection(lock, ctx);
1002
1003	return ret;
1004}
1005EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
1006
1007#endif
1008
1009/*
1010 * Release the lock, slowpath:
1011 */
1012static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
 
1013{
1014	struct task_struct *next = NULL;
1015	DEFINE_WAKE_Q(wake_q);
1016	unsigned long owner;
1017
1018	mutex_release(&lock->dep_map, 1, ip);
1019
1020	/*
1021	 * Release the lock before (potentially) taking the spinlock such that
1022	 * other contenders can get on with things ASAP.
1023	 *
1024	 * Except when HANDOFF, in that case we must not clear the owner field,
1025	 * but instead set it to the top waiter.
1026	 */
1027	owner = atomic_long_read(&lock->owner);
1028	for (;;) {
1029		unsigned long old;
1030
1031#ifdef CONFIG_DEBUG_MUTEXES
1032		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
1033		DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
1034#endif
1035
1036		if (owner & MUTEX_FLAG_HANDOFF)
1037			break;
1038
1039		old = atomic_long_cmpxchg_release(&lock->owner, owner,
1040						  __owner_flags(owner));
1041		if (old == owner) {
1042			if (owner & MUTEX_FLAG_WAITERS)
1043				break;
1044
1045			return;
1046		}
1047
1048		owner = old;
1049	}
1050
1051	spin_lock(&lock->wait_lock);
1052	debug_mutex_unlock(lock);
 
1053	if (!list_empty(&lock->wait_list)) {
1054		/* get the first entry from the wait-list: */
1055		struct mutex_waiter *waiter =
1056			list_first_entry(&lock->wait_list,
1057					 struct mutex_waiter, list);
1058
1059		next = waiter->task;
1060
1061		debug_mutex_wake_waiter(lock, waiter);
1062		wake_q_add(&wake_q, next);
1063	}
1064
1065	if (owner & MUTEX_FLAG_HANDOFF)
1066		__mutex_handoff(lock, next);
1067
1068	spin_unlock(&lock->wait_lock);
 
1069
1070	wake_up_q(&wake_q);
 
 
 
 
 
 
1071}
1072
1073#ifndef CONFIG_DEBUG_LOCK_ALLOC
1074/*
1075 * Here come the less common (and hence less performance-critical) APIs:
1076 * mutex_lock_interruptible() and mutex_trylock().
1077 */
1078static noinline int __sched
1079__mutex_lock_killable_slowpath(struct mutex *lock);
1080
1081static noinline int __sched
1082__mutex_lock_interruptible_slowpath(struct mutex *lock);
1083
1084/**
1085 * mutex_lock_interruptible() - Acquire the mutex, interruptible by signals.
1086 * @lock: The mutex to be acquired.
1087 *
1088 * Lock the mutex like mutex_lock().  If a signal is delivered while the
1089 * process is sleeping, this function will return without acquiring the
1090 * mutex.
 
1091 *
1092 * Context: Process context.
1093 * Return: 0 if the lock was successfully acquired or %-EINTR if a
1094 * signal arrived.
1095 */
1096int __sched mutex_lock_interruptible(struct mutex *lock)
1097{
1098	might_sleep();
1099
1100	if (__mutex_trylock_fast(lock))
 
 
 
1101		return 0;
1102
1103	return __mutex_lock_interruptible_slowpath(lock);
1104}
1105
1106EXPORT_SYMBOL(mutex_lock_interruptible);
1107
1108/**
1109 * mutex_lock_killable() - Acquire the mutex, interruptible by fatal signals.
1110 * @lock: The mutex to be acquired.
1111 *
1112 * Lock the mutex like mutex_lock().  If a signal which will be fatal to
1113 * the current process is delivered while the process is sleeping, this
1114 * function will return without acquiring the mutex.
1115 *
1116 * Context: Process context.
1117 * Return: 0 if the lock was successfully acquired or %-EINTR if a
1118 * fatal signal arrived.
1119 */
1120int __sched mutex_lock_killable(struct mutex *lock)
1121{
1122	might_sleep();
1123
1124	if (__mutex_trylock_fast(lock))
 
 
 
1125		return 0;
1126
1127	return __mutex_lock_killable_slowpath(lock);
1128}
1129EXPORT_SYMBOL(mutex_lock_killable);
1130
1131/**
1132 * mutex_lock_io() - Acquire the mutex and mark the process as waiting for I/O
1133 * @lock: The mutex to be acquired.
1134 *
1135 * Lock the mutex like mutex_lock().  While the task is waiting for this
1136 * mutex, it will be accounted as being in the IO wait state by the
1137 * scheduler.
1138 *
1139 * Context: Process context.
1140 */
1141void __sched mutex_lock_io(struct mutex *lock)
1142{
1143	int token;
1144
1145	token = io_schedule_prepare();
1146	mutex_lock(lock);
1147	io_schedule_finish(token);
1148}
1149EXPORT_SYMBOL_GPL(mutex_lock_io);
1150
1151static noinline void __sched
1152__mutex_lock_slowpath(struct mutex *lock)
1153{
1154	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
1155}
1156
1157static noinline int __sched
1158__mutex_lock_killable_slowpath(struct mutex *lock)
1159{
1160	return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
 
1161}
1162
1163static noinline int __sched
1164__mutex_lock_interruptible_slowpath(struct mutex *lock)
1165{
1166	return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
 
1167}
1168
1169static noinline int __sched
1170__ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1171{
1172	return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL,
1173			       _RET_IP_, ctx);
1174}
1175
1176static noinline int __sched
1177__ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
1178					    struct ww_acquire_ctx *ctx)
1179{
1180	return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL,
1181			       _RET_IP_, ctx);
1182}
1183
1184#endif
1185
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1186/**
1187 * mutex_trylock - try to acquire the mutex, without waiting
1188 * @lock: the mutex to be acquired
1189 *
1190 * Try to acquire the mutex atomically. Returns 1 if the mutex
1191 * has been acquired successfully, and 0 on contention.
1192 *
1193 * NOTE: this function follows the spin_trylock() convention, so
1194 * it is negated from the down_trylock() return values! Be careful
1195 * about this when converting semaphore users to mutexes.
1196 *
1197 * This function must not be used in interrupt context. The
1198 * mutex must be released by the same task that acquired it.
1199 */
1200int __sched mutex_trylock(struct mutex *lock)
1201{
1202	bool locked = __mutex_trylock(lock);
1203
1204	if (locked)
1205		mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 
1206
1207	return locked;
1208}
1209EXPORT_SYMBOL(mutex_trylock);
1210
1211#ifndef CONFIG_DEBUG_LOCK_ALLOC
1212int __sched
1213ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1214{
 
 
1215	might_sleep();
1216
1217	if (__mutex_trylock_fast(&lock->base)) {
1218		if (ctx)
1219			ww_mutex_set_context_fastpath(lock, ctx);
1220		return 0;
1221	}
1222
1223	return __ww_mutex_lock_slowpath(lock, ctx);
 
 
 
 
 
1224}
1225EXPORT_SYMBOL(ww_mutex_lock);
1226
1227int __sched
1228ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
1229{
 
 
1230	might_sleep();
1231
1232	if (__mutex_trylock_fast(&lock->base)) {
1233		if (ctx)
1234			ww_mutex_set_context_fastpath(lock, ctx);
1235		return 0;
1236	}
1237
1238	return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
 
 
 
 
 
1239}
1240EXPORT_SYMBOL(ww_mutex_lock_interruptible);
1241
1242#endif
1243
1244/**
1245 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
1246 * @cnt: the atomic which we are to dec
1247 * @lock: the mutex to return holding if we dec to 0
1248 *
1249 * return true and hold lock if we dec to 0, return false otherwise
1250 */
1251int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
1252{
1253	/* dec if we can't possibly hit 0 */
1254	if (atomic_add_unless(cnt, -1, 1))
1255		return 0;
1256	/* we might hit 0, so take the lock */
1257	mutex_lock(lock);
1258	if (!atomic_dec_and_test(cnt)) {
1259		/* when we actually did the dec, we didn't hit 0 */
1260		mutex_unlock(lock);
1261		return 0;
1262	}
1263	/* we hit 0, and we hold the lock */
1264	return 1;
1265}
1266EXPORT_SYMBOL(atomic_dec_and_mutex_lock);