Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Ingo Molnar: "The main changes in this cycle were: - Implement wraparound-safe refcount_t and kref_t types based on generic atomic primitives (Peter Zijlstra) - Improve and fix the ww_mutex code (Nicolai Hähnle) - Add self-tests to the ww_mutex code (Chris Wilson) - Optimize percpu-rwsems with the 'rcuwait' mechanism (Davidlohr Bueso) - Micro-optimize the current-task logic all around the core kernel (Davidlohr Bueso) - Tidy up after recent optimizations: remove stale code and APIs, clean up the code (Waiman Long) - ... plus misc fixes, updates and cleanups" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (50 commits) fork: Fix task_struct alignment locking/spinlock/debug: Remove spinlock lockup detection code lockdep: Fix incorrect condition to print bug msgs for MAX_LOCKDEP_CHAIN_HLOCKS lkdtm: Convert to refcount_t testing kref: Implement 'struct kref' using refcount_t refcount_t: Introduce a special purpose refcount type sched/wake_q: Clarify queue reinit comment sched/wait, rcuwait: Fix typo in comment locking/mutex: Fix lockdep_assert_held() fail locking/rtmutex: Flip unlikely() branch to likely() in __rt_mutex_slowlock() locking/rwsem: Reinit wake_q after use locking/rwsem: Remove unnecessary atomic_long_t casts jump_labels: Move header guard #endif down where it belongs locking/atomic, kref: Implement kref_put_lock() locking/ww_mutex: Turn off __must_check for now locking/atomic, kref: Avoid more abuse locking/atomic, kref: Use kref_get_unless_zero() more locking/atomic, kref: Kill kref_sub() locking/atomic, kref: Add kref_read() locking/atomic, kref: Add KREF_INIT() ...
2017-02-20 13:23:30 -08:00
parent 828cad8ea0 95cb64c1fe
commit 42e1b14b6e
116 changed files with 1872 additions and 769 deletions
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -50,16 +50,17 @@ EXPORT_SYMBOL(__mutex_init);
 /*
 * @owner: contains: 'struct task_struct *' to the current lock owner,
 * NULL means not owned. Since task_struct pointers are aligned at
- * ARCH_MIN_TASKALIGN (which is at least sizeof(void *)), we have low
- * bits to store extra state.
+ * at least L1_CACHE_BYTES, we have low bits to store extra state.
 *
 * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
 * Bit1 indicates unlock needs to hand the lock to the top-waiter
+ * Bit2 indicates handoff has been done and we're waiting for pickup.
 */
 #define MUTEX_FLAG_WAITERS	0x01
 #define MUTEX_FLAG_HANDOFF	0x02
+#define MUTEX_FLAG_PICKUP	0x04

-#define MUTEX_FLAGS		0x03
+#define MUTEX_FLAGS		0x07

 static inline struct task_struct *__owner_task(unsigned long owner)
 {
@@ -72,38 +73,29 @@ static inline unsigned long __owner_flags(unsigned long owner)
 }

 /*
- * Actual trylock that will work on any unlocked state.
- *
- * When setting the owner field, we must preserve the low flag bits.
- *
- * Be careful with @handoff, only set that in a wait-loop (where you set
- * HANDOFF) to avoid recursive lock attempts.
+ * Trylock variant that retuns the owning task on failure.
 */
-static inline bool __mutex_trylock(struct mutex *lock, const bool handoff)
+static inline struct task_struct *__mutex_trylock_or_owner(struct mutex *lock)
 {
 	unsigned long owner, curr = (unsigned long)current;

 	owner = atomic_long_read(&lock->owner);
 	for (;;) { /* must loop, can race against a flag */
 		unsigned long old, flags = __owner_flags(owner);
+		unsigned long task = owner & ~MUTEX_FLAGS;

-		if (__owner_task(owner)) {
-			if (handoff && unlikely(__owner_task(owner) == current)) {
-				/*
-				 * Provide ACQUIRE semantics for the lock-handoff.
-				 *
-				 * We cannot easily use load-acquire here, since
-				 * the actual load is a failed cmpxchg, which
-				 * doesn't imply any barriers.
-				 *
-				 * Also, this is a fairly unlikely scenario, and
-				 * this contains the cost.
-				 */
-				smp_mb(); /* ACQUIRE */
-				return true;
-			}
+		if (task) {
+			if (likely(task != curr))
+				break;

-			return false;
+			if (likely(!(flags & MUTEX_FLAG_PICKUP)))
+				break;
+
+			flags &= ~MUTEX_FLAG_PICKUP;
+		} else {
+#ifdef CONFIG_DEBUG_MUTEXES
+			DEBUG_LOCKS_WARN_ON(flags & MUTEX_FLAG_PICKUP);
+#endif
 		}

 		/*
@@ -111,15 +103,24 @@ static inline bool __mutex_trylock(struct mutex *lock, const bool handoff)
 		 * past the point where we acquire it. This would be possible
 		 * if we (accidentally) set the bit on an unlocked mutex.
 		 */
-		if (handoff)
-			flags &= ~MUTEX_FLAG_HANDOFF;
+		flags &= ~MUTEX_FLAG_HANDOFF;

 		old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
 		if (old == owner)
-			return true;
+			return NULL;

 		owner = old;
 	}
+
+	return __owner_task(owner);
+}
+
+/*
+ * Actual trylock that will work on any unlocked state.
+ */
+static inline bool __mutex_trylock(struct mutex *lock)
+{
+	return !__mutex_trylock_or_owner(lock);
 }

 #ifndef CONFIG_DEBUG_LOCK_ALLOC
@@ -171,9 +172,9 @@ static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_wait

 /*
 * Give up ownership to a specific task, when @task = NULL, this is equivalent
- * to a regular unlock. Clears HANDOFF, preserves WAITERS. Provides RELEASE
- * semantics like a regular unlock, the __mutex_trylock() provides matching
- * ACQUIRE semantics for the handoff.
+ * to a regular unlock. Sets PICKUP on a handoff, clears HANDOF, preserves
+ * WAITERS. Provides RELEASE semantics like a regular unlock, the
+ * __mutex_trylock() provides a matching ACQUIRE semantics for the handoff.
 */
 static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
 {
@@ -184,10 +185,13 @@ static void __mutex_handoff(struct mutex *lock, struct task_struct *task)

 #ifdef CONFIG_DEBUG_MUTEXES
 		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
+		DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
 #endif

 		new = (owner & MUTEX_FLAG_WAITERS);
 		new |= (unsigned long)task;
+		if (task)
+			new |= MUTEX_FLAG_PICKUP;

 		old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
 		if (old == owner)
@@ -237,8 +241,8 @@ void __sched mutex_lock(struct mutex *lock)
 EXPORT_SYMBOL(mutex_lock);
 #endif

-static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww,
-						   struct ww_acquire_ctx *ww_ctx)
+static __always_inline void
+ww_mutex_lock_acquired(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx)
 {
 #ifdef CONFIG_DEBUG_MUTEXES
 	/*
@@ -277,17 +281,50 @@ static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww,
 	ww_ctx->acquired++;
 }

+static inline bool __sched
+__ww_ctx_stamp_after(struct ww_acquire_ctx *a, struct ww_acquire_ctx *b)
+{
+	return a->stamp - b->stamp <= LONG_MAX &&
+	       (a->stamp != b->stamp || a > b);
+}
+
+/*
+ * Wake up any waiters that may have to back off when the lock is held by the
+ * given context.
+ *
+ * Due to the invariants on the wait list, this can only affect the first
+ * waiter with a context.
+ *
+ * The current task must not be on the wait list.
+ */
+static void __sched
+__ww_mutex_wakeup_for_backoff(struct mutex *lock, struct ww_acquire_ctx *ww_ctx)
+{
+	struct mutex_waiter *cur;
+
+	lockdep_assert_held(&lock->wait_lock);
+
+	list_for_each_entry(cur, &lock->wait_list, list) {
+		if (!cur->ww_ctx)
+			continue;
+
+		if (cur->ww_ctx->acquired > 0 &&
+		    __ww_ctx_stamp_after(cur->ww_ctx, ww_ctx)) {
+			debug_mutex_wake_waiter(lock, cur);
+			wake_up_process(cur->task);
+		}
+
+		break;
+	}
+}
+
 /*
 * After acquiring lock with fastpath or when we lost out in contested
 * slowpath, set ctx and wake up any waiters so they can recheck.
 */
 static __always_inline void
-ww_mutex_set_context_fastpath(struct ww_mutex *lock,
-			       struct ww_acquire_ctx *ctx)
+ww_mutex_set_context_fastpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
-	unsigned long flags;
-	struct mutex_waiter *cur;
-
 	ww_mutex_lock_acquired(lock, ctx);

 	lock->ctx = ctx;
@@ -311,46 +348,79 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock,
 	 * Uh oh, we raced in fastpath, wake up everyone in this case,
 	 * so they can see the new lock->ctx.
 	 */
-	spin_lock_mutex(&lock->base.wait_lock, flags);
-	list_for_each_entry(cur, &lock->base.wait_list, list) {
-		debug_mutex_wake_waiter(&lock->base, cur);
-		wake_up_process(cur->task);
-	}
-	spin_unlock_mutex(&lock->base.wait_lock, flags);
+	spin_lock(&lock->base.wait_lock);
+	__ww_mutex_wakeup_for_backoff(&lock->base, ctx);
+	spin_unlock(&lock->base.wait_lock);
 }

 /*
- * After acquiring lock in the slowpath set ctx and wake up any
- * waiters so they can recheck.
+ * After acquiring lock in the slowpath set ctx.
+ *
+ * Unlike for the fast path, the caller ensures that waiters are woken up where
+ * necessary.
 *
 * Callers must hold the mutex wait_lock.
 */
 static __always_inline void
-ww_mutex_set_context_slowpath(struct ww_mutex *lock,
-			      struct ww_acquire_ctx *ctx)
+ww_mutex_set_context_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
-	struct mutex_waiter *cur;
-
 	ww_mutex_lock_acquired(lock, ctx);
 	lock->ctx = ctx;
-
-	/*
-	 * Give any possible sleeping processes the chance to wake up,
-	 * so they can recheck if they have to back off.
-	 */
-	list_for_each_entry(cur, &lock->base.wait_list, list) {
-		debug_mutex_wake_waiter(&lock->base, cur);
-		wake_up_process(cur->task);
-	}
 }

 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
+
+static inline
+bool ww_mutex_spin_on_owner(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
+			    struct mutex_waiter *waiter)
+{
+	struct ww_mutex *ww;
+
+	ww = container_of(lock, struct ww_mutex, base);
+
+	/*
+	 * If ww->ctx is set the contents are undefined, only
+	 * by acquiring wait_lock there is a guarantee that
+	 * they are not invalid when reading.
+	 *
+	 * As such, when deadlock detection needs to be
+	 * performed the optimistic spinning cannot be done.
+	 *
+	 * Check this in every inner iteration because we may
+	 * be racing against another thread's ww_mutex_lock.
+	 */
+	if (ww_ctx->acquired > 0 && READ_ONCE(ww->ctx))
+		return false;
+
+	/*
+	 * If we aren't on the wait list yet, cancel the spin
+	 * if there are waiters. We want  to avoid stealing the
+	 * lock from a waiter with an earlier stamp, since the
+	 * other thread may already own a lock that we also
+	 * need.
+	 */
+	if (!waiter && (atomic_long_read(&lock->owner) & MUTEX_FLAG_WAITERS))
+		return false;
+
+	/*
+	 * Similarly, stop spinning if we are no longer the
+	 * first waiter.
+	 */
+	if (waiter && !__mutex_waiter_is_first(lock, waiter))
+		return false;
+
+	return true;
+}
+
 /*
- * Look out! "owner" is an entirely speculative pointer
- * access and not reliable.
+ * Look out! "owner" is an entirely speculative pointer access and not
+ * reliable.
+ *
+ * "noinline" so that this function shows up on perf profiles.
 */
 static noinline
-bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
+bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner,
+			 struct ww_acquire_ctx *ww_ctx, struct mutex_waiter *waiter)
 {
 	bool ret = true;

@@ -373,6 +443,11 @@ bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
 			break;
 		}

+		if (ww_ctx && !ww_mutex_spin_on_owner(lock, ww_ctx, waiter)) {
+			ret = false;
+			break;
+		}
+
 		cpu_relax();
 	}
 	rcu_read_unlock();
@@ -431,12 +506,10 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock)
 * with the spinner at the head of the OSQ, if present, until the owner is
 * changed to itself.
 */
-static bool mutex_optimistic_spin(struct mutex *lock,
-				  struct ww_acquire_ctx *ww_ctx,
-				  const bool use_ww_ctx, const bool waiter)
+static __always_inline bool
+mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
+		      const bool use_ww_ctx, struct mutex_waiter *waiter)
 {
-	struct task_struct *task = current;
-
 	if (!waiter) {
 		/*
 		 * The purpose of the mutex_can_spin_on_owner() function is
@@ -460,40 +533,17 @@ static bool mutex_optimistic_spin(struct mutex *lock,
 	for (;;) {
 		struct task_struct *owner;

-		if (use_ww_ctx && ww_ctx->acquired > 0) {
-			struct ww_mutex *ww;
-
-			ww = container_of(lock, struct ww_mutex, base);
-			/*
-			 * If ww->ctx is set the contents are undefined, only
-			 * by acquiring wait_lock there is a guarantee that
-			 * they are not invalid when reading.
-			 *
-			 * As such, when deadlock detection needs to be
-			 * performed the optimistic spinning cannot be done.
-			 */
-			if (READ_ONCE(ww->ctx))
-				goto fail_unlock;
-		}
+		/* Try to acquire the mutex... */
+		owner = __mutex_trylock_or_owner(lock);
+		if (!owner)
+			break;

 		/*
-		 * If there's an owner, wait for it to either
+		 * There's an owner, wait for it to either
 		 * release the lock or go to sleep.
 		 */
-		owner = __mutex_owner(lock);
-		if (owner) {
-			if (waiter && owner == task) {
-				smp_mb(); /* ACQUIRE */
-				break;
-			}
-
-			if (!mutex_spin_on_owner(lock, owner))
-				goto fail_unlock;
-		}
-
-		/* Try to acquire the mutex if it is unlocked. */
-		if (__mutex_trylock(lock, waiter))
-			break;
+		if (!mutex_spin_on_owner(lock, owner, ww_ctx, waiter))
+			goto fail_unlock;

 		/*
 		 * The cpu_relax() call is a compiler barrier which forces
@@ -532,9 +582,9 @@ fail:
 	return false;
 }
 #else
-static bool mutex_optimistic_spin(struct mutex *lock,
-				  struct ww_acquire_ctx *ww_ctx,
-				  const bool use_ww_ctx, const bool waiter)
+static __always_inline bool
+mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
+		      const bool use_ww_ctx, struct mutex_waiter *waiter)
 {
 	return false;
 }
@@ -594,24 +644,89 @@ void __sched ww_mutex_unlock(struct ww_mutex *lock)
 EXPORT_SYMBOL(ww_mutex_unlock);

 static inline int __sched
-__ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)
+__ww_mutex_lock_check_stamp(struct mutex *lock, struct mutex_waiter *waiter,
+			    struct ww_acquire_ctx *ctx)
 {
 	struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
 	struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx);
+	struct mutex_waiter *cur;

-	if (!hold_ctx)
-		return 0;
+	if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx))
+		goto deadlock;

-	if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&
-	    (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) {
-#ifdef CONFIG_DEBUG_MUTEXES
-		DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
-		ctx->contending_lock = ww;
-#endif
-		return -EDEADLK;
+	/*
+	 * If there is a waiter in front of us that has a context, then its
+	 * stamp is earlier than ours and we must back off.
+	 */
+	cur = waiter;
+	list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) {
+		if (cur->ww_ctx)
+			goto deadlock;
 	}

 	return 0;
+
+deadlock:
+#ifdef CONFIG_DEBUG_MUTEXES
+	DEBUG_LOCKS_WARN_ON(ctx->contending_lock);
+	ctx->contending_lock = ww;
+#endif
+	return -EDEADLK;
+}
+
+static inline int __sched
+__ww_mutex_add_waiter(struct mutex_waiter *waiter,
+		      struct mutex *lock,
+		      struct ww_acquire_ctx *ww_ctx)
+{
+	struct mutex_waiter *cur;
+	struct list_head *pos;
+
+	if (!ww_ctx) {
+		list_add_tail(&waiter->list, &lock->wait_list);
+		return 0;
+	}
+
+	/*
+	 * Add the waiter before the first waiter with a higher stamp.
+	 * Waiters without a context are skipped to avoid starving
+	 * them.
+	 */
+	pos = &lock->wait_list;
+	list_for_each_entry_reverse(cur, &lock->wait_list, list) {
+		if (!cur->ww_ctx)
+			continue;
+
+		if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {
+			/* Back off immediately if necessary. */
+			if (ww_ctx->acquired > 0) {
+#ifdef CONFIG_DEBUG_MUTEXES
+				struct ww_mutex *ww;
+
+				ww = container_of(lock, struct ww_mutex, base);
+				DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
+				ww_ctx->contending_lock = ww;
+#endif
+				return -EDEADLK;
+			}
+
+			break;
+		}
+
+		pos = &cur->list;
+
+		/*
+		 * Wake up the waiter so that it gets a chance to back
+		 * off.
+		 */
+		if (cur->ww_ctx->acquired > 0) {
+			debug_mutex_wake_waiter(lock, cur);
+			wake_up_process(cur->task);
+		}
+	}
+
+	list_add_tail(&waiter->list, pos);
+	return 0;
 }

 /*
@@ -622,15 +737,15 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 		    struct lockdep_map *nest_lock, unsigned long ip,
 		    struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
 {
-	struct task_struct *task = current;
 	struct mutex_waiter waiter;
-	unsigned long flags;
 	bool first = false;
 	struct ww_mutex *ww;
 	int ret;

-	if (use_ww_ctx) {
-		ww = container_of(lock, struct ww_mutex, base);
+	might_sleep();
+
+	ww = container_of(lock, struct ww_mutex, base);
+	if (use_ww_ctx && ww_ctx) {
 		if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
 			return -EALREADY;
 	}
@@ -638,36 +753,54 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 	preempt_disable();
 	mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);

-	if (__mutex_trylock(lock, false) ||
-	    mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, false)) {
+	if (__mutex_trylock(lock) ||
+	    mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, NULL)) {
 		/* got the lock, yay! */
 		lock_acquired(&lock->dep_map, ip);
-		if (use_ww_ctx)
+		if (use_ww_ctx && ww_ctx)
 			ww_mutex_set_context_fastpath(ww, ww_ctx);
 		preempt_enable();
 		return 0;
 	}

-	spin_lock_mutex(&lock->wait_lock, flags);
+	spin_lock(&lock->wait_lock);
 	/*
 	 * After waiting to acquire the wait_lock, try again.
 	 */
-	if (__mutex_trylock(lock, false))
+	if (__mutex_trylock(lock)) {
+		if (use_ww_ctx && ww_ctx)
+			__ww_mutex_wakeup_for_backoff(lock, ww_ctx);
+
 		goto skip_wait;
+	}

 	debug_mutex_lock_common(lock, &waiter);
-	debug_mutex_add_waiter(lock, &waiter, task);
+	debug_mutex_add_waiter(lock, &waiter, current);

-	/* add waiting tasks to the end of the waitqueue (FIFO): */
-	list_add_tail(&waiter.list, &lock->wait_list);
-	waiter.task = task;
+	lock_contended(&lock->dep_map, ip);
+
+	if (!use_ww_ctx) {
+		/* add waiting tasks to the end of the waitqueue (FIFO): */
+		list_add_tail(&waiter.list, &lock->wait_list);
+
+#ifdef CONFIG_DEBUG_MUTEXES
+		waiter.ww_ctx = MUTEX_POISON_WW_CTX;
+#endif
+	} else {
+		/* Add in stamp order, waking up waiters that must back off. */
+		ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
+		if (ret)
+			goto err_early_backoff;
+
+		waiter.ww_ctx = ww_ctx;
+	}
+
+	waiter.task = current;

 	if (__mutex_waiter_is_first(lock, &waiter))
 		__mutex_set_flag(lock, MUTEX_FLAG_WAITERS);

-	lock_contended(&lock->dep_map, ip);
-
-	set_task_state(task, state);
+	set_current_state(state);
 	for (;;) {
 		/*
 		 * Once we hold wait_lock, we're serialized against
@@ -675,7 +808,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 		 * before testing the error conditions to make sure we pick up
 		 * the handoff.
 		 */
-		if (__mutex_trylock(lock, first))
+		if (__mutex_trylock(lock))
 			goto acquired;

 		/*
@@ -683,42 +816,47 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 		 * wait_lock. This ensures the lock cancellation is ordered
 		 * against mutex_unlock() and wake-ups do not go missing.
 		 */
-		if (unlikely(signal_pending_state(state, task))) {
+		if (unlikely(signal_pending_state(state, current))) {
 			ret = -EINTR;
 			goto err;
 		}

-		if (use_ww_ctx && ww_ctx->acquired > 0) {
-			ret = __ww_mutex_lock_check_stamp(lock, ww_ctx);
+		if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) {
+			ret = __ww_mutex_lock_check_stamp(lock, &waiter, ww_ctx);
 			if (ret)
 				goto err;
 		}

-		spin_unlock_mutex(&lock->wait_lock, flags);
+		spin_unlock(&lock->wait_lock);
 		schedule_preempt_disabled();

-		if (!first && __mutex_waiter_is_first(lock, &waiter)) {
-			first = true;
-			__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
+		/*
+		 * ww_mutex needs to always recheck its position since its waiter
+		 * list is not FIFO ordered.
+		 */
+		if ((use_ww_ctx && ww_ctx) || !first) {
+			first = __mutex_waiter_is_first(lock, &waiter);
+			if (first)
+				__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
 		}

-		set_task_state(task, state);
+		set_current_state(state);
 		/*
 		 * Here we order against unlock; we must either see it change
 		 * state back to RUNNING and fall through the next schedule(),
 		 * or we must see its unlock and acquire.
 		 */
-		if ((first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, true)) ||
-		     __mutex_trylock(lock, first))
+		if (__mutex_trylock(lock) ||
+		    (first && mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, &waiter)))
 			break;

-		spin_lock_mutex(&lock->wait_lock, flags);
+		spin_lock(&lock->wait_lock);
 	}
-	spin_lock_mutex(&lock->wait_lock, flags);
+	spin_lock(&lock->wait_lock);
 acquired:
-	__set_task_state(task, TASK_RUNNING);
+	__set_current_state(TASK_RUNNING);

-	mutex_remove_waiter(lock, &waiter, task);
+	mutex_remove_waiter(lock, &waiter, current);
 	if (likely(list_empty(&lock->wait_list)))
 		__mutex_clear_flag(lock, MUTEX_FLAGS);

@@ -728,30 +866,44 @@ skip_wait:
 	/* got the lock - cleanup and rejoice! */
 	lock_acquired(&lock->dep_map, ip);

-	if (use_ww_ctx)
+	if (use_ww_ctx && ww_ctx)
 		ww_mutex_set_context_slowpath(ww, ww_ctx);

-	spin_unlock_mutex(&lock->wait_lock, flags);
+	spin_unlock(&lock->wait_lock);
 	preempt_enable();
 	return 0;

 err:
-	__set_task_state(task, TASK_RUNNING);
-	mutex_remove_waiter(lock, &waiter, task);
-	spin_unlock_mutex(&lock->wait_lock, flags);
+	__set_current_state(TASK_RUNNING);
+	mutex_remove_waiter(lock, &waiter, current);
+err_early_backoff:
+	spin_unlock(&lock->wait_lock);
 	debug_mutex_free_waiter(&waiter);
 	mutex_release(&lock->dep_map, 1, ip);
 	preempt_enable();
 	return ret;
 }

+static int __sched
+__mutex_lock(struct mutex *lock, long state, unsigned int subclass,
+	     struct lockdep_map *nest_lock, unsigned long ip)
+{
+	return __mutex_lock_common(lock, state, subclass, nest_lock, ip, NULL, false);
+}
+
+static int __sched
+__ww_mutex_lock(struct mutex *lock, long state, unsigned int subclass,
+		struct lockdep_map *nest_lock, unsigned long ip,
+		struct ww_acquire_ctx *ww_ctx)
+{
+	return __mutex_lock_common(lock, state, subclass, nest_lock, ip, ww_ctx, true);
+}
+
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 void __sched
 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
 {
-	might_sleep();
-	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
-			    subclass, NULL, _RET_IP_, NULL, 0);
+	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);
 }

 EXPORT_SYMBOL_GPL(mutex_lock_nested);
@@ -759,27 +911,21 @@ EXPORT_SYMBOL_GPL(mutex_lock_nested);
 void __sched
 _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
 {
-	might_sleep();
-	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
-			    0, nest, _RET_IP_, NULL, 0);
+	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);
 }
 EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);

 int __sched
 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
 {
-	might_sleep();
-	return __mutex_lock_common(lock, TASK_KILLABLE,
-				   subclass, NULL, _RET_IP_, NULL, 0);
+	return __mutex_lock(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);
 }
 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);

 int __sched
 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
 {
-	might_sleep();
-	return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
-				   subclass, NULL, _RET_IP_, NULL, 0);
+	return __mutex_lock(lock, TASK_INTERRUPTIBLE, subclass, NULL, _RET_IP_);
 }
 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);

@@ -824,35 +970,37 @@ ww_mutex_deadlock_injection(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 }

 int __sched
-__ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
 	int ret;

 	might_sleep();
-	ret =  __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE,
-				   0, &ctx->dep_map, _RET_IP_, ctx, 1);
-	if (!ret && ctx->acquired > 1)
+	ret =  __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE,
+			       0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
+			       ctx);
+	if (!ret && ctx && ctx->acquired > 1)
 		return ww_mutex_deadlock_injection(lock, ctx);

 	return ret;
 }
-EXPORT_SYMBOL_GPL(__ww_mutex_lock);
+EXPORT_SYMBOL_GPL(ww_mutex_lock);

 int __sched
-__ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
 	int ret;

 	might_sleep();
-	ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE,
-				  0, &ctx->dep_map, _RET_IP_, ctx, 1);
+	ret = __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE,
+			      0, ctx ? &ctx->dep_map : NULL, _RET_IP_,
+			      ctx);

-	if (!ret && ctx->acquired > 1)
+	if (!ret && ctx && ctx->acquired > 1)
 		return ww_mutex_deadlock_injection(lock, ctx);

 	return ret;
 }
-EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible);
+EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);

 #endif

@@ -862,8 +1010,8 @@ EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible);
 static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
 {
 	struct task_struct *next = NULL;
-	unsigned long owner, flags;
 	DEFINE_WAKE_Q(wake_q);
+	unsigned long owner;

 	mutex_release(&lock->dep_map, 1, ip);

@@ -880,6 +1028,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne

 #ifdef CONFIG_DEBUG_MUTEXES
 		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
+		DEBUG_LOCKS_WARN_ON(owner & MUTEX_FLAG_PICKUP);
 #endif

 		if (owner & MUTEX_FLAG_HANDOFF)
@@ -897,7 +1046,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 		owner = old;
 	}

-	spin_lock_mutex(&lock->wait_lock, flags);
+	spin_lock(&lock->wait_lock);
 	debug_mutex_unlock(lock);
 	if (!list_empty(&lock->wait_list)) {
 		/* get the first entry from the wait-list: */
@@ -914,7 +1063,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
 	if (owner & MUTEX_FLAG_HANDOFF)
 		__mutex_handoff(lock, next);

-	spin_unlock_mutex(&lock->wait_lock, flags);
+	spin_unlock(&lock->wait_lock);

 	wake_up_q(&wake_q);
 }
@@ -977,37 +1126,34 @@ EXPORT_SYMBOL_GPL(mutex_lock_io);
 static noinline void __sched
 __mutex_lock_slowpath(struct mutex *lock)
 {
-	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0,
-			    NULL, _RET_IP_, NULL, 0);
+	__mutex_lock(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);
 }

 static noinline int __sched
 __mutex_lock_killable_slowpath(struct mutex *lock)
 {
-	return __mutex_lock_common(lock, TASK_KILLABLE, 0,
-				   NULL, _RET_IP_, NULL, 0);
+	return __mutex_lock(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);
 }

 static noinline int __sched
 __mutex_lock_interruptible_slowpath(struct mutex *lock)
 {
-	return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0,
-				   NULL, _RET_IP_, NULL, 0);
+	return __mutex_lock(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);
 }

 static noinline int __sched
 __ww_mutex_lock_slowpath(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
-	return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0,
-				   NULL, _RET_IP_, ctx, 1);
+	return __ww_mutex_lock(&lock->base, TASK_UNINTERRUPTIBLE, 0, NULL,
+			       _RET_IP_, ctx);
 }

 static noinline int __sched
 __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
 					    struct ww_acquire_ctx *ctx)
 {
-	return __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, 0,
-				   NULL, _RET_IP_, ctx, 1);
+	return __ww_mutex_lock(&lock->base, TASK_INTERRUPTIBLE, 0, NULL,
+			       _RET_IP_, ctx);
 }

 #endif
@@ -1028,7 +1174,7 @@ __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
 */
 int __sched mutex_trylock(struct mutex *lock)
 {
-	bool locked = __mutex_trylock(lock, false);
+	bool locked = __mutex_trylock(lock);

 	if (locked)
 		mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
@@ -1039,32 +1185,34 @@ EXPORT_SYMBOL(mutex_trylock);

 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 int __sched
-__ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
 	might_sleep();

 	if (__mutex_trylock_fast(&lock->base)) {
-		ww_mutex_set_context_fastpath(lock, ctx);
+		if (ctx)
+			ww_mutex_set_context_fastpath(lock, ctx);
 		return 0;
 	}

 	return __ww_mutex_lock_slowpath(lock, ctx);
 }
-EXPORT_SYMBOL(__ww_mutex_lock);
+EXPORT_SYMBOL(ww_mutex_lock);

 int __sched
-__ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
+ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
 	might_sleep();

 	if (__mutex_trylock_fast(&lock->base)) {
-		ww_mutex_set_context_fastpath(lock, ctx);
+		if (ctx)
+			ww_mutex_set_context_fastpath(lock, ctx);
 		return 0;
 	}

 	return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
 }
-EXPORT_SYMBOL(__ww_mutex_lock_interruptible);
+EXPORT_SYMBOL(ww_mutex_lock_interruptible);

 #endif