1 files changed, 340 insertions, 248 deletions

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index a70b90db3909..9b349619f431 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -27,41 +27,176 @@
 #include <linux/debug_locks.h>
 #include <linux/osq_lock.h>
 
-/*
- * In the DEBUG case we are using the "NULL fastpath" for mutexes,
- * which forces all calls into the slowpath:
- */
 #ifdef CONFIG_DEBUG_MUTEXES
 # include "mutex-debug.h"
-# include <asm-generic/mutex-null.h>
-/*
- * Must be 0 for the debug case so we do not do the unlock outside of the
- * wait_lock region. debug_mutex_unlock() will do the actual unlock in this
- * case.
- */
-# undef __mutex_slowpath_needs_to_unlock
-# define  __mutex_slowpath_needs_to_unlock()	0
 #else
 # include "mutex.h"
-# include <asm/mutex.h>
 #endif
 
 void
 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
 {
-	atomic_set(&lock->count, 1);
+	atomic_long_set(&lock->owner, 0);
 	spin_lock_init(&lock->wait_lock);
 	INIT_LIST_HEAD(&lock->wait_list);
-	mutex_clear_owner(lock);
 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
 	osq_lock_init(&lock->osq);
 #endif
 
 	debug_mutex_init(lock, name, key);
 }
-
 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.
+ *
+ * Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
+ * Bit1 indicates unlock needs to hand the lock to the top-waiter
+ */
+#define MUTEX_FLAG_WAITERS	0x01
+#define MUTEX_FLAG_HANDOFF	0x02
+
+#define MUTEX_FLAGS		0x03
+
+static inline struct task_struct *__owner_task(unsigned long owner)
+{
+	return (struct task_struct *)(owner & ~MUTEX_FLAGS);
+}
+
+static inline unsigned long __owner_flags(unsigned long owner)
+{
+	return owner & MUTEX_FLAGS;
+}
+
+/*
+ * 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.
+ */
+static inline bool __mutex_trylock(struct mutex *lock, const bool handoff)
+{
+	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);
+
+		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;
+			}
+
+			return false;
+		}
+
+		/*
+		 * We set the HANDOFF bit, we must make sure it doesn't live
+		 * 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;
+
+		old = atomic_long_cmpxchg_acquire(&lock->owner, owner, curr | flags);
+		if (old == owner)
+			return true;
+
+		owner = old;
+	}
+}
+
+#ifndef CONFIG_DEBUG_LOCK_ALLOC
+/*
+ * Lockdep annotations are contained to the slow paths for simplicity.
+ * There is nothing that would stop spreading the lockdep annotations outwards
+ * except more code.
+ */
+
+/*
+ * Optimistic trylock that only works in the uncontended case. Make sure to
+ * follow with a __mutex_trylock() before failing.
+ */
+static __always_inline bool __mutex_trylock_fast(struct mutex *lock)
+{
+	unsigned long curr = (unsigned long)current;
+
+	if (!atomic_long_cmpxchg_acquire(&lock->owner, 0UL, curr))
+		return true;
+
+	return false;
+}
+
+static __always_inline bool __mutex_unlock_fast(struct mutex *lock)
+{
+	unsigned long curr = (unsigned long)current;
+
+	if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr)
+		return true;
+
+	return false;
+}
+#endif
+
+static inline void __mutex_set_flag(struct mutex *lock, unsigned long flag)
+{
+	atomic_long_or(flag, &lock->owner);
+}
+
+static inline void __mutex_clear_flag(struct mutex *lock, unsigned long flag)
+{
+	atomic_long_andnot(flag, &lock->owner);
+}
+
+static inline bool __mutex_waiter_is_first(struct mutex *lock, struct mutex_waiter *waiter)
+{
+	return list_first_entry(&lock->wait_list, struct mutex_waiter, list) == waiter;
+}
+
+/*
+ * 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.
+ */
+static void __mutex_handoff(struct mutex *lock, struct task_struct *task)
+{
+	unsigned long owner = atomic_long_read(&lock->owner);
+
+	for (;;) {
+		unsigned long old, new;
+
+#ifdef CONFIG_DEBUG_MUTEXES
+		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
+#endif
+
+		new = (owner & MUTEX_FLAG_WAITERS);
+		new |= (unsigned long)task;
+
+		old = atomic_long_cmpxchg_release(&lock->owner, owner, new);
+		if (old == owner)
+			break;
+
+		owner = old;
+	}
+}
+
 #ifndef CONFIG_DEBUG_LOCK_ALLOC
 /*
  * We split the mutex lock/unlock logic into separate fastpath and
@@ -69,7 +204,7 @@ EXPORT_SYMBOL(__mutex_init);
  * We also put the fastpath first in the kernel image, to make sure the
  * branch is predicted by the CPU as default-untaken.
  */
-__visible void __sched __mutex_lock_slowpath(atomic_t *lock_count);
+static void __sched __mutex_lock_slowpath(struct mutex *lock);
 
 /**
  * mutex_lock - acquire the mutex
@@ -95,14 +230,10 @@ __visible void __sched __mutex_lock_slowpath(atomic_t *lock_count);
 void __sched mutex_lock(struct mutex *lock)
 {
 	might_sleep();
-	/*
-	 * The locking fastpath is the 1->0 transition from
-	 * 'unlocked' into 'locked' state.
-	 */
-	__mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
-	mutex_set_owner(lock);
-}
 
+	if (!__mutex_trylock_fast(lock))
+		__mutex_lock_slowpath(lock);
+}
 EXPORT_SYMBOL(mutex_lock);
 #endif
 
@@ -149,9 +280,6 @@ static __always_inline void ww_mutex_lock_acquired(struct ww_mutex *ww,
 /*
  * After acquiring lock with fastpath or when we lost out in contested
  * slowpath, set ctx and wake up any waiters so they can recheck.
- *
- * This function is never called when CONFIG_DEBUG_LOCK_ALLOC is set,
- * as the fastpath and opportunistic spinning are disabled in that case.
  */
 static __always_inline void
 ww_mutex_set_context_fastpath(struct ww_mutex *lock,
@@ -176,7 +304,7 @@ ww_mutex_set_context_fastpath(struct ww_mutex *lock,
 	/*
 	 * Check if lock is contended, if not there is nobody to wake up
 	 */
-	if (likely(atomic_read(&lock->base.count) == 0))
+	if (likely(!(atomic_long_read(&lock->base.owner) & MUTEX_FLAG_WAITERS)))
 		return;
 
 	/*
@@ -227,7 +355,7 @@ bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
 	bool ret = true;
 
 	rcu_read_lock();
-	while (lock->owner == owner) {
+	while (__mutex_owner(lock) == owner) {
 		/*
 		 * Ensure we emit the owner->on_cpu, dereference _after_
 		 * checking lock->owner still matches owner. If that fails,
@@ -236,12 +364,16 @@ bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner)
 		 */
 		barrier();
 
-		if (!owner->on_cpu || need_resched()) {
+		/*
+		 * Use vcpu_is_preempted to detect lock holder preemption issue.
+		 */
+		if (!owner->on_cpu || need_resched() ||
+				vcpu_is_preempted(task_cpu(owner))) {
 			ret = false;
 			break;
 		}
 
-		cpu_relax_lowlatency();
+		cpu_relax();
 	}
 	rcu_read_unlock();
 
@@ -260,27 +392,25 @@ static inline int mutex_can_spin_on_owner(struct mutex *lock)
 		return 0;
 
 	rcu_read_lock();
-	owner = READ_ONCE(lock->owner);
+	owner = __mutex_owner(lock);
+
+	/*
+	 * As lock holder preemption issue, we both skip spinning if task is not
+	 * on cpu or its cpu is preempted
+	 */
 	if (owner)
-		retval = owner->on_cpu;
+		retval = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
 	rcu_read_unlock();
+
 	/*
-	 * if lock->owner is not set, the mutex owner may have just acquired
-	 * it and not set the owner yet or the mutex has been released.
+	 * If lock->owner is not set, the mutex has been released. Return true
+	 * such that we'll trylock in the spin path, which is a faster option
+	 * than the blocking slow path.
 	 */
 	return retval;
 }
 
 /*
- * Atomically try to take the lock when it is available
- */
-static inline bool mutex_try_to_acquire(struct mutex *lock)
-{
-	return !mutex_is_locked(lock) &&
-		(atomic_cmpxchg_acquire(&lock->count, 1, 0) == 1);
-}
-
-/*
  * Optimistic spinning.
  *
  * We try to spin for acquisition when we find that the lock owner
@@ -288,13 +418,6 @@ static inline bool mutex_try_to_acquire(struct mutex *lock)
  * need to reschedule. The rationale is that if the lock owner is
  * running, it is likely to release the lock soon.
  *
- * Since this needs the lock owner, and this mutex implementation
- * doesn't track the owner atomically in the lock field, we need to
- * track it non-atomically.
- *
- * We can't do this for DEBUG_MUTEXES because that relies on wait_lock
- * to serialize everything.
- *
  * The mutex spinners are queued up using MCS lock so that only one
  * spinner can compete for the mutex. However, if mutex spinning isn't
  * going to happen, there is no point in going through the lock/unlock
@@ -302,24 +425,39 @@ static inline bool mutex_try_to_acquire(struct mutex *lock)
  *
  * Returns true when the lock was taken, otherwise false, indicating
  * that we need to jump to the slowpath and sleep.
+ *
+ * The waiter flag is set to true if the spinner is a waiter in the wait
+ * queue. The waiter-spinner will spin on the lock directly and concurrently
+ * 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)
+				  struct ww_acquire_ctx *ww_ctx,
+				  const bool use_ww_ctx, const bool waiter)
 {
 	struct task_struct *task = current;
 
-	if (!mutex_can_spin_on_owner(lock))
-		goto done;
+	if (!waiter) {
+		/*
+		 * The purpose of the mutex_can_spin_on_owner() function is
+		 * to eliminate the overhead of osq_lock() and osq_unlock()
+		 * in case spinning isn't possible. As a waiter-spinner
+		 * is not going to take OSQ lock anyway, there is no need
+		 * to call mutex_can_spin_on_owner().
+		 */
+		if (!mutex_can_spin_on_owner(lock))
+			goto fail;
 
-	/*
-	 * In order to avoid a stampede of mutex spinners trying to
-	 * acquire the mutex all at once, the spinners need to take a
-	 * MCS (queued) lock first before spinning on the owner field.
-	 */
-	if (!osq_lock(&lock->osq))
-		goto done;
+		/*
+		 * In order to avoid a stampede of mutex spinners trying to
+		 * acquire the mutex all at once, the spinners need to take a
+		 * MCS (queued) lock first before spinning on the owner field.
+		 */
+		if (!osq_lock(&lock->osq))
+			goto fail;
+	}
 
-	while (true) {
+	for (;;) {
 		struct task_struct *owner;
 
 		if (use_ww_ctx && ww_ctx->acquired > 0) {
@@ -335,40 +473,26 @@ static bool mutex_optimistic_spin(struct mutex *lock,
 			 * performed the optimistic spinning cannot be done.
 			 */
 			if (READ_ONCE(ww->ctx))
-				break;
+				goto fail_unlock;
 		}
 
 		/*
 		 * If there's an owner, wait for it to either
 		 * release the lock or go to sleep.
 		 */
-		owner = READ_ONCE(lock->owner);
-		if (owner && !mutex_spin_on_owner(lock, owner))
-			break;
-
-		/* Try to acquire the mutex if it is unlocked. */
-		if (mutex_try_to_acquire(lock)) {
-			lock_acquired(&lock->dep_map, ip);
-
-			if (use_ww_ctx) {
-				struct ww_mutex *ww;
-				ww = container_of(lock, struct ww_mutex, base);
-
-				ww_mutex_set_context_fastpath(ww, ww_ctx);
+		owner = __mutex_owner(lock);
+		if (owner) {
+			if (waiter && owner == task) {
+				smp_mb(); /* ACQUIRE */
+				break;
 			}
 
-			mutex_set_owner(lock);
-			osq_unlock(&lock->osq);
-			return true;
+			if (!mutex_spin_on_owner(lock, owner))
+				goto fail_unlock;
 		}
 
-		/*
-		 * When there's no owner, we might have preempted between the
-		 * owner acquiring the lock and setting the owner field. If
-		 * we're an RT task that will live-lock because we won't let
-		 * the owner complete.
-		 */
-		if (!owner && (need_resched() || rt_task(task)))
+		/* Try to acquire the mutex if it is unlocked. */
+		if (__mutex_trylock(lock, waiter))
 			break;
 
 		/*
@@ -377,11 +501,20 @@ static bool mutex_optimistic_spin(struct mutex *lock,
 		 * memory barriers as we'll eventually observe the right
 		 * values at the cost of a few extra spins.
 		 */
-		cpu_relax_lowlatency();
+		cpu_relax();
 	}
 
-	osq_unlock(&lock->osq);
-done:
+	if (!waiter)
+		osq_unlock(&lock->osq);
+
+	return true;
+
+
+fail_unlock:
+	if (!waiter)
+		osq_unlock(&lock->osq);
+
+fail:
 	/*
 	 * If we fell out of the spin path because of need_resched(),
 	 * reschedule now, before we try-lock the mutex. This avoids getting
@@ -400,14 +533,14 @@ done:
 }
 #else
 static bool mutex_optimistic_spin(struct mutex *lock,
-				  struct ww_acquire_ctx *ww_ctx, const bool use_ww_ctx)
+				  struct ww_acquire_ctx *ww_ctx,
+				  const bool use_ww_ctx, const bool waiter)
 {
 	return false;
 }
 #endif
 
-__visible __used noinline
-void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
+static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip);
 
 /**
  * mutex_unlock - release the mutex
@@ -422,21 +555,12 @@ void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
  */
 void __sched mutex_unlock(struct mutex *lock)
 {
-	/*
-	 * The unlocking fastpath is the 0->1 transition from 'locked'
-	 * into 'unlocked' state:
-	 */
-#ifndef CONFIG_DEBUG_MUTEXES
-	/*
-	 * When debugging is enabled we must not clear the owner before time,
-	 * the slow path will always be taken, and that clears the owner field
-	 * after verifying that it was indeed current.
-	 */
-	mutex_clear_owner(lock);
+#ifndef CONFIG_DEBUG_LOCK_ALLOC
+	if (__mutex_unlock_fast(lock))
+		return;
 #endif
-	__mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
+	__mutex_unlock_slowpath(lock, _RET_IP_);
 }
-
 EXPORT_SYMBOL(mutex_unlock);
 
 /**
@@ -465,15 +589,7 @@ void __sched ww_mutex_unlock(struct ww_mutex *lock)
 		lock->ctx = NULL;
 	}
 
-#ifndef CONFIG_DEBUG_MUTEXES
-	/*
-	 * When debugging is enabled we must not clear the owner before time,
-	 * the slow path will always be taken, and that clears the owner field
-	 * after verifying that it was indeed current.
-	 */
-	mutex_clear_owner(&lock->base);
-#endif
-	__mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath);
+	mutex_unlock(&lock->base);
 }
 EXPORT_SYMBOL(ww_mutex_unlock);
 
@@ -509,10 +625,12 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 	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) {
-		struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
+		ww = container_of(lock, struct ww_mutex, base);
 		if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
 			return -EALREADY;
 	}
@@ -520,20 +638,21 @@ __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_optimistic_spin(lock, ww_ctx, use_ww_ctx)) {
+	if (__mutex_trylock(lock, false) ||
+	    mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, false)) {
 		/* got the lock, yay! */
+		lock_acquired(&lock->dep_map, ip);
+		if (use_ww_ctx)
+			ww_mutex_set_context_fastpath(ww, ww_ctx);
 		preempt_enable();
 		return 0;
 	}
 
 	spin_lock_mutex(&lock->wait_lock, flags);
-
 	/*
-	 * Once more, try to acquire the lock. Only try-lock the mutex if
-	 * it is unlocked to reduce unnecessary xchg() operations.
+	 * After waiting to acquire the wait_lock, try again.
 	 */
-	if (!mutex_is_locked(lock) &&
-	    (atomic_xchg_acquire(&lock->count, 0) == 1))
+	if (__mutex_trylock(lock, false))
 		goto skip_wait;
 
 	debug_mutex_lock_common(lock, &waiter);
@@ -543,26 +662,26 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 	list_add_tail(&waiter.list, &lock->wait_list);
 	waiter.task = task;
 
+	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);
 	for (;;) {
 		/*
-		 * Lets try to take the lock again - this is needed even if
-		 * we get here for the first time (shortly after failing to
-		 * acquire the lock), to make sure that we get a wakeup once
-		 * it's unlocked. Later on, if we sleep, this is the
-		 * operation that gives us the lock. We xchg it to -1, so
-		 * that when we release the lock, we properly wake up the
-		 * other waiters. We only attempt the xchg if the count is
-		 * non-negative in order to avoid unnecessary xchg operations:
+		 * Once we hold wait_lock, we're serialized against
+		 * mutex_unlock() handing the lock off to us, do a trylock
+		 * before testing the error conditions to make sure we pick up
+		 * the handoff.
 		 */
-		if (atomic_read(&lock->count) >= 0 &&
-		    (atomic_xchg_acquire(&lock->count, -1) == 1))
-			break;
+		if (__mutex_trylock(lock, first))
+			goto acquired;
 
 		/*
-		 * got a signal? (This code gets eliminated in the
-		 * TASK_UNINTERRUPTIBLE case.)
+		 * Check for signals and wound conditions while holding
+		 * 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))) {
 			ret = -EINTR;
@@ -575,36 +694,49 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
 				goto err;
 		}
 
-		__set_task_state(task, state);
-
-		/* didn't get the lock, go to sleep: */
 		spin_unlock_mutex(&lock->wait_lock, flags);
 		schedule_preempt_disabled();
+
+		if (!first && __mutex_waiter_is_first(lock, &waiter)) {
+			first = true;
+			__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
+		}
+
+		set_task_state(task, 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))
+			break;
+
 		spin_lock_mutex(&lock->wait_lock, flags);
 	}
+	spin_lock_mutex(&lock->wait_lock, flags);
+acquired:
 	__set_task_state(task, TASK_RUNNING);
 
 	mutex_remove_waiter(lock, &waiter, task);
-	/* set it to 0 if there are no waiters left: */
 	if (likely(list_empty(&lock->wait_list)))
-		atomic_set(&lock->count, 0);
+		__mutex_clear_flag(lock, MUTEX_FLAGS);
+
 	debug_mutex_free_waiter(&waiter);
 
 skip_wait:
 	/* got the lock - cleanup and rejoice! */
 	lock_acquired(&lock->dep_map, ip);
-	mutex_set_owner(lock);
 
-	if (use_ww_ctx) {
-		struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
+	if (use_ww_ctx)
 		ww_mutex_set_context_slowpath(ww, ww_ctx);
-	}
 
 	spin_unlock_mutex(&lock->wait_lock, flags);
 	preempt_enable();
 	return 0;
 
 err:
+	__set_task_state(task, TASK_RUNNING);
 	mutex_remove_waiter(lock, &waiter, task);
 	spin_unlock_mutex(&lock->wait_lock, flags);
 	debug_mutex_free_waiter(&waiter);
@@ -631,7 +763,6 @@ _mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest)
 	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE,
 			    0, nest, _RET_IP_, NULL, 0);
 }
-
 EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock);
 
 int __sched
@@ -650,7 +781,6 @@ mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
 	return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
 				   subclass, NULL, _RET_IP_, NULL, 0);
 }
-
 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
 
 static inline int
@@ -715,54 +845,64 @@ EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible);
 /*
  * Release the lock, slowpath:
  */
-static inline void
-__mutex_unlock_common_slowpath(struct mutex *lock, int nested)
+static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
 {
-	unsigned long flags;
-	WAKE_Q(wake_q);
+	struct task_struct *next = NULL;
+	unsigned long owner, flags;
+	DEFINE_WAKE_Q(wake_q);
+
+	mutex_release(&lock->dep_map, 1, ip);
 
 	/*
-	 * As a performance measurement, release the lock before doing other
-	 * wakeup related duties to follow. This allows other tasks to acquire
-	 * the lock sooner, while still handling cleanups in past unlock calls.
-	 * This can be done as we do not enforce strict equivalence between the
-	 * mutex counter and wait_list.
-	 *
+	 * Release the lock before (potentially) taking the spinlock such that
+	 * other contenders can get on with things ASAP.
 	 *
-	 * Some architectures leave the lock unlocked in the fastpath failure
-	 * case, others need to leave it locked. In the later case we have to
-	 * unlock it here - as the lock counter is currently 0 or negative.
+	 * Except when HANDOFF, in that case we must not clear the owner field,
+	 * but instead set it to the top waiter.
 	 */
-	if (__mutex_slowpath_needs_to_unlock())
-		atomic_set(&lock->count, 1);
+	owner = atomic_long_read(&lock->owner);
+	for (;;) {
+		unsigned long old;
+
+#ifdef CONFIG_DEBUG_MUTEXES
+		DEBUG_LOCKS_WARN_ON(__owner_task(owner) != current);
+#endif
+
+		if (owner & MUTEX_FLAG_HANDOFF)
+			break;
+
+		old = atomic_long_cmpxchg_release(&lock->owner, owner,
+						  __owner_flags(owner));
+		if (old == owner) {
+			if (owner & MUTEX_FLAG_WAITERS)
+				break;
+
+			return;
+		}
+
+		owner = old;
+	}
 
 	spin_lock_mutex(&lock->wait_lock, flags);
-	mutex_release(&lock->dep_map, nested, _RET_IP_);
 	debug_mutex_unlock(lock);
-
 	if (!list_empty(&lock->wait_list)) {
 		/* get the first entry from the wait-list: */
 		struct mutex_waiter *waiter =
-				list_entry(lock->wait_list.next,
-					   struct mutex_waiter, list);
+			list_first_entry(&lock->wait_list,
+					 struct mutex_waiter, list);
+
+		next = waiter->task;
 
 		debug_mutex_wake_waiter(lock, waiter);
-		wake_q_add(&wake_q, waiter->task);
+		wake_q_add(&wake_q, next);
 	}
 
-	spin_unlock_mutex(&lock->wait_lock, flags);
-	wake_up_q(&wake_q);
-}
+	if (owner & MUTEX_FLAG_HANDOFF)
+		__mutex_handoff(lock, next);
 
-/*
- * Release the lock, slowpath:
- */
-__visible void
-__mutex_unlock_slowpath(atomic_t *lock_count)
-{
-	struct mutex *lock = container_of(lock_count, struct mutex, count);
+	spin_unlock_mutex(&lock->wait_lock, flags);
 
-	__mutex_unlock_common_slowpath(lock, 1);
+	wake_up_q(&wake_q);
 }
 
 #ifndef CONFIG_DEBUG_LOCK_ALLOC
@@ -789,38 +929,30 @@ __mutex_lock_interruptible_slowpath(struct mutex *lock);
  */
 int __sched mutex_lock_interruptible(struct mutex *lock)
 {
-	int ret;
-
 	might_sleep();
-	ret =  __mutex_fastpath_lock_retval(&lock->count);
-	if (likely(!ret)) {
-		mutex_set_owner(lock);
+
+	if (__mutex_trylock_fast(lock))
 		return 0;
-	} else
-		return __mutex_lock_interruptible_slowpath(lock);
+
+	return __mutex_lock_interruptible_slowpath(lock);
 }
 
 EXPORT_SYMBOL(mutex_lock_interruptible);
 
 int __sched mutex_lock_killable(struct mutex *lock)
 {
-	int ret;
-
 	might_sleep();
-	ret = __mutex_fastpath_lock_retval(&lock->count);
-	if (likely(!ret)) {
-		mutex_set_owner(lock);
+
+	if (__mutex_trylock_fast(lock))
 		return 0;
-	} else
-		return __mutex_lock_killable_slowpath(lock);
+
+	return __mutex_lock_killable_slowpath(lock);
 }
 EXPORT_SYMBOL(mutex_lock_killable);
 
-__visible void __sched
-__mutex_lock_slowpath(atomic_t *lock_count)
+static noinline void __sched
+__mutex_lock_slowpath(struct mutex *lock)
 {
-	struct mutex *lock = container_of(lock_count, struct mutex, count);
-
 	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0,
 			    NULL, _RET_IP_, NULL, 0);
 }
@@ -856,37 +988,6 @@ __ww_mutex_lock_interruptible_slowpath(struct ww_mutex *lock,
 
 #endif
 
-/*
- * Spinlock based trylock, we take the spinlock and check whether we
- * can get the lock:
- */
-static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
-{
-	struct mutex *lock = container_of(lock_count, struct mutex, count);
-	unsigned long flags;
-	int prev;
-
-	/* No need to trylock if the mutex is locked. */
-	if (mutex_is_locked(lock))
-		return 0;
-
-	spin_lock_mutex(&lock->wait_lock, flags);
-
-	prev = atomic_xchg_acquire(&lock->count, -1);
-	if (likely(prev == 1)) {
-		mutex_set_owner(lock);
-		mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
-	}
-
-	/* Set it back to 0 if there are no waiters: */
-	if (likely(list_empty(&lock->wait_list)))
-		atomic_set(&lock->count, 0);
-
-	spin_unlock_mutex(&lock->wait_lock, flags);
-
-	return prev == 1;
-}
-
 /**
  * mutex_trylock - try to acquire the mutex, without waiting
  * @lock: the mutex to be acquired
@@ -903,13 +1004,12 @@ static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
  */
 int __sched mutex_trylock(struct mutex *lock)
 {
-	int ret;
+	bool locked = __mutex_trylock(lock, false);
 
-	ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath);
-	if (ret)
-		mutex_set_owner(lock);
+	if (locked)
+		mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
 
-	return ret;
+	return locked;
 }
 EXPORT_SYMBOL(mutex_trylock);
 
@@ -917,36 +1017,28 @@ EXPORT_SYMBOL(mutex_trylock);
 int __sched
 __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
-	int ret;
-
 	might_sleep();
 
-	ret = __mutex_fastpath_lock_retval(&lock->base.count);
-
-	if (likely(!ret)) {
+	if (__mutex_trylock_fast(&lock->base)) {
 		ww_mutex_set_context_fastpath(lock, ctx);
-		mutex_set_owner(&lock->base);
-	} else
-		ret = __ww_mutex_lock_slowpath(lock, ctx);
-	return ret;
+		return 0;
+	}
+
+	return __ww_mutex_lock_slowpath(lock, ctx);
 }
 EXPORT_SYMBOL(__ww_mutex_lock);
 
 int __sched
 __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
 {
-	int ret;
-
 	might_sleep();
 
-	ret = __mutex_fastpath_lock_retval(&lock->base.count);
-
-	if (likely(!ret)) {
+	if (__mutex_trylock_fast(&lock->base)) {
 		ww_mutex_set_context_fastpath(lock, ctx);
-		mutex_set_owner(&lock->base);
-	} else
-		ret = __ww_mutex_lock_interruptible_slowpath(lock, ctx);
-	return ret;
+		return 0;
+	}
+
+	return __ww_mutex_lock_interruptible_slowpath(lock, ctx);
 }
 EXPORT_SYMBOL(__ww_mutex_lock_interruptible);