2 files changed, 26 insertions, 3 deletions

diff --git a/arch/x86/include/asm/mutex.h b/arch/x86/include/asm/mutex.h
index 7d3a48275394..bc2a0b0dcea6 100644
--- a/arch/x86/include/asm/mutex.h
+++ b/arch/x86/include/asm/mutex.h
@@ -3,3 +3,13 @@
 #else
 # include <asm/mutex_64.h>
 #endif
+
+#ifndef __ASM_MUTEX_H
+#define __ASM_MUTEX_H
+/*
+ * For the x86 architecture, it allows any negative number (besides -1) in
+ * the mutex count to indicate that some other threads are waiting on the
+ * mutex.
+ */
+#define __ARCH_ALLOW_ANY_NEGATIVE_MUTEX_COUNT   1
+#endif
diff --git a/kernel/mutex.c b/kernel/mutex.c
index 262d7177adad..70ebd855d9e8 100644
--- a/kernel/mutex.c
+++ b/kernel/mutex.c
@@ -37,6 +37,17 @@
 # include <asm/mutex.h>
 #endif
 
+/*
+ * A mutex count of -1 indicates that waiters are sleeping waiting for the
+ * mutex. Some architectures can allow any negative number, not just -1, for
+ * this purpose.
+ */
+#ifdef __ARCH_ALLOW_ANY_NEGATIVE_MUTEX_COUNT
+#define MUTEX_SHOW_NO_WAITER(mutex)     (atomic_read(&(mutex)->count) >= 0)
+#else
+#define MUTEX_SHOW_NO_WAITER(mutex)     (atomic_read(&(mutex)->count) != -1)
+#endif
+
 void
 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
 {
@@ -217,7 +228,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                 if (owner && !mutex_spin_on_owner(lock, owner))
                         break;
 
-                if (atomic_cmpxchg(&lock->count, 1, 0) == 1) {
+                if ((atomic_read(&lock->count) == 1) &&
+                    (atomic_cmpxchg(&lock->count, 1, 0) == 1)) {
                         lock_acquired(&lock->dep_map, ip);
                         mutex_set_owner(lock);
                         preempt_enable();
@@ -251,7 +263,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
         list_add_tail(&waiter.list, &lock->wait_list);
         waiter.task = task;
 
-        if (atomic_xchg(&lock->count, -1) == 1)
+        if (MUTEX_SHOW_NO_WAITER(lock) && (atomic_xchg(&lock->count, -1) == 1))
                 goto done;
 
         lock_contended(&lock->dep_map, ip);
@@ -266,7 +278,8 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
                  * that when we release the lock, we properly wake up the
                  * other waiters:
                  */
-                if (atomic_xchg(&lock->count, -1) == 1)
+                if (MUTEX_SHOW_NO_WAITER(lock) &&
+                   (atomic_xchg(&lock->count, -1) == 1))
                         break;
 
                 /*