locking/mutex: Optimize mutex_trylock() fast-path

[cascardo/linux.git] / include / asm-generic / mutex-xchg.h

diff --git a/include/asm-generic/mutex-xchg.h b/include/asm-generic/mutex-xchg.h
index a6b4a7b..3269ec4 100644 (file)
--- a/include/asm-generic/mutex-xchg.h
+++ b/include/asm-generic/mutex-xchg.h
@@ -91,8 +91,12 @@ __mutex_fastpath_unlock(atomic_t *count, void (*fail_fn)(atomic_t *))
 static inline int
 __mutex_fastpath_trylock(atomic_t *count, int (*fail_fn)(atomic_t *))
 {
-       int prev = atomic_xchg_acquire(count, 0);
+       int prev;
 
+       if (atomic_read(count) != 1)
+               return 0;
+
+       prev = atomic_xchg_acquire(count, 0);
        if (unlikely(prev < 0)) {
                /*
                 * The lock was marked contended so we must restore that