[PATCH] kexec: Use atomic_try_cmpxchg_acquire() in kexec_trylock()

[Uros Bizjak]

Use atomic_try_cmpxchg_acquire(*ptr, &old, new) instead of
atomic_cmpxchg_acquire(*ptr, old, new) == old in kexec_trylock().
x86 CMPXCHG instruction returns success in ZF flag, so
this change saves a compare after cmpxchg.

Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
---
 kernel/kexec_internal.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/kexec_internal.h b/kernel/kexec_internal.h
index 2595defe8c0d..d35d9792402d 100644
--- a/kernel/kexec_internal.h
+++ b/kernel/kexec_internal.h
@@ -23,7 +23,8 @@ int kimage_is_destination_range(struct kimage *image,
 extern atomic_t __kexec_lock;
 static inline bool kexec_trylock(void)
 {
-	return atomic_cmpxchg_acquire(&__kexec_lock, 0, 1) == 0;
+	int old = 0;
+	return atomic_try_cmpxchg_acquire(&__kexec_lock, &old, 1);
 }
 static inline void kexec_unlock(void)
 {
-- 
2.42.0