Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old
in get_acl. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
---
 fs/posix_acl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index d7bc81fc0840..420c689e1bec 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -174,7 +174,7 @@ static struct posix_acl *__get_acl(struct user_namespace *mnt_userns,
 	 * Cache the result, but only if our sentinel is still in place.
 	 */
 	posix_acl_dup(acl);
-	if (unlikely(cmpxchg(p, sentinel, acl) != sentinel))
+	if (unlikely(!try_cmpxchg(p, &sentinel, acl)))
 		posix_acl_release(acl);
 	return acl;
 }
-- 
2.38.1

On Wed, Dec 21, 2022 at 08:35:40PM +0100, Uros Bizjak wrote:
> Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old
> in get_acl. x86 CMPXCHG instruction returns success in ZF flag,
> so this change saves a compare after cmpxchg (and related move
> instruction in front of cmpxchg).
> 
> No functional change intended.
> 
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> ---

Looks ok to me. But it's not urgent so I'll circle back to this post
-rc1.

Thanks!
Christian

On Fri, Dec 23, 2022 at 11:47:24AM +0100, Christian Brauner wrote:
> On Wed, Dec 21, 2022 at 08:35:40PM +0100, Uros Bizjak wrote:
> > Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old
> > in get_acl. x86 CMPXCHG instruction returns success in ZF flag,
> > so this change saves a compare after cmpxchg (and related move
> > instruction in front of cmpxchg).
> > 
> > No functional change intended.
> > 
> > Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
> > Cc: Christian Brauner <brauner@kernel.org>
> > Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> > ---
> 
> Looks ok to me. But it's not urgent so I'll circle back to this post
> -rc1.

Seems good to me. So if there are no objectsions, then applied, thanks!

[1/1] posix_acl: Use try_cmpxchg in get_acl
      commit: 4e1da8fe031303599e78f88e0dad9f44272e4f99