epoll: use try_cmpxchg in list_add_tail_lockless

Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
list_add_tail_lockless.  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.

Link: https://lkml.kernel.org/r/20220714173255.12987-1-ubizjak@gmail.comSigned-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/eventpoll.c

@@ -1065,7 +1065,7 @@ static inline bool list_add_tail_lockless(struct list_head *new,
 	 * added to the list from another CPU: the winner observes
 	 * new->next == new.
 	 */
-	if (cmpxchg(&new->next, new, head) != new)
+	if (!try_cmpxchg(&new->next, &new, head))
 		return false;
 
 	/*