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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.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Uros Bizjak 2022-07-14 19:32:55 +02:00 committed by Andrew Morton
parent aa06a9bd85
commit 693fc06e98
1 changed files with 1 additions and 1 deletions
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2
fs/eventpoll.c
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@ -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;
/*