This is a note to let you know that I've just added the patch titled
jump_label: Use atomic_try_cmpxchg() in static_key_slow_inc_cpuslocked()
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
jump_label-use-atomic_try_cmpxchg-in-static_key_slow.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit ee1559a0e746c10261a4b85509174c59bee930db
Author: Uros Bizjak <ubizjak@xxxxxxxxx>
Date: Wed Oct 19 16:08:50 2022 +0200
jump_label: Use atomic_try_cmpxchg() in static_key_slow_inc_cpuslocked()
[ Upstream commit d0c006402e7941558e5283ae434e2847c7999378 ]
Use atomic_try_cmpxchg() instead of atomic_cmpxchg (*ptr, old, new) ==
old in static_key_slow_inc_cpuslocked(). x86 CMPXCHG instruction
returns success in ZF flag, so this change saves a compare after
cmpxchg (and related move instruction in front of cmpxchg).
Also, atomic_try_cmpxchg() implicitly assigns old *ptr value to "old" when
cmpxchg fails, enabling further code simplifications.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20221019140850.3395-1-ubizjak@xxxxxxxxx
Stable-dep-of: 83ab38ef0a0b ("jump_label: Fix concurrency issues in static_key_slow_dec()")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 714ac4c3b556d..4d6c6f5f60db8 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -115,8 +115,6 @@ EXPORT_SYMBOL_GPL(static_key_count);
void static_key_slow_inc_cpuslocked(struct static_key *key)
{
- int v, v1;
-
STATIC_KEY_CHECK_USE(key);
lockdep_assert_cpus_held();
@@ -132,11 +130,9 @@ void static_key_slow_inc_cpuslocked(struct static_key *key)
* so it counts as "enabled" in jump_label_update(). Note that
* atomic_inc_unless_negative() checks >= 0, so roll our own.
*/
- for (v = atomic_read(&key->enabled); v > 0; v = v1) {
- v1 = atomic_cmpxchg(&key->enabled, v, v + 1);
- if (likely(v1 == v))
+ for (int v = atomic_read(&key->enabled); v > 0; )
+ if (likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)))
return;
- }
jump_label_lock();
if (atomic_read(&key->enabled) == 0) {
