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authorUros Bizjak <ubizjak@gmail.com>2022-10-19 16:08:50 +0200
committerPeter Zijlstra <peterz@infradead.org>2022-10-27 10:35:41 +0200
commitd0c006402e7941558e5283ae434e2847c7999378 (patch)
treeb55cbec0a50b075fd546c6713d83d65f8b67d290 /kernel/jump_label.c
parent247f34f7b80357943234f93f247a1ae6b6c3a740 (diff)
jump_label: Use atomic_try_cmpxchg() in static_key_slow_inc_cpuslocked()
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@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20221019140850.3395-1-ubizjak@gmail.com
Diffstat (limited to 'kernel/jump_label.c')
-rw-r--r--kernel/jump_label.c8
1 files changed, 2 insertions, 6 deletions
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 714ac4c3b556..4d6c6f5f60db 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) {