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jump_label: Simplify and clarify static_key_fast_inc_cpus_locked()

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[ Upstream commit 9bc2ff871f ]

Make the code more obvious and add proper comments to avoid future head
scratching.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20240610124406.548322963@linutronix.de
Stable-dep-of: 1d7f856c2c ("jump_label: Fix static_key_slow_dec() yet again")
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Thomas Gleixner 2024-06-10 14:46:39 +02:00 committed by Greg Kroah-Hartman
parent e67534bd31
commit 33f3e83227
1 changed files with 11 additions and 9 deletions
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20
kernel/jump_label.c
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@ -159,22 +159,24 @@ bool static_key_slow_inc_cpuslocked(struct static_key *key)
if (static_key_fast_inc_not_disabled(key)) if (static_key_fast_inc_not_disabled(key))
return true; return true;
jump_label_lock(); guard(mutex)(&jump_label_mutex);
if (atomic_read(&key->enabled) == 0) { /* Try to mark it as 'enabling in progress. */
atomic_set(&key->enabled, -1); if (!atomic_cmpxchg(&key->enabled, 0, -1)) {
jump_label_update(key); jump_label_update(key);
/* /*
* Ensure that if the above cmpxchg loop observes our positive * Ensure that when static_key_fast_inc_not_disabled() or
* value, it must also observe all the text changes. * static_key_slow_try_dec() observe the positive value,
* they must also observe all the text changes.
*/ */
atomic_set_release(&key->enabled, 1); atomic_set_release(&key->enabled, 1);
} else { } else {
if (WARN_ON_ONCE(!static_key_fast_inc_not_disabled(key))) { /*
jump_label_unlock(); * While holding the mutex this should never observe
* anything else than a value >= 1 and succeed
*/
if (WARN_ON_ONCE(!static_key_fast_inc_not_disabled(key)))
return false; return false;
}
} }
jump_label_unlock();
return true; return true;
} }