unimore/kernel-hacking-2024-linux-steffo
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jump_label: Simplify and clarify static_key_fast_inc_cpus_locked()

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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
This commit is contained in:
Thomas Gleixner 2024-06-10 14:46:39 +02:00 committed by Peter Zijlstra
parent 695ef79646
commit 9bc2ff871f
1 changed files with 11 additions and 9 deletions
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20
kernel/jump_label.c
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@ -162,22 +162,24 @@ bool static_key_slow_inc_cpuslocked(struct static_key *key)
if (static_key_fast_inc_not_disabled(key))
return true;
jump_label_lock();
if (atomic_read(&key->enabled) == 0) {
atomic_set(&key->enabled, -1);
guard(mutex)(&jump_label_mutex);
/* Try to mark it as 'enabling in progress. */
if (!atomic_cmpxchg(&key->enabled, 0, -1)) {
jump_label_update(key);
/*
* Ensure that if the above cmpxchg loop observes our positive
* value, it must also observe all the text changes.
* Ensure that when static_key_fast_inc_not_disabled() or
* static_key_slow_try_dec() observe the positive value,
* they must also observe all the text changes.
*/
atomic_set_release(&key->enabled, 1);
} 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;
}
}
jump_label_unlock();
return true;
}