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jump_label: Clarify condition in static_key_fast_inc_not_disabled()

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The second part of

      if (v <= 0 || (v + 1) < 0)

is not immediately obvious that it acts as overflow protection.

Check explicitely for v == INT_MAX instead and add a proper comment how
this is used at the call sites.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20240610124406.484973160@linutronix.de
This commit is contained in:
Thomas Gleixner 2024-06-10 14:46:37 +02:00 committed by Peter Zijlstra
parent 83ab38ef0a
commit 695ef79646
1 changed files with 6 additions and 3 deletions
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9
kernel/jump_label.c
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@ -132,12 +132,15 @@ bool static_key_fast_inc_not_disabled(struct static_key *key)
/*
* Negative key->enabled has a special meaning: it sends
* static_key_slow_inc/dec() down the slow path, and it is non-zero
* so it counts as "enabled" in jump_label_update(). Note that
* atomic_inc_unless_negative() checks >= 0, so roll our own.
* so it counts as "enabled" in jump_label_update().
*
* The INT_MAX overflow condition is either used by the networking
* code to reset or detected in the slow path of
* static_key_slow_inc_cpuslocked().
*/
v = atomic_read(&key->enabled);
do {
if (v <= 0 || (v + 1) < 0)
if (v <= 0 || v == INT_MAX)
return false;
} while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)));