6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Thomas Gleixner <tglx@xxxxxxxxxxxxx> [ Upstream commit 9bc2ff871f00437ad2f10c1eceff51aaa72b478f ] Make the code more obvious and add proper comments to avoid future head scratching. Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20240610124406.548322963@xxxxxxxxxxxxx Stable-dep-of: 1d7f856c2ca4 ("jump_label: Fix static_key_slow_dec() yet again") Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> --- kernel/jump_label.c | 20 +++++++++++--------- 1 file changed, 11 insertions(+), 9 deletions(-) diff --git a/kernel/jump_label.c b/kernel/jump_label.c index 1ed269b2c4035..7374053bbe049 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -159,22 +159,24 @@ 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; } -- 2.43.0
