6.1-stable review patch. If anyone has any objections, please let me know.
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From: Uros Bizjak ubizjak@gmail.com
[ Upstream commit d0c006402e7941558e5283ae434e2847c7999378 ]
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 Stable-dep-of: 83ab38ef0a0b ("jump_label: Fix concurrency issues in static_key_slow_dec()") Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/jump_label.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/kernel/jump_label.c b/kernel/jump_label.c index 714ac4c3b556d..4d6c6f5f60db8 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) {