[ Upstream commit a1247d06d01045d7ab2882a9c074fbf21137c690 ]
Even though the atomic_dec_and_mutex_lock() in __static_key_slow_dec_cpuslocked() can never see a negative value in key->enabled the subsequent sanity check is re-reading key->enabled, which may have been set to -1 in the meantime by static_key_slow_inc_cpuslocked().
CPU A CPU B
__static_key_slow_dec_cpuslocked(): static_key_slow_inc_cpuslocked(): # enabled = 1 atomic_dec_and_mutex_lock() # enabled = 0 atomic_read() == 0 atomic_set(-1) # enabled = -1 val = atomic_read() # Oops - val == -1!
The test case is TCP's clean_acked_data_enable() / clean_acked_data_disable() as tickled by KTLS (net/ktls).
Suggested-by: Jakub Kicinski jakub.kicinski@netronome.com Reported-by: Jakub Kicinski jakub.kicinski@netronome.com Tested-by: Jakub Kicinski jakub.kicinski@netronome.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Paul E. McKenney paulmck@linux.vnet.ibm.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Will Deacon will.deacon@arm.com Cc: ard.biesheuvel@linaro.org Cc: oss-drivers@netronome.com Cc: pbonzini@redhat.com Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/jump_label.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-)
diff --git a/kernel/jump_label.c b/kernel/jump_label.c index bad96b476eb6e..a799b1ac6b2fe 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -206,6 +206,8 @@ static void __static_key_slow_dec_cpuslocked(struct static_key *key, unsigned long rate_limit, struct delayed_work *work) { + int val; + lockdep_assert_cpus_held();
/* @@ -215,17 +217,20 @@ static void __static_key_slow_dec_cpuslocked(struct static_key *key, * returns is unbalanced, because all other static_key_slow_inc() * instances block while the update is in progress. */ - if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex)) { - WARN(atomic_read(&key->enabled) < 0, - "jump label: negative count!\n"); + val = atomic_fetch_add_unless(&key->enabled, -1, 1); + if (val != 1) { + WARN(val < 0, "jump label: negative count!\n"); return; }
- if (rate_limit) { - atomic_inc(&key->enabled); - schedule_delayed_work(work, rate_limit); - } else { - jump_label_update(key); + jump_label_lock(); + if (atomic_dec_and_test(&key->enabled)) { + if (rate_limit) { + atomic_inc(&key->enabled); + schedule_delayed_work(work, rate_limit); + } else { + jump_label_update(key); + } } jump_label_unlock(); }