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author | Peter Zijlstra <peterz@infradead.org> | 2019-03-19 13:18:56 +0100 |
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committer | Ingo Molnar <mingo@kernel.org> | 2019-04-03 11:42:33 +0200 |
commit | a1247d06d01045d7ab2882a9c074fbf21137c690 (patch) | |
tree | de30aa6f8d6a1f35a5bf17932d0ea5fe1c598c62 /kernel/jump_label.c | |
parent | 5e7a8ca319268a70a6c7c3c1fde5bea38e1e5539 (diff) | |
download | linux-a1247d06d01045d7ab2882a9c074fbf21137c690.tar.gz |
locking/static_key: Fix false positive warnings on concurrent dec/inc
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>
Diffstat (limited to 'kernel/jump_label.c')
-rw-r--r-- | kernel/jump_label.c | 21 |
1 files changed, 13 insertions, 8 deletions
diff --git a/kernel/jump_label.c b/kernel/jump_label.c index bad96b476eb6..a799b1ac6b2f 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(); } |