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authorPeter Zijlstra <peterz@infradead.org>2019-03-19 13:18:56 +0100
committerIngo Molnar <mingo@kernel.org>2019-04-03 11:42:33 +0200
commita1247d06d01045d7ab2882a9c074fbf21137c690 (patch)
treede30aa6f8d6a1f35a5bf17932d0ea5fe1c598c62
parent5e7a8ca319268a70a6c7c3c1fde5bea38e1e5539 (diff)
downloadlinux-a1247d06d01045d7ab2882a9c074fbf21137c690.tar.bz2
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>
-rw-r--r--kernel/jump_label.c21
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();
}