Commit-ID: a1247d06d01045d7ab2882a9c074fbf21137c690
Gitweb: https://git.kernel.org/tip/a1247d06d01045d7ab2882a9c074fbf21137c690
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Tue, 19 Mar 2019 13:18:56 +0100
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 3 Apr 2019 11:42:33 +0200
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@xxxxxxxxxxxxx>
Reported-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Tested-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: ard.biesheuvel@xxxxxxxxxx
Cc: oss-drivers@xxxxxxxxxxxxx
Cc: pbonzini@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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 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();
}
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