mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-11-23 04:04:26 +08:00
jump_label: Fix static_key_slow_dec() yet again
While commit83ab38ef0a
("jump_label: Fix concurrency issues in static_key_slow_dec()") fixed one problem, it created yet another, notably the following is now possible: slow_dec if (try_dec) // dec_not_one-ish, false // enabled == 1 slow_inc if (inc_not_disabled) // inc_not_zero-ish // enabled == 2 return guard((mutex)(&jump_label_mutex); if (atomic_cmpxchg(1,0)==1) // false, we're 2 slow_dec if (try-dec) // dec_not_one, true // enabled == 1 return else try_dec() // dec_not_one, false WARN Use dec_and_test instead of cmpxchg(), like it was prior to83ab38ef0a
. Add a few WARNs for the paranoid. Fixes:83ab38ef0a
("jump_label: Fix concurrency issues in static_key_slow_dec()") Reported-by: "Darrick J. Wong" <djwong@kernel.org> Tested-by: Klara Modin <klarasmodin@gmail.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
This commit is contained in:
parent
fe513c2ef0
commit
1d7f856c2c
@ -168,7 +168,7 @@ bool static_key_slow_inc_cpuslocked(struct static_key *key)
|
||||
jump_label_update(key);
|
||||
/*
|
||||
* Ensure that when static_key_fast_inc_not_disabled() or
|
||||
* static_key_slow_try_dec() observe the positive value,
|
||||
* static_key_dec_not_one() observe the positive value,
|
||||
* they must also observe all the text changes.
|
||||
*/
|
||||
atomic_set_release(&key->enabled, 1);
|
||||
@ -250,7 +250,7 @@ void static_key_disable(struct static_key *key)
|
||||
}
|
||||
EXPORT_SYMBOL_GPL(static_key_disable);
|
||||
|
||||
static bool static_key_slow_try_dec(struct static_key *key)
|
||||
static bool static_key_dec_not_one(struct static_key *key)
|
||||
{
|
||||
int v;
|
||||
|
||||
@ -274,6 +274,14 @@ static bool static_key_slow_try_dec(struct static_key *key)
|
||||
* enabled. This suggests an ordering problem on the user side.
|
||||
*/
|
||||
WARN_ON_ONCE(v < 0);
|
||||
|
||||
/*
|
||||
* Warn about underflow, and lie about success in an attempt to
|
||||
* not make things worse.
|
||||
*/
|
||||
if (WARN_ON_ONCE(v == 0))
|
||||
return true;
|
||||
|
||||
if (v <= 1)
|
||||
return false;
|
||||
} while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v - 1)));
|
||||
@ -284,15 +292,27 @@ static bool static_key_slow_try_dec(struct static_key *key)
|
||||
static void __static_key_slow_dec_cpuslocked(struct static_key *key)
|
||||
{
|
||||
lockdep_assert_cpus_held();
|
||||
int val;
|
||||
|
||||
if (static_key_slow_try_dec(key))
|
||||
if (static_key_dec_not_one(key))
|
||||
return;
|
||||
|
||||
guard(mutex)(&jump_label_mutex);
|
||||
if (atomic_cmpxchg(&key->enabled, 1, 0) == 1)
|
||||
val = atomic_read(&key->enabled);
|
||||
/*
|
||||
* It should be impossible to observe -1 with jump_label_mutex held,
|
||||
* see static_key_slow_inc_cpuslocked().
|
||||
*/
|
||||
if (WARN_ON_ONCE(val == -1))
|
||||
return;
|
||||
/*
|
||||
* Cannot already be 0, something went sideways.
|
||||
*/
|
||||
if (WARN_ON_ONCE(val == 0))
|
||||
return;
|
||||
|
||||
if (atomic_dec_and_test(&key->enabled))
|
||||
jump_label_update(key);
|
||||
else
|
||||
WARN_ON_ONCE(!static_key_slow_try_dec(key));
|
||||
}
|
||||
|
||||
static void __static_key_slow_dec(struct static_key *key)
|
||||
@ -329,7 +349,7 @@ void __static_key_slow_dec_deferred(struct static_key *key,
|
||||
{
|
||||
STATIC_KEY_CHECK_USE(key);
|
||||
|
||||
if (static_key_slow_try_dec(key))
|
||||
if (static_key_dec_not_one(key))
|
||||
return;
|
||||
|
||||
schedule_delayed_work(work, timeout);
|
||||
|
Loading…
Reference in New Issue
Block a user