On Wed, Mar 26, 2025 at 02:26:53PM -0400, Waiman Long wrote:
On 3/26/25 2:08 PM, Boqun Feng wrote:
Currently, when a lock class is allocated, nr_unused_locks will be increased by 1, until it gets used: nr_unused_locks will be decreased by 1 in mark_lock(). However, one scenario is missed: a lock class may be zapped without even being used once. This could result into a situation that nr_unused_locks != 0 but no unused lock class is active in the system, and when `cat /proc/lockdep_stats`, a WARN_ON() will be triggered in a CONFIG_DEBUG_LOCKDEP=y kernel:
[...] DEBUG_LOCKS_WARN_ON(debug_atomic_read(nr_unused_locks) != nr_unused) [...] WARNING: CPU: 41 PID: 1121 at kernel/locking/lockdep_proc.c:283 lockdep_stats_show+0xba9/0xbd0
And as a result, lockdep will be disabled after this.
Therefore, nr_unused_locks needs to be accounted correctly at zap_class() time.
Cc: stable@vger.kernel.org Signee-off-by: Boqun Feng boqun.feng@gmail.com
Typo: "Signee-off-by"?
Oops, yeah.
Other than that, LGTM
Reviewed-by: Waiman Long longman@redhat.com
Thanks!
Regards, Boqun
kernel/locking/lockdep.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index b15757e63626..686546d52337 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -6264,6 +6264,9 @@ static void zap_class(struct pending_free *pf, struct lock_class *class) hlist_del_rcu(&class->hash_entry); WRITE_ONCE(class->key, NULL); WRITE_ONCE(class->name, NULL);
/* class allocated but not used, -1 in nr_unused_locks */if (class->usage_mask == 0)debug_atomic_dec(nr_unused_locks);