Re: [PATCH] locking/lockdep: Avoid potential access of invalid memory in lock_class

[Waiman Long <longman@redhat.com>]

On 1/3/22 12:47, Bart Van Assche wrote:
> On 1/2/22 18:35, Waiman Long wrote:
>> -    WARN_ON_ONCE(!found);
>> -    __lockdep_free_key_range(pf, key, 1);
>> -    call_rcu_zapped(pf);
>> -    graph_unlock();
>> -out_irq:
>> +    WARN_ON_ONCE(!found && debug_locks);
>
> lockdep_unregister_key() should only be called for a registered key so 
> I'd
> like to keep the WARN_ON_ONCE(!found) here instead of changing it into
> WARN_ON_ONCE(!found && debug_locks). Otherwise this patch looks good 
> to me.

The reason for this change is to handle the case that a 
lockdep_register_key()/lockdep_unregister_key() pair may be called after 
debug_locks is turned off. Without that change, we are going to get the 
warning in lockdep_unregister_key(). That is the motivation of your 
original commit 8b39adbee805 ("locking/lockdep: Make 
lockdep_unregister_key() honor 'debug_locks' again").

Cheers,
Longman