Re: Lockups with btrfs on 3.16-rc1 - bisected

[Waiman Long <waiman.long@hp.com>]

On 06/18/2014 10:11 PM, Chris Mason wrote:
> On 06/18/2014 10:03 PM, Marc Dionne wrote:
>> On Wed, Jun 18, 2014 at 8:41 PM, Marc Dionne<marc.c.dionne@gmail.com>  wrote:
>>> On Wed, Jun 18, 2014 at 8:08 PM, Waiman Long<waiman.long@hp.com>  wrote:
>>>> On 06/18/2014 08:03 PM, Marc Dionne wrote:
>> And for an additional data point, just removing those
>> CONFIG_DEBUG_LOCK_ALLOC ifdefs looks like it's sufficient to prevent
>> the symptoms when lockdep is not enabled.
> Ok, somehow we've added a lock inversion here that wasn't here before.
> Thanks for confirming, I'll nail it down.
>
> -chris
>

I am pretty sure that the hangup is caused by the following kind of code 
fragment in the locking.c file:

  if (eb->lock_nested) {
                 read_lock(&eb->lock);
                 if (eb->lock_nested && current->pid == eb->lock_owner) {

Is it possible to do the check without taking the read_lock?

-Longman