Re: [PATCH] zbd: Restore check_swd()

[Jens Axboe <axboe@kernel.dk>]

On 9/28/18 2:25 PM, Bart Van Assche wrote:
> On Fri, 2018-09-28 at 08:54 -0600, Jens Axboe wrote:
>> +	for (z = zb; z < ze; z++) {
>> +		pthread_mutex_lock(&z->mutex);
>> +		swd += z->wp - z->start;
>> +	}
>> +	pthread_mutex_lock(&f->zbd_info->mutex);
>>
>> Can 'z' ever end up being f->zbd_info? That would surely explain the
>> deadlock.
> 
> Hi Jens,
> 
> f->zbd_info and z have a different type so unless something very weird is going
> on &z->mutex can't be identical to &f->zbd_info->mutex.

Obviously I didn't look too closely :-)

> What I think is going on is traditional lock inversion: check_swd() triggers
> lock inversion if it is called while any of the z->mutex objects are held. One
> such mutex is held where Damien tried to restore the calls of this function. I
> will submit a patch that inserts these calls elsewhere.

That makes sense.

-- 
Jens Axboe