Hi,
On Thu, 19 Apr 2018, Sebastian Ott wrote:
> Since commit 1d9bd5161ba3 ("blk-mq: replace timeout synchronization with a
> RCU and generation based scheme") I observe lockdep complaints (full
> message attached):
>
> [ 21.763369] CPU0 CPU1
> [ 21.763370] ---- ----
> [ 21.763371] lock(&rq->gstate_seq);
> [ 21.763374] local_irq_disable();
> [ 21.763375] lock(&(&dq->lock)->rlock);
> [ 21.763377] lock(&rq->gstate_seq);
> [ 21.763379] <Interrupt>
> [ 21.763380] lock(&(&dq->lock)->rlock);
> [ 21.763382]
> *** DEADLOCK ***
>
>
> This only happens in combination with DASD (s390 specific) and another
> blk-mq driver (scsi, null_blk). The distinctive behavior of DASD is that
> it calls blk_mq_start_request with irqs disabled.
>
> This is a false positive since gstate_seq on CPU0 is from a different
> request queue / block driver than gstate_seq on CPU1.
>
> Possible fixes are to use local_irq_save/restore in blk_mq_start_request.
> Or, since it's a false positive, teach lockdep that these are different
> locks - like below:
Something we can do here? I've send 2 proposals to address this. Do they
make sense?
Regards,
Sebastian
