Re: [dm-devel] dm-rq: don't queue request during suspend

[Ming Lei <ming.lei@redhat.com>]

On Wed, Oct 06, 2021 at 10:15:58AM -0400, Mike Snitzer wrote:
> On Thu, Sep 23 2021 at  5:11P -0400,
> Ming Lei <ming.lei@redhat.com> wrote:
> 
> > DM uses blk-mq's quiesce/unquiesce to stop/start device mapper queue.
> > 
> > But blk-mq's unquiesce may come from outside events, such as elevator
> > switch, updating nr_requests or others, and request may come during
> > suspend, so simply ask for blk-mq to requeue it.
> > 
> > Fixes one kernel panic issue when running updating nr_requests and
> > dm-mpath suspend/resume stress test.
> > 
> > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > ---
> >  drivers/md/dm-rq.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
> > index 5b95eea517d1..a896dea9750e 100644
> > --- a/drivers/md/dm-rq.c
> > +++ b/drivers/md/dm-rq.c
> > @@ -490,6 +490,14 @@ static blk_status_t dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
> >  	struct mapped_device *md = tio->md;
> >  	struct dm_target *ti = md->immutable_target;
> >  
> > +	/*
> > +	 * blk-mq's unquiesce may come from outside events, such as
> > +	 * elevator switch, updating nr_requests or others, and request may
> > +	 * come during suspend, so simply ask for blk-mq to requeue it.
> > +	 */
> > +	if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)))
> > +		return BLK_STS_RESOURCE;
> > +
> >  	if (unlikely(!ti)) {
> >  		int srcu_idx;
> >  		struct dm_table *map = dm_get_live_table(md, &srcu_idx);
> > -- 
> > 2.31.1
> > 
> 
> Hey Ming,
> 
> I've marked this for stable@ and queued this up.  BUT this test is
> racey, could easily be that device gets suspended just after your
> test.

Hello Mike,

I understand the device shouldn't be suspended after the test given
it is just like the following two tasks running contiguously in the
test:

1) task1
- suspend device mapper
- resume device mapper

2) task2
- updating nr_requests of the device mapper

BTW, it is reported as RH BZ1891486 in which it is easily reproduced,
however, seems device suspended isn't observed.

thanks, 
Ming

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