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

[Mike Snitzer]

On Thu, Sep 23 2021 at  5:11P -0400,
Ming Lei <ming.lei at 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 at 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.

Mike