On Dec 03, 2021 / 20:07, Ming Lei wrote:
> Hi Shinichiro,
>
> On Fri, Dec 03, 2021 at 10:01:33AM +0000, Shinichiro Kawasaki wrote:
> > On Dec 03, 2021 / 10:39, Ming Lei wrote:
> > > There isn't any reason to not allow zero poll queues from user
> > > viewpoint.
> > >
> > > Also sometimes we need to compare io poll between poll mode and irq
> > > mode, so not allowing poll queues is bad.
> > >
> > > Fixes: 15dfc662ef31 ("null_blk: Fix handling of submit_queues and poll_queues attributes")
> > > Cc: Shin'ichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
> > > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> >
> > Hi Ming,
> >
> > It is good to know that the zero poll queues is useful. Having said that, I
> > observe zero division error [1] with your patch and the commands below. Don' we
> > need some more code changes to avoid the error?
> >
> > # modprobe null_blk
> > # cd /sys/kernel/config/nullb
> > # mkdir test
> > # echo 0 > test/poll_queues
> > # echo 1 > test/power
> > Segmentation fault
>
> I guess the following change may fix the error:
>
> diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
> index 20534a2daf17..96c55d06401d 100644
> --- a/drivers/block/null_blk/main.c
> +++ b/drivers/block/null_blk/main.c
> @@ -1892,7 +1892,7 @@ static int null_init_tag_set(struct nullb *nullb, struct blk_mq_tag_set *set)
> if (g_shared_tag_bitmap)
> set->flags |= BLK_MQ_F_TAG_HCTX_SHARED;
> set->driver_data = nullb;
> - if (g_poll_queues)
> + if (poll_queues)
> set->nr_maps = 3;
> else
> set->nr_maps = 1;
>
Yes, I confirmed that this change avoids the error. Thank you!
--
Best Regards,
Shin'ichiro Kawasaki
