Re: [PATCH 18/20] block: refator submit_bio_noacct

[Naresh Kamboju <naresh.kamboju@linaro.org>]

On Thu, 2 Jul 2020 at 20:45, Christoph Hellwig <hch@lst.de> wrote:
>
> On Thu, Jul 02, 2020 at 10:10:10AM -0400, Qian Cai wrote:
> > On Mon, Jun 29, 2020 at 09:39:45PM +0200, Christoph Hellwig wrote:
> > > Split out a __submit_bio_noacct helper for the actual de-recursion
> > > algorithm, and simplify the loop by using a continue when we can't
> > > enter the queue for a bio.
> > >
> > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> >
> > Reverting this commit and its dependencies,
> >
> > 5a6c35f9af41 block: remove direct_make_request
> > ff93ea0ce763 block: shortcut __submit_bio_noacct for blk-mq drivers
> >
> > fixed the stack-out-of-bounds during boot,
> >
> > https://lore.kernel.org/linux-block/000000000000bcdeaa05a97280e4@google.com/
>
> Yikes.  bio_alloc_bioset pokes into bio_list[1] in a totally
> undocumented way.  But even with that the problem should only show
> up with "block: shortcut __submit_bio_noacct for blk-mq drivers".
>
> Can you try this patch?

Applied your patch on top of linux-next 20200702 and tested on
arm64 and x86_64 devices and the reported BUG fixed.

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>

>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index bf882b8d84450c..9f1bf8658b611a 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1155,11 +1155,10 @@ static blk_qc_t __submit_bio_noacct(struct bio *bio)
>  static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
>  {
>         struct gendisk *disk = bio->bi_disk;
> -       struct bio_list bio_list;
> +       struct bio_list bio_list[2] = { };
>         blk_qc_t ret = BLK_QC_T_NONE;
>
> -       bio_list_init(&bio_list);
> -       current->bio_list = &bio_list;
> +       current->bio_list = bio_list;
>
>         do {
>                 WARN_ON_ONCE(bio->bi_disk != disk);
> @@ -1174,7 +1173,7 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
>                 }
>
>                 ret = blk_mq_submit_bio(bio);
> -       } while ((bio = bio_list_pop(&bio_list)));
> +       } while ((bio = bio_list_pop(&bio_list[0])));
>
>         current->bio_list = NULL;
>         return ret;

ref:
https://lkft.validation.linaro.org/scheduler/job/1538359#L288
https://lkft.validation.linaro.org/scheduler/job/1538360#L572


- Naresh
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