Re: [PATCH] md: add support for REQ_NOWAIT

[Song Liu <song@xxxxxxxxxx>]

On Mon, Nov 1, 2021 at 2:52 PM Vishal Verma <vverma@xxxxxxxxxxxxxxxx> wrote:
>
> commit 021a24460dc2 ("block: add QUEUE_FLAG_NOWAIT") added support
> for checking whether a given bdev supports handling of REQ_NOWAIT or not.
> Since then commit 6abc49468eea ("dm: add support for REQ_NOWAIT and enable
> it for linear target") added support for REQ_NOWAIT for dm. This uses
> a similar approach to incorporate REQ_NOWAIT for md based bios.
>
> Signed-off-by: Vishal Verma <vverma@xxxxxxxxxxxxxxxx>
> ---
>  drivers/md/md.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 5111ed966947..51b2df32aed5 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -419,6 +419,12 @@ void md_handle_request(struct mddev *mddev, struct bio *bio)
>         if (is_suspended(mddev, bio)) {
>                 DEFINE_WAIT(__wait);
>                 for (;;) {
> +                       /* Bail out if REQ_NOWAIT is set for the bio */
> +                       if (bio->bi_opf & REQ_NOWAIT) {
> +                               bio_wouldblock_error(bio);
> +                               break;

This doesn't look right to me. We already run bio_endio() in
bio_wouldblock_error(), then we still feed the bio to make_request().
Did I misread the logic?

Please also explain how this patch was tested.

Thanks,
Song

> +                       }
> +
>                         prepare_to_wait(&mddev->sb_wait, &__wait,
>                                         TASK_UNINTERRUPTIBLE);
>                         if (!is_suspended(mddev, bio))


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