On Wed, Jul 26, 2017 at 06:57:59PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgold...@suse.com>
> 
> Set queue flags to QUEUE_FLAG_NOWAIT to indicate REQ_NOWAIT
> will be handled.
> 
> If an I/O on the md will be delayed, it would bail by calling
> bio_wouldblock_error(). The conditions when this could happen are:
> 
>  + MD is suspended
>  + There is a change pending on the SB, and current I/O would
>    block until that is complete.
> 
> Signed-off-by: Goldwyn Rodrigues <rgold...@suse.com>
> ---
>  drivers/md/md.c | 27 +++++++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 8cdca0296749..d96c27d16841 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -285,6 +285,13 @@ static blk_qc_t md_make_request(struct request_queue *q, 
> struct bio *bio)
>               bio_endio(bio);
>               return BLK_QC_T_NONE;
>       }
> +
> +     if (mddev->suspended && (bio->bi_opf & REQ_NOWAIT)) {
> +             bio_wouldblock_error(bio);
> +             rcu_read_unlock();

this unlock is not required.

> +             return BLK_QC_T_NONE;
> +     }
> +
>  check_suspended:
>       rcu_read_lock();
>       if (mddev->suspended) {
> @@ -5274,6 +5281,10 @@ static int md_alloc(dev_t dev, char *name)
>               mddev->queue = NULL;
>               goto abort;
>       }
> +
> +     /* Set the NOWAIT flags to show support */
> +     queue_flag_set_unlocked(QUEUE_FLAG_NOWAIT, mddev->queue);
> +
>       disk->major = MAJOR(mddev->unit);
>       disk->first_minor = unit << shift;
>       if (name)
> @@ -8010,8 +8021,20 @@ bool md_write_start(struct mddev *mddev, struct bio 
> *bi)
>       rcu_read_unlock();
>       if (did_change)
>               sysfs_notify_dirent_safe(mddev->sysfs_state);
> -     wait_event(mddev->sb_wait,
> -                !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags) && 
> !mddev->suspended);
> +
> +     /* Don't wait for sb writes if marked with REQ_NOWAIT */
> +     if (test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags) ||
> +                     mddev->suspended) {
> +             if (bi->bi_opf & REQ_NOWAIT) {
> +                     bio_wouldblock_error(bi);
> +                     percpu_ref_put(&mddev->writes_pending);
> +                     return false;
> +             }
> +
> +             wait_event(mddev->sb_wait,
> +                             !test_bit(MD_SB_CHANGE_PENDING, 
> &mddev->sb_flags) && !mddev->suspended);
> +     }
> +
>       if (test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
>               percpu_ref_put(&mddev->writes_pending);
>               return false;
> -- 
> 2.12.3
> 
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