On Wed, Jul 26, 2017 at 06:57:59PM -0500, Goldwyn Rodrigues wrote:
> From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
>
> 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 <rgoldwyn@xxxxxxxx>
> ---
> 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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