On Tue, May 25 2021 at 5:24P -0400,
Damien Le Moal <damien.lem...@wdc.com> wrote:
> A target map method requesting the requeue of a bio with
> DM_MAPIO_REQUEUE or completing it with DM_ENDIO_REQUEUE can cause
> unaligned write errors if the bio is a write operation targeting a
> sequential zone. If a zoned target request such a requeue, warn about
> it and kill the IO.
>
> The function dm_is_zone_write() is introduced to detect write operations
> to zoned targets.
>
> This change does not affect the target drivers supporting zoned devices
> and exposing a zoned device, namely dm-crypt, dm-linear and dm-flakey as
> none of these targets ever request a requeue.
>
> Signed-off-by: Damien Le Moal <damien.lem...@wdc.com>
> Reviewed-by: Hannes Reinecke <h...@suse.de>
> Reviewed-by: Himanshu Madhani <himanshu.madh...@oracle.com>
> ---
> drivers/md/dm-zone.c | 17 +++++++++++++++++
> drivers/md/dm.c | 18 +++++++++++++++---
> drivers/md/dm.h | 5 +++++
> 3 files changed, 37 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/md/dm-zone.c b/drivers/md/dm-zone.c
> index b42474043249..edc3bbb45637 100644
> --- a/drivers/md/dm-zone.c
> +++ b/drivers/md/dm-zone.c
> @@ -104,6 +104,23 @@ int dm_report_zones(struct block_device *bdev, sector_t
> start, sector_t sector,
> }
> EXPORT_SYMBOL_GPL(dm_report_zones);
>
> +bool dm_is_zone_write(struct mapped_device *md, struct bio *bio)
> +{
> + struct request_queue *q = md->queue;
> +
> + if (!blk_queue_is_zoned(q))
> + return false;
> +
> + switch (bio_op(bio)) {
> + case REQ_OP_WRITE_ZEROES:
> + case REQ_OP_WRITE_SAME:
> + case REQ_OP_WRITE:
> + return !op_is_flush(bio->bi_opf) && bio_sectors(bio);
> + default:
> + return false;
> + }
> +}
> +
> void dm_set_zones_restrictions(struct dm_table *t, struct request_queue *q)
> {
> if (!blk_queue_is_zoned(q))
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index c49976cc4e44..ed8c5a8df2e5 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -846,11 +846,15 @@ static void dec_pending(struct dm_io *io, blk_status_t
> error)
> * Target requested pushing back the I/O.
> */
> spin_lock_irqsave(&md->deferred_lock, flags);
> - if (__noflush_suspending(md))
> + if (__noflush_suspending(md) &&
> + !WARN_ON_ONCE(dm_is_zone_write(md, bio)))
> /* NOTE early return due to BLK_STS_DM_REQUEUE
> below */
> bio_list_add_head(&md->deferred, io->orig_bio);
> else
> - /* noflush suspend was interrupted. */
> + /*
> + * noflush suspend was interrupted or this is
> + * a write to a zoned target.
> + */
> io->status = BLK_STS_IOERR;
> spin_unlock_irqrestore(&md->deferred_lock, flags);
> }
So I now see this incremental fix:
https://patchwork.kernel.org/project/dm-devel/patch/20210604004703.408562-1-damien.lem...@opensource.wdc.com/
And I've folded it in...
> @@ -947,7 +951,15 @@ static void clone_endio(struct bio *bio)
> int r = endio(tio->ti, bio, &error);
> switch (r) {
> case DM_ENDIO_REQUEUE:
> - error = BLK_STS_DM_REQUEUE;
> + /*
> + * Requeuing writes to a sequential zone of a zoned
> + * target will break the sequential write pattern:
> + * fail such IO.
> + */
> + if (WARN_ON_ONCE(dm_is_zone_write(md, bio)))
> + error = BLK_STS_IOERR;
> + else
> + error = BLK_STS_DM_REQUEUE;
> fallthrough;
> case DM_ENDIO_DONE:
> break;
But I'm left wondering why dec_pending, now dm_io_dec_pending, needs
to be modified to also check dm_is_zone_write() if clone_endio() is
already dealing with it?
Not that big a deal, just not loving how we're sprinkling special
zoned code around...
Mike
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