Re: [dm-devel] [PATCH v4 08/11] dm: Forbid requeue of writes to zones

[Himanshu Madhani <himanshu.madhani@oracle.com>]

On 5/24/21 9:25 PM, Damien Le Moal 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.lemoal@wdc.com>
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> ---
>   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 45d2dc2ee844..4426019a89cc 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);
>   		}
> @@ -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;
> diff --git a/drivers/md/dm.h b/drivers/md/dm.h
> index fdf1536a4b62..39c243258e24 100644
> --- a/drivers/md/dm.h
> +++ b/drivers/md/dm.h
> @@ -107,8 +107,13 @@ void dm_set_zones_restrictions(struct dm_table *t, struct request_queue *q);
>   #ifdef CONFIG_BLK_DEV_ZONED
>   int dm_blk_report_zones(struct gendisk *disk, sector_t sector,
>   			unsigned int nr_zones, report_zones_cb cb, void *data);
> +bool dm_is_zone_write(struct mapped_device *md, struct bio *bio);
>   #else
>   #define dm_blk_report_zones	NULL
> +static inline bool dm_is_zone_write(struct mapped_device *md, struct bio *bio)
> +{
> +	return false;
> +}
>   #endif
>   
>   /*-----------------------------------------------------------------
> 

Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>

-- 
Himanshu Madhani                                Oracle Linux Engineering

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