[PATCH 2/2][SRU][ARTFUL] block: cope with WRITE ZEROES failing in blkdev_issue_zeroout()

[Kleber Souza]

On 11/21/17 18:05, Colin King wrote:
> From: Ilya Dryomov <idryomov at gmail.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1726818
> 
> sd_config_write_same() ignores ->max_ws_blocks == 0 and resets it to
> permit trying WRITE SAME on older SCSI devices, unless ->no_write_same
> is set.  Because REQ_OP_WRITE_ZEROES is implemented in terms of WRITE
> SAME, blkdev_issue_zeroout() may fail with -EREMOTEIO:
> 
>   $ fallocate -zn -l 1k /dev/sdg
>   fallocate: fallocate failed: Remote I/O error
>   $ fallocate -zn -l 1k /dev/sdg  # OK
>   $ fallocate -zn -l 1k /dev/sdg  # OK
> 
> The following calls succeed because sd_done() sets ->no_write_same in
> response to a sense that would become BLK_STS_TARGET/-EREMOTEIO, causing
> __blkdev_issue_zeroout() to fall back to generating ZERO_PAGE bios.
> 
> This means blkdev_issue_zeroout() must cope with WRITE ZEROES failing
> and fall back to manually zeroing, unless BLKDEV_ZERO_NOFALLBACK is
> specified.  For BLKDEV_ZERO_NOFALLBACK case, return -EOPNOTSUPP if
> sd_done() has just set ->no_write_same thus indicating lack of offload
> support.
> 
> Fixes: c20cfc27a473 ("block: stop using blkdev_issue_write_same for zeroing")
> Cc: Hannes Reinecke <hare at suse.com>
> Reviewed-by: Christoph Hellwig <hch at lst.de>
> Reviewed-by: Martin K. Petersen <martin.petersen at oracle.com>
> Signed-off-by: Ilya Dryomov <idryomov at gmail.com>
> Signed-off-by: Jens Axboe <axboe at kernel.dk>

Hi Colin,

This patch is missing the "backported/cherry picked from" tag and your SOB.

The first patch of the series has you as the author, but mainline commit
425a4dba7953e35ffd096771973add6d2f40d2ed has "Ilya Dryomov
<idryomov at gmail.com>" as author. This we can fix when applying the
patch, but the SOB for the second one needs to come from you.

Thanks,
Kleber

> ---
>  block/blk-lib.c | 45 +++++++++++++++++++++++++++++++++++----------
>  1 file changed, 35 insertions(+), 10 deletions(-)
> 
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 4ef942c..595517c 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -321,12 +321,6 @@ static int __blkdev_issue_zero_pages(struct block_device *bdev,
>   *  Zero-fill a block range, either using hardware offload or by explicitly
>   *  writing zeroes to the device.
>   *
> - *  Note that this function may fail with -EOPNOTSUPP if the driver signals
> - *  zeroing offload support, but the device fails to process the command (for
> - *  some devices there is no non-destructive way to verify whether this
> - *  operation is actually supported).  In this case the caller should call
> - *  retry the call to blkdev_issue_zeroout() and the fallback path will be used.
> - *
>   *  If a device is using logical block provisioning, the underlying space will
>   *  not be released if %flags contains BLKDEV_ZERO_NOUNMAP.
>   *
> @@ -370,18 +364,49 @@ EXPORT_SYMBOL(__blkdev_issue_zeroout);
>  int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
>  		sector_t nr_sects, gfp_t gfp_mask, unsigned flags)
>  {
> -	int ret;
> -	struct bio *bio = NULL;
> +	int ret = 0;
> +	sector_t bs_mask;
> +	struct bio *bio;
>  	struct blk_plug plug;
> +	bool try_write_zeroes = !!bdev_write_zeroes_sectors(bdev);
>  
> +	bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
> +	if ((sector | nr_sects) & bs_mask)
> +		return -EINVAL;
> +
> +retry:
> +	bio = NULL;
>  	blk_start_plug(&plug);
> -	ret = __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask,
> -			&bio, flags);
> +	if (try_write_zeroes) {
> +		ret = __blkdev_issue_write_zeroes(bdev, sector, nr_sects,
> +						  gfp_mask, &bio, flags);
> +	} else if (!(flags & BLKDEV_ZERO_NOFALLBACK)) {
> +		ret = __blkdev_issue_zero_pages(bdev, sector, nr_sects,
> +						gfp_mask, &bio);
> +	} else {
> +		/* No zeroing offload support */
> +		ret = -EOPNOTSUPP;
> +	}
>  	if (ret == 0 && bio) {
>  		ret = submit_bio_wait(bio);
>  		bio_put(bio);
>  	}
>  	blk_finish_plug(&plug);
> +	if (ret && try_write_zeroes) {
> +		if (!(flags & BLKDEV_ZERO_NOFALLBACK)) {
> +			try_write_zeroes = false;
> +			goto retry;
> +		}
> +		if (!bdev_write_zeroes_sectors(bdev)) {
> +			/*
> +			 * Zeroing offload support was indicated, but the
> +			 * device reported ILLEGAL REQUEST (for some devices
> +			 * there is no non-destructive way to verify whether
> +			 * WRITE ZEROES is actually supported).
> +			 */
> +			ret = -EOPNOTSUPP;
> +		}
> +	}
>  
>  	return ret;
>  }
>