On Thu, Sep 21, 2017 at 07:12:52PM +0200, Ilya Dryomov wrote:
> 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: Christoph Hellwig <hch@xxxxxx>
> Cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
> Cc: Hannes Reinecke <hare@xxxxxxxx>
> Signed-off-by: Ilya Dryomov <idryomov@xxxxxxxxx>
> ---
> block/blk-lib.c | 27 +++++++++++++++++++++------
> 1 file changed, 21 insertions(+), 6 deletions(-)
>
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 6b97feb71065..1cb402beb983 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -316,12 +316,6 @@ static void __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.
> *
> @@ -374,6 +368,27 @@ int blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
> &bio, flags);
> if (ret == 0 && bio) {
> ret = submit_bio_wait(bio);
> + /*
> + * Fall back to a manual zeroout on any error, if allowed.
> + *
> + * Particularly, WRITE ZEROES may fail with -EREMOTEIO 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).
> + */
> + if (ret && bio_op(bio) == REQ_OP_WRITE_ZEROES) {
No need for the additional levels of indentation here. Also I
really do not like the logic, we shouldn't have to duplicate much
of the logic multiple times.
I'd more go for something like (sketched in mail):
bool try_write_zeroes = !!bdev_write_zeroes_sectors(bdev);
retry:
bio = NULL;
blk_start_plug(&plug);
if (try_write_zeroes)
ret = __blkdev_issue_write_zeroes(...)
else
ret = __blkdev_issue_zero_pages(...)
if (ret == 0 && bio) {
ret = submit_bio_wait(bio);
bio_put(bio);
}
blk_finish_plug(&plug);
if (ret && try_write_zeroes) {
try_write_zeroes = false;
goto retry;
}
