On Tue, Oct 3, 2017 at 10:04 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> 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;
> }
Yeah, I didn't like the code flow either but we are going to duplicate
some of it either way. In particular, !bdev_write_zeroes_sectors() ->
ret = -EOPNOTSUPP part is still needed to avoid propagating -EREMOTEIO
in BLKDEV_ZERO_NOFALLBACK case:
if (try_write_zeroes)
ret = __blkdev_issue_write_zeroes(...);
else if (!(flags & BLKDEV_ZERO_NOFALLBACK))
ret = __blkdev_issue_zero_pages(...);
else if (!bdev_write_zeroes_sectors(bdev))
ret = -EOPNOTSUPP;
bs_mask check from __blkdev_issue_zeroout() too.
I'll post v2 in a few.
Thanks,
Ilya
