[PATCH v3 0/2] block: cope with WRITE ZEROES failing in blkdev_issue_zeroout()

[PATCH v3 0/2] block: cope with WRITE ZEROES failing in blkdev_issue_zeroout()

[Ilya Dryomov]

Hi Christoph, Martin,

blkdev_issue_zeroout() now checks for any error.  This required a minor
refactor, so I dropped the stable tag, Jens can add it back if needed.

v2 -> v3:
- another code flow change in blkdev_issue_zeroout() suggested by
  Christoph -- no functional changes

v1 -> v2:
- changed code flow in blkdev_issue_zeroout() according to Christoph's
  suggestion
- this required adding additional checks to blkdev_issue_zeroout() and
  __blkdev_issue_zero_pages(), the latter is no longer void

Previous version at

  https://marc.info/?l=linux-block&m=150712940922089&w=2

Thanks,

                Ilya


Ilya Dryomov (2):
  block: factor out __blkdev_issue_zero_pages()
  block: cope with WRITE ZEROES failing in blkdev_issue_zeroout()

 block/blk-lib.c | 108 +++++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 72 insertions(+), 36 deletions(-)

-- 
2.4.3

[PATCH v3 1/2] block: factor out __blkdev_issue_zero_pages()

[Ilya Dryomov]

blkdev_issue_zeroout() will use this in !BLKDEV_ZERO_NOFALLBACK case.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
 block/blk-lib.c | 63 +++++++++++++++++++++++++++++++++------------------------
 1 file changed, 37 insertions(+), 26 deletions(-)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 62240f8832ca..9d2ab8bba52a 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -274,6 +274,40 @@ static unsigned int __blkdev_sectors_to_bio_pages(sector_t nr_sects)
 	return min(pages, (sector_t)BIO_MAX_PAGES);
 }
 
+static int __blkdev_issue_zero_pages(struct block_device *bdev,
+		sector_t sector, sector_t nr_sects, gfp_t gfp_mask,
+		struct bio **biop)
+{
+	struct request_queue *q = bdev_get_queue(bdev);
+	struct bio *bio = *biop;
+	int bi_size = 0;
+	unsigned int sz;
+
+	if (!q)
+		return -ENXIO;
+
+	while (nr_sects != 0) {
+		bio = next_bio(bio, __blkdev_sectors_to_bio_pages(nr_sects),
+			       gfp_mask);
+		bio->bi_iter.bi_sector = sector;
+		bio_set_dev(bio, bdev);
+		bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
+
+		while (nr_sects != 0) {
+			sz = min((sector_t) PAGE_SIZE, nr_sects << 9);
+			bi_size = bio_add_page(bio, ZERO_PAGE(0), sz, 0);
+			nr_sects -= bi_size >> 9;
+			sector += bi_size >> 9;
+			if (bi_size < sz)
+				break;
+		}
+		cond_resched();
+	}
+
+	*biop = bio;
+	return 0;
+}
+
 /**
  * __blkdev_issue_zeroout - generate number of zero filed write bios
  * @bdev:	blockdev to issue
@@ -304,9 +338,6 @@ int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
 		unsigned flags)
 {
 	int ret;
-	int bi_size = 0;
-	struct bio *bio = *biop;
-	unsigned int sz;
 	sector_t bs_mask;
 
 	bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
@@ -316,30 +347,10 @@ int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
 	ret = __blkdev_issue_write_zeroes(bdev, sector, nr_sects, gfp_mask,
 			biop, flags);
 	if (ret != -EOPNOTSUPP || (flags & BLKDEV_ZERO_NOFALLBACK))
-		goto out;
-
-	ret = 0;
-	while (nr_sects != 0) {
-		bio = next_bio(bio, __blkdev_sectors_to_bio_pages(nr_sects),
-			       gfp_mask);
-		bio->bi_iter.bi_sector = sector;
-		bio_set_dev(bio, bdev);
-		bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
-
-		while (nr_sects != 0) {
-			sz = min((sector_t) PAGE_SIZE, nr_sects << 9);
-			bi_size = bio_add_page(bio, ZERO_PAGE(0), sz, 0);
-			nr_sects -= bi_size >> 9;
-			sector += bi_size >> 9;
-			if (bi_size < sz)
-				break;
-		}
-		cond_resched();
-	}
+		return ret;
 
-	*biop = bio;
-out:
-	return ret;
+	return __blkdev_issue_zero_pages(bdev, sector, nr_sects, gfp_mask,
+					 biop);
 }
 EXPORT_SYMBOL(__blkdev_issue_zeroout);
 
-- 
2.4.3

Re: [PATCH v3 1/2] block: factor out __blkdev_issue_zero_pages()

[Christoph Hellwig]

Looks fine,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v3 1/2] block: factor out __blkdev_issue_zero_pages()

[Martin K. Petersen]

Ilya,

> blkdev_issue_zeroout() will use this in !BLKDEV_ZERO_NOFALLBACK case.

Looks good to me.

Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>

-- 
Martin K. Petersen	Oracle Linux Engineering

[PATCH v3 2/2] block: cope with WRITE ZEROES failing in blkdev_issue_zeroout()

[Ilya Dryomov]

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@lst.de>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: Hannes Reinecke <hare@suse.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
 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 9d2ab8bba52a..23411ec7f3cc 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;
 }
-- 
2.4.3

Re: [PATCH v3 2/2] block: cope with WRITE ZEROES failing in blkdev_issue_zeroout()

[Christoph Hellwig]

Looks fine,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v3 2/2] block: cope with WRITE ZEROES failing in blkdev_issue_zeroout()

[Martin K. Petersen]

Ilya,

> sd_config_write_same() ignores ->max_ws_blocks == 0 and resets it to

I'm not so keen on that description.

sd is the entity that owns max_ws_blocks so it certainly doesn't ignore
it. The default is for max_ws_blocks to be set because we have no
generic, non-destructive way of finding out whether a WRITE SAME command
is going to work or not. If a WRITE SAME subsequently fails, we'll
disable the feature by clearing max_write_same_sectors in the queue
limits.

> 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:

Other than that patch looks good.

Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: [PATCH v3 0/2] block: cope with WRITE ZEROES failing in blkdev_issue_zeroout()

[Ilya Dryomov]

On Mon, Oct 16, 2017 at 3:59 PM, Ilya Dryomov <idryomov@gmail.com> wrote:
> Hi Christoph, Martin,
>
> blkdev_issue_zeroout() now checks for any error.  This required a minor
> refactor, so I dropped the stable tag, Jens can add it back if needed.
>
> v2 -> v3:
> - another code flow change in blkdev_issue_zeroout() suggested by
>   Christoph -- no functional changes
>
> v1 -> v2:
> - changed code flow in blkdev_issue_zeroout() according to Christoph's
>   suggestion
> - this required adding additional checks to blkdev_issue_zeroout() and
>   __blkdev_issue_zero_pages(), the latter is no longer void
>
> Previous version at
>
>   https://marc.info/?l=linux-block&m=150712940922089&w=2
>
> Thanks,
>
>                 Ilya
>
>
> Ilya Dryomov (2):
>   block: factor out __blkdev_issue_zero_pages()
>   block: cope with WRITE ZEROES failing in blkdev_issue_zeroout()
>
>  block/blk-lib.c | 108 +++++++++++++++++++++++++++++++++++++-------------------
>  1 file changed, 72 insertions(+), 36 deletions(-)

Jens, can you pick these up?  Technically this is a user-visible
regression (Fixes tag in 2/2), but we are late in the cycle so I'm not
sure what is the right thing to do here.

Thanks,

                Ilya

Re: [PATCH v3 0/2] block: cope with WRITE ZEROES failing in blkdev_issue_zeroout()

[Jens Axboe]

On 10/24/2017 11:27 PM, Ilya Dryomov wrote:
> On Mon, Oct 16, 2017 at 3:59 PM, Ilya Dryomov <idryomov@gmail.com> wrote:
>> Hi Christoph, Martin,
>>
>> blkdev_issue_zeroout() now checks for any error.  This required a minor
>> refactor, so I dropped the stable tag, Jens can add it back if needed.
>>
>> v2 -> v3:
>> - another code flow change in blkdev_issue_zeroout() suggested by
>>   Christoph -- no functional changes
>>
>> v1 -> v2:
>> - changed code flow in blkdev_issue_zeroout() according to Christoph's
>>   suggestion
>> - this required adding additional checks to blkdev_issue_zeroout() and
>>   __blkdev_issue_zero_pages(), the latter is no longer void
>>
>> Previous version at
>>
>>   https://marc.info/?l=linux-block&m=150712940922089&w=2
>>
>> Thanks,
>>
>>                 Ilya
>>
>>
>> Ilya Dryomov (2):
>>   block: factor out __blkdev_issue_zero_pages()
>>   block: cope with WRITE ZEROES failing in blkdev_issue_zeroout()
>>
>>  block/blk-lib.c | 108 +++++++++++++++++++++++++++++++++++++-------------------
>>  1 file changed, 72 insertions(+), 36 deletions(-)
> 
> Jens, can you pick these up?  Technically this is a user-visible
> regression (Fixes tag in 2/2), but we are late in the cycle so I'm not
> sure what is the right thing to do here.

It wasn't introduced in this cycle, so there's little point in trying
to rush it for 4.14. I have applied it for 4.15, thanks.

-- 
Jens Axboe