[PATCH] block: cope with WRITE SAME failing in blkdev_issue_zeroout()

[Ilya Dryomov <idryomov@gmail.com>]

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.  This means blkdev_issue_zeroout() must cope with WRITE SAME
failing with BLK_STS_TARGET/-EREMOTEIO and explicitly write zeroes,
unless BLKDEV_ZERO_NOFALLBACK is specified.

Commit 71027e97d796 ("block: stop using discards for zeroing") added
the following to __blkdev_issue_zeroout() comment:

  "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."

But __blkdev_issue_zeroout() doesn't fail in this case: if WRITE SAME
support is indicated, a REQ_OP_WRITE_ZEROES bio is built and returned
to blkdev_issue_zeroout().  -EREMOTEIO is then propagated up:

  $ fallocate -zn -l 1k /dev/sdg
  fallocate: fallocate failed: Remote I/O error
  $ fallocate -zn -l 1k /dev/sdg  # OK

(The second fallocate(1) succeeds because sd_done() sets ->no_write_same
in response to a sense that would become BLK_STS_TARGET.)

Retry __blkdev_issue_zeroout() if the I/O fails with -EREMOTEIO.  This
is roughly what we did until 4.12, sans BLKDEV_ZERO_NOFALLBACK knob.

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>
Cc: stable@vger.kernel.org # 4.12+
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
 block/blk-lib.c | 49 +++++++++++++++++++++++++++++++++----------------
 1 file changed, 33 insertions(+), 16 deletions(-)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index 3fe0aec90597..876b5478c1a2 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -287,12 +287,6 @@ static unsigned int __blkdev_sectors_to_bio_pages(sector_t nr_sects)
  *  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.
  *
@@ -343,6 +337,34 @@ int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
 }
 EXPORT_SYMBOL(__blkdev_issue_zeroout);
 
+/*
+ * This function 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).  In this case the caller should
+ * retry and the fallback path in __blkdev_issue_zeroout() will be used
+ * unless %flags contains BLKDEV_ZERO_NOFALLBACK.
+ */
+static int __blkdev_issue_zeroout_wait(struct block_device *bdev,
+				       sector_t sector, sector_t nr_sects,
+				       gfp_t gfp_mask, unsigned flags)
+{
+	int ret;
+	struct bio *bio = NULL;
+	struct blk_plug plug;
+
+	blk_start_plug(&plug);
+	ret = __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask,
+			&bio, flags);
+	if (ret == 0 && bio) {
+		ret = submit_bio_wait(bio);
+		bio_put(bio);
+	}
+	blk_finish_plug(&plug);
+
+	return ret;
+}
+
 /**
  * blkdev_issue_zeroout - zero-fill a block range
  * @bdev:	blockdev to write
@@ -360,17 +382,12 @@ 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;
-	struct blk_plug plug;
 
-	blk_start_plug(&plug);
-	ret = __blkdev_issue_zeroout(bdev, sector, nr_sects, gfp_mask,
-			&bio, flags);
-	if (ret == 0 && bio) {
-		ret = submit_bio_wait(bio);
-		bio_put(bio);
-	}
-	blk_finish_plug(&plug);
+	ret = __blkdev_issue_zeroout_wait(bdev, sector, nr_sects,
+					  gfp_mask, flags);
+	if (ret == -EREMOTEIO)
+		ret = __blkdev_issue_zeroout_wait(bdev, sector, nr_sects,
+						  gfp_mask, flags);
 
 	return ret;
 }
-- 
2.4.3