I created a dm-raid1 device backed by a device that supports DISCARD
and another device that does NOT support DISCARD with the following
dm configuration:
# echo '0 2048 mirror core 1 512 2 /dev/sda 0 /dev/sdb 0' | dmsetup create moo
# lsblk -D
NAME DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
sda 0 4K 1G 0
`-moo (dm-0) 0 4K 1G 0
sdb 0 0B 0B 0
`-moo (dm-0) 0 4K 1G 0
Notice that the mirror device /dev/mapper/moo advertises DISCARD
support even though one of the mirror halves doesn't.
If I issue a DISCARD request (via fstrim, mount -o discard, or ioctl
BLKDISCARD) through the mirror, kmirrord gets stuck in an infinite
loop in do_region() when it tries to issue a DISCARD request to sdb.
The problem is that when we call do_region() against sdb, num_sectors
is set to zero because q->limits.max_discard_sectors is zero.
Therefore, "remaining" never decreases and the loop never terminates.
Before entering the loop, check for the combination of REQ_DISCARD and
no discard and return -EOPNOTSUPP to avoid hanging up the mirror
device. Fix the same problem with WRITE_DISCARD while we're at it.
This bug was found by the unfortunate coincidence of pvmove and a
discard operation in the RHEL 6.5 kernel; 3.19 is also affected.
Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
Cc: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx>
Cc: Srinivas Eeda <srinivas.eeda@xxxxxxxxxx>
---
drivers/md/dm-io.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
index c09359d..32d330a 100644
--- a/drivers/md/dm-io.c
+++ b/drivers/md/dm-io.c
@@ -290,6 +290,13 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
unsigned short logical_block_size = queue_logical_block_size(q);
sector_t num_sectors;
+ /* Reject unsupported discard/write same requests */
+ if (((rw & REQ_DISCARD) && !blk_queue_discard(q)) ||
+ ((rw & REQ_WRITE_SAME) && !bdev_write_same(where->bdev))) {
+ dec_count(io, region, -EOPNOTSUPP);
+ return;
+ }
+
/*
* where->count may be zero if rw holds a flush and we need to
* send a zero-sized flush.
--
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