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dm io: reject unsupported DISCARD requests with EOPNOTSUPP 

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.

To fix this: before entering the loop, check for the combination of
REQ_DISCARD and no discard and return -EOPNOTSUPP to avoid hanging up
the mirror device.

This bug was found by the unfortunate coincidence of pvmove and a
discard operation in the RHEL 6.5 kernel; upstream is also affected.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Acked-by: "Martin K. Petersen" <martin.petersen@oracle.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
This commit is contained in:
Darrick J. Wong 2015-02-13 11:05:37 -08:00 committed by Mike Snitzer
parent f2ed51ac64
commit 37527b8692
1 changed files with 6 additions and 0 deletions
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6
drivers/md/dm-io.c
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@ -290,6 +290,12 @@ 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 requests */
if ((rw & REQ_DISCARD) && !blk_queue_discard(q)) {
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.