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Darrick J. Wong authored
commit 37527b86 upstream. 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> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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