lkml.org 
[lkml]   [2015]   [May]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Date
    Subject[PATCH 3.2 045/221] dm io: reject unsupported DISCARD requests with EOPNOTSUPP
    3.2.69-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: "Darrick J. Wong" <darrick.wong@oracle.com>

    commit 37527b869207ad4c208b1e13967d69b8bba1fbf9 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>
    ---
    drivers/md/dm-io.c | 6 ++++++
    1 file changed, 6 insertions(+)

    --- a/drivers/md/dm-io.c
    +++ b/drivers/md/dm-io.c
    @@ -300,6 +300,12 @@ static void do_region(int rw, unsigned r
    struct request_queue *q = bdev_get_queue(where->bdev);
    sector_t discard_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.


    \
     
     \ /
      Last update: 2015-05-05 04:21    [W:2.807 / U:0.104 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site