releases/3.19.2/dm-io-reject-unsupported-discard-requests-with-eopnotsupp.patch

   1 From 37527b869207ad4c208b1e13967d69b8bba1fbf9 Mon Sep 17 00:00:00 2001
   2 From: "Darrick J. Wong" <darrick.wong@oracle.com>
   3 Date: Fri, 13 Feb 2015 11:05:37 -0800
   4 Subject: dm io: reject unsupported DISCARD requests with EOPNOTSUPP
   5
   6 From: "Darrick J. Wong" <darrick.wong@oracle.com>
   7
   8 commit 37527b869207ad4c208b1e13967d69b8bba1fbf9 upstream.
   9
  10 I created a dm-raid1 device backed by a device that supports DISCARD
  11 and another device that does NOT support DISCARD with the following
  12 dm configuration:
  13
  14  #  echo '0 2048 mirror core 1 512 2 /dev/sda 0 /dev/sdb 0' | dmsetup create moo
  15  # lsblk -D
  16  NAME         DISC-ALN DISC-GRAN DISC-MAX DISC-ZERO
  17  sda                 0        4K       1G         0
  18  `-moo (dm-0)        0        4K       1G         0
  19  sdb                 0        0B       0B         0
  20  `-moo (dm-0)        0        4K       1G         0
  21
  22 Notice that the mirror device /dev/mapper/moo advertises DISCARD
  23 support even though one of the mirror halves doesn't.
  24
  25 If I issue a DISCARD request (via fstrim, mount -o discard, or ioctl
  26 BLKDISCARD) through the mirror, kmirrord gets stuck in an infinite
  27 loop in do_region() when it tries to issue a DISCARD request to sdb.
  28 The problem is that when we call do_region() against sdb, num_sectors
  29 is set to zero because q->limits.max_discard_sectors is zero.
  30 Therefore, "remaining" never decreases and the loop never terminates.
  31
  32 To fix this: before entering the loop, check for the combination of
  33 REQ_DISCARD and no discard and return -EOPNOTSUPP to avoid hanging up
  34 the mirror device.
  35
  36 This bug was found by the unfortunate coincidence of pvmove and a
  37 discard operation in the RHEL 6.5 kernel; upstream is also affected.
  38
  39 Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
  40 Acked-by: "Martin K. Petersen" <martin.petersen@oracle.com>
  41 Signed-off-by: Mike Snitzer <snitzer@redhat.com>
  42 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  43
  44 ---
  45  drivers/md/dm-io.c |    6 ++++++
  46  1 file changed, 6 insertions(+)
  47
  48 --- a/drivers/md/dm-io.c
  49 +++ b/drivers/md/dm-io.c
  50 @@ -290,6 +290,12 @@ static void do_region(int rw, unsigned r
  51         unsigned short logical_block_size = queue_logical_block_size(q);
  52         sector_t num_sectors;
  53
  54 +       /* Reject unsupported discard requests */
  55 +       if ((rw & REQ_DISCARD) && !blk_queue_discard(q)) {
  56 +               dec_count(io, region, -EOPNOTSUPP);
  57 +               return;
  58 +       }
  59 +
  60         /*
  61          * where->count may be zero if rw holds a flush and we need to
  62          * send a zero-sized flush.