releases/3.4.92/nbd-fsync-and-kill-block-device-on-shutdown.patch

   1 From 3a2d63f87989e01437ba994df5f297528c353d7d Mon Sep 17 00:00:00 2001
   2 From: Paolo Bonzini <pbonzini@redhat.com>
   3 Date: Wed, 27 Feb 2013 17:05:25 -0800
   4 Subject: nbd: fsync and kill block device on shutdown
   5
   6 From: Paolo Bonzini <pbonzini@redhat.com>
   7
   8 commit 3a2d63f87989e01437ba994df5f297528c353d7d upstream.
   9
  10 There are two problems with shutdown in the NBD driver.
  11
  12 1: Receiving the NBD_DISCONNECT ioctl does not sync the filesystem.
  13
  14    This patch adds the sync operation into __nbd_ioctl()'s
  15    NBD_DISCONNECT handler.  This is useful because BLKFLSBUF is restricted
  16    to processes that have CAP_SYS_ADMIN, and the NBD client may not
  17    possess it (fsync of the block device does not sync the filesystem,
  18    either).
  19
  20 2: Once we clear the socket we have no guarantee that later reads will
  21    come from the same backing storage.
  22
  23    The patch adds calls to kill_bdev() in __nbd_ioctl()'s socket
  24    clearing code so the page cache is cleaned, lest reads that hit on the
  25    page cache will return stale data from the previously-accessible disk.
  26
  27 Example:
  28
  29     # qemu-nbd -r -c/dev/nbd0 /dev/sr0
  30     # file -s /dev/nbd0
  31     /dev/stdin: # UDF filesystem data (version 1.5) etc.
  32     # qemu-nbd -d /dev/nbd0
  33     # qemu-nbd -r -c/dev/nbd0 /dev/sda
  34     # file -s /dev/nbd0
  35     /dev/stdin: # UDF filesystem data (version 1.5) etc.
  36
  37 While /dev/sda has:
  38
  39     # file -s /dev/sda
  40     /dev/sda: x86 boot sector; etc.
  41
  42 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
  43 Acked-by: Paul Clements <Paul.Clements@steeleye.com>
  44 Cc: Alex Bligh <alex@alex.org.uk>
  45 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  46 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  47 [bwh: Backported to 3.2:
  48  - Adjusted context
  49  - s/\bnbd\b/lo/
  50  - Incorporate export of kill_bdev() from commit ff01bb483265
  51    ('fs: move code out of buffer.c')]
  52 Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
  53 [hq: Backported to 3.4: Adjusted context]
  54 Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>
  55 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  56 ---
  57  drivers/block/nbd.c |    9 +++++++++
  58  1 file changed, 9 insertions(+)
  59
  60 --- a/drivers/block/nbd.c
  61 +++ b/drivers/block/nbd.c
  62 @@ -584,10 +584,17 @@ static int __nbd_ioctl(struct block_devi
  63                 struct request sreq;
  64
  65                 dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");
  66 +               if (!nbd->sock)
  67 +                       return -EINVAL;
  68
  69 +               mutex_unlock(&nbd->tx_lock);
  70 +               fsync_bdev(bdev);
  71 +               mutex_lock(&nbd->tx_lock);
  72                 blk_rq_init(NULL, &sreq);
  73                 sreq.cmd_type = REQ_TYPE_SPECIAL;
  74                 nbd_cmd(&sreq) = NBD_CMD_DISC;
  75 +
  76 +               /* Check again after getting mutex back.  */
  77                 if (!nbd->sock)
  78                         return -EINVAL;
  79
  80 @@ -606,6 +613,7 @@ static int __nbd_ioctl(struct block_devi
  81                 nbd_clear_que(nbd);
  82                 BUG_ON(!list_empty(&nbd->queue_head));
  83                 BUG_ON(!list_empty(&nbd->waiting_queue));
  84 +               kill_bdev(bdev);
  85                 if (file)
  86                         fput(file);
  87                 return 0;
  88 @@ -688,6 +696,7 @@ static int __nbd_ioctl(struct block_devi
  89                 nbd->file = NULL;
  90                 nbd_clear_que(nbd);
  91                 dev_warn(disk_to_dev(nbd->disk), "queue cleared\n");
  92 +               kill_bdev(bdev);
  93                 if (file)
  94                         fput(file);
  95                 nbd->bytesize = 0;