debian/patches/extra/0010-mirror-Drop-permissions-on-s-target-on-completion.patch

   1 From 95166cdeaeaa9d00330483988b818abfcc473efe Mon Sep 17 00:00:00 2001
   2 From: Kevin Wolf <kwolf@redhat.com>
   3 Date: Mon, 29 May 2017 14:08:32 +0200
   4 Subject: [PATCH 10/15] mirror: Drop permissions on s->target on completion
   5
   6 This fixes an assertion failure that was triggered by qemu-iotests 129
   7 on some CI host, while the same test case didn't seem to fail on other
   8 hosts.
   9
  10 Essentially the problem is that the blk_unref(s->target) in
  11 mirror_exit() doesn't necessarily mean that the BlockBackend goes away
  12 immediately. It is possible that the job completion was triggered nested
  13 in mirror_drain(), which looks like this:
  14
  15     BlockBackend *target = s->target;
  16     blk_ref(target);
  17     blk_drain(target);
  18     blk_unref(target);
  19
  20 In this case, the write permissions for s->target are retained until
  21 after blk_drain(), which makes removing mirror_top_bs fail for the
  22 active commit case (can't have a writable backing file in the chain
  23 without the filter driver).
  24
  25 Explicitly dropping the permissions first means that the additional
  26 reference doesn't hurt and the job can complete successfully even if
  27 called from the nested blk_drain().
  28
  29 Cc: qemu-stable@nongnu.org
  30 Signed-off-by: Kevin Wolf <kwolf@redhat.com>
  31 Acked-by: Paolo Bonzini <pbonzini@redhat.com>
  32 Reviewed-by: Max Reitz <mreitz@redhat.com>
  33 ---
  34  block/mirror.c | 7 ++++++-
  35  1 file changed, 6 insertions(+), 1 deletion(-)
  36
  37 diff --git a/block/mirror.c b/block/mirror.c
  38 index 164438f422..779b753b8a 100644
  39 --- a/block/mirror.c
  40 +++ b/block/mirror.c
  41 @@ -514,7 +514,12 @@ static void mirror_exit(BlockJob *job, void *opaque)
  42
  43      /* Remove target parent that still uses BLK_PERM_WRITE/RESIZE before
  44       * inserting target_bs at s->to_replace, where we might not be able to get
  45 -     * these permissions. */
  46 +     * these permissions.
  47 +     *
  48 +     * Note that blk_unref() alone doesn't necessarily drop permissions because
  49 +     * we might be running nested inside mirror_drain(), which takes an extra
  50 +     * reference, so use an explicit blk_set_perm() first. */
  51 +    blk_set_perm(s->target, 0, BLK_PERM_ALL, &error_abort);
  52      blk_unref(s->target);
  53      s->target = NULL;
  54
  55 --
  56 2.11.0
  57