[05/10] block: Fix blockdev-snapshot error handling
diff mbox

Message ID 1488817322-11397-6-git-send-email-kwolf@redhat.com
State New
Headers show

Commit Message

Kevin Wolf March 6, 2017, 4:21 p.m. UTC
For blockdev-snapshot, external_snapshot_prepare() accepts an arbitrary
node reference at first and only checks later whether it already has a
backing file. Between those places, other errors can occur.

Therefore checking in external_snapshot_abort() whether state->new_bs
has a backing file is not sufficient to tell whether bdrv_append() was
already completed or not. Trying to undo the bdrv_append() when it
wasn't even executed is wrong.

Introduce a new boolean flag in the state to fix this.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 blockdev.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Comments

Eric Blake March 6, 2017, 8:23 p.m. UTC | #1
On 03/06/2017 10:21 AM, Kevin Wolf wrote:
> For blockdev-snapshot, external_snapshot_prepare() accepts an arbitrary
> node reference at first and only checks later whether it already has a
> backing file. Between those places, other errors can occur.
> 
> Therefore checking in external_snapshot_abort() whether state->new_bs
> has a backing file is not sufficient to tell whether bdrv_append() was
> already completed or not. Trying to undo the bdrv_append() when it
> wasn't even executed is wrong.
> 
> Introduce a new boolean flag in the state to fix this.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  blockdev.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>

By the way, how are you finding all these spots? Is it existing qemu-io
tests that are failing? And if so, would mentioning which test exposed
the problem being fixed be worth adding in the commit messages?  If not,
are there some qemu-io tests to be added?
Kevin Wolf March 7, 2017, 12:32 p.m. UTC | #2
Am 06.03.2017 um 21:23 hat Eric Blake geschrieben:
> On 03/06/2017 10:21 AM, Kevin Wolf wrote:
> > For blockdev-snapshot, external_snapshot_prepare() accepts an arbitrary
> > node reference at first and only checks later whether it already has a
> > backing file. Between those places, other errors can occur.
> > 
> > Therefore checking in external_snapshot_abort() whether state->new_bs
> > has a backing file is not sufficient to tell whether bdrv_append() was
> > already completed or not. Trying to undo the bdrv_append() when it
> > wasn't even executed is wrong.
> > 
> > Introduce a new boolean flag in the state to fix this.
> > 
> > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > ---
> >  blockdev.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> 
> Reviewed-by: Eric Blake <eblake@redhat.com>
> 
> By the way, how are you finding all these spots? Is it existing qemu-io
> tests that are failing? And if so, would mentioning which test exposed
> the problem being fixed be worth adding in the commit messages?  If not,
> are there some qemu-io tests to be added?

Most of the fixes here are based on qemu-iotests failures that only
appeared after fixing the error path in change_parent_backing_link(),
which is now later in this series. So there is no commit at which
qemu-iotests cases are actually failing, even though they helped me spot
some problems.

Kevin

Patch
diff mbox

diff --git a/blockdev.c b/blockdev.c
index 8eb4e84..af67ce4 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1614,6 +1614,7 @@  typedef struct ExternalSnapshotState {
     BlockDriverState *old_bs;
     BlockDriverState *new_bs;
     AioContext *aio_context;
+    bool overlay_appended;
 } ExternalSnapshotState;
 
 static void external_snapshot_prepare(BlkActionState *common,
@@ -1780,6 +1781,7 @@  static void external_snapshot_prepare(BlkActionState *common,
         error_propagate(errp, local_err);
         return;
     }
+    state->overlay_appended = true;
 }
 
 static void external_snapshot_commit(BlkActionState *common)
@@ -1803,7 +1805,7 @@  static void external_snapshot_abort(BlkActionState *common)
     ExternalSnapshotState *state =
                              DO_UPCAST(ExternalSnapshotState, common, common);
     if (state->new_bs) {
-        if (state->new_bs->backing) {
+        if (state->overlay_appended) {
             bdrv_replace_in_backing_chain(state->new_bs, state->old_bs);
         }
     }