[Qemu-devel] [PATCH v2] block: fix bdrv_flush() ordering in bdrv_close()

[Qemu-devel] [PATCH v2] block: fix bdrv_flush() ordering in bdrv_close()

[Stefan Hajnoczi]

Since 80ccf93b we flush the block device during close.  The
bdrv_drain_all() call should come before bdrv_flush() to ensure guest
write requests have completed.  Otherwise we may miss pending writes
when flushing.

Call bdrv_drain_all() again for safety as the final step after
bdrv_flush().  This should not be necessary but we can be paranoid here
in case bdrv_flush() left I/O pending.

Cc: qemu-stable@nongnu.org
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
v2:
 * Drain after block_job_cancel_sync() [kwolf]

 block.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/block.c b/block.c
index 6c493ad..183fec8 100644
--- a/block.c
+++ b/block.c
@@ -1358,11 +1358,12 @@ void bdrv_reopen_abort(BDRVReopenState *reopen_state)
 
 void bdrv_close(BlockDriverState *bs)
 {
-    bdrv_flush(bs);
     if (bs->job) {
         block_job_cancel_sync(bs->job);
     }
-    bdrv_drain_all();
+    bdrv_drain_all(); /* complete I/O */
+    bdrv_flush(bs);
+    bdrv_drain_all(); /* in case flush left pending I/O */
     notifier_list_notify(&bs->close_notifiers, bs);
 
     if (bs->drv) {
-- 
1.8.1.4

Re: [Qemu-devel] [PATCH v2] block: fix bdrv_flush() ordering in bdrv_close()

[Kevin Wolf]

Am 02.07.2013 um 15:36 hat Stefan Hajnoczi geschrieben:
> Since 80ccf93b we flush the block device during close.  The
> bdrv_drain_all() call should come before bdrv_flush() to ensure guest
> write requests have completed.  Otherwise we may miss pending writes
> when flushing.
> 
> Call bdrv_drain_all() again for safety as the final step after
> bdrv_flush().  This should not be necessary but we can be paranoid here
> in case bdrv_flush() left I/O pending.
> 
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Kevin Wolf <kwolf@redhat.com>

Re: [Qemu-devel] [PATCH v2] block: fix bdrv_flush() ordering in bdrv_close()

[Stefan Hajnoczi]

On Tue, Jul 02, 2013 at 03:36:25PM +0200, Stefan Hajnoczi wrote:
> Since 80ccf93b we flush the block device during close.  The
> bdrv_drain_all() call should come before bdrv_flush() to ensure guest
> write requests have completed.  Otherwise we may miss pending writes
> when flushing.
> 
> Call bdrv_drain_all() again for safety as the final step after
> bdrv_flush().  This should not be necessary but we can be paranoid here
> in case bdrv_flush() left I/O pending.
> 
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> v2:
>  * Drain after block_job_cancel_sync() [kwolf]
> 
>  block.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)

Applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan