[Qemu-stable] [PATCH 25/79] blockdev: use drained_begin/end for qmp_block_resize

[Michael Roth]

From: John Snow <address@hidden>

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1447551

If one tries to issue a block_resize while a guest is busy
accessing the disk, it is possible that qemu may deadlock
when invoking aio_poll from both the main loop and the iothread.

Replace another instance of bdrv_drain_all that doesn't
quite belong.

Cc: address@hidden
Suggested-by: Paolo Bonzini <address@hidden>
Signed-off-by: John Snow <address@hidden>
Reviewed-by: Eric Blake <address@hidden>
Reviewed-by: Paolo Bonzini <address@hidden>
Signed-off-by: Kevin Wolf <address@hidden>
(cherry picked from commit 698bdfa07d66b5ec218a60229e58eae1dcde00e5)
Signed-off-by: Michael Roth <address@hidden>
---
 blockdev.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/blockdev.c b/blockdev.c
index 78e1204..e8a9a65 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2923,10 +2923,9 @@ void qmp_block_resize(bool has_device, const char 
*device,
         goto out;
     }
 
-    /* complete all in-flight operations before resizing the device */
-    bdrv_drain_all();
-
+    bdrv_drained_begin(bs);
     ret = blk_truncate(blk, size, errp);
+    bdrv_drained_end(bs);
 
 out:
     blk_unref(blk);
-- 
2.7.4