path: root/block.c
diff options
authorKevin Wolf <kwolf@redhat.com>2015-06-10 13:33:17 +0200
committerKevin Wolf <kwolf@redhat.com>2015-06-12 17:04:59 +0200
commit6ee4ce1ee75a651c246d926c2302281b51981f6d (patch)
treed0949db11848e03524342ccc7f56db08dd11739f /block.c
parentf3930ed0bb1945b59da8e591072b5c79606d0760 (diff)
block: Drain requests before swapping nodes in bdrv_swap()
bdrv_swap() requires that there are no requests in flight on either of the two devices. The request coroutine would work on the wrong BlockDriverState object (with bs->opaque even being interpreted as a different type potentially) and all sorts of bad things would result from this. The currently existing callers mostly ensure that there is no I/O pending on nodes that are swapped. In detail, this is: 1. Live snapshots. This goes through qmp_transaction(), which calls bdrv_drain_all() before doing anything. The command is executed synchronously, so no new I/O can be issued concurrently. 2. snapshot=on in bdrv_open(). We're in the middle of opening the image (both the original image and its temporary overlay), so there can't be any I/O in flight yet. 3. Mirroring. bdrv_drain() is already used on the source device so that the mirror doesn't miss anything. However, the main loop runs between that and the bdrv_swap() (which is actually a bug, being addressed in another series), so there is a small window in which new I/O might be issued that would be in flight during bdrv_swap(). It is safer to just drain the request queue of both devices in bdrv_swap() instead of relying on callers to do the right thing. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Max Reitz <mreitz@redhat.com>
Diffstat (limited to 'block.c')
1 files changed, 6 insertions, 0 deletions
diff --git a/block.c b/block.c
index 3c04446f7f..9a860f12c7 100644
--- a/block.c
+++ b/block.c
@@ -1959,6 +1959,9 @@ void bdrv_swap(BlockDriverState *bs_new, BlockDriverState *bs_old)
BlockDriverState tmp;
+ bdrv_drain(bs_new);
+ bdrv_drain(bs_old);
/* The code needs to swap the node_name but simply swapping node_list won't
* work so first remove the nodes from the graph list, do the swap then
* insert them back if needed.
@@ -2002,6 +2005,9 @@ void bdrv_swap(BlockDriverState *bs_new, BlockDriverState *bs_old)
QTAILQ_INSERT_TAIL(&graph_bdrv_states, bs_old, node_list);
+ assert(QLIST_EMPTY(&bs_old->tracked_requests));
+ assert(QLIST_EMPTY(&bs_new->tracked_requests));