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[Qemu-devel] [PATCH v2 09/13] block: Drain requests before swapping node
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PATCH v2 09/13] block: Drain requests before swapping nodes in bdrv_swap() |
Date: |
Wed, 10 Jun 2015 15:47:03 +0200 |
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 <address@hidden>
---
block.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/block.c b/block.c
index 7ba0edd..f1ceb26 100644
--- a/block.c
+++ b/block.c
@@ -1947,6 +1947,9 @@ 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.
@@ -1990,6 +1993,9 @@ 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));
+
bdrv_rebind(bs_new);
bdrv_rebind(bs_old);
}
--
1.8.3.1
- [Qemu-devel] [PATCH v2 03/13] check-qdict: Test cases for new functions, (continued)
- [Qemu-devel] [PATCH v2 03/13] check-qdict: Test cases for new functions, Kevin Wolf, 2015/06/10
- [Qemu-devel] [PATCH v2 02/13] qdict: Add qdict_{set, copy}_default(), Kevin Wolf, 2015/06/10
- [Qemu-devel] [PATCH v2 05/13] vmdk: Use bdrv_open_image(), Kevin Wolf, 2015/06/10
- [Qemu-devel] [PATCH v2 07/13] block: Use QemuOpts in bdrv_open_common(), Kevin Wolf, 2015/06/10
- [Qemu-devel] [PATCH v2 04/13] quorum: Use bdrv_open_image(), Kevin Wolf, 2015/06/10
- [Qemu-devel] [PATCH v2 09/13] block: Drain requests before swapping nodes in bdrv_swap(),
Kevin Wolf <=
- [Qemu-devel] [PATCH v2 10/13] queue.h: Add QLIST_FIX_HEAD_PTR(), Kevin Wolf, 2015/06/10
- [Qemu-devel] [PATCH v2 12/13] block: Add BlockDriverState.inherits_from, Kevin Wolf, 2015/06/10
- [Qemu-devel] [PATCH v2 11/13] block: Add list of children to BlockDriverState, Kevin Wolf, 2015/06/10
- [Qemu-devel] [PATCH v2 08/13] block: Move flag inheritance to bdrv_open_inherit(), Kevin Wolf, 2015/06/10