From: Kevin Wolf <kwolf@redhat.com>
Date: Wed, 29 Nov 2017 10:25:10 +0000 (+0100)
Subject: block: Expect graph changes in bdrv_parent_drained_begin/end
X-Git-Tag: v2.11.0-rc3~1^2~4
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=02d213009d571bcd7171e3ff9234722a11d30d1b;p=thirdparty%2Fqemu.git

block: Expect graph changes in bdrv_parent_drained_begin/end

The .drained_begin/end callbacks can (directly or indirectly via
aio_poll()) cause block nodes to be removed or the current BdrvChild to
point to a different child node.

Use QLIST_FOREACH_SAFE() to make sure we don't access invalid
BlockDriverStates or accidentally continue iterating the parents of the
new child node instead of the node we actually came from.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Tested-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---

diff --git a/block/io.c b/block/io.c
index 4fdf93a0144..6773926fc14 100644
--- a/block/io.c
+++ b/block/io.c
@@ -42,9 +42,9 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
 
 void bdrv_parent_drained_begin(BlockDriverState *bs)
 {
-    BdrvChild *c;
+    BdrvChild *c, *next;
 
-    QLIST_FOREACH(c, &bs->parents, next_parent) {
+    QLIST_FOREACH_SAFE(c, &bs->parents, next_parent, next) {
         if (c->role->drained_begin) {
             c->role->drained_begin(c);
         }
@@ -53,9 +53,9 @@ void bdrv_parent_drained_begin(BlockDriverState *bs)
 
 void bdrv_parent_drained_end(BlockDriverState *bs)
 {
-    BdrvChild *c;
+    BdrvChild *c, *next;
 
-    QLIST_FOREACH(c, &bs->parents, next_parent) {
+    QLIST_FOREACH_SAFE(c, &bs->parents, next_parent, next) {
         if (c->role->drained_end) {
             c->role->drained_end(c);
         }