block: Fix AioContext locking in bdrv_open_child()
bdrv_attach_child() requires that the caller holds the AioContext lock
for the new child node. Take it in bdrv_open_child() and document that
the caller must not hold any AioContext apart from the main AioContext.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230605085711.21261-5-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index 0637265..213a096 100644
--- a/block.c
+++ b/block.c
@@ -3654,6 +3654,7 @@
*
* The BlockdevRef will be removed from the options QDict.
*
+ * The caller must hold the lock of the main AioContext and no other AioContext.
* @parent can move to a different AioContext in this function. Callers must
* make sure that their AioContext locking is still correct after this.
*/
@@ -3665,6 +3666,8 @@
bool allow_none, Error **errp)
{
BlockDriverState *bs;
+ BdrvChild *child;
+ AioContext *ctx;
GLOBAL_STATE_CODE();
@@ -3674,13 +3677,19 @@
return NULL;
}
- return bdrv_attach_child(parent, bs, bdref_key, child_class, child_role,
- errp);
+ ctx = bdrv_get_aio_context(bs);
+ aio_context_acquire(ctx);
+ child = bdrv_attach_child(parent, bs, bdref_key, child_class, child_role,
+ errp);
+ aio_context_release(ctx);
+
+ return child;
}
/*
* Wrapper on bdrv_open_child() for most popular case: open primary child of bs.
*
+ * The caller must hold the lock of the main AioContext and no other AioContext.
* @parent can move to a different AioContext in this function. Callers must
* make sure that their AioContext locking is still correct after this.
*/
