diff mbox series

[PULL,05/23] block: Fix AioContext locking in bdrv_attach_child_common()

Message ID 20230628141526.293104-6-kwolf@redhat.com
State New
Headers show
Series [PULL,01/23] iotests: Test active commit with iothread and background I/O | expand

Commit Message

Kevin Wolf June 28, 2023, 2:15 p.m. UTC 
The function can move the child node to a different AioContext. In this
case, it also must take the AioContext lock for the new context before
calling functions that require the caller to hold the AioContext for the
child node.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230605085711.21261-6-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/block.c b/block.c
index 213a09643d..2c8a3ffe19 100644
--- a/block.c
+++ b/block.c
@@ -2989,6 +2989,10 @@  static TransactionActionDrv bdrv_attach_child_common_drv = {
  * Function doesn't update permissions, caller is responsible for this.
  *
  * Returns new created child.
+ *
+ * The caller must hold the AioContext lock for @child_bs. Both @parent_bs and
+ * @child_bs can move to a different AioContext in this function. Callers must
+ * make sure that their AioContext locking is still correct after this.
  */
 static BdrvChild *bdrv_attach_child_common(BlockDriverState *child_bs,
                                            const char *child_name,
@@ -2999,7 +3003,7 @@  static BdrvChild *bdrv_attach_child_common(BlockDriverState *child_bs,
                                            Transaction *tran, Error **errp)
 {
     BdrvChild *new_child;
-    AioContext *parent_ctx;
+    AioContext *parent_ctx, *new_child_ctx;
     AioContext *child_ctx = bdrv_get_aio_context(child_bs);
 
     assert(child_class->get_parent_desc);
@@ -3050,6 +3054,12 @@  static BdrvChild *bdrv_attach_child_common(BlockDriverState *child_bs,
         }
     }
 
+    new_child_ctx = bdrv_get_aio_context(child_bs);
+    if (new_child_ctx != child_ctx) {
+        aio_context_release(child_ctx);
+        aio_context_acquire(new_child_ctx);
+    }
+
     bdrv_ref(child_bs);
     /*
      * Let every new BdrvChild start with a drained parent. Inserting the child
@@ -3079,11 +3089,20 @@  static BdrvChild *bdrv_attach_child_common(BlockDriverState *child_bs,
     };
     tran_add(tran, &bdrv_attach_child_common_drv, s);
 
+    if (new_child_ctx != child_ctx) {
+        aio_context_release(new_child_ctx);
+        aio_context_acquire(child_ctx);
+    }
+
     return new_child;
 }
 
 /*
  * Function doesn't update permissions, caller is responsible for this.
+ *
+ * The caller must hold the AioContext lock for @child_bs. Both @parent_bs and
+ * @child_bs can move to a different AioContext in this function. Callers must
+ * make sure that their AioContext locking is still correct after this.
  */
 static BdrvChild *bdrv_attach_child_noperm(BlockDriverState *parent_bs,
                                            BlockDriverState *child_bs,