The final bdrv_set_backing_hd() could be working on already freed nodes
because the commit job drops its references (through BlockBackends) to
both overlay_bs and top already a bit earlier.
One way to trigger the bug is hot unplugging a disk for which
blockdev_mark_auto_del() cancels the block job.
Fix this by taking BDS-level references while we're still using the
nodes.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
block/commit.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/block/commit.c b/block/commit.c
index a3028b2..af6fa68 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -89,6 +89,10 @@ static void commit_complete(BlockJob *job, void *opaque)
int ret = data->ret;
bool remove_commit_top_bs = false;
+ /* Make sure overlay_bs and top stay around until bdrv_set_backing_hd() */
+ bdrv_ref(top);
+ bdrv_ref(overlay_bs);
+
/* Remove base node parent that still uses BLK_PERM_WRITE/RESIZE before
* the normal backing chain can be restored. */
blk_unref(s->base);
@@ -124,6 +128,9 @@ static void commit_complete(BlockJob *job, void *opaque)
if (remove_commit_top_bs) {
bdrv_set_backing_hd(overlay_bs, top, &error_abort);
}
+
+ bdrv_unref(overlay_bs);
+ bdrv_unref(top);
}
static void coroutine_fn commit_run(void *opaque)
--
1.8.3.1