Draining a BDS child may lead to other children of the same parent being
detached and/or deleted. We should prepare for the former case (by
copying the children list before iterating through it) and prevent the
latter (by bdrv_ref()'ing all nodes if we are in the main loop).
Signed-off-by: Max Reitz <mre...@redhat.com>
---
block/io.c | 40 ++++++++++++++++++++++++++++++----------
1 file changed, 30 insertions(+), 10 deletions(-)
diff --git a/block/io.c b/block/io.c
index 4d3d1f640a..ead12c4136 100644
--- a/block/io.c
+++ b/block/io.c
@@ -189,31 +189,51 @@ static void bdrv_drain_invoke(BlockDriverState *bs, bool
begin, bool recursive)
static bool bdrv_drain_recurse(BlockDriverState *bs)
{
- BdrvChild *child, *tmp;
+ BdrvChild *child;
bool waited;
+ struct BDSToDrain {
+ BlockDriverState *bs;
+ QLIST_ENTRY(BDSToDrain) next;
+ };
+ QLIST_HEAD(, BDSToDrain) bs_list = QLIST_HEAD_INITIALIZER(bs_list);
+ bool in_main_loop =
+ qemu_get_current_aio_context() == qemu_get_aio_context();
/* Wait for drained requests to finish */
waited = BDRV_POLL_WHILE(bs, atomic_read(&bs->in_flight) > 0);
- QLIST_FOREACH_SAFE(child, &bs->children, next, tmp) {
- BlockDriverState *bs = child->bs;
- bool in_main_loop =
- qemu_get_current_aio_context() == qemu_get_aio_context();
- assert(bs->refcnt > 0);
+ /* Draining children may result in other children being removed from this
+ * parent and maybe even deleted, so copy the children list first */
+ QLIST_FOREACH(child, &bs->children, next) {
+ struct BDSToDrain *bs2d = g_new0(struct BDSToDrain, 1);
+
+ bs2d->bs = child->bs;
if (in_main_loop) {
/* In case the recursive bdrv_drain_recurse processes a
* block_job_defer_to_main_loop BH and modifies the graph,
- * let's hold a reference to bs until we are done.
+ * let's hold a reference to the BDS until we are done.
*
* IOThread doesn't have such a BH, and it is not safe to call
* bdrv_unref without BQL, so skip doing it there.
*/
- bdrv_ref(bs);
+ bdrv_ref(bs2d->bs);
}
- waited |= bdrv_drain_recurse(bs);
+
+ QLIST_INSERT_HEAD(&bs_list, bs2d, next);
+ }
+
+ while (!QLIST_EMPTY(&bs_list)) {
+ struct BDSToDrain *bs2d = QLIST_FIRST(&bs_list);
+ QLIST_REMOVE(bs2d, next);
+
+ assert(bs2d->bs->refcnt > 0);
+
+ waited |= bdrv_drain_recurse(bs2d->bs);
if (in_main_loop) {
- bdrv_unref(bs);
+ bdrv_unref(bs2d->bs);
}
+
+ g_free(bs2d);
}
return waited;
--
2.14.3
