Drainined a BDS child may lead to both the original BDS and/or its other children being deleted (e.g. if the original BDS represents a block job). We should prepare for this in both bdrv_drain_recurse() and bdrv_drained_begin() by monitoring whether the BDS we are about to drain still exists at all.
Signed-off-by: Max Reitz <mre...@redhat.com> --- block/io.c | 72 +++++++++++++++++++++++++++++++++++++++++++++----------------- 1 file changed, 52 insertions(+), 20 deletions(-) diff --git a/block/io.c b/block/io.c index 4378ae4c7d..8ec1a564ad 100644 --- a/block/io.c +++ b/block/io.c @@ -182,33 +182,57 @@ static void bdrv_drain_invoke(BlockDriverState *bs) static bool bdrv_drain_recurse(BlockDriverState *bs) { - BdrvChild *child, *tmp; + BdrvChild *child; bool waited; + struct BDSToDrain { + BlockDriverState *bs; + BdrvDeletedStatus del_stat; + 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(); waited = BDRV_POLL_WHILE(bs, atomic_read(&bs->in_flight) > 0); /* Ensure any pending metadata writes are submitted to bs->file. */ bdrv_drain_invoke(bs); - 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); - 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. - * - * 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); - } - waited |= bdrv_drain_recurse(bs); - if (in_main_loop) { - bdrv_unref(bs); + /* Draining children may result in other children being removed 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; + QLIST_INSERT_HEAD(&bs->deleted_status, &bs2d->del_stat, next); + + QLIST_INSERT_HEAD(&bs_list, bs2d, next); + } + + while (!QLIST_EMPTY(&bs_list)) { + struct BDSToDrain *bs2d = QLIST_FIRST(&bs_list); + QLIST_REMOVE(bs2d, next); + + if (!bs2d->del_stat.deleted) { + QLIST_REMOVE(&bs2d->del_stat, next); + + 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 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(bs2d->bs); + } + waited |= bdrv_drain_recurse(bs2d->bs); + if (in_main_loop) { + bdrv_unref(bs2d->bs); + } } + + g_free(bs2d); } return waited; @@ -252,17 +276,25 @@ static void coroutine_fn bdrv_co_yield_to_drain(BlockDriverState *bs) void bdrv_drained_begin(BlockDriverState *bs) { + BdrvDeletedStatus del_stat = { .deleted = false }; + if (qemu_in_coroutine()) { bdrv_co_yield_to_drain(bs); return; } + QLIST_INSERT_HEAD(&bs->deleted_status, &del_stat, next); + if (atomic_fetch_inc(&bs->quiesce_counter) == 0) { aio_disable_external(bdrv_get_aio_context(bs)); bdrv_parent_drained_begin(bs); } - bdrv_drain_recurse(bs); + if (!del_stat.deleted) { + QLIST_REMOVE(&del_stat, next); + + bdrv_drain_recurse(bs); + } } void bdrv_drained_end(BlockDriverState *bs) -- 2.13.5