From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55364) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1edkGT-0005hB-S5 for qemu-devel@nongnu.org; Mon, 22 Jan 2018 17:08:30 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1edkGS-0003LQ-QL for qemu-devel@nongnu.org; Mon, 22 Jan 2018 17:08:29 -0500 From: Max Reitz Date: Mon, 22 Jan 2018 23:07:51 +0100 Message-Id: <20180122220806.22154-2-mreitz@redhat.com> In-Reply-To: <20180122220806.22154-1-mreitz@redhat.com> References: <20180122220806.22154-1-mreitz@redhat.com> Subject: [Qemu-devel] [PATCH v2 01/16] block: BDS deletion during bdrv_drain_recurse List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org Cc: qemu-devel@nongnu.org, Max Reitz , Kevin Wolf , John Snow , Fam Zheng , Stefan Hajnoczi 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 --- block/io.c | 40 ++++++++++++++++++++++++++++++---------- 1 file changed, 30 insertions(+), 10 deletions(-) diff --git a/block/io.c b/block/io.c index 7ea402352e..ca7dfecfc9 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