From patchwork Mon Jan 22 22:07:51 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Max Reitz X-Patchwork-Id: 10179357 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 2088E600F5 for ; Mon, 22 Jan 2018 22:09:43 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 10B2226E3A for ; Mon, 22 Jan 2018 22:09:43 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 04E3F28569; Mon, 22 Jan 2018 22:09:43 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 8AC1728535 for ; Mon, 22 Jan 2018 22:09:42 +0000 (UTC) Received: from localhost ([::1]:41416 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1edkHb-0006b1-9e for patchwork-qemu-devel@patchwork.kernel.org; Mon, 22 Jan 2018 17:09:39 -0500 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 Received: from mx1.redhat.com ([209.132.183.28]:53745) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1edkGQ-0003K5-49; Mon, 22 Jan 2018 17:08:26 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 52B6F5F15F; Mon, 22 Jan 2018 22:08:25 +0000 (UTC) Received: from localhost (ovpn-204-78.brq.redhat.com [10.40.204.78]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 979CC67645; Mon, 22 Jan 2018 22:08:24 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org 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> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Mon, 22 Jan 2018 22:08:25 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH v2 01/16] block: BDS deletion during bdrv_drain_recurse X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Fam Zheng , qemu-devel@nongnu.org, Max Reitz , Stefan Hajnoczi , John Snow Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP 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;