From nobody Wed Nov 5 12:43:25 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) client-ip=208.118.235.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 208.118.235.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com Return-Path: Received: from lists.gnu.org (208.118.235.17 [208.118.235.17]) by mx.zohomail.com with SMTPS id 1534525861806683.6511242906988; Fri, 17 Aug 2018 10:11:01 -0700 (PDT) Received: from localhost ([::1]:35513 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fqiGy-0002aT-CR for importer@patchew.org; Fri, 17 Aug 2018 13:10:52 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58670) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fqi9N-0002j2-Cq for qemu-devel@nongnu.org; Fri, 17 Aug 2018 13:03:02 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fqi9M-0002EO-Hd for qemu-devel@nongnu.org; Fri, 17 Aug 2018 13:03:01 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:47024 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fqi9K-0002BX-JR; Fri, 17 Aug 2018 13:02:58 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 460B9401DEC6; Fri, 17 Aug 2018 17:02:58 +0000 (UTC) Received: from localhost.localdomain.com (ovpn-116-205.ams2.redhat.com [10.36.116.205]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4F0F5112D197; Fri, 17 Aug 2018 17:02:57 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Date: Fri, 17 Aug 2018 19:02:45 +0200 Message-Id: <20180817170246.14641-5-kwolf@redhat.com> In-Reply-To: <20180817170246.14641-1-kwolf@redhat.com> References: <20180817170246.14641-1-kwolf@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Fri, 17 Aug 2018 17:02:58 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.6]); Fri, 17 Aug 2018 17:02:58 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'kwolf@redhat.com' RCPT:'' X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 66.187.233.73 Subject: [Qemu-devel] [RFC PATCH 4/5] block: Drop AioContext lock in bdrv_drain_poll_top_level() 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: kwolf@redhat.com, famz@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RDMRC_1 RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Simimlar to AIO_WAIT_WHILE(), bdrv_drain_poll_top_level() needs to release the AioContext lock of the node to be drained before calling aio_poll(). Otherwise, callbacks called by aio_poll() would possibly take the lock a second time and run into a deadlock with a nested AIO_WAIT_WHILE() call. Signed-off-by: Kevin Wolf --- block/io.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/block/io.c b/block/io.c index 7100344c7b..832d2536bf 100644 --- a/block/io.c +++ b/block/io.c @@ -268,9 +268,32 @@ bool bdrv_drain_poll(BlockDriverState *bs, bool recurs= ive, static bool bdrv_drain_poll_top_level(BlockDriverState *bs, bool recursive, BdrvChild *ignore_parent) { + AioContext *ctx =3D bdrv_get_aio_context(bs); + + /* + * We cannot easily release the lock unconditionally here because many + * callers of drain function (like qemu initialisation, tools, etc.) d= on't + * even hold the main context lock. + * + * This means that we fix potential deadlocks for the case where we ar= e in + * the main context and polling a BDS in a different AioContext, but + * draining a BDS in the main context from a different I/O thread would + * still have this problem. Fortunately, this isn't supposed to happen + * anyway. + */ + if (ctx !=3D qemu_get_aio_context()) { + aio_context_release(ctx); + } else { + assert(qemu_get_current_aio_context() =3D=3D qemu_get_aio_context(= )); + } + /* Execute pending BHs first and check everything else only after the = BHs * have executed. */ - while (aio_poll(bs->aio_context, false)); + while (aio_poll(ctx, false)); + + if (ctx !=3D qemu_get_aio_context()) { + aio_context_acquire(ctx); + } =20 return bdrv_drain_poll(bs, recursive, ignore_parent, false); } --=20 2.13.6