From patchwork Thu Sep 12 18:19:25 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sergio Lopez Pascual X-Patchwork-Id: 11143655 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id C2AD0924 for ; Thu, 12 Sep 2019 18:22:07 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A517820684 for ; Thu, 12 Sep 2019 18:22:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A517820684 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Received: from localhost ([::1]:37576 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8TjK-0006WD-Ln for patchwork-qemu-devel@patchwork.kernel.org; Thu, 12 Sep 2019 14:22:06 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54888) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8Thl-0005GR-Jz for qemu-devel@nongnu.org; Thu, 12 Sep 2019 14:20:30 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i8Thk-00042P-Hw for qemu-devel@nongnu.org; Thu, 12 Sep 2019 14:20:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:21839) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i8Thd-0003wz-RO; Thu, 12 Sep 2019 14:20:23 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id AE6F9309174E; Thu, 12 Sep 2019 18:20:19 +0000 (UTC) Received: from dritchie.redhat.com (unknown [10.33.36.24]) by smtp.corp.redhat.com (Postfix) with ESMTP id 93D9C453B; Thu, 12 Sep 2019 18:20:02 +0000 (UTC) From: Sergio Lopez To: qemu-block@nongnu.org Date: Thu, 12 Sep 2019 20:19:25 +0200 Message-Id: <20190912181924.48539-1-slp@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Thu, 12 Sep 2019 18:20:19 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [RFC PATCH] virtio-blk: schedule virtio_notify_config to run on main context X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, Sergio Lopez , mst@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com, stefanha@redhat.com Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" Another AioContext-related issue, and this is a tricky one. Executing a QMP block_resize request for a virtio-blk device running on an iothread may cause a deadlock involving the following mutexes: - main thead * Has acquired: qemu_mutex_global. * Is trying the acquire: iothread AioContext lock via AIO_WAIT_WHILE (after aio_poll). - iothread * Has acquired: AioContext lock. * Is trying to acquire: qemu_mutex_global (via virtio_notify_config->prepare_mmio_access). With this change, virtio_blk_resize checks if it's being called from a coroutine context running on a non-main thread, and if that's the case, creates a new coroutine and schedules it to be run on the main thread. This works, but means the actual operation is done asynchronously, perhaps opening a window in which a "device_del" operation may fit and remove the VirtIODevice before virtio_notify_config() is executed. I *think* it shouldn't be possible, as BHs will be processed before any new QMP/monitor command, but I'm open to a different approach. RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=1744955 Signed-off-by: Sergio Lopez --- hw/block/virtio-blk.c | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c index 18851601cb..c763d071f6 100644 --- a/hw/block/virtio-blk.c +++ b/hw/block/virtio-blk.c @@ -16,6 +16,7 @@ #include "qemu/iov.h" #include "qemu/module.h" #include "qemu/error-report.h" +#include "qemu/main-loop.h" #include "trace.h" #include "hw/block/block.h" #include "hw/qdev-properties.h" @@ -1086,11 +1087,33 @@ static int virtio_blk_load_device(VirtIODevice *vdev, QEMUFile *f, return 0; } +static void coroutine_fn virtio_resize_co_entry(void *opaque) +{ + VirtIODevice *vdev = opaque; + + assert(qemu_get_current_aio_context() == qemu_get_aio_context()); + virtio_notify_config(vdev); + aio_wait_kick(); +} + static void virtio_blk_resize(void *opaque) { VirtIODevice *vdev = VIRTIO_DEVICE(opaque); + Coroutine *co; - virtio_notify_config(vdev); + if (qemu_in_coroutine() && + qemu_get_current_aio_context() != qemu_get_aio_context()) { + /* + * virtio_notify_config() needs to acquire the global mutex, + * so calling it from a coroutine running on a non-main context + * may cause a deadlock. Instead, create a new coroutine and + * schedule it to be run on the main thread. + */ + co = qemu_coroutine_create(virtio_resize_co_entry, vdev); + aio_co_schedule(qemu_get_aio_context(), co); + } else { + virtio_notify_config(vdev); + } } static const BlockDevOps virtio_block_ops = {