From nobody Wed Nov 12 03:42:19 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1568312548; cv=none; d=zoho.com; s=zohoarc; b=hTM3TMAu+f6Fs/Zj70hia0IPN25kYd+Ck8kY81Jgrdj1tC7SwjK2WBrfDyFLuWRQEumc0nWjDYzwgORKlhVRCTWDLkWV1WjbB7JCbmUcxK8gbO2g5Zg2z50k+PnYuqL0P5hlIpS0HtE5Rc5lv5bOW8Y1KpO9w42OpDI2fMNXKUo= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; s=zohoarc; t=1568312548; h=Content-Transfer-Encoding:Cc:Date:From:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:Sender:Subject:To:ARC-Authentication-Results; bh=cT/34meb+jKKkHRjLIfPTcbUK7uBFpMhHc+GMzLvlrQ=; b=blBP5H2SS3Dag6rHVI7Pju8b8420Bm8j9+Es7ctlatkH8MAQB/TIcJs/zlW43CKZzJw5VTASN9vL1BCIddJqc62tugdQUjNAYA1CvQFxPDFibjw0S9j5XzMtkvrUPvppAINtPYYnfNoC3fWksG/EHV7sDK3zfwYNXQ7lFHcgY3M= ARC-Authentication-Results: i=1; mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 156831254867256.21790806549893; Thu, 12 Sep 2019 11:22:28 -0700 (PDT) Received: from localhost ([::1]:37576 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8Tjc-0006WD-66 for importer@patchew.org; Thu, 12 Sep 2019 14:22:24 -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) Content-Transfer-Encoding: quoted-printable 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+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Type: text/plain; charset="utf-8" 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=3D1744955 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 *vde= v, QEMUFile *f, return 0; } =20 +static void coroutine_fn virtio_resize_co_entry(void *opaque) +{ + VirtIODevice *vdev =3D opaque; + + assert(qemu_get_current_aio_context() =3D=3D qemu_get_aio_context()); + virtio_notify_config(vdev); + aio_wait_kick(); +} + static void virtio_blk_resize(void *opaque) { VirtIODevice *vdev =3D VIRTIO_DEVICE(opaque); + Coroutine *co; =20 - virtio_notify_config(vdev); + if (qemu_in_coroutine() && + qemu_get_current_aio_context() !=3D 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 =3D qemu_coroutine_create(virtio_resize_co_entry, vdev); + aio_co_schedule(qemu_get_aio_context(), co); + } else { + virtio_notify_config(vdev); + } } =20 static const BlockDevOps virtio_block_ops =3D { --=20 2.21.0