From nobody Wed Oct 22 13:01:18 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 (lists.gnu.org [208.118.235.17]) by mx.zohomail.com with SMTPS id 1520434012868465.06383153129025; Wed, 7 Mar 2018 06:46:52 -0800 (PST) Received: from localhost ([::1]:33823 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1etaLC-0006Li-G8 for importer@patchew.org; Wed, 07 Mar 2018 09:46:50 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53092) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1etaGx-0002oA-UE for qemu-devel@nongnu.org; Wed, 07 Mar 2018 09:42:33 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1etaGw-0005AH-VX for qemu-devel@nongnu.org; Wed, 07 Mar 2018 09:42:27 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:51502 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 1etaGm-0004qk-Sr; Wed, 07 Mar 2018 09:42:17 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id CFDC18182D0C; Wed, 7 Mar 2018 14:42:15 +0000 (UTC) Received: from localhost (ovpn-116-116.ams2.redhat.com [10.36.116.116]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7CED3215CDA7; Wed, 7 Mar 2018 14:42:15 +0000 (UTC) From: Stefan Hajnoczi To: Date: Wed, 7 Mar 2018 14:42:03 +0000 Message-Id: <20180307144205.20619-3-stefanha@redhat.com> In-Reply-To: <20180307144205.20619-1-stefanha@redhat.com> References: <20180307144205.20619-1-stefanha@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Wed, 07 Mar 2018 14:42:15 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Wed, 07 Mar 2018 14:42:15 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'stefanha@redhat.com' RCPT:'' X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 66.187.233.73 Subject: [Qemu-devel] [PATCH v3 2/4] virtio-blk: fix race between .ioeventfd_stop() and vq handler 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-block@nongnu.org, Peter Crosthwaite , "Michael S. Tsirkin" , Max Reitz , Stefan Hajnoczi , Paolo Bonzini , Richard Henderson Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail: RSF_0 Z_629925259 SPT_0 Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" If the main loop thread invokes .ioeventfd_stop() just as the vq handler function begins in the IOThread then the handler may lose the race for the AioContext lock. By the time the vq handler is able to acquire the AioContext lock the ioeventfd has already been removed and the handler isn't supposed to run anymore! Use the new aio_wait_bh_oneshot() function to perform ioeventfd removal from within the IOThread. This way no races with the vq handler are possible. Signed-off-by: Stefan Hajnoczi --- hw/block/dataplane/virtio-blk.c | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-bl= k.c index 2cb990997e..d3bb09bc4e 100644 --- a/hw/block/dataplane/virtio-blk.c +++ b/hw/block/dataplane/virtio-blk.c @@ -229,6 +229,22 @@ int virtio_blk_data_plane_start(VirtIODevice *vdev) return -ENOSYS; } =20 +/* Stop notifications for new requests from guest. + * + * Context: BH in IOThread + */ +static void virtio_blk_data_plane_stop_bh(void *opaque) +{ + VirtIOBlockDataPlane *s =3D opaque; + unsigned i; + + for (i =3D 0; i < s->conf->num_queues; i++) { + VirtQueue *vq =3D virtio_get_queue(s->vdev, i); + + virtio_queue_aio_set_host_notifier_handler(vq, s->ctx, NULL); + } +} + /* Context: QEMU global mutex held */ void virtio_blk_data_plane_stop(VirtIODevice *vdev) { @@ -253,13 +269,7 @@ void virtio_blk_data_plane_stop(VirtIODevice *vdev) trace_virtio_blk_data_plane_stop(s); =20 aio_context_acquire(s->ctx); - - /* Stop notifications for new requests from guest */ - for (i =3D 0; i < nvqs; i++) { - VirtQueue *vq =3D virtio_get_queue(s->vdev, i); - - virtio_queue_aio_set_host_notifier_handler(vq, s->ctx, NULL); - } + aio_wait_bh_oneshot(s->ctx, virtio_blk_data_plane_stop_bh, s); =20 /* Drain and switch bs back to the QEMU main loop */ blk_set_aio_context(s->conf->conf.blk, qemu_get_aio_context()); --=20 2.14.3