From nobody Wed Oct 22 13:01:19 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 1519842452587489.37131571894133; Wed, 28 Feb 2018 10:27:32 -0800 (PST) Received: from localhost ([::1]:46097 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1er6Rv-0007Md-5M for importer@patchew.org; Wed, 28 Feb 2018 13:27:31 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46017) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1er6KZ-00082o-Cw for qemu-devel@nongnu.org; Wed, 28 Feb 2018 13:19:56 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1er6KY-0000i5-E2 for qemu-devel@nongnu.org; Wed, 28 Feb 2018 13:19:55 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:54122 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 1er6KW-0000g5-5z; Wed, 28 Feb 2018 13:19:52 -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 C6B754040855; Wed, 28 Feb 2018 18:19:51 +0000 (UTC) Received: from localhost (ovpn-117-50.ams2.redhat.com [10.36.117.50]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7232F2144B21; Wed, 28 Feb 2018 18:19:51 +0000 (UTC) From: Stefan Hajnoczi To: Date: Wed, 28 Feb 2018 18:19:44 +0000 Message-Id: <20180228181946.22958-3-stefanha@redhat.com> In-Reply-To: <20180228181946.22958-1-stefanha@redhat.com> References: <20180228181946.22958-1-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 [10.11.55.5]); Wed, 28 Feb 2018 18:19:51 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.5]); Wed, 28 Feb 2018 18:19:51 +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 v2 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 , Paolo Bonzini , Fam Zheng , Stefan Hajnoczi , qemu-block@nongnu.org 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