From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:35770) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hIfPs-0005wn-V2 for qemu-devel@nongnu.org; Mon, 22 Apr 2019 16:19:54 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hIfLE-0006TY-Lt for qemu-devel@nongnu.org; Mon, 22 Apr 2019 16:15:05 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:53848) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hIfLE-0006So-FO for qemu-devel@nongnu.org; Mon, 22 Apr 2019 16:15:04 -0400 Received: from mail-it1-f200.google.com ([209.85.166.200]) by youngberry.canonical.com with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.76) (envelope-from ) id 1hIfLC-0004Ta-Tb for qemu-devel@nongnu.org; Mon, 22 Apr 2019 20:15:03 +0000 Received: by mail-it1-f200.google.com with SMTP id m128so13600852itm.6 for ; Mon, 22 Apr 2019 13:15:02 -0700 (PDT) MIME-Version: 1.0 References: <20190416184624.15397-1-dan.streetman@canonical.com> <20190416184624.15397-2-dan.streetman@canonical.com> <9f3dac2a-15fe-8463-6aee-f6916b8d5e1c@redhat.com> In-Reply-To: <9f3dac2a-15fe-8463-6aee-f6916b8d5e1c@redhat.com> From: Dan Streetman Date: Mon, 22 Apr 2019 16:14:25 -0400 Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 1/2] add VirtIONet vhost_stopped flag to prevent multiple stops List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jason Wang Cc: "Michael S. Tsirkin" , qemu-devel@nongnu.org, qemu-stable@nongnu.org On Sun, Apr 21, 2019 at 10:50 PM Jason Wang wrote: > > > On 2019/4/17 =E4=B8=8A=E5=8D=882:46, Dan Streetman wrote: > > From: Dan Streetman > > > > Buglink: https://launchpad.net/bugs/1823458 > > > > There is a race condition when using the vhost-user driver, between a g= uest > > shutdown and the vhost-user interface being closed. This is explained = in > > more detail at the bug link above; the short explanation is the vhost-u= ser > > device can be closed while the main thread is in the middle of stopping > > the vhost_net. In this case, the main thread handling shutdown will > > enter virtio_net_vhost_status() and move into the n->vhost_started (els= e) > > block, and call vhost_net_stop(); while it is running that function, > > another thread is notified that the vhost-user device has been closed, > > and (indirectly) calls into virtio_net_vhost_status() also. > > > I think we need figure out why there are multiple vhost_net_stop() calls > simultaneously. E.g vhost-user register fd handlers like: > > qemu_chr_fe_set_handlers(&s->chr, NULL, NULL, > net_vhost_user_event, NULL, nc0->name, > NULL, > true); > > which uses default main context, so it should only be called only in > main thread. net_vhost_user_event() schedules chr_closed_bh() to do its bottom half work; does aio_bh_schedule_oneshot() execute its events from the main thread? For reference, the call chain is: chr_closed_bh() qmp_set_link() nc->info->link_status_changed() -> virtio_net_set_link_status() virtio_net_set_status() virtio_net_vhost_status() > > Thanks > > > > Since the > > vhost_net status hasn't yet changed, the second thread also enters > > the n->vhost_started block, and also calls vhost_net_stop(). This > > causes problems for the second thread when it tries to stop the network > > that's already been stopped. > > > > This adds a flag to the struct that's atomically set to prevent more th= an > > one thread from calling vhost_net_stop(). The atomic_fetch_inc() is li= kely > > overkill and probably could be done with a simple check-and-set, but > > since it's a race condition there would still be a (very, very) small > > window without using an atomic to set it. > > > > Signed-off-by: Dan Streetman > > --- > > hw/net/virtio-net.c | 3 ++- > > include/hw/virtio/virtio-net.h | 1 + > > 2 files changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > index ffe0872fff..d36f50d5dd 100644 > > --- a/hw/net/virtio-net.c > > +++ b/hw/net/virtio-net.c > > @@ -13,6 +13,7 @@ > > > > #include "qemu/osdep.h" > > #include "qemu/iov.h" > > +#include "qemu/atomic.h" > > #include "hw/virtio/virtio.h" > > #include "net/net.h" > > #include "net/checksum.h" > > @@ -240,7 +241,7 @@ static void virtio_net_vhost_status(VirtIONet *n, u= int8_t status) > > "falling back on userspace virtio", -r); > > n->vhost_started =3D 0; > > } > > - } else { > > + } else if (atomic_fetch_inc(&n->vhost_stopped) =3D=3D 0) { > > vhost_net_stop(vdev, n->nic->ncs, queues); > > n->vhost_started =3D 0; > > } > > diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-= net.h > > index b96f0c643f..d03fd933d0 100644 > > --- a/include/hw/virtio/virtio-net.h > > +++ b/include/hw/virtio/virtio-net.h > > @@ -164,6 +164,7 @@ struct VirtIONet { > > uint8_t nouni; > > uint8_t nobcast; > > uint8_t vhost_started; > > + int vhost_stopped; > > struct { > > uint32_t in_use; > > uint32_t first_multi; From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CB551C10F11 for ; Mon, 22 Apr 2019 20:21:26 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 94E7B20693 for ; 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Mon, 22 Apr 2019 13:15:01 -0700 (PDT) X-Google-Smtp-Source: APXvYqyQxsdQXVntrAqfjClMeW4mnUwY9/NLWbr8FUnz/bQet017IhYL2J1grW/cFeaPKnW1kjJbpEDdBz9tYNr6ePA= X-Received: by 2002:a02:ad07:: with SMTP id s7mr5840212jan.103.1555964101527; Mon, 22 Apr 2019 13:15:01 -0700 (PDT) MIME-Version: 1.0 References: <20190416184624.15397-1-dan.streetman@canonical.com> <20190416184624.15397-2-dan.streetman@canonical.com> <9f3dac2a-15fe-8463-6aee-f6916b8d5e1c@redhat.com> In-Reply-To: <9f3dac2a-15fe-8463-6aee-f6916b8d5e1c@redhat.com> From: Dan Streetman Date: Mon, 22 Apr 2019 16:14:25 -0400 Message-ID: To: Jason Wang Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 3.x X-Received-From: 91.189.89.112 Subject: Re: [Qemu-devel] [PATCH 1/2] add VirtIONet vhost_stopped flag to prevent multiple stops 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: qemu-stable@nongnu.org, qemu-devel@nongnu.org, "Michael S. Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Message-ID: <20190422201425.srHNSS211G7XhJYgkglQoseexMDcPt8R7opCuITIuTI@z> On Sun, Apr 21, 2019 at 10:50 PM Jason Wang wrote: > > > On 2019/4/17 =E4=B8=8A=E5=8D=882:46, Dan Streetman wrote: > > From: Dan Streetman > > > > Buglink: https://launchpad.net/bugs/1823458 > > > > There is a race condition when using the vhost-user driver, between a g= uest > > shutdown and the vhost-user interface being closed. This is explained = in > > more detail at the bug link above; the short explanation is the vhost-u= ser > > device can be closed while the main thread is in the middle of stopping > > the vhost_net. In this case, the main thread handling shutdown will > > enter virtio_net_vhost_status() and move into the n->vhost_started (els= e) > > block, and call vhost_net_stop(); while it is running that function, > > another thread is notified that the vhost-user device has been closed, > > and (indirectly) calls into virtio_net_vhost_status() also. > > > I think we need figure out why there are multiple vhost_net_stop() calls > simultaneously. E.g vhost-user register fd handlers like: > > qemu_chr_fe_set_handlers(&s->chr, NULL, NULL, > net_vhost_user_event, NULL, nc0->name, > NULL, > true); > > which uses default main context, so it should only be called only in > main thread. net_vhost_user_event() schedules chr_closed_bh() to do its bottom half work; does aio_bh_schedule_oneshot() execute its events from the main thread? For reference, the call chain is: chr_closed_bh() qmp_set_link() nc->info->link_status_changed() -> virtio_net_set_link_status() virtio_net_set_status() virtio_net_vhost_status() > > Thanks > > > > Since the > > vhost_net status hasn't yet changed, the second thread also enters > > the n->vhost_started block, and also calls vhost_net_stop(). This > > causes problems for the second thread when it tries to stop the network > > that's already been stopped. > > > > This adds a flag to the struct that's atomically set to prevent more th= an > > one thread from calling vhost_net_stop(). The atomic_fetch_inc() is li= kely > > overkill and probably could be done with a simple check-and-set, but > > since it's a race condition there would still be a (very, very) small > > window without using an atomic to set it. > > > > Signed-off-by: Dan Streetman > > --- > > hw/net/virtio-net.c | 3 ++- > > include/hw/virtio/virtio-net.h | 1 + > > 2 files changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c > > index ffe0872fff..d36f50d5dd 100644 > > --- a/hw/net/virtio-net.c > > +++ b/hw/net/virtio-net.c > > @@ -13,6 +13,7 @@ > > > > #include "qemu/osdep.h" > > #include "qemu/iov.h" > > +#include "qemu/atomic.h" > > #include "hw/virtio/virtio.h" > > #include "net/net.h" > > #include "net/checksum.h" > > @@ -240,7 +241,7 @@ static void virtio_net_vhost_status(VirtIONet *n, u= int8_t status) > > "falling back on userspace virtio", -r); > > n->vhost_started =3D 0; > > } > > - } else { > > + } else if (atomic_fetch_inc(&n->vhost_stopped) =3D=3D 0) { > > vhost_net_stop(vdev, n->nic->ncs, queues); > > n->vhost_started =3D 0; > > } > > diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-= net.h > > index b96f0c643f..d03fd933d0 100644 > > --- a/include/hw/virtio/virtio-net.h > > +++ b/include/hw/virtio/virtio-net.h > > @@ -164,6 +164,7 @@ struct VirtIONet { > > uint8_t nouni; > > uint8_t nobcast; > > uint8_t vhost_started; > > + int vhost_stopped; > > struct { > > uint32_t in_use; > > uint32_t first_multi;