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Tsirkin" , Dima Stepanov References: <20200511092541.GA27558@dimastep-nix> <20200512093521.GA5363@dimastep-nix> <20200512235934-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: Date: Wed, 13 May 2020 13:56:18 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200512235934-mutt-send-email-mst@kernel.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.120; envelope-from=jasowang@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/13 01:56:38 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action 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: fam@euphon.net, kwolf@redhat.com, stefanha@redhat.com, qemu-block@nongnu.org, dgilbert@redhat.com, qemu-devel@nongnu.org, arei.gonglei@huawei.com, fengli@smartx.com, yc-core@yandex-team.ru, pbonzini@redhat.com, marcandre.lureau@redhat.com, raphael.norwitz@nutanix.com, mreitz@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 2020/5/13 下午12:15, Michael S. Tsirkin wrote: > On Tue, May 12, 2020 at 12:35:30PM +0300, Dima Stepanov wrote: >> On Tue, May 12, 2020 at 11:32:50AM +0800, Jason Wang wrote: >>> On 2020/5/11 下午5:25, Dima Stepanov wrote: >>>> On Mon, May 11, 2020 at 11:15:53AM +0800, Jason Wang wrote: >>>>> On 2020/4/30 下午9:36, Dima Stepanov wrote: >>>>>> If vhost-user daemon is used as a backend for the vhost device, then we >>>>>> should consider a possibility of disconnect at any moment. If such >>>>>> disconnect happened in the vhost_migration_log() routine the vhost >>>>>> device structure will be clean up. >>>>>> At the start of the vhost_migration_log() function there is a check: >>>>>> if (!dev->started) { >>>>>> dev->log_enabled = enable; >>>>>> return 0; >>>>>> } >>>>>> To be consistent with this check add the same check after calling the >>>>>> vhost_dev_set_log() routine. This in general help not to break a >>>>>> migration due the assert() message. But it looks like that this code >>>>>> should be revised to handle these errors more carefully. >>>>>> >>>>>> In case of vhost-user device backend the fail paths should consider the >>>>>> state of the device. In this case we should skip some function calls >>>>>> during rollback on the error paths, so not to get the NULL dereference >>>>>> errors. >>>>>> >>>>>> Signed-off-by: Dima Stepanov >>>>>> --- >>>>>> hw/virtio/vhost.c | 39 +++++++++++++++++++++++++++++++++++---- >>>>>> 1 file changed, 35 insertions(+), 4 deletions(-) >>>>>> >>>>>> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c >>>>>> index 3ee50c4..d5ab96d 100644 >>>>>> --- a/hw/virtio/vhost.c >>>>>> +++ b/hw/virtio/vhost.c >>>>>> @@ -787,6 +787,17 @@ static int vhost_dev_set_features(struct vhost_dev *dev, >>>>>> static int vhost_dev_set_log(struct vhost_dev *dev, bool enable_log) >>>>>> { >>>>>> int r, i, idx; >>>>>> + >>>>>> + if (!dev->started) { >>>>>> + /* >>>>>> + * If vhost-user daemon is used as a backend for the >>>>>> + * device and the connection is broken, then the vhost_dev >>>>>> + * structure will be reset all its values to 0. >>>>>> + * Add additional check for the device state. >>>>>> + */ >>>>>> + return -1; >>>>>> + } >>>>>> + >>>>>> r = vhost_dev_set_features(dev, enable_log); >>>>>> if (r < 0) { >>>>>> goto err_features; >>>>>> @@ -801,12 +812,19 @@ static int vhost_dev_set_log(struct vhost_dev *dev, bool enable_log) >>>>>> } >>>>>> return 0; >>>>>> err_vq: >>>>>> - for (; i >= 0; --i) { >>>>>> + /* >>>>>> + * Disconnect with the vhost-user daemon can lead to the >>>>>> + * vhost_dev_cleanup() call which will clean up vhost_dev >>>>>> + * structure. >>>>>> + */ >>>>>> + for (; dev->started && (i >= 0); --i) { >>>>>> idx = dev->vhost_ops->vhost_get_vq_index( >>>>> Why need the check of dev->started here, can started be modified outside >>>>> mainloop? If yes, I don't get the check of !dev->started in the beginning of >>>>> this function. >>>>> >>>> No dev->started can't change outside the mainloop. The main problem is >>>> only for the vhost_user_blk daemon. Consider the case when we >>>> successfully pass the dev->started check at the beginning of the >>>> function, but after it we hit the disconnect on the next call on the >>>> second or third iteration: >>>> r = vhost_virtqueue_set_addr(dev, dev->vqs + i, idx, enable_log); >>>> The unix socket backend device will call the disconnect routine for this >>>> device and reset the structure. So the structure will be reset (and >>>> dev->started set to false) inside this set_addr() call. >>> I still don't get here. I think the disconnect can not happen in the middle >>> of vhost_dev_set_log() since both of them were running in mainloop. And even >>> if it can, we probably need other synchronization mechanism other than >>> simple check here. >> Disconnect isn't happened in the separate thread it is happened in this >> routine inside vhost_dev_set_log. When for instance vhost_user_write() >> call failed: >> vhost_user_set_log_base() >> vhost_user_write() >> vhost_user_blk_disconnect() >> vhost_dev_cleanup() >> vhost_user_backend_cleanup() >> So the point is that if we somehow got a disconnect with the >> vhost-user-blk daemon before the vhost_user_write() call then it will >> continue clean up by running vhost_user_blk_disconnect() function. I >> wrote a more detailed backtrace stack in the separate thread, which is >> pretty similar to what we have here: >> Re: [PATCH v2 4/5] vhost: check vring address before calling unmap >> The places are different but the problem is pretty similar. >> >> So if vhost-user commands handshake then everything is fine and >> reconnect will work as expected. The only problem is how to handle >> reconnect properly between vhost-user command send/receive. > > So vhost net had this problem too. > > commit e7c83a885f865128ae3cf1946f8cb538b63cbfba > Author: Marc-André Lureau > Date: Mon Feb 27 14:49:56 2017 +0400 > > vhost-user: delay vhost_user_stop > > Since commit b0a335e351103bf92f3f9d0bd5759311be8156ac, a socket write > may trigger a disconnect events, calling vhost_user_stop() and clearing > all the vhost_dev strutures holding data that vhost.c functions expect > to remain valid. Delay the cleanup to keep the vhost_dev structure > valid during the vhost.c functions. > > Signed-off-by: Marc-André Lureau > Message-id:20170227104956.24729-1-marcandre.lureau@redhat.com > Signed-off-by: Peter Maydell > > it now has this code to address this: > > > case CHR_EVENT_CLOSED: > /* a close event may happen during a read/write, but vhost > * code assumes the vhost_dev remains setup, so delay the > * stop & clear to idle. > * FIXME: better handle failure in vhost code, remove bh > */ > if (s->watch) { > AioContext *ctx = qemu_get_current_aio_context(); > > g_source_remove(s->watch); > s->watch = 0; > qemu_chr_fe_set_handlers(&s->chr, NULL, NULL, NULL, NULL, > NULL, NULL, false); > > aio_bh_schedule_oneshot(ctx, chr_closed_bh, opaque); > } > break; > > I think it's time we dropped the FIXME and moved the handling to common > code. Jason? Marc-André? I agree. Just to confirm, do you prefer bh or doing changes like what is done in this series? It looks to me bh can have more easier codes. Thanks > > > > >