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[79.180.2.31]) by smtp.gmail.com with ESMTPSA id l1sm3861719wmq.17.2021.02.10.13.39.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Feb 2021 13:39:09 -0800 (PST) Date: Wed, 10 Feb 2021 16:39:06 -0500 From: "Michael S. Tsirkin" To: Vivek Goyal Subject: Re: [RFC PATCH 0/6] vhost-user: Shutdown/Flush slave channel properly Message-ID: <20210210163830-mutt-send-email-mst@kernel.org> References: <20210125180115.22936-1-vgoyal@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210125180115.22936-1-vgoyal@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -33 X-Spam_score: -3.4 X-Spam_bar: --- X-Spam_report: (-3.4 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.568, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no 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: virtio-fs@redhat.com, marcandre.lureau@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com, dgilbert@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jan 25, 2021 at 01:01:09PM -0500, Vivek Goyal wrote: > Hi, > > We are working on DAX support in virtiofs and have some patches out of > the tree hosted here. > > https://gitlab.com/virtio-fs/qemu/-/commits/virtio-fs-dev > > These patches have not been proposed for merge yet, becasue David > Gilbert noticed that we can run into a deadlock during an emergency > reboot of guest kernel. (echo b > /proc/sysrq-trigger). > > I have provided details of deadlock in 4th path of the series with > subject "qemu, vhost-user: Extend protocol to start/stop/flush slave > channel". > > Basic problem seems to be that we don't have a proper mechanism to > shutdown slave channel when vhost-user device is stopping. This means > there might be pending messages in slave channel and slave is blocked > and waiting for response. > > This is an RFC patch series to enhance vhost-user protocol to > properly shutdown/flush slave channel and avoid the deadlock. Though > we faced the issue in the context of virtiofs, any vhost-user > device using slave channel can potentially run into issues and > can benefit from these patches. > > Any feedback is welcome. Currently patches are based on out of > tree code but after I get some feedback, I can only take pieces > which are relevant to upstream and post separately. > > Thanks > Vivek No comments so far - do you plan to post a non-RFC patchset? > Vivek Goyal (6): > virtiofsd: Drop ->vu_dispatch_rwlock while waiting for thread to exit > libvhost-user: Use slave_mutex in all slave messages > vhost-user: Return error code from slave_read() > qemu, vhost-user: Extend protocol to start/stop/flush slave channel > libvhost-user: Add support to start/stop/flush slave channel > virtiofsd: Opt in for slave start/stop/shutdown functionality > > hw/virtio/vhost-user.c | 151 +++++++++++++++++++++- > subprojects/libvhost-user/libvhost-user.c | 147 +++++++++++++++++---- > subprojects/libvhost-user/libvhost-user.h | 8 +- > tools/virtiofsd/fuse_virtio.c | 20 +++ > 4 files changed, 294 insertions(+), 32 deletions(-) > > -- > 2.25.4