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[99.254.121.117]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6b61ba74bdcsm26565426d6.97.2024.07.11.08.38.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Jul 2024 08:38:40 -0700 (PDT) Date: Thu, 11 Jul 2024 11:38:38 -0400 From: Peter Xu To: Prasad Pandit Cc: qemu-devel@nongnu.org, Fabiano Rosas , Jason Wang , "Michael S . Tsirkin" , mcoqueli@redhat.com, Prasad Pandit Subject: Re: [PATCH 0/2] Postcopy migration and vhost-user errors Message-ID: References: <20240711131424.181615-1-ppandit@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20240711131424.181615-1-ppandit@redhat.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.142, 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_H4=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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, Jul 11, 2024 at 06:44:22PM +0530, Prasad Pandit wrote: > From: Prasad Pandit > > Hello, > > * virsh(1) offers multiple options to initiate Postcopy migration: > > 1) virsh migrate --postcopy --postcopy-after-precopy > 2) virsh migrate --postcopy + virsh migrate-postcopy > 3) virsh migrate --postcopy --timeout --timeout-postcopy > > When Postcopy migration is invoked via method (2) or (3) above, > the guest on the destination host seems to hang or get stuck sometimes. > > * During Postcopy migration, multiple threads are spawned on the destination > host to start the guest and setup devices. One such thread starts vhost > device via vhost_dev_start() function and another called fault_thread handles Hmm, I thought it was one of the vcpu threads that invoked vhost_dev_start(), rather than any migration thread? > page faults in user space using kernel's userfaultfd(2) system. > > When fault_thread exits upon completion of Postcopy migration, it sends a > 'postcopy_end' message to the vhost-user device. But sometimes 'postcopy_end' > message is sent while vhost device is being setup via vhost_dev_start(). > > Thread-1 Thread-2 > > vhost_dev_start postcopy_ram_incoming_cleanup > vhost_device_iotlb_miss postcopy_notify > vhost_backend_update_device_iotlb vhost_user_postcopy_notifier > vhost_user_send_device_iotlb_msg vhost_user_postcopy_end > process_message_reply process_message_reply > vhost_user_read vhost_user_read > vhost_user_read_header vhost_user_read_header > "Fail to update device iotlb" "Failed to receive reply to postcopy_end" > > This creates confusion when vhost device receives 'postcopy_end' message while > it is still trying to update IOTLB entries. > > This seems to leave the guest in a stranded/hung state because fault_thread > has exited saying Postcopy migration has ended, but vhost-device is probably > still expecting updates. QEMU logs following errors on the destination host > === > ... > qemu-kvm: vhost_user_read_header: 700871,700871: Failed to read msg header. Flags 0x0 instead of 0x5. > qemu-kvm: vhost_device_iotlb_miss: 700871,700871: Fail to update device iotlb > qemu-kvm: vhost_user_postcopy_end: 700871,700900: Failed to receive reply to postcopy_end > qemu-kvm: vhost_user_read_header: 700871,700871: Failed to read msg header. Flags 0x0 instead of 0x5. > qemu-kvm: vhost_device_iotlb_miss: 700871,700871: Fail to update device iotlb > qemu-kvm: vhost_user_read_header: 700871,700871: Failed to read msg header. Flags 0x8 instead of 0x5. > qemu-kvm: vhost_device_iotlb_miss: 700871,700871: Fail to update device iotlb > qemu-kvm: vhost_user_read_header: 700871,700871: Failed to read msg header. Flags 0x16 instead of 0x5. > qemu-kvm: vhost_device_iotlb_miss: 700871,700871: Fail to update device iotlb > qemu-kvm: vhost_user_read_header: 700871,700871: Failed to read msg header. Flags 0x0 instead of 0x5. > qemu-kvm: vhost_device_iotlb_miss: 700871,700871: Fail to update device iotlb > === > > * Couple of patches here help to fix/handle these errors. I remember after you added the rwlock, there's still a hang issue. Did you investigated that? Or do you mean this series will fix all the problems? Thanks, > > Thank you. > --- > Prasad Pandit (2): > vhost-user: add a write-read lock > vhost: fail device start if iotlb update fails > > hw/virtio/vhost-user.c | 423 +++++++++++++++++++-------------- > hw/virtio/vhost.c | 6 +- > include/hw/virtio/vhost-user.h | 3 + > 3 files changed, 259 insertions(+), 173 deletions(-) > > -- > 2.45.2 > -- Peter Xu