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[2.214.8.136]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47fd458ab61sm25607861f8f.25.2026.08.02.10.41.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 02 Aug 2026 10:41:05 -0700 (PDT) From: Abhin Parekadan Jose To: mst@redhat.com, jasowangio@gmail.com, xuanzhuo@linux.alibaba.com, eperezma@redhat.com Cc: virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, Abhin Parekadan Jose Subject: [PATCH 0/2] virtio_pci_modern: fix vp_reset() hang on unresponsive device Date: Sun, 2 Aug 2026 17:40:57 +0000 Message-ID: <20260802174059.4082-1-abhinjoses@gmail.com> X-Mailer: git-send-email 2.51.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit While investigating a syzbot report of a WARN_ON_ONCE firing in virtio_dev_remove() [1], I found a related but more serious issue: vp_reset() in the modern virtio-pci transport can hang indefinitely if PCI_COMMAND memory-space decode is disabled while the device is bound (e.g. surprise removal, hardware fault, or -- as reproduced here -- a direct write to the PCI_COMMAND register). The status register poll loop has no way to distinguish "device still resetting" from "device unreachable," so it never terminates. Patch 1 adds a VIRTIO_STATUS_ERROR() check that recognizes an all-ones status read as invalid (per spec, bits 4-5 are reserved and can never legitimately be set) and warns once at the point the bad read actually happens. Patch 2 uses that check to break out of vp_reset()'s poll loop instead of spinning forever. Reproduced on a modern-transport virtio-blk-pci device: # printf '\x00\x00' | dd of=/sys/bus/pci/devices/0000:01:00.0/config \ bs=1 seek=4 count=2 conv=notrunc # echo 1 > /sys/bus/pci/devices/0000:01:00.0/remove The second command hangs indefinitely without this series; gdb confirms the CPU is stuck in vp_reset()'s status-polling loop, with vp_modern_get_status() consistently returning 0xff. [1] https://syzbot.org/bug?extid=a1c8effc62c569d4bd25 Abhin Parekadan Jose (2): virtio_pci_modern_dev: warn once on invalid status virtio_pci_modern: avoid infinite loop in vp_reset() on invalid status drivers/virtio/virtio_pci_modern.c | 6 +++++- drivers/virtio/virtio_pci_modern_dev.c | 8 +++++++- include/uapi/linux/virtio_config.h | 16 ++++++++++++++++ 3 files changed, 28 insertions(+), 2 deletions(-) -- 2.51.1