From: Ryosuke Yasuoka Date: Mon, 13 Jul 2026 13:01:00 +0000 (+0900) Subject: drm/virtio: fix deadlock in display_info_cb by removing hotplug from dequeue worker X-Git-Tag: v7.2-rc4~13^2~3^2~11 X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=d1b894c5bbb3fee0012bd14356286dc2384e8213;p=thirdparty%2Fkernel%2Flinux.git drm/virtio: fix deadlock in display_info_cb by removing hotplug from dequeue worker A probe-time deadlock can occur between the dequeue worker and drm_client_register(). During probe, drm_client_register() holds clientlist_mutex and calls the fbdev hotplug callback, which triggers an atomic commit that ends up sleeping in virtio_gpu_queue_ctrl_sgs() waiting for virtqueue space. The dequeue worker that would free that space calls virtio_gpu_cmd_get_display_info_cb(), which invokes drm_kms_helper_hotplug_event() -> drm_client_dev_hotplug(), attempting to acquire the same clientlist_mutex. Since wake_up() is only called after the resp_cb loop, the probe thread is never woken and both threads deadlock. Fix this by removing the hotplug notification from virtio_gpu_cmd_get_display_info_cb(). The display data (outputs[i].info) is still updated synchronously in the callback. For the init path, drm_client_register() already fires an initial hotplug when the client is registered, which picks up the connector state updated by display_info_cb. For the runtime config_changed path, add a wait_event_timeout() in config_changed_work_func() so that display_info_cb updates the connector data before the hotplug notification is sent. Also replace drm_helper_hpd_irq_event() with drm_kms_helper_hotplug_event() since virtio-gpu never calls drm_kms_helper_poll_init() and thus drm_helper_hpd_irq_event() always returns false without doing anything. Fixes: 27655b9bb9f0 ("drm/client: Send hotplug event after registering a client") Closes: https://syzkaller.appspot.com/bug?id=d6dd6f86d3aaf7eebe7406e45c1c6e549453f224 Closes: https://syzkaller.appspot.com/bug?id=908bd910da5dd79b88de4cf7baf376cc873a922e Suggested-by: Dmitry Osipenko Signed-off-by: Ryosuke Yasuoka Signed-off-by: Dmitry Osipenko Link: https://patch.msgid.link/20260713-virtiogpu_syzbot-v2-1-2958fa37d46d@redhat.com --- diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c b/drivers/gpu/drm/virtio/virtgpu_kms.c index cfde9f573df6..b4329f28e976 100644 --- a/drivers/gpu/drm/virtio/virtgpu_kms.c +++ b/drivers/gpu/drm/virtio/virtgpu_kms.c @@ -49,7 +49,10 @@ static void virtio_gpu_config_changed_work_func(struct work_struct *work) virtio_gpu_cmd_get_edids(vgdev); virtio_gpu_cmd_get_display_info(vgdev); virtio_gpu_notify(vgdev); - drm_helper_hpd_irq_event(vgdev->ddev); + wait_event_timeout(vgdev->resp_wq, + !vgdev->display_info_pending, + 5 * HZ); + drm_kms_helper_hotplug_event(vgdev->ddev); } events_clear |= VIRTIO_GPU_EVENT_DISPLAY; } diff --git a/drivers/gpu/drm/virtio/virtgpu_vq.c b/drivers/gpu/drm/virtio/virtgpu_vq.c index c8b9475a7472..e5e1af8b8e8a 100644 --- a/drivers/gpu/drm/virtio/virtgpu_vq.c +++ b/drivers/gpu/drm/virtio/virtgpu_vq.c @@ -840,9 +840,6 @@ static void virtio_gpu_cmd_get_display_info_cb(struct virtio_gpu_device *vgdev, vgdev->display_info_pending = false; spin_unlock(&vgdev->display_info_lock); wake_up(&vgdev->resp_wq); - - if (!drm_helper_hpd_irq_event(vgdev->ddev)) - drm_kms_helper_hotplug_event(vgdev->ddev); } static void virtio_gpu_cmd_get_capset_info_cb(struct virtio_gpu_device *vgdev,