virtio_gpu_deinit() calls mutex_destroy() on obj_restore_lock, but
deinit runs from virtio_gpu_remove() at unbind or PCI remove, and GEM
objects can outlive that. An open /dev/fb0 keeps the fbdev buffer
alive, and the fbdev DRM client holds a drm_device reference. When the
fd is finally closed, the buffer is freed and takes the destroyed lock:
fb_release()
drm_fbdev_shmem_fb_destroy()
drm_client_buffer_delete()
virtio_gpu_free_object()
virtio_gpu_remove_from_restore_list()
mutex_lock(&vgdev->obj_restore_lock)
DEBUG_LOCKS_WARN_ON(lock->magic != lock)
WARNING: kernel/locking/mutex.c:625 at __mutex_lock+0xf2c/0x12ec
virtio_gpu_deinit() should only do hardware teardown in this case
related virtio, its queues and others. Software state that GEM callbacks
still use belongs in virtio_gpu_release(), which runs on the final
drm_dev_put().
There are two equivalent ways to tie the mutex lifetime to the
drm_device:
1) Move mutex_destroy() from virtio_gpu_deinit() to the end of
virtio_gpu_release(). This is what this patch does. It is the
smallest change and keeps the teardown next to the rest of the
final-put software cleanup.
2) Initialise the lock with drmm_mutex_init() (checking its return
value) and drop mutex_destroy() from virtio_gpu_deinit(), so DRM's
managed release destroys it. This also covers the virtio_gpu_init()
error path, where release returns early because dev_private is
NULL. Skipping mutex_destroy() there is harmless, since it only
matters for mutex debugging.
Either fix removes the WARN. Option 1 is sent as the smaller change,
and option 2 can be done instead if preferred.
Reproduced on arm64 QEMU (-device virtio-gpu-pci) with DEBUG_MUTEXES
and PROVE_LOCKING: open /dev/fb0, write 1 to
/sys/bus/pci/devices/0000:00:01.0/remove, then close the fd. With this
patch the WARN is gone, and rebinding brings back /dev/fb0 and
/dev/dri/card0.
Fixes: 54a970048296 ("drm/virtio: Add support for saving and restoring
virtio_gpu_objects")
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=3590d97d8a586fa955c2
Assisted-by: LLM
Signed-off-by: Abhin Parekadan Jose <[email protected]>
---
drivers/gpu/drm/virtio/virtgpu_kms.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/virtio/virtgpu_kms.c
b/drivers/gpu/drm/virtio/virtgpu_kms.c
index 1d4d3bf46a20..0ec755c35050 100644
--- a/drivers/gpu/drm/virtio/virtgpu_kms.c
+++ b/drivers/gpu/drm/virtio/virtgpu_kms.c
@@ -354,7 +354,6 @@ void virtio_gpu_deinit(struct drm_device *dev)
virtio_reset_device(vgdev->vdev);
virtio_gpu_reclaim_vbufs(vgdev);
vgdev->vdev->config->del_vqs(vgdev->vdev);
- mutex_destroy(&vgdev->obj_restore_lock);
}
void virtio_gpu_release(struct drm_device *dev)
@@ -370,6 +369,8 @@ void virtio_gpu_release(struct drm_device *dev)
if (vgdev->has_host_visible)
drm_mm_takedown(&vgdev->host_visible_mm);
+
+ mutex_destroy(&vgdev->obj_restore_lock);
}
int virtio_gpu_driver_open(struct drm_device *dev, struct drm_file *file)
base-commit: 72d3fcf802c45d00b300f25b848a93c3a2bd7c7e
--
2.51.1
