In the Linux kernel, the following vulnerability has been resolved:

drm/amdkfd: wq_release signals dma_fence only when available

kfd_process_wq_release() signals eviction fence by
dma_fence_signal() which wanrs if dma_fence
is NULL.

kfd_process->ef is initialized by kfd_process_device_init_vm()
through ioctl. That means the fence is NULL for a new
created kfd_process, and close a kfd_process right
after open it will trigger the warning.

This commit conditionally signals the eviction fence
in kfd_process_wq_release() only when it is available.

[  503.660882] WARNING: CPU: 0 PID: 9 at drivers/dma-buf/dma-fence.c:467 dma_fence_signal+0x74/0xa0
[  503.782940] Workqueue: kfd_process_wq kfd_process_wq_release [amdgpu]
[  503.789640] RIP: 0010:dma_fence_signal+0x74/0xa0
[  503.877620] Call Trace:
[  503.880066]  <TASK>
[  503.882168]  ? __warn+0xcd/0x260
[  503.885407]  ? dma_fence_signal+0x74/0xa0
[  503.889416]  ? report_bug+0x288/0x2d0
[  503.893089]  ? handle_bug+0x53/0xa0
[  503.896587]  ? exc_invalid_op+0x14/0x50
[  503.900424]  ? asm_exc_invalid_op+0x16/0x20
[  503.904616]  ? dma_fence_signal+0x74/0xa0
[  503.908626]  kfd_process_wq_release+0x6b/0x370 [amdgpu]
[  503.914081]  process_one_work+0x654/0x10a0
[  503.918186]  worker_thread+0x6c3/0xe70
[  503.921943]  ? srso_alias_return_thunk+0x5/0xfbef5
[  503.926735]  ? srso_alias_return_thunk+0x5/0xfbef5
[  503.931527]  ? __kthread_parkme+0x82/0x140
[  503.935631]  ? __pfx_worker_thread+0x10/0x10
[  503.939904]  kthread+0x2a8/0x380
[  503.943132]  ? __pfx_kthread+0x10/0x10
[  503.946882]  ret_from_fork+0x2d/0x70
[  503.950458]  ? __pfx_kthread+0x10/0x10
[  503.954210]  ret_from_fork_asm+0x1a/0x30
[  503.958142]  </TASK>
[  503.960328] ---[ end trace 0000000000000000 ]---

(cherry picked from commit 2774ef7625adb5fb9e9265c26a59dca7b8fd171e)