Observed on gfx8 ASIC where KFD_IOC_ALLOC_MEM_FLAGS_AQL_QUEUE_MEM is used.
Two attachments use the same VM, root PD would be locked twice.

[   57.910418] Call Trace:
[   57.793726]  ? reserve_bo_and_cond_vms+0x111/0x1c0 [amdgpu]
[   57.793820]  amdgpu_amdkfd_gpuvm_unmap_memory_from_gpu+0x6c/0x1c0 [amdgpu]
[   57.793923]  ? idr_get_next_ul+0xbe/0x100
[   57.793933]  kfd_process_device_free_bos+0x7e/0xf0 [amdgpu]
[   57.794041]  kfd_process_wq_release+0x2ae/0x3c0 [amdgpu]
[   57.794141]  ? process_scheduled_works+0x29c/0x580
[   57.794147]  process_scheduled_works+0x303/0x580
[   57.794157]  ? __pfx_worker_thread+0x10/0x10
[   57.794160]  worker_thread+0x1a2/0x370
[   57.794165]  ? __pfx_worker_thread+0x10/0x10
[   57.794167]  kthread+0x11b/0x150
[   57.794172]  ? __pfx_kthread+0x10/0x10
[   57.794177]  ret_from_fork+0x3d/0x60
[   57.794181]  ? __pfx_kthread+0x10/0x10
[   57.794184]  ret_from_fork_asm+0x1b/0x30

Signed-off-by: Lang Yu <Lang.Yu@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>