drm/amdgpu: Fix out-of-bounds issue in user fence

Fix out-of-bounds issue in userq fence create when
accessing the userq xa structure. Added a lock to
protect the race condition.

v2:(Christian)
  - Allocate memory with GFP_ATOMIC.

v3:
  - Moved to 2 xa approach.

v4:(Christian)
  - Lock the xa_for_each blocks and memory allocation part
    as well to make sure that xa is not modified in between
    the 2 xa_for_each blocks.

BUG: KASAN: slab-out-of-bounds in amdgpu_userq_fence_create+0x726/0x880 [amdgpu]
[  +0.000006] Call Trace:
[  +0.000005]  <TASK>
[  +0.000005]  dump_stack_lvl+0x6c/0x90
[  +0.000011]  print_report+0xc4/0x5e0
[  +0.000009]  ? srso_return_thunk+0x5/0x5f
[  +0.000008]  ? kasan_complete_mode_report_info+0x26/0x1d0
[  +0.000007]  ? amdgpu_userq_fence_create+0x726/0x880 [amdgpu]
[  +0.000405]  kasan_report+0xdf/0x120
[  +0.000009]  ? amdgpu_userq_fence_create+0x726/0x880 [amdgpu]
[  +0.000405]  __asan_report_store8_noabort+0x17/0x20
[  +0.000007]  amdgpu_userq_fence_create+0x726/0x880 [amdgpu]
[  +0.000406]  ? __pfx_amdgpu_userq_fence_create+0x10/0x10 [amdgpu]
[  +0.000408]  ? srso_return_thunk+0x5/0x5f
[  +0.000008]  ? ttm_resource_move_to_lru_tail+0x235/0x4f0 [ttm]
[  +0.000013]  ? srso_return_thunk+0x5/0x5f
[  +0.000008]  amdgpu_userq_signal_ioctl+0xd29/0x1c70 [amdgpu]
[  +0.000412]  ? __pfx_amdgpu_userq_signal_ioctl+0x10/0x10 [amdgpu]
[  +0.000404]  ? try_to_wake_up+0x165/0x1840
[  +0.000010]  ? __pfx_futex_wake_mark+0x10/0x10
[  +0.000011]  drm_ioctl_kernel+0x178/0x2f0 [drm]
[  +0.000050]  ? __pfx_amdgpu_userq_signal_ioctl+0x10/0x10 [amdgpu]
[  +0.000404]  ? __pfx_drm_ioctl_kernel+0x10/0x10 [drm]
[  +0.000043]  ? __kasan_check_read+0x11/0x20
[  +0.000007]  ? srso_return_thunk+0x5/0x5f
[  +0.000007]  ? __kasan_check_write+0x14/0x20
[  +0.000008]  drm_ioctl+0x513/0xd20 [drm]
[  +0.000040]  ? __pfx_amdgpu_userq_signal_ioctl+0x10/0x10 [amdgpu]
[  +0.000407]  ? __pfx_drm_ioctl+0x10/0x10 [drm]
[  +0.000044]  ? srso_return_thunk+0x5/0x5f
[  +0.000007]  ? _raw_spin_lock_irqsave+0x99/0x100
[  +0.000007]  ? __pfx__raw_spin_lock_irqsave+0x10/0x10
[  +0.000006]  ? __rseq_handle_notify_resume+0x188/0xc30
[  +0.000008]  ? srso_return_thunk+0x5/0x5f
[  +0.000008]  ? srso_return_thunk+0x5/0x5f
[  +0.000006]  ? _raw_spin_unlock_irqrestore+0x27/0x50
[  +0.000010]  amdgpu_drm_ioctl+0xcd/0x1d0 [amdgpu]
[  +0.000388]  __x64_sys_ioctl+0x135/0x1b0
[  +0.000009]  x64_sys_call+0x1205/0x20d0
[  +0.000007]  do_syscall_64+0x4d/0x120
[  +0.000008]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[  +0.000007] RIP: 0033:0x7f7c3d31a94f

Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>