[PATCH] drm/ttm: fix one use-after-free

[Lang Yu <Lang.Yu@amd.com>]

[   67.399887] refcount_t: underflow; use-after-free.
[   67.399901] WARNING: CPU: 0 PID: 3172 at lib/refcount.c:28 refcount_warn_saturate+0xc2/0x110
[   67.400124] RIP: 0010:refcount_warn_saturate+0xc2/0x110
[   67.400173] Call Trace:
[   67.400176]  <TASK>
[   67.400181]  ttm_mem_evict_first+0x4fe/0x5b0 [ttm]
[   67.400216]  ttm_bo_mem_space+0x1e3/0x240 [ttm]
[   67.400239]  ttm_bo_validate+0xc7/0x190 [ttm]
[   67.400253]  ? ww_mutex_trylock+0x1b1/0x390
[   67.400266]  ttm_bo_init_reserved+0x183/0x1c0 [ttm]
[   67.400280]  ? __rwlock_init+0x3d/0x70
[   67.400292]  amdgpu_bo_create+0x1cd/0x4f0 [amdgpu]
[   67.400607]  ? __pfx_amdgpu_bo_user_destroy+0x10/0x10 [amdgpu]
[   67.400980]  amdgpu_bo_create_user+0x38/0x70 [amdgpu]
[   67.401291]  amdgpu_gem_object_create+0x77/0xb0 [amdgpu]
[   67.401641]  ? __pfx_amdgpu_bo_user_destroy+0x10/0x10 [amdgpu]
[   67.401958]  amdgpu_amdkfd_gpuvm_alloc_memory_of_gpu+0x228/0xa30 [amdgpu]
[   67.402433]  kfd_ioctl_alloc_memory_of_gpu+0x14e/0x390 [amdgpu]
[   67.402824]  ? lock_release+0x13f/0x290
[   67.402838]  kfd_ioctl+0x1e0/0x640 [amdgpu]
[   67.403205]  ? __pfx_kfd_ioctl_alloc_memory_of_gpu+0x10/0x10 [amdgpu]
[   67.403579]  ? tomoyo_file_ioctl+0x19/0x20
[   67.403590]  __x64_sys_ioctl+0x95/0xd0
[   67.403601]  do_syscall_64+0x3b/0x90
[   67.403609]  entry_SYSCALL_64_after_hwframe+0x72/0xdc

Fixes: 9bff18d13473 ("drm/ttm: use per BO cleanup workers")

Signed-off-by: Lang Yu <Lang.Yu@amd.com>
---
 drivers/gpu/drm/ttm/ttm_bo.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
index bd5dae4d1624..e047b191001c 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -308,6 +308,9 @@ static void ttm_bo_delayed_delete(struct work_struct *work)
 
 	bo = container_of(work, typeof(*bo), delayed_delete);
 
+	if (!ttm_bo_get_unless_zero(bo))
+		return;
+
 	dma_resv_wait_timeout(bo->base.resv, DMA_RESV_USAGE_BOOKKEEP, false,
 			      MAX_SCHEDULE_TIMEOUT);
 	dma_resv_lock(bo->base.resv, NULL);
-- 
2.25.1