[PATCH AUTOSEL 6.1 04/25] drm/amdkfd: Fix a race condition of vram buffer unref in svm code

[Sasha Levin]

From: Xiaogang Chen <xiaogang.c...@amd.com>

[ Upstream commit 709c348261618da7ed89d6c303e2ceb9e453ba74 ]

prange->svm_bo unref can happen in both mmu callback and a callback after
migrate to system ram. Both are async call in different tasks. Sync svm_bo
unref operation to avoid random "use-after-free".

Signed-off-by: Xiaogang Chen <xiaogang.c...@amd.com>
Reviewed-by: Philip Yang <philip.y...@amd.com>
Reviewed-by: Jesse Zhang <jesse.zh...@amd.com>
Tested-by: Jesse Zhang <jesse.zh...@amd.com>
Signed-off-by: Alex Deucher <alexander.deuc...@amd.com>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 drivers/gpu/drm/amd/amdkfd/kfd_svm.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c 
b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
index 63feea08904cb..86a6d6143f008 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_svm.c
@@ -612,8 +612,15 @@ svm_range_vram_node_new(struct amdgpu_device *adev, struct 
svm_range *prange,
 
 void svm_range_vram_node_free(struct svm_range *prange)
 {
-       svm_range_bo_unref(prange->svm_bo);
-       prange->ttm_res = NULL;
+       /* serialize prange->svm_bo unref */
+       mutex_lock(&prange->lock);
+       /* prange->svm_bo has not been unref */
+       if (prange->ttm_res) {
+               prange->ttm_res = NULL;
+               mutex_unlock(&prange->lock);
+               svm_range_bo_unref(prange->svm_bo);
+       } else
+               mutex_unlock(&prange->lock);
 }
 
 struct amdgpu_device *
-- 
2.42.0