[PATCH] drm/amdgpu: Add NULL check for 'bo_va' in update_bo_mapping

[Srinivasan Shanmugam]

This change adds a check to ensure that 'bo_va' is not null before
dereferencing it. If 'bo_va' is null, the function returns early,
preventing any potential crashes or undefined behavior

Fixes the below:
	drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c:139 amdgpu_gem_update_bo_mapping()
	error: we previously assumed 'bo_va' could be null (see line 124)

drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
    115 static void
    116 amdgpu_gem_update_bo_mapping(struct drm_file *filp,
    117                              struct amdgpu_bo_va *bo_va,
    118                              uint32_t operation,
    119                              uint64_t point,
    120                              struct dma_fence *fence,
    121                              struct drm_syncobj *syncobj,
    122                              struct dma_fence_chain *chain)
    123 {
    124         struct amdgpu_bo *bo = bo_va ? bo_va->base.bo : NULL;
                                  ^^^^^^^^^^ If bo_va is NULL then bo is also NULL

	...
    135         case AMDGPU_VA_OP_REPLACE:
    136                 if (bo && (bo->tbo.base.resv == vm->root.bo->tbo.base.resv))
                            ^^

    137                         last_update = vm->last_update;
    138                 else
--> 139                         last_update = bo_va->last_pt_update;
                                              ^^^^^ This pointer is dereferenced without being checked.

    140                 break;

Fixes: 16856d135622 ("drm/amdgpu: update userqueue BOs and PDs")
Cc: Christian König <christian.koenig at amd.com>
Cc: Alex Deucher <alexander.deucher at amd.com>
Reported-by: Dan Carpenter <dan.carpenter at linaro.org>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
index c1d8cee7894b..247fbd014b7f 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_gem.c
@@ -134,8 +134,10 @@ amdgpu_gem_update_bo_mapping(struct drm_file *filp,
 	case AMDGPU_VA_OP_REPLACE:
 		if (bo && (bo->tbo.base.resv == vm->root.bo->tbo.base.resv))
 			last_update = vm->last_update;
-		else
+		else if (bo_va)
 			last_update = bo_va->last_pt_update;
+		else
+			return;
 		break;
 	case AMDGPU_VA_OP_UNMAP:
 	case AMDGPU_VA_OP_CLEAR:
-- 
2.34.1