[PATCH AUTOSEL 6.16-6.1] drm/amd/display: Only finalize atomic_obj if it was initialized

[Sasha Levin <sashal@kernel.org>]

From: Mario Limonciello <mario.limonciello@amd.com>

[ Upstream commit b174084b3fe15ad1acc69530e673c1535d2e4f85 ]

[Why]
If amdgpu_dm failed to initalize before amdgpu_dm_initialize_drm_device()
completed then freeing atomic_obj will lead to list corruption.

[How]
Check if atomic_obj state is initialized before trying to free.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Ivan Lipski <ivan.lipski@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

Now I have a clear understanding of the issue. Let me provide my
analysis:

**Backport Status: YES**

This commit should be backported to stable kernel trees for the
following reasons:

## Bug Fix Analysis

1. **Clear Bug Fix**: The commit fixes a critical bug that can cause
   list corruption during cleanup. The issue occurs when
   `amdgpu_dm_destroy_drm_device()` is called after initialization
   failure, but before `drm_atomic_private_obj_init()` has been
   executed.

2. **Crash Prevention**: Looking at the `drm_atomic_private_obj_fini()`
   implementation in drivers/gpu/drm/drm_atomic.c:
  ```c
  list_del(&obj->head);
  obj->funcs->atomic_destroy_state(obj, obj->state);
  ```
  If `atomic_obj` was never initialized, calling `list_del()` on
  uninitialized list_head will cause list corruption, and dereferencing
  `obj->state` and `obj->funcs` will likely cause a kernel panic.

3. **Small and Contained Fix**: The fix is minimal - just adding a
   simple NULL check:
  ```c
  if (dm->atomic_obj.state)
  drm_atomic_private_obj_fini(&dm->atomic_obj);
  ```

4. **Clear Failure Path**: The initialization sequence shows:
   - `amdgpu_dm_initialize_drm_device()` calls
     `amdgpu_dm_mode_config_init()`
   - `amdgpu_dm_mode_config_init()` calls
     `drm_atomic_private_obj_init()` to initialize `atomic_obj`
   - If `amdgpu_dm_initialize_drm_device()` fails before reaching
     `amdgpu_dm_mode_config_init()`, the `atomic_obj` remains
     uninitialized
   - The error path calls `amdgpu_dm_fini()` which calls
     `amdgpu_dm_destroy_drm_device()`
   - Without this fix, `drm_atomic_private_obj_fini()` operates on
     uninitialized memory

5. **No Side Effects**: The fix only adds a defensive check and doesn't
   change any existing functionality. It only prevents cleanup of an
   uninitialized object.

6. **Follows Stable Rules**: This fix:
   - Fixes a real bug (list corruption/crash)
   - Is minimal (2 lines of code)
   - Has low risk of regression
   - Doesn't introduce new features
   - Is confined to the AMD display driver subsystem

7. **Initialization Order Issue**: The atomic_obj initialization happens
   relatively late in the initialization sequence, making this race
   condition possible in various failure scenarios during driver probe.

This is a textbook example of a commit that should be backported to
stable - it fixes a real crash bug with a minimal, safe change that
prevents operating on uninitialized data structures.

 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index f58fa5da7fe5..2d92dff6a77a 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -5368,7 +5368,8 @@ static int amdgpu_dm_initialize_drm_device(struct amdgpu_device *adev)
 
 static void amdgpu_dm_destroy_drm_device(struct amdgpu_display_manager *dm)
 {
-	drm_atomic_private_obj_fini(&dm->atomic_obj);
+	if (dm->atomic_obj.state)
+		drm_atomic_private_obj_fini(&dm->atomic_obj);
 }
 
 /******************************************************************************
-- 
2.39.5