From: Wayne Lin <wayne.lin@amd.com>

[ Upstream commit fcf6a49d79923a234844b8efe830a61f3f0584e4 ]

[Why]
When unplug one of monitors connected after mst hub, encounter null pointer dereference.

It's due to dc_sink get released immediately in early_unregister() or detect_ctx(). When
commit new state which directly referring to info stored in dc_sink will cause null pointer
dereference.

[how]
Remove redundant checking condition. Relevant condition should already be covered by checking
if dsc_aux is null or not. Also reset dsc_aux to NULL when the connector is disconnected.

Reviewed-by: Jerry Zuo <jerry.zuo@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Jianqi Ren <jianqi.ren.cn@windriver.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
index 1acef5f3838f..a1619f4569cf 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -183,6 +183,8 @@ amdgpu_dm_mst_connector_early_unregister(struct drm_connector *connector)
 		dc_sink_release(dc_sink);
 		aconnector->dc_sink = NULL;
 		aconnector->edid = NULL;
+		aconnector->dsc_aux = NULL;
+		port->passthrough_aux = NULL;
 	}
 
 	aconnector->mst_status = MST_STATUS_DEFAULT;
@@ -487,6 +489,8 @@ dm_dp_mst_detect(struct drm_connector *connector,
 		dc_sink_release(aconnector->dc_sink);
 		aconnector->dc_sink = NULL;
 		aconnector->edid = NULL;
+		aconnector->dsc_aux = NULL;
+		port->passthrough_aux = NULL;
 
 		amdgpu_dm_set_mst_status(&aconnector->mst_status,
 			MST_REMOTE_EDID | MST_ALLOCATE_NEW_PAYLOAD | MST_CLEAR_ALLOCATED_PAYLOAD,
-- 
2.25.1

On Wed, Dec 11, 2024 at 06:15:44PM +0800, jianqi.ren.cn@windriver.com wrote:
> From: Wayne Lin <wayne.lin@amd.com>
> 
> [ Upstream commit fcf6a49d79923a234844b8efe830a61f3f0584e4 ]
> 
> [Why]
> When unplug one of monitors connected after mst hub, encounter null pointer dereference.
> 
> It's due to dc_sink get released immediately in early_unregister() or detect_ctx(). When
> commit new state which directly referring to info stored in dc_sink will cause null pointer
> dereference.
> 
> [how]
> Remove redundant checking condition. Relevant condition should already be covered by checking
> if dsc_aux is null or not. Also reset dsc_aux to NULL when the connector is disconnected.
> 
> Reviewed-by: Jerry Zuo <jerry.zuo@amd.com>
> Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
> Signed-off-by: Wayne Lin <wayne.lin@amd.com>
> Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
> Signed-off-by: Jianqi Ren <jianqi.ren.cn@windriver.com>
> ---
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c | 4 ++++
>  1 file changed, 4 insertions(+)

You sent this 3 times, all different, so I have no idea what to do.

Ok, I give up.  I'm deleting ALL of your pending stable patches from my
review queue now due to all of the problems that these have had.

Please work with a more experienced kernel developer at your company to
get these backports correct, and complete, and send them as a patch
series with the correct information and documentation as to what is
going on, so that we have a chance to get this right.

thanks,

greg k-h