[PATCH] drm/amd/display: guard dc_sink dereferences in MST mode validation

[Hari Mishal]

dm_dp_mst_is_port_support_mode() reads
aconnector->dc_sink->dsc_caps... for the DSC branch-throughput check,
and get_conv_frl_bw()'s HDMI-PCON FRL-bandwidth path reads
aconnector->dc_sink->edid_caps.max_frl_rate, both without a NULL
check. dc_sink is cleared asynchronously on MST unplug, and both
functions run from paths that the driver's own comments document as
racing that teardown: the connector probe worker's ->mode_valid
callback and a compositor's atomic check, neither of which holds the
MST manager lock that the teardown path uses. The former does have an
existing dsc_aux NULL check, but dsc_aux isn't reliably cleared in
every path that clears dc_sink, so it doesn't cover this.

Fail the port-support check and skip the FRL conversion path when the
sink is already gone.

Fixes: f04d275d94e1 ("drm/amd/display: add mst port output bw check")
Fixes: 5c9b8b27a883 ("drm/amd/display: Tie FRL support into amdgpu_dm")
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: gkh_clanker_t1000
Signed-off-by: Hari Mishal <harimishal1@xxxxxxxxx>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

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 045a7f88b754..7261317d4c0f 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
@@ -1231,7 +1231,8 @@ static bool get_conv_frl_bw(struct amdgpu_dm_connector *aconnector,
 	unsigned int max_sink_bw_in_kbps = 0;
 	unsigned int dsc_max_sink_bw_in_kbps = 0;
 
-	if (aconnector->dc_link->dc->caps.dp_hdmi21_pcon_support &&
+	if (aconnector->dc_sink &&
+	    aconnector->dc_link->dc->caps.dp_hdmi21_pcon_support &&
 	    aconnector->mst_downstream_port_caps.bytes.byte0.bits.DWN_STRM_PORTX_TYPE == DOWN_STREAM_DETAILED_HDMI) {
 		max_conv_bw_in_kbps = dc_link_bw_kbps_from_raw_frl_link_rate_data(
 				aconnector->dc_link->dc,
@@ -1996,6 +1997,9 @@ enum dc_status dm_dp_mst_is_port_support_mode(
 	struct dc_dsc_config_options dsc_options = {0};
 	uint32_t stream_kbps;
 
+	if (!aconnector->dc_sink)
+		return DC_FAIL_BANDWIDTH_VALIDATE;
+
 	/* DSC unnecessary case
 	 * Check if timing could be supported within end-to-end BW
 	 */
-- 
2.43.0