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

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")
Assisted-by: gkh_clanker_t1000
Signed-off-by: Hari Mishal <harimishal1@gmail.com>
Reviewed-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 7c3db8da4e039698ae198c870712428644e965c7)
Cc: stable@vger.kernel.org

0 files changed, 0 insertions, 0 deletions