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drm/amd/display: Do not skip unrelated mode changes in DSC validation

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Starting with commit 17ce8a6907 ("drm/amd/display: Add dsc pre-validation in
atomic check"), amdgpu resets the CRTC state mode_changed flag to false when
recomputing the DSC configuration results in no timing change for a particular
stream.

However, this is incorrect in scenarios where a change in MST/DSC configuration
happens in the same KMS commit as another (unrelated) mode change. For example,
the integrated panel of a laptop may be configured differently (e.g., HDR
enabled/disabled) depending on whether external screens are attached. In this
case, plugging in external DP-MST screens may result in the mode_changed flag
being dropped incorrectly for the integrated panel if its DSC configuration
did not change during precomputation in pre_validate_dsc().

At this point, however, dm_update_crtc_state() has already created new streams
for CRTCs with DSC-independent mode changes. In turn,
amdgpu_dm_commit_streams() will never release the old stream, resulting in a
memory leak. amdgpu_dm_atomic_commit_tail() will never acquire a reference to
the new stream either, which manifests as a use-after-free when the stream gets
disabled later on:

BUG: KASAN: use-after-free in dc_stream_release+0x25/0x90 [amdgpu]
Write of size 4 at addr ffff88813d836524 by task kworker/9:9/29977

Workqueue: events drm_mode_rmfb_work_fn
Call Trace:
 <TASK>
 dump_stack_lvl+0x6e/0xa0
 print_address_description.constprop.0+0x88/0x320
 ? dc_stream_release+0x25/0x90 [amdgpu]
 print_report+0xfc/0x1ff
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? __virt_addr_valid+0x225/0x4e0
 ? dc_stream_release+0x25/0x90 [amdgpu]
 kasan_report+0xe1/0x180
 ? dc_stream_release+0x25/0x90 [amdgpu]
 kasan_check_range+0x125/0x200
 dc_stream_release+0x25/0x90 [amdgpu]
 dc_state_destruct+0x14d/0x5c0 [amdgpu]
 dc_state_release.part.0+0x4e/0x130 [amdgpu]
 dm_atomic_destroy_state+0x3f/0x70 [amdgpu]
 drm_atomic_state_default_clear+0x8ee/0xf30
 ? drm_mode_object_put.part.0+0xb1/0x130
 __drm_atomic_state_free+0x15c/0x2d0
 atomic_remove_fb+0x67e/0x980

Since there is no reliable way of figuring out whether a CRTC has unrelated
mode changes pending at the time of DSC validation, remember the value of the
mode_changed flag from before the point where a CRTC was marked as potentially
affected by a change in DSC configuration. Reset the mode_changed flag to this
earlier value instead in pre_validate_dsc().

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/5004
Fixes: 17ce8a6907 ("drm/amd/display: Add dsc pre-validation in atomic check")
Signed-off-by: Yussuf Khalil <dev@pp3345.net>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit cc7c7121ae082b7b82891baa7280f1ff2608f22b)
This commit is contained in:
Yussuf Khalil
2026-03-06 12:06:35 +00:00
committed by Alex Deucher
parent c369299895
commit aed3d041ab
3 changed files with 9 additions and 1 deletions
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5
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
View File

@@ -12523,6 +12523,11 @@ static int amdgpu_dm_atomic_check(struct drm_device *dev,
}
if (dc_resource_is_dsc_encoding_supported(dc)) {
for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state, new_crtc_state, i) {
dm_new_crtc_state = to_dm_crtc_state(new_crtc_state);
dm_new_crtc_state->mode_changed_independent_from_dsc = new_crtc_state->mode_changed;
}
for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state, new_crtc_state, i) {
if (drm_atomic_crtc_needs_modeset(new_crtc_state)) {
ret = add_affected_mst_dsc_crtcs(state, crtc);