[PATCH] drm/amd/display: move the nonblocking commit helpers appropriately

[Shirish S]

[Why]
In multi-monitor scenario, if first crtc's flip done event occurs delayed
(but within timeout), due to non-blocking design of commit_tail(), there
are more than one commit's scheduled by the time the second crtc's
wait_for_completion_timeout() is called in drm_atomic_helper_wait_for_flip_done.

Due to these in-between additions and deletions in the atomic state, it is
found that the system fails while accessing common data structures of the
second crtc in drm_atomic_helper_wait_for_flip_done(), leading to crash as
below:

	BUG: unable to handle kernel paging request at 000000010000001c
	IP: do_raw_spin_lock+0xf/0x94
	PGD 0 P4D 0
	Oops: 0000 [#1] PREEMPT SMP NOPTI
	Call Trace:
	 __wait_for_common+0x36/0x60
	 drm_atomic_helper_wait_for_flip_done+0x47/0x89
	 amdgpu_dm_atomic_commit_tail+0xf4b/0xf84
	 ? drm_atomic_helper_wait_for_dependencies+0x1cd/0x217
	 commit_tail+0x41/0x5f

[How]
Move drm_atomic_helper_commit_hw_done() post wait_for_flip_done(),
which cleans up the atomic state's commit and completes pending hw_done and
flip_done works as a result there wont be dangling flip waits on random commits.

Signed-off-by: Shirish S <shirish.s at amd.com>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

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 0f10d92..41a1958 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -4626,12 +4626,17 @@ static void amdgpu_dm_atomic_commit_tail(struct drm_atomic_state *state)
 	}
 	spin_unlock_irqrestore(&adev->ddev->event_lock, flags);
 
-	/* Signal HW programming completion */
-	drm_atomic_helper_commit_hw_done(state);
 
 	if (wait_for_vblank)
 		drm_atomic_helper_wait_for_flip_done(dev, state);
 
+	/* Atomic state pointer gets corrupted in case of frequent
+	 * modesets operations like changing resolutions.
+	 * Hence discard state->commit before signalling to user
+	 * space.
+	 */
+	drm_atomic_helper_commit_hw_done(state);
+
 	drm_atomic_helper_cleanup_planes(dev, state);
 
 	/*
-- 
2.7.4