drm/atomic: fix self-refresh helpers crtc state dereference

drm_self_refresh_helper_update_avg_times() was incorrectly accessing the
new incoming state after drm_atomic_helper_commit_hw_done().  But this
state might have already been superceeded by an !nonblock atomic update
resulting in dereferencing an already free'd crtc_state.

TODO I *think* this will more or less do the right thing.. althought I'm
not 100% sure if, for example, we enter psr in a nonblock commit, and
then leave psr in a !nonblock commit that overtakes the completion of
the nonblock commit.  Not sure if this sort of scenario can happen in
practice.  But not crashing is better than crashing, so I guess we
should either take this patch or rever the self-refresh helpers until
Sean can figure out a better solution.

Fixes: d4da4e33341c ("drm: Measure Self Refresh Entry/Exit times to avoid thrashing")
Cc: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>
[seanpaul fixed up some checkpatch warns]
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191104173737.142558-1-robdclark@gmail.com

2 files changed, 25 insertions, 8 deletions

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 3ef2ac52ce94..2dd2cd87cdbb 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -1581,8 +1581,11 @@ static void commit_tail(struct drm_atomic_state *old_state)
 {
 	struct drm_device *dev = old_state->dev;
 	const struct drm_mode_config_helper_funcs *funcs;
+	struct drm_crtc_state *new_crtc_state;
+	struct drm_crtc *crtc;
 	ktime_t start;
 	s64 commit_time_ms;
+	unsigned int i, new_self_refresh_mask = 0;
 
 	funcs = dev->mode_config.helper_private;
 
@@ -1602,6 +1605,15 @@ static void commit_tail(struct drm_atomic_state *old_state)
 
 	drm_atomic_helper_wait_for_dependencies(old_state);
 
+	/*
+	 * We cannot safely access new_crtc_state after
+	 * drm_atomic_helper_commit_hw_done() so figure out which crtc's have
+	 * self-refresh active beforehand:
+	 */
+	for_each_new_crtc_in_state(old_state, crtc, new_crtc_state, i)
+		if (new_crtc_state->self_refresh_active)
+			new_self_refresh_mask |= BIT(i);
+
 	if (funcs && funcs->atomic_commit_tail)
 		funcs->atomic_commit_tail(old_state);
 	else
@@ -1610,7 +1622,8 @@ static void commit_tail(struct drm_atomic_state *old_state)
 	commit_time_ms = ktime_ms_delta(ktime_get(), start);
 	if (commit_time_ms > 0)
 		drm_self_refresh_helper_update_avg_times(old_state,
-						 (unsigned long)commit_time_ms);
+						 (unsigned long)commit_time_ms,
+						 new_self_refresh_mask);
 
 	drm_atomic_helper_commit_cleanup_done(old_state);
 
diff --git a/drivers/gpu/drm/drm_self_refresh_helper.c b/drivers/gpu/drm/drm_self_refresh_helper.c
index 68f4765a5896..dd33fec5aabd 100644
--- a/drivers/gpu/drm/drm_self_refresh_helper.c
+++ b/drivers/gpu/drm/drm_self_refresh_helper.c
@@ -133,29 +133,33 @@ out_drop_locks:
  * drm_self_refresh_helper_update_avg_times - Updates a crtc's SR time averages
  * @state: the state which has just been applied to hardware
  * @commit_time_ms: the amount of time in ms that this commit took to complete
+ * @new_self_refresh_mask: bitmask of crtc's that have self_refresh_active in
+ *    new state
  *
  * Called after &drm_mode_config_funcs.atomic_commit_tail, this function will
  * update the average entry/exit self refresh times on self refresh transitions.
  * These averages will be used when calculating how long to delay before
  * entering self refresh mode after activity.
  */
-void drm_self_refresh_helper_update_avg_times(struct drm_atomic_state *state,
-					      unsigned int commit_time_ms)
+void
+drm_self_refresh_helper_update_avg_times(struct drm_atomic_state *state,
+					 unsigned int commit_time_ms,
+					 unsigned int new_self_refresh_mask)
 {
 	struct drm_crtc *crtc;
-	struct drm_crtc_state *old_crtc_state, *new_crtc_state;
+	struct drm_crtc_state *old_crtc_state;
 	int i;
 
-	for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state,
-				      new_crtc_state, i) {
+	for_each_old_crtc_in_state(state, crtc, old_crtc_state, i) {
+		bool new_self_refresh_active = new_self_refresh_mask & BIT(i);
 		struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
 		struct ewma_psr_time *time;
 
 		if (old_crtc_state->self_refresh_active ==
-		    new_crtc_state->self_refresh_active)
+		    new_self_refresh_active)
 			continue;
 
-		if (new_crtc_state->self_refresh_active)
+		if (new_self_refresh_active)
 			time = &sr_data->entry_avg_ms;
 		else
 			time = &sr_data->exit_avg_ms;