Patch "drm/nouveau/tmr: handle races with hw when updating the next alarm time" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

drm/nouveau/tmr: handle races with hw when updating the next alarm time

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
drm-nouveau-tmr-handle-races-with-hw-when-updating-the-next-alarm-time.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ben Skeggs <[email protected]>
Date: Thu, 11 May 2017 17:19:48 +1000
Subject: drm/nouveau/tmr: handle races with hw when updating the next alarm time

From: Ben Skeggs <[email protected]>

commit 1b0f84380b10ee97f7d2dd191294de9017e94d1d upstream.

If the time to the next alarm is short enough, we could race with HW and end up with an ~4 second delay until it triggers.

Fix this by checking again after we update HW.

---
 drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c |   26 ++++++++++++++---------
 1 file changed, 16 insertions(+), 10 deletions(-)

@@ -36,23 +36,29 @@ nvkm_timer_alarm_trigger(struct nvkm_tim
 	unsigned long flags;
 	LIST_HEAD(exec);
 
-	/* move any due alarms off the pending list */
+	/* Process pending alarms. */
 	spin_lock_irqsave(&tmr->lock, flags);
 	list_for_each_entry_safe(alarm, atemp, &tmr->alarms, head) {
-		if (alarm->timestamp <= nvkm_timer_read(tmr))
-			list_move_tail(&alarm->head, &exec);
+		/* Have we hit the earliest alarm that hasn't gone off? */
+		if (alarm->timestamp > nvkm_timer_read(tmr)) {
+			/* Schedule it.  If we didn't race, we're done. */
+			tmr->func->alarm_init(tmr, alarm->timestamp);
+			if (alarm->timestamp > nvkm_timer_read(tmr))
+				break;
+		}
+
+		/* Move to completed list.  We'll drop the lock before
+		 * executing the callback so it can reschedule itself.
+		 */
+		list_move_tail(&alarm->head, &exec);
 	}
 
-	/* reschedule interrupt for next alarm time */
-	if (!list_empty(&tmr->alarms)) {
-		alarm = list_first_entry(&tmr->alarms, typeof(*alarm), head);
-		tmr->func->alarm_init(tmr, alarm->timestamp);
-	} else {
+	/* Shut down interrupt if no more pending alarms. */
+	if (list_empty(&tmr->alarms))
 		tmr->func->alarm_fini(tmr);
-	}
 	spin_unlock_irqrestore(&tmr->lock, flags);
 
-	/* execute any pending alarm handlers */
+	/* Execute completed callbacks. */
 	list_for_each_entry_safe(alarm, atemp, &exec, head) {
 		list_del_init(&alarm->head);
 		alarm->func(alarm);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/drm-nouveau-tmr-ack-interrupt-before-processing-alarms.patch queue-4.9/drm-nouveau-tmr-fix-corruption-of-the-pending-list-when-rescheduling-an-alarm.patch queue-4.9/drm-nouveau-tmr-avoid-processing-completed-alarms-when-adding-a-new-one.patch queue-4.9/drm-nouveau-mmu-nv4a-use-nv04-mmu-rather-than-the-nv44-one.patch queue-4.9/drm-nouveau-therm-remove-ineffective-workarounds-for-alarm-bugs.patch queue-4.9/drm-nouveau-tmr-handle-races-with-hw-when-updating-the-next-alarm-time.patch