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

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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.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Cc: stable@vger.kernel.org
This commit is contained in:
Ben Skeggs 2017-05-11 17:19:48 +10:00
parent 3733bd8b40
commit 1b0f84380b
1 changed files with 16 additions and 10 deletions
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26
drivers/gpu/drm/nouveau/nvkm/subdev/timer/base.c
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@ -36,23 +36,29 @@ nvkm_timer_alarm_trigger(struct nvkm_timer *tmr)
unsigned long flags; unsigned long flags;
LIST_HEAD(exec); LIST_HEAD(exec);
/* move any due alarms off the pending list */ /* Process pending alarms. */
spin_lock_irqsave(&tmr->lock, flags); spin_lock_irqsave(&tmr->lock, flags);
list_for_each_entry_safe(alarm, atemp, &tmr->alarms, head) { list_for_each_entry_safe(alarm, atemp, &tmr->alarms, head) {
if (alarm->timestamp <= nvkm_timer_read(tmr)) /* Have we hit the earliest alarm that hasn't gone off? */
list_move_tail(&alarm->head, &exec); 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 */ /* Shut down interrupt if no more pending alarms. */
if (!list_empty(&tmr->alarms)) { if (list_empty(&tmr->alarms))
alarm = list_first_entry(&tmr->alarms, typeof(*alarm), head);
tmr->func->alarm_init(tmr, alarm->timestamp);
} else {
tmr->func->alarm_fini(tmr); tmr->func->alarm_fini(tmr);
}
spin_unlock_irqrestore(&tmr->lock, flags); spin_unlock_irqrestore(&tmr->lock, flags);
/* execute any pending alarm handlers */ /* Execute completed callbacks. */
list_for_each_entry_safe(alarm, atemp, &exec, head) { list_for_each_entry_safe(alarm, atemp, &exec, head) {
list_del_init(&alarm->head); list_del_init(&alarm->head);
alarm->func(alarm); alarm->func(alarm);