Re: [PATCH] sched: tg_set_cfs_bandwidth() causes rq->lock deadlock

Roman Gushchin
2014-05-19T11:38:09Z

At Mon, 19 May 2014 12:32:47 +0200,
Peter Zijlstra wrote:
>
> OK, so can someone explain this ->timer_active thing? esp. what's the
> 'obvious' difference with hrtimer_active()?

A good question :)

> Ideally we'd change the lot to not have this, but if we have to keep it
> we'll need to make it lockdep visible because all this stinks

If the patch below is what Ben means, timer_active will become even more unused.
It seems to me now, that it will be perfectly possible to just drop it.
I'll try to prepare a patch for.

--

index 7570dd9..be7865e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3408,7 +3408,6 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
u64 runtime, runtime_expires;
int idle = 1, throttled;

- raw_spin_lock(&cfs_b->lock);
/* no need to continue the timer with no bandwidth constraint */
if (cfs_b->quota == RUNTIME_INF)
goto out_unlock;
@@ -3477,7 +3476,6 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
out_unlock:
if (idle)
cfs_b->timer_active = 0;
- raw_spin_unlock(&cfs_b->lock);

return idle;
}
@@ -3656,6 +3654,8 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
int overrun;
int idle = 0;

+ raw_spin_lock(&cfs_b->lock);
+
for (;;) {
now = hrtimer_cb_get_time(timer);
overrun = hrtimer_forward(timer, now, cfs_b->period);
@@ -3666,6 +3666,8 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
idle = do_sched_cfs_period_timer(cfs_b, overrun);
}

+ raw_spin_unlock(&cfs_b->lock);
+
return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
}