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Message-ID: <1546925459.17252.2.camel@gmx.de>
Date: Tue, 08 Jan 2019 06:30:59 +0100
From: Mike Galbraith <efault@....de>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Tom Putzeys <tom.putzeys@...atlascopco.com>,
"mingo@...hat.com" <mingo@...hat.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: CFS scheduler: spin_lock usage causes dead lock when
smp_apic_timer_interrupt occurs
On Mon, 2019-01-07 at 13:52 +0100, Peter Zijlstra wrote:
> On Mon, Jan 07, 2019 at 01:28:34PM +0100, Mike Galbraith wrote:
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 960ad0ce77d7..420624c49f38 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -5007,9 +5007,9 @@ void init_cfs_bandwidth(struct cfs_bandwidth *cfs_b)
> > cfs_b->period = ns_to_ktime(default_cfs_period());
> >
> > INIT_LIST_HEAD(&cfs_b->throttled_cfs_rq);
> > - hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED);
> > + hrtimer_init(&cfs_b->period_timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD);
> > cfs_b->period_timer.function = sched_cfs_period_timer;
> > - hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> > + hrtimer_init(&cfs_b->slack_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
> > cfs_b->slack_timer.function = sched_cfs_slack_timer;
> > }
>
> Right, that should sort it. But I'm not sure this is the best solution
> though. That cfs-runtime crud can (IIRC) iterate lists etc.. so running
> it from the softirq isn't a bad idea. We just need to fix that locking
> up a bit.
>
> Something a wee bit like so perhaps..
I plugged that into 4.19-rt along with revert of hard irq context, and
it (as expected) does the trick.
> ---
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 13776fac7b74..3cfe26aa098a 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4566,7 +4566,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
> struct rq *rq = rq_of(cfs_rq);
> struct rq_flags rf;
>
> - rq_lock(rq, &rf);
> + rq_lock_irqsave(rq, &rf);
> if (!cfs_rq_throttled(cfs_rq))
> goto next;
>
> @@ -4583,7 +4583,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
> unthrottle_cfs_rq(cfs_rq);
>
> next:
> - rq_unlock(rq, &rf);
> + rq_unlock_irqrestore(rq, &rf);
>
> if (!remaining)
> break;
> @@ -4599,7 +4599,7 @@ static u64 distribute_cfs_runtime(struct cfs_bandwidth *cfs_b,
> * period the timer is deactivated until scheduling resumes; cfs_b->idle is
> * used to track this state.
> */
> -static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
> +static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun, unsigned long flags)
> {
> u64 runtime, runtime_expires;
> int throttled;
> @@ -4641,11 +4641,11 @@ static int do_sched_cfs_period_timer(struct cfs_bandwidth *cfs_b, int overrun)
> while (throttled && cfs_b->runtime > 0 && !cfs_b->distribute_running) {
> runtime = cfs_b->runtime;
> cfs_b->distribute_running = 1;
> - raw_spin_unlock(&cfs_b->lock);
> + raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
> /* we can't nest cfs_b->lock while distributing bandwidth */
> runtime = distribute_cfs_runtime(cfs_b, runtime,
> runtime_expires);
> - raw_spin_lock(&cfs_b->lock);
> + raw_spin_lock_irqsave(&cfs_b->lock, flags);
>
> cfs_b->distribute_running = 0;
> throttled = !list_empty(&cfs_b->throttled_cfs_rq);
> @@ -4754,17 +4754,18 @@ static __always_inline void return_cfs_rq_runtime(struct cfs_rq *cfs_rq)
> static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
> {
> u64 runtime = 0, slice = sched_cfs_bandwidth_slice();
> + unsigned long flags;
> u64 expires;
>
> /* confirm we're still not at a refresh boundary */
> - raw_spin_lock(&cfs_b->lock);
> + raw_spin_lock_irqsave(&cfs_b->lock, flags);
> if (cfs_b->distribute_running) {
> - raw_spin_unlock(&cfs_b->lock);
> + raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
> return;
> }
>
> if (runtime_refresh_within(cfs_b, min_bandwidth_expiration)) {
> - raw_spin_unlock(&cfs_b->lock);
> + raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
> return;
> }
>
> @@ -4775,18 +4776,18 @@ static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b)
> if (runtime)
> cfs_b->distribute_running = 1;
>
> - raw_spin_unlock(&cfs_b->lock);
> + raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
>
> if (!runtime)
> return;
>
> runtime = distribute_cfs_runtime(cfs_b, runtime, expires);
>
> - raw_spin_lock(&cfs_b->lock);
> + raw_spin_lock_irqsave(&cfs_b->lock, flags);
> if (expires == cfs_b->runtime_expires)
> lsub_positive(&cfs_b->runtime, runtime);
> cfs_b->distribute_running = 0;
> - raw_spin_unlock(&cfs_b->lock);
> + raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
> }
>
> /*
> @@ -4864,20 +4865,21 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer)
> {
> struct cfs_bandwidth *cfs_b =
> container_of(timer, struct cfs_bandwidth, period_timer);
> + unsigned long flags;
> int overrun;
> int idle = 0;
>
> - raw_spin_lock(&cfs_b->lock);
> + raw_spin_lock_irqsave(&cfs_b->lock, flags);
> for (;;) {
> overrun = hrtimer_forward_now(timer, cfs_b->period);
> if (!overrun)
> break;
>
> - idle = do_sched_cfs_period_timer(cfs_b, overrun);
> + idle = do_sched_cfs_period_timer(cfs_b, overrun, flags);
> }
> if (idle)
> cfs_b->period_active = 0;
> - raw_spin_unlock(&cfs_b->lock);
> + raw_spin_unlock_irqrestore(&cfs_b->lock, flags);
>
> return idle ? HRTIMER_NORESTART : HRTIMER_RESTART;
> }
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