Messages in this thread | | | Subject | Re: CFS scheduler: spin_lock usage causes dead lock when smp_apic_timer_interrupt occurs | From | Mike Galbraith <> | Date | Tue, 08 Jan 2019 06:30:59 +0100 |
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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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