Messages in this thread Patch in this message |  | | Date | Mon, 7 Jan 2019 13:52:31 +0100 | | From | Peter Zijlstra <> | | Subject | Re: CFS scheduler: spin_lock usage causes dead lock when smp_apic_timer_interrupt occurs |
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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..
--- 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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