On Tue, Jan 08, 2019 at 06:30:59AM +0100, Mike Galbraith wrote: > 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.
Much appreciated; I queued it as the below. --- Subject: sched/fair: Robustify CFS-bandwidth timer locking From: Peter Zijlstra <[email protected]> Date: Mon, 7 Jan 2019 13:52:31 +0100 Traditionally hrtimer callbacks were run with IRQs disabled, but with the introduction of HRTIMER_MODE_SOFT it is possible they run from SoftIRQ context, which does _NOT_ have IRQs disabled. Allow for the CFS bandwidth timers (period_timer and slack_timer) to be ran from SoftIRQ context; this entails removing the assumption that IRQs are already disabled from the locking. While mainline doesn't strictly need this, -RT forces all timers not explicitly marked with MODE_HARD into MODE_SOFT and trips over this. And marking these timers as MODE_HARD doesn't make sense as they're not required for RT operation and can potentially be quite expensive. Cc: Ingo Molnar <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Sebastian Andrzej Siewior <[email protected]> Reported-by: Tom Putzeys <[email protected]> Tested-by: Mike Galbraith <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Link: https://lkml.kernel.org/r/[email protected] --- kernel/sched/fair.c | 30 ++++++++++++++++-------------- 1 file changed, 16 insertions(+), 14 deletions(-) --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4566,7 +4566,7 @@ static u64 distribute_cfs_runtime(struct 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 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 * 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(str 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_r 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(str 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_pe { 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; }
