Hi Greg, On Tue, Apr 23, 2019 at 10:51:12PM +0200 gregkh@xxxxxxxxxxxxxxxxxxx wrote: > > The patch below does not apply to the 5.0-stable tree. > If someone wants it applied there, or to any other stable or longterm > tree, then please email the backport, including the original git commit > id to <stable@xxxxxxxxxxxxxxx>. I sent the stable backport version as a reply to the tip-bot mail as Sasha had suggested. Is there something else I needed to do? Clearly :) Thanks, Phil > > thanks, > > greg k-h > > ------------------ original commit in Linus's tree ------------------ > > From 2e8e19226398db8265a8e675fcc0118b9e80c9e8 Mon Sep 17 00:00:00 2001 > From: Phil Auld <pauld@xxxxxxxxxx> > Date: Tue, 19 Mar 2019 09:00:05 -0400 > Subject: [PATCH] sched/fair: Limit sched_cfs_period_timer() loop to avoid hard > lockup > > With extremely short cfs_period_us setting on a parent task group with a large > number of children the for loop in sched_cfs_period_timer() can run until the > watchdog fires. There is no guarantee that the call to hrtimer_forward_now() > will ever return 0. The large number of children can make > do_sched_cfs_period_timer() take longer than the period. > > NMI watchdog: Watchdog detected hard LOCKUP on cpu 24 > RIP: 0010:tg_nop+0x0/0x10 > <IRQ> > walk_tg_tree_from+0x29/0xb0 > unthrottle_cfs_rq+0xe0/0x1a0 > distribute_cfs_runtime+0xd3/0xf0 > sched_cfs_period_timer+0xcb/0x160 > ? sched_cfs_slack_timer+0xd0/0xd0 > __hrtimer_run_queues+0xfb/0x270 > hrtimer_interrupt+0x122/0x270 > smp_apic_timer_interrupt+0x6a/0x140 > apic_timer_interrupt+0xf/0x20 > </IRQ> > > To prevent this we add protection to the loop that detects when the loop has run > too many times and scales the period and quota up, proportionally, so that the timer > can complete before then next period expires. This preserves the relative runtime > quota while preventing the hard lockup. > > A warning is issued reporting this state and the new values. > > Signed-off-by: Phil Auld <pauld@xxxxxxxxxx> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Cc: Anton Blanchard <anton@xxxxxxxxxx> > Cc: Ben Segall <bsegall@xxxxxxxxxx> > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Link: https://lkml.kernel.org/r/20190319130005.25492-1-pauld@xxxxxxxxxx > Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 40bd1e27b1b7..a4d9e14bf138 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4885,6 +4885,8 @@ static enum hrtimer_restart sched_cfs_slack_timer(struct hrtimer *timer) > return HRTIMER_NORESTART; > } > > +extern const u64 max_cfs_quota_period; > + > static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer) > { > struct cfs_bandwidth *cfs_b = > @@ -4892,6 +4894,7 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer) > unsigned long flags; > int overrun; > int idle = 0; > + int count = 0; > > raw_spin_lock_irqsave(&cfs_b->lock, flags); > for (;;) { > @@ -4899,6 +4902,28 @@ static enum hrtimer_restart sched_cfs_period_timer(struct hrtimer *timer) > if (!overrun) > break; > > + if (++count > 3) { > + u64 new, old = ktime_to_ns(cfs_b->period); > + > + new = (old * 147) / 128; /* ~115% */ > + new = min(new, max_cfs_quota_period); > + > + cfs_b->period = ns_to_ktime(new); > + > + /* since max is 1s, this is limited to 1e9^2, which fits in u64 */ > + cfs_b->quota *= new; > + cfs_b->quota = div64_u64(cfs_b->quota, old); > + > + pr_warn_ratelimited( > + "cfs_period_timer[cpu%d]: period too short, scaling up (new cfs_period_us %lld, cfs_quota_us = %lld)\n", > + smp_processor_id(), > + div_u64(new, NSEC_PER_USEC), > + div_u64(cfs_b->quota, NSEC_PER_USEC)); > + > + /* reset count so we don't come right back in here */ > + count = 0; > + } > + > idle = do_sched_cfs_period_timer(cfs_b, overrun, flags); > } > if (idle) > --
