Hi Sasha, On Tue, Apr 16, 2019 at 08:32:09AM -0700 tip-bot for Phil Auld wrote: > Commit-ID: 2e8e19226398db8265a8e675fcc0118b9e80c9e8 > Gitweb: https://git.kernel.org/tip/2e8e19226398db8265a8e675fcc0118b9e80c9e8 > Author: Phil Auld <pauld@xxxxxxxxxx> > AuthorDate: Tue, 19 Mar 2019 09:00:05 -0400 > Committer: Ingo Molnar <mingo@xxxxxxxxxx> > CommitDate: Tue, 16 Apr 2019 16:50:05 +0200 > > 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> > --- The above commit won't work on the stable trees. Below is an updated version that will work on v5.0.7, v4.19.34, v4.14.111, v4.9.168, and v4.4.178 with increasing offsets. I believe v3.18.138 will require more so that one is not included. There is only a minor change to context, none of actual changes in the patch are different. Thanks, Phil diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 310d0637fe4b..f0380229b6f2 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4859,12 +4859,15 @@ 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 = container_of(timer, struct cfs_bandwidth, period_timer); int overrun; int idle = 0; + int count = 0; raw_spin_lock(&cfs_b->lock); for (;;) { @@ -4872,6 +4875,28 @@ 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); } if (idle) --
