| Message ID | 20190718030559.9913-2-matthew.ruffell@canonical.com |
|---|---|
| State | New |
| Headers | show |
| Series | [SRU,Bionic,1/1] sched/fair: Limit sched_cfs_period_timer() loop to avoid hard lockup | expand |
On 18.07.19 05:05, Matthew Ruffell wrote: > From: Phil Auld <pauld@redhat.com> > > BugLink: https://bugs.launchpad.net/bugs/1836971 > > [ Upstream commit 2e8e19226398db8265a8e675fcc0118b9e80c9e8 ] > > 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@redhat.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Cc: <stable@vger.kernel.org> > Cc: Anton Blanchard <anton@ozlabs.org> > Cc: Ben Segall <bsegall@google.com> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Link: https://lkml.kernel.org/r/20190319130005.25492-1-pauld@redhat.com > Signed-off-by: Ingo Molnar <mingo@kernel.org> > Signed-off-by: Sasha Levin <sashal@kernel.org> > (cherry picked from d069fe4844f8d799d771659a745fe91870c93fda 4.14.y) > Signed-off-by: Matthew Ruffell <matthew.ruffell@canonical.com> Acked-by: Stefan Bader <stefan.bader@canonical.com> > --- > kernel/sched/fair.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 61365fcbe148..11744dd6bbff 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4981,12 +4981,15 @@ 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 (;;) { > @@ -4994,6 +4997,28 @@ 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) >
On 7/17/19 8:05 PM, Matthew Ruffell wrote: > From: Phil Auld <pauld@redhat.com> > > BugLink: https://bugs.launchpad.net/bugs/1836971 > > [ Upstream commit 2e8e19226398db8265a8e675fcc0118b9e80c9e8 ] > > 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@redhat.com> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > Cc: <stable@vger.kernel.org> > Cc: Anton Blanchard <anton@ozlabs.org> > Cc: Ben Segall <bsegall@google.com> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Thomas Gleixner <tglx@linutronix.de> > Link: https://lkml.kernel.org/r/20190319130005.25492-1-pauld@redhat.com > Signed-off-by: Ingo Molnar <mingo@kernel.org> > Signed-off-by: Sasha Levin <sashal@kernel.org> > (cherry picked from d069fe4844f8d799d771659a745fe91870c93fda 4.14.y) > Signed-off-by: Matthew Ruffell <matthew.ruffell@canonical.com> Acked-by: Connor Kuehl <connor.kuehl@canonical.com> > --- > kernel/sched/fair.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 61365fcbe148..11744dd6bbff 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4981,12 +4981,15 @@ 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 (;;) { > @@ -4994,6 +4997,28 @@ 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) >
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 61365fcbe148..11744dd6bbff 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4981,12 +4981,15 @@ 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 (;;) { @@ -4994,6 +4997,28 @@ 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)