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Date: Sat, 2 Sep 2017 14:54:47 +0800 From: Ethan Zhao <ethan.kernel@...il.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Ethan Zhao <ethan.zhao@...cle.com>, mingo@...hat.com, LKML <linux-kernel@...r.kernel.org>, James Puthukattukaran <james.puthukattukaran@...cle.com> Subject: Re: [PATCH] sched: reset sysctl_sched_time_avg to default when Peter, V2 sent, tested okay on stable 4.1, re-factor a little, could apply to v4.13-rc5, please review. [root@ ~]# sysctl kernel.sched_time_avg_ms kernel.sched_time_avg_ms = 1000 [root@ ~]# sysctl kernel.sched_time_avg_ms=0 sysctl: setting key "kernel.sched_time_avg_ms": Invalid argument kernel.sched_time_avg_ms = 0 [root@ ~]# sysctl kernel.sched_time_avg_ms kernel.sched_time_avg_ms = 1000 [root@ ~]# sysctl kernel.sched_time_avg_ms=900 kernel.sched_time_avg_ms = 900 [root@ ~]# sysctl kernel.sched_time_avg_ms kernel.sched_time_avg_ms = 900 Thanks, Ethan On Sat, Sep 2, 2017 at 8:33 AM, Ethan Zhao <ethan.kernel@...il.com> wrote: > Yep, that is the first place I considered to set the limit, but that would > break KABI ? > > Thanks, > Ethan > > On Fri, Sep 1, 2017 at 8:32 PM, Peter Zijlstra <peterz@...radead.org> wrote: >> On Fri, Sep 01, 2017 at 07:31:54PM +0800, Ethan Zhao wrote: >>> System will hang if user set sysctl_sched_time_avg to 0 by >>> >>> [root@XXX ~]# sysctl kernel.sched_time_avg_ms=0 >>> >>> Stack traceback for pid 0 >>> 0xffff883f6406c600 0 0 1 3 R 0xffff883f6406cf50 *swapper/3 >>> ffff883f7ccc3ae8 0000000000000018 ffffffff810c4dd0 0000000000000000 >>> 0000000000017800 ffff883f7ccc3d78 0000000000000003 ffff883f7ccc3bf8 >>> ffffffff810c4fc9 ffff883f7ccc3c08 00000000810c5043 ffff883f7ccc3c08 >>> Call Trace: >>> <IRQ> [<ffffffff810c4dd0>] ? update_group_capacity+0x110/0x200 >>> [<ffffffff810c4fc9>] ? update_sd_lb_stats+0x109/0x600 >>> [<ffffffff810c5507>] ? find_busiest_group+0x47/0x530 >>> [<ffffffff810c5b84>] ? load_balance+0x194/0x900 >>> [<ffffffff810ad5ca>] ? update_rq_clock.part.83+0x1a/0xe0 >>> [<ffffffff810c6d42>] ? rebalance_domains+0x152/0x290 >>> [<ffffffff810c6f5c>] ? run_rebalance_domains+0xdc/0x1d0 >>> [<ffffffff8108a75b>] ? __do_softirq+0xfb/0x320 >>> [<ffffffff8108ac85>] ? irq_exit+0x125/0x130 >>> [<ffffffff810b3a17>] ? scheduler_ipi+0x97/0x160 >>> [<ffffffff81052709>] ? smp_reschedule_interrupt+0x29/0x30 >>> [<ffffffff8173a1be>] ? reschedule_interrupt+0x6e/0x80 >>> <EOI> [<ffffffff815bc83c>] ? cpuidle_enter_state+0xcc/0x230 >>> [<ffffffff815bc80c>] ? cpuidle_enter_state+0x9c/0x230 >>> [<ffffffff815bc9d7>] ? cpuidle_enter+0x17/0x20 >>> [<ffffffff810cd6dc>] ? cpu_startup_entry+0x38c/0x420 >>> [<ffffffff81053373>] ? start_secondary+0x173/0x1e0 >>> >>> Because divide-by-zero error happens in function >>> >>> update_group_capacity() >>> update_cpu_capacity() >>> scale_rt_capacity() >>> { >>> ... >>> total = sched_avg_period() + delta; >>> used = div_u64(avg, total); >>> ... >>> } >>> >>> Seems this issue could be reproduced on all I tried stable 4.1 - last >>> kernel. >>> >>> To fix this issue, reset sysctl_sched_time_avg to default value >>> MSEC_PER_SEC if user input invalid value in function >>> >>> sched_avg_period() >>> >>> Reported-by: James Puthukattukaran <james.puthukattukaran@...cle.com> >>> Signed-off-by: Ethan Zhao <ethan.zhao@...cle.com> >>> --- >>> Tested on stable 4.1, compiled on stable 4.13-rc5 >>> kernel/sched/sched.h | 3 +++ >>> 1 file changed, 3 insertions(+) >>> >>> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h >>> index eeef1a3..b398560 100644 >>> --- a/kernel/sched/sched.h >>> +++ b/kernel/sched/sched.h >>> @@ -1620,6 +1620,9 @@ static inline void rq_last_tick_reset(struct rq *rq) >>> >>> static inline u64 sched_avg_period(void) >>> { >>> + if (unlikely(sysctl_sched_time_avg <= 0)) >>> + sysctl_sched_time_avg = MSEC_PER_SEC; >>> + >> >> Sight, no.. you can set limits in the sysctl table.
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