Messages in this thread | | | Date | Fri, 17 Aug 2018 11:27:34 +0100 | From | Matt Fleming <> | Subject | Re: [PATCH] sched/fair: Avoid divide by zero when rebalancing domains |
| |
On Thu, 05 Jul, at 05:54:02PM, Valentin Schneider wrote: > On 05/07/18 14:27, Matt Fleming wrote: > > On Thu, 05 Jul, at 11:10:42AM, Valentin Schneider wrote: > >> Hi, > >> > >> On 04/07/18 15:24, Matt Fleming wrote: > >>> It's possible that the CPU doing nohz idle balance hasn't had its own > >>> load updated for many seconds. This can lead to huge deltas between > >>> rq->avg_stamp and rq->clock when rebalancing, and has been seen to > >>> cause the following crash: > >>> > >>> divide error: 0000 [#1] SMP > >>> Call Trace: > >>> [<ffffffff810bcba8>] update_sd_lb_stats+0xe8/0x560 > > My confusion comes from not seeing where that crash happens. Would you mind > sharing the associated line number? I can feel the "how did I not see this" > from there but it can't be helped :(
The divide by zero comes from scale_rt_capacity() where 'total' is a u64 but gets truncated when passed to div_u64() since the divisor parameter is u32.
Sure, you could use div64_u64() instead, but the real issue is that the load hasn't been updated for a very long time and that we're trying to balance the domains with stale data.
| |