Messages in this thread | | | Date | Mon, 29 Jul 2019 12:38:30 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: sched: Unexpected reschedule of offline CPU#2! |
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On Mon, 29 Jul 2019, Peter Zijlstra wrote: > On Mon, Jul 29, 2019 at 11:58:24AM +0200, Thomas Gleixner wrote: > > On Mon, 29 Jul 2019, Peter Zijlstra wrote: > > > On Sat, Jul 27, 2019 at 09:44:50AM -0700, Guenter Roeck wrote: > > > > [ 61.348866] Call Trace: > > > > [ 61.349392] kick_ilb+0x90/0xa0 > > > > [ 61.349629] trigger_load_balance+0xf0/0x5c0 > > > > [ 61.349859] ? check_preempt_wakeup+0x1b0/0x1b0 > > > > [ 61.350057] scheduler_tick+0xa7/0xd0 > > > > > > kick_ilb() iterates nohz.idle_cpus_mask to find itself an idle_cpu(). > > > > > > idle_cpus_mask() is set from nohz_balance_enter_idle() and cleared from > > > nohz_balance_exit_idle(). nohz_balance_enter_idle() is called from > > > __tick_nohz_idle_stop_tick() when entering nohz idle, this includes the > > > cpu_is_offline() clause of the idle loop. > > > > > > However, when offline, cpu_active() should also be false, and this > > > function should no-op. > > > > Ha. That reboot mess is not clearing cpu active as it's not going through > > the regular cpu hotplug path. It's using reboot IPI which 'stops' the cpus > > dead in their tracks after clearing cpu online.... > > $string-of-cock-compliant-curses > > What a trainwreck... > > So if it doesn't play by the normal rules; how does it expect to work? > > So what do we do? 'Fix' reboot or extend the rules?
Reboot has two modes:
- Regular reboot initiated from user space
- Panic reboot
For the regular reboot we can make it go through proper hotplug, for the panic case not so much.
thanks,
tglx
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