Re: [PATCH 18/19] sched: prctl() core-scheduling interface

[Eugene Syromiatnikov]

On Tue, Aug 17, 2021 at 05:52:43PM +0200, Peter Zijlstra wrote:
> Urgh... lemme guess, your HP BIOS is funny and reports more possible
> CPUs than you actually have resulting in cpu_possible_mask !=
> cpu_online_mask. Alternatively, you booted with nr_cpus= or something
> daft like that.

Yep, it seems to be the case:

    # cat /sys/devices/system/cpu/possible
    0-7
    # cat /sys/devices/system/cpu/online
    0-3

> 
> That code does for_each_possible_cpus(i) { rq_lock_irq(cpu_rq(i)); },
> which, because of core-sched, needs rq->core set-up, but because these
> CPUs have never been online, that's not done and *BOOM*.
> 
> Or something like that.. I'll try and have a look tomorrow, I'm in dire
> need of sleep.
>