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SubjectRe: [PATCH 3/8] Use process freezer for cpu-hotplug

* Nathan Lynch <ntl@pobox.com> wrote:

> > - raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu);
> > + if (freeze_processes(FE_HOTPLUG_CPU)) {
> > + thaw_processes(FE_HOTPLUG_CPU);
> > + return -EBUSY;
> > + }
> > +
>
> If I'm understanding correctly, this will cause
>
> # echo 0 > /sys/devices/system/cpu/cpuX/online
>
> to sometimes fail, and userspace is expected to try again? This will
> break existing applications.
>
> Perhaps drivers/base/cpu.c:store_online should retry as long as
> cpu_up/down return -EBUSY. That would avoid a userspace-visible
> interface change.

yeah. I'd even suggest a freeze_processes_nofail() API instead, that
does this internally, without burdening the callsites. (and once the
freezer becomes complete then freeze_processes_nofail() ==
freeze_processes())

Ingo
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