Ingo Molnar wrote:
>
> * Nathan Lynch <[email protected]> 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())
Yeah, I just realized that an implementation of my proposal would busy
loop in the kernel forever if a silly admin tried to offline the last
cpu (we're already using -EBUSY for that case), so
freeze_processes_nofail is a better idea :-)
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