Hi.
On Fri, 2007-04-06 at 12:47 -0500, Nathan Lynch wrote:
> 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 :-)
If there's only one online cpu, shouldn't it return -EINVAL?
Regards,
Nigel
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