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

[Ingo Molnar]

* Nathan Lynch <ntl@xxxxxxxxx> 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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