Re: [PATCH]broadcast IPI race condition on CPU hotplug

[Zwane Mwaikambo <zwane@arm.linux.org.uk>]

On Tue, 26 Apr 2005, Andi Kleen wrote:

> On Tue, Apr 26, 2005 at 10:20:44AM +0800, Li Shaohua wrote:
> > Hi,
> > After a CPU is booted but before it's officially up (set online map, and
> > enable interrupt), the CPU possibly will receive a broadcast IPI. After
> > it's up, it will handle the stale interrupt soon and maybe cause oops if
> > it's a smp-call-function-interrupt. This is quite possible in CPU
> > hotplug case, but nearly can't occur at boot time. Below patch replaces
> > broadcast IPI with send_ipi_mask just like the cluster mode.
> 
> No way we are making this common operation much slower just
> to fix an obscure race at boot time. PLease come up with a fix
> that only impacts the boot process.

The fix only for smp_call_function seems fine to me since we really don't 
want to broadcast to all processors but only online ones. 
smp_call_function is particularly dangerous because the interrupt handler 
accesses stack data which wouldn't be persistent due to the calling 
processor not waiting for non online processors.

Thanks,
	Zwane

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