Date: Sat, 25 Mar 2006 03:47:44 -0800
From: Andrew Morton <akpm@osdl.org>
To: "David S. Miller" <davem@davemloft.net>
Cc: linux-kernel@vger.kernel.org
Subject: Re: SMP busted on non-cpu-hotplug systems
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"David S. Miller" <davem@davemloft.net> wrote:
>
> 
> I just noticed this on sparc64, as I lost 31 cpus on my
> Niagara box due to it :)
> 
> boot_cpu_init() sets the boot processor ID in cpu_present_map.
> 
> But fixup_cpu_present_map() will only populate the cpu_present_map if
> it is empty, which it won't be because of what boot_cpu_init() just
> did.

oops.  I guess most architectures set cpu_present_map while bringing up the
APs.

I think it'd be cleanest to require that the arch do that -
fixup_cpu_present_map() looks like a bit of a hack.

I guess if we want to perpetuate fixup_cpu_present_map() then we should
teach it to ignore the boot cpu.   (cpus_weight(&cpu_present_map) == 1)
would do that.
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