Re: [PATCH] Do not use cpu_to_node() to find an offlined cpu'snode.

From: David Rientjes
Date: Wed Oct 10 2012 - 16:57:08 EST


On Wed, 10 Oct 2012, Andrew Morton wrote:

> > > So for now, let me NACK that patch. You cannot go change stuff like
> > > that.
> > >
> >
> > Agreed, that makes the nack-count up to 2 now. Andrew, please remove
> > cpu_hotplug-unmap-cpu2node-when-the-cpu-is-hotremoved.patch
> > cpu_hotplug-unmap-cpu2node-when-the-cpu-is-hotremoved-fix.patch
> > from -mm.
>
> Nope. It fixes a BUG() and so I'll be keeping it around until I see a
> better fix. It's one of the ways in which I prevent things from falling
> through cracks.
>

It fixes a BUG() that only affects users who are doing node hot-remove,
which is still radically under development, and nobody cares about except
those on the cc list, but it also introduces the NULL pointer dereference
that is attempting to be addressed in this patch. The "fix" that causes
this NULL pointer is clearly not the direction we want to go, I think we
have agreement at node hot-remove to iterate all possible cpus are map all
offline cpus with cpu_to_node(cpu) == node to NUMA_NO_NODE instead in the
generic hotplug code.

Regardless, this shouldn't be touching the acpi code which
cpu_hotplug-unmap-cpu2node-when-the-cpu-is-hotremoved.patch and
cpu_hotplug-unmap-cpu2node-when-the-cpu-is-hotremoved-fix.patch do since
it makes the behavior inconsistent across interfaces and architectures.
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