Christoph Lameter wrote:
>
> On Mon, 3 Apr 2006, Nathan Lynch wrote:
>
> > In this case, disabling preempt around the for_each_online_cpu loop
> > would prevent any cpu from going down in the meantime. But since this
> > function doesn't look like it's a hot path, and we're potentially
> > traversing lots of zones and cpus, lock_cpu_hotplug might be preferable.
> >
> > As Paul noted, the fix as it stands isn't adequate.
>
> There are many other for_each_*_cpu loops in the kernel that do not have
> any of the instrumentation you suggest. I suggest you come up with a
> general solution and then go through all of them and fix this. Please be
> aware that many of these loops are performance critical.
But this one isn't, right?
And I'm afraid there's a misunderstanding here -- only
for_each_online_cpu (or accessing the cpu online map in general) has
such restrictions -- for_each_possible_cpu doesn't require any locking
or preempt tricks since cpu_possible_map must not change after boot.
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