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SubjectRe: [PATCH v1] mm/mempolicy.c: Fix get_nodes() off-by-one error.
On Thu 12-10-17 08:28:25, Andi Kleen wrote:
> On Thu, Oct 12, 2017 at 10:46:33AM +0200, Michal Hocko wrote:
> > [CC Christoph who seems to be the author of the code]
> Actually you can blame me. I did the mistake originally.
> It was found many years ago, but then it was already too late
> to change.
> > Andi has voiced a concern about backward compatibility but I am not sure
> > the risk is very high. The current behavior is simply broken unless you
> > use a large maxnode anyway. What kind of breakage would you envision
> > Andi?
> libnuma uses the available number of nodes as max.
> So it would always lose the last one with your chance.

I must be missing something because libnuma does
if (set_mempolicy(policy, bmp->maskp, bmp->size + 1) < 0)

so it sets max as size + 1 which is exactly what the man page describes.

> Your change would be catastrophic.

I am not sure which change do you mean here. I wasn't proposing any
patch (yet). All I was saying is that the docuementation diagrees with
the in kernel implementation. The only applications that would break
would be those which do not comply to the documentation AFAICS, no?
Michal Hocko

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