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SubjectRe: [PATCH 2/9] perf_counter: fix update_userpage()
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On Thu, 2009-04-02 at 20:21 +1100, Paul Mackerras wrote:
> Peter Zijlstra writes:
>
> > The below might work:
> >
> > u32 seq;
> > s64 count;
> >
> > again:
> > seq = pc->lock;
> >
> > if (unlikely(seq & 1)) {
>
> I don't believe we can ever see this condition, since pc->lock is
> updated in the kernel either at interrupt level on the cpu this task
> is running on, or in the kernel in the context of this task. So this
> userspace code can never run in the middle of the kernel updating
> things.

Colour me paranoid ;-)


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