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    SubjectRe: [PATCH 5/5] tracing: Do not record user stack trace from NMI context
    On Sun, Mar 14, 2010 at 12:58:40PM -0400, Steven Rostedt wrote:
    > On Sun, 2010-03-14 at 11:27 +0100, Frederic Weisbecker wrote:
    >
    > >
    > > Wow, that's a race :)
    > >
    > > In perf this is dealt with a special copy_from_user_nmi()
    > > (see in arch/x86/kernel/cpu/perf_event.c)
    > >
    > > May be save_stack_trace_user() should use that instead
    > > of a __copy_from_user_inatomic() based thing, just to
    > > cover such NMI corner race case.
    > >
    >
    > Yeah, we should move the __copy_from_user_nmi() out of the perf code and
    > into the normal uaccess code. Then we could do as you suggest, and have
    > the stack code do:
    >
    > if (in_nmi())
    > __copy_from_user_nmi();
    > else
    > __copy_from_user_inatomic();
    >
    > Or maybe it would be best to have the __copy_from_user_inatomic() handle
    > it.


    Yeah, agreed.



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