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    SubjectRe: [BUG] perf and kmemcheck : fatal combination

    * Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

    > On Mon, 2011-04-25 at 18:08 +0200, Eric Dumazet wrote:
    > > Hi guys
    > >
    > > Just got a panic on a kmemcheck kernel, latest linux-2.6 tree.
    > >
    > > I forgot I had kmemcheck enabled, and started "perf top" just because my
    > > machine was damn slow... Oh well...
    > >
    > > Crash in do_nmi -> nmi_enter() -> BUG_ON(in_nmi());
    >
    > Hmm,. I bet because kmemcheck triggers faults from nmi context because
    > it messes about with the page protection bits a lot to track things.
    >
    > Can't really think of anything except not making perf available on
    > kmemcheck kernels.
    >
    > ---
    > init/Kconfig | 1 +
    > 1 files changed, 1 insertions(+), 0 deletions(-)
    >
    > diff --git a/init/Kconfig b/init/Kconfig
    > index 32745bf..94735b4 100644
    > --- a/init/Kconfig
    > +++ b/init/Kconfig
    > @@ -1125,6 +1125,7 @@ config PERF_EVENTS
    > bool "Kernel performance events and counters"
    > default y if (PROFILING || PERF_COUNTERS)
    > depends on HAVE_PERF_EVENTS
    > + depends on !KMEMCHECK
    > select ANON_INODES
    > select IRQ_WORK
    > help

    Eric, does it manage to limp along if you remove the BUG_ON()?

    That risks NMI recursion but maybe it allows you to see why things are slow,
    before it crashes ;-)

    Thanks,

    Ingo


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