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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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