Prev: [PATCH 08/13] jump label v9: initialize workqueue tracepoints *before* they are registered
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From: Frederic Weisbecker on 9 Jun 2010 18:00
On Wed, Jun 09, 2010 at 05:38:52PM -0400, Jason Baron wrote:
> From: Mathieu Desnoyers <mathieu.desnoyers(a)polymtl.ca>
>
> In LTTng, being able to use the atomic notifier from cpu idle entry to
> ensure the tracer flush the last events in the current subbuffer
> requires the rcu read-side to be marked "notrace", otherwise it can end
> up calling back into lockdep and the tracer.
>
> Also apply to the the die notifier.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers(a)polymtl.ca>
> Signed-off-by: Jason Baron <jbaron(a)redhat.com>
> Reviewed-by: Masami Hiramatsu <mhiramat(a)redhat.com>
> ---



I don't understand the purpose of this patch. The only notifier
I see that is used by jmp label is the module notifier, and I
don't see how it can do bad things if we don't use the notrace
version.

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From: Jason Baron on 10 Jun 2010 11:40
On Wed, Jun 09, 2010 at 11:58:13PM +0200, Frederic Weisbecker wrote:
> On Wed, Jun 09, 2010 at 05:38:52PM -0400, Jason Baron wrote:
> > From: Mathieu Desnoyers <mathieu.desnoyers(a)polymtl.ca>
> >
> > In LTTng, being able to use the atomic notifier from cpu idle entry to
> > ensure the tracer flush the last events in the current subbuffer
> > requires the rcu read-side to be marked "notrace", otherwise it can end
> > up calling back into lockdep and the tracer.
> >
> > Also apply to the the die notifier.
> >
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers(a)polymtl.ca>
> > Signed-off-by: Jason Baron <jbaron(a)redhat.com>
> > Reviewed-by: Masami Hiramatsu <mhiramat(a)redhat.com>
> > ---
>
>
>
> I don't understand the purpose of this patch. The only notifier
> I see that is used by jmp label is the module notifier, and I
> don't see how it can do bad things if we don't use the notrace
> version.
>

hmmm...yeah, this patch was introduced b/c of the use of the 'int3'
notifier when updating the kernel text. We got into a recursive loop
without it. However, since the current implementation is using
stop_machine() to do text updates, I don't think this patch is necessary
until we have the more optimal text updating mechanism in place. I'll
re-test without this patch.

thanks,

-Jason
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