linux-kernel - Re: [PATCH 01/13] jump label v9: notifier atomic call chain notrace

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Message-ID: <20100610153432.GB3923@redhat.com>
Date:	Thu, 10 Jun 2010 11:34:33 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu,
	mathieu.desnoyers@...ymtl.ca, hpa@...or.com, tglx@...utronix.de,
	rostedt@...dmis.org, andi@...stfloor.org, roland@...hat.com,
	rth@...hat.com, mhiramat@...hat.com, avi@...hat.com,
	davem@...emloft.net, vgoyal@...hat.com, sam@...nborg.org
Subject: Re: [PATCH 01/13] jump label v9: notifier atomic call chain notrace

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@...ymtl.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@...ymtl.ca>
> > Signed-off-by: Jason Baron <jbaron@...hat.com>
> > Reviewed-by: Masami Hiramatsu <mhiramat@...hat.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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