linux-kernel - Re: [PATCH 2/5][RFC] tracing: move function profiler data out of function struct

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Date:	Wed, 25 Mar 2009 19:02:03 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Tim Bird <tim.bird@...sony.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/5][RFC] tracing: move function profiler data out of
	function struct


* Steven Rostedt <rostedt@...dmis.org> wrote:

> 
> On Wed, 25 Mar 2009, Ingo Molnar wrote:
> 
> > > The atomic_inc_return protects against NMIs, since this is the only place 
> > > the lock is taken.
> > 
> > i mean, if this code executes _ni_ an NMI. Or that cannot happen? We 
> > trace nmis too, dont we?
> 
> Yes, it can execute in an NMI, but we have no issues there. If the 
> lock was taken the atomic inc is set. If an NMI comes in, it will 
> fail the atomic inc counter test and never try to take the lock.

You are misunderstanding me. Can this bit:

> > +   if (!profile_pages->next && alloc_safe)
> > +           profile_pages->next = (void *)get_zeroed_page(GFP_ATOMIC);

run in NMI context?

or is alloc_safe false in that case? Even if it's safe it looks 
really messy ...

	Ingo
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