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Date: Wed, 25 Mar 2009 19:02:03 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Andrew Morton <akpm@linux-foundation.org>,
       Thomas Gleixner <tglx@linutronix.de>,
       Peter Zijlstra <peterz@infradead.org>,
       Frederic Weisbecker <fweisbec@gmail.com>,
       Tim Bird <tim.bird@am.sony.com>, Steven Rostedt <srostedt@redhat.com>
Subject: Re: [PATCH 2/5][RFC] tracing: move function profiler data out of
	function struct
Message-ID: <20090325180203.GB25518@elte.hu>
References: <20090325035646.662994901@goodmis.org> <20090325040832.443420395@goodmis.org> <20090325100746.GI2341@elte.hu> <alpine.DEB.2.00.0903251142470.5675@gandalf.stny.rr.com> <20090325174446.GE14250@elte.hu> <alpine.DEB.2.00.0903251354020.5675@gandalf.stny.rr.com>
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* Steven Rostedt <rostedt@goodmis.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