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Date: Fri, 26 Mar 2010 18:43:20 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>,
       Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] lockdep: Make lockstats counting per cpu
Message-ID: <20100326174318.GF5188@nowhere>
References: <1269570142-13965-1-git-send-regression-fweisbec@gmail.com> <1269586358.12097.117.camel@laptop> <1269589714.12097.122.camel@laptop>
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On Fri, Mar 26, 2010 at 08:48:34AM +0100, Peter Zijlstra wrote:
> On Fri, 2010-03-26 at 07:52 +0100, Peter Zijlstra wrote:
> > On Fri, 2010-03-26 at 03:22 +0100, Frederic Weisbecker wrote:
> > > We can't use irqsafe per cpu counters for that as
> > > these stats might be also written from NMI path, and irqsafe per
> > > cpu counters are not NMI safe, but local_t operations are.
> > > 
> > lockdep shouldn't do NMI, nmi_enter() has an explicit lockdep_off().
> 
> Also, more importantly, you simply should never use locks in NMI context
> to begin with ;-)


Right. I just thought ther could be some path that use rcu_read_lock
things there or whatever check. I mean, NMI don't need rcu_read_lock
but it could call helpers that use it.

Whatever, lockdep is off there. Looks like I can safely use per cpu counters.