linux-kernel - Re: [PATCH] lockdep: Make lockstats counting per cpu

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Message-ID: <20100326174318.GF5188@nowhere>
Date:	Fri, 26 Mar 2010 18:43:20 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] lockdep: Make lockstats counting per cpu

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.

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