From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: current_thread_info() vs task_thread_info(current) Date: Mon, 18 Jul 2011 20:04:04 -0700 Message-ID: <20110719030404.GA2355@linux.vnet.ibm.com> References: <1310988183.13765.56.camel@twins> <1310990097.25044.307.camel@pasglop> <20110718143731.GA2312@linux.vnet.ibm.com> <1311024983.25044.325.camel@pasglop> <20110719003930.GF2312@linux.vnet.ibm.com> <1311037057.25044.346.camel@pasglop> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e4.ny.us.ibm.com ([32.97.182.144]:40534 "EHLO e4.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751230Ab1GSDEH (ORCPT ); Mon, 18 Jul 2011 23:04:07 -0400 Content-Disposition: inline In-Reply-To: <1311037057.25044.346.camel@pasglop> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Benjamin Herrenschmidt Cc: Peter Zijlstra , linux-arch@vger.kernel.org, linux-kernel , Thomas Gleixner On Tue, Jul 19, 2011 at 10:57:37AM +1000, Benjamin Herrenschmidt wrote: > On Mon, 2011-07-18 at 17:39 -0700, Paul E. McKenney wrote: > > > Hrm, no I don't see that happening no. The preempt count when > > exiting an > > > irq or softirq stack should be the exact same as when entering it, > > which > > > is why we don't bother copying it over. Do you see any case where > > that > > > wouldn't hold ? > > > > Nope, other than seeing preempt_count() transition from zero to three > > across a spin_unlock_irqrestore() for no good reason that I could see. > > Do you have a nice repro-case ? :-) > > That sounds really nasty ... smells really like something bad's > happening from an interrupt, but we don't copy back the preempt-count > from the interrupt stacks at all, so that's really really odd. Good question... The system I reproduced on four times over the weekend is out of commission. Trying the same test on another system with a minimal patch -- will let you know how it goes. Thanx, Paul