From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752498Ab3C0ORu (ORCPT ); Wed, 27 Mar 2013 10:17:50 -0400 Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:41202 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750716Ab3C0ORs (ORCPT ); Wed, 27 Mar 2013 10:17:48 -0400 Message-ID: <1364393852.5053.74.camel@laptop> Subject: Re: BUG: using smp_processor_id() in preemptible [00000000] code: asm/8267 From: Peter Zijlstra To: Joerg Roedel Cc: Borislav Petkov , Ingo Molnar , Arnaldo Carvalho de Melo , lkml , Stephane Eranian , Namhyung Kim , Jiri Olsa , paulmck Date: Wed, 27 Mar 2013 15:17:32 +0100 In-Reply-To: <20130327131532.GL30540@8bytes.org> References: <20130324115556.GA4866@pd.tnic> <20130324155924.GB4866@pd.tnic> <20130326183452.GC27518@pd.tnic> <20130327131532.GL30540@8bytes.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.2-0ubuntu0.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2013-03-27 at 14:15 +0100, Joerg Roedel wrote: > What makes me wonder here is that the code is preemptible in an > rcu_read_locked section. As far as I know preemption needs to be > disabled while holding the rcu_read_lock(). Nah, a long long time ago some -rt people complained to paulmck that keeping preemption disabled over all this RCU stuff was killing latencies. Paul liked the challenge and came up with some mind twisting stuff to make it work. If you're into that kind of pain, look at CONFIG_*_PREEMPT_RCU :-) But yeah, you need to have that stuff enabled before you can hit this particular snag.