Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762487AbZDALfY (ORCPT ); Wed, 1 Apr 2009 07:35:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762232AbZDALe7 (ORCPT ); Wed, 1 Apr 2009 07:34:59 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:38003 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761839AbZDALe5 (ORCPT ); Wed, 1 Apr 2009 07:34:57 -0400 Date: Wed, 1 Apr 2009 13:34:38 +0200 From: Ingo Molnar To: "Metzger, Markus T" Cc: Oleg Nesterov , "linux-kernel@vger.kernel.org" , "tglx@linutronix.de" , "hpa@zytor.com" , "markus.t.metzger@gmail.com" , "roland@redhat.com" , "eranian@googlemail.com" , "Villacis, Juan" , "ak@linux.jf.intel.com" Subject: Re: [patch 1/21] x86, bts: fix race when bts tracer is removed Message-ID: <20090401113438.GA23678@elte.hu> References: <20090331145051.A12111@sedona.ch.intel.com> <20090331234823.GB28228@redhat.com> <928CFBE8E7CB0040959E56B4EA41A77E926D5095@irsmsx504.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <928CFBE8E7CB0040959E56B4EA41A77E926D5095@irsmsx504.ger.corp.intel.com> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2385 Lines: 63 * Metzger, Markus T wrote: > >-----Original Message----- > >From: Oleg Nesterov [mailto:oleg@redhat.com] > >Sent: Wednesday, April 01, 2009 1:48 AM > >To: Metzger, Markus T > >Cc: linux-kernel@vger.kernel.org; mingo@elte.hu; tglx@linutronix.de; hpa@zytor.com; > >markus.t.metzger@gmail.com; roland@redhat.com; eranian@googlemail.com; Villacis, Juan; > >ak@linux.jf.intel.com > >Subject: Re: [patch 1/21] x86, bts: fix race when bts tracer is removed > > > >On 03/31, Markus Metzger wrote: > >> > >> Read the tracer once during a context switch. > >> ... > >> @@ -1044,36 +1051,39 @@ void ds_switch_to(struct task_struct *pr > >> { > >> struct ds_context *prev_ctx = prev->thread.ds_ctx; > >> struct ds_context *next_ctx = next->thread.ds_ctx; > >> + unsigned long debugctlmsr = next->thread.debugctlmsr; > >> > >> if (prev_ctx) { > >> + struct bts_tracer *tracer = prev_ctx->bts_master; > >> + > >> update_debugctlmsr(0); > >> > >> - if (prev_ctx->bts_master && > >> - (prev_ctx->bts_master->trace.ds.flags & BTS_TIMESTAMPS)) { > >> + if (tracer && (tracer->flags & BTS_TIMESTAMPS)) { > > > >In theory, we need barrier() after reading ->bts_master. > > > >(actually, I did see the bug reports when the compiler read the pointer > > twice with the code like above). > > I guess the same is true for prev_ctx, next_ctx, and debugctlmsr, then. > > Ingo, > would it be OK to resend this one patch with the barrier()s added? Sure - but note that i have put the series on hold until you get broad Ack's from Oleg for the ptrace bits. Please fix the review feedback from Oleg and propagate his acks into the commit logs as well. Oleg is finding bugs we missed in the past so his review work is very valuable. Also - minor patch submission technicality observation: currently each of your mails goes into a separate discussion thread, making it hard to review them as a group. The preferred way to send such series is to use "git format-patch" + "git send-email". (That will give a nice 0/21 mail and a properly threaded discussion with proper References header lines.) Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/