Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761271AbZDAIMe (ORCPT ); Wed, 1 Apr 2009 04:12:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755368AbZDAIMP (ORCPT ); Wed, 1 Apr 2009 04:12:15 -0400 Received: from mga11.intel.com ([192.55.52.93]:41512 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753373AbZDAIMN convert rfc822-to-8bit (ORCPT ); Wed, 1 Apr 2009 04:12:13 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.39,305,1235980800"; d="scan'208";a="677748888" From: "Metzger, Markus T" To: Oleg Nesterov , "mingo@elte.hu" CC: "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" Date: Wed, 1 Apr 2009 09:10:43 +0100 Subject: RE: [patch 1/21] x86, bts: fix race when bts tracer is removed Thread-Topic: [patch 1/21] x86, bts: fix race when bts tracer is removed Thread-Index: AcmyW6lev8d1y5X3QH6TxXUeb1BF9gAOovWw Message-ID: <928CFBE8E7CB0040959E56B4EA41A77E926D5095@irsmsx504.ger.corp.intel.com> References: <20090331145051.A12111@sedona.ch.intel.com> <20090331234823.GB28228@redhat.com> In-Reply-To: <20090331234823.GB28228@redhat.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2597 Lines: 73 >-----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? >Off-topic, but afaics modulo bts_task_departs/bts_task_arrives we >have the identical code for prev_ctx/next_ctx, perhaps it makes >sense to make a helper which calls bts_write(). Agreed. >To clarify, even _if_ I am right and _if_ you agree, we can do this >later, I am not suggesting to change this patch right now. Agreed, as well. thanks and regards, markus. --------------------------------------------------------------------- Intel GmbH Dornacher Strasse 1 85622 Feldkirchen/Muenchen Germany Sitz der Gesellschaft: Feldkirchen bei Muenchen Geschaeftsfuehrer: Douglas Lusk, Peter Gleissner, Hannes Schwaderer Registergericht: Muenchen HRB 47456 Ust.-IdNr. VAT Registration No.: DE129385895 Citibank Frankfurt (BLZ 502 109 00) 600119052 This e-mail and any attachments may contain confidential material for the sole use of the intended recipient(s). Any review or distribution by others is strictly prohibited. If you are not the intended recipient, please contact the sender and delete all copies. -- 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/