Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759446AbZDCGXr (ORCPT ); Fri, 3 Apr 2009 02:23:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753730AbZDCGXh (ORCPT ); Fri, 3 Apr 2009 02:23:37 -0400 Received: from mga11.intel.com ([192.55.52.93]:62012 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751590AbZDCGXh convert rfc822-to-8bit (ORCPT ); Fri, 3 Apr 2009 02:23:37 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.39,318,1235980800"; d="scan'208";a="678411580" From: "Metzger, Markus T" To: Ingo Molnar CC: "tglx@linutronix.de" , "hpa@zytor.com" , "markus.t.metzger@gmail.com" , "roland@redhat.com" , "eranian@googlemail.com" , "oleg@redhat.com" , "Villacis, Juan" , "ak@linux.jf.intel.com" , "linux-kernel@vger.kernel.org" Date: Fri, 3 Apr 2009 07:19:56 +0100 Subject: RE: [patch 01/18] x86, bts: fix race when bts tracer is removed Thread-Topic: [patch 01/18] x86, bts: fix race when bts tracer is removed Thread-Index: AcmzwzWaOsx60ovwSfmp6ywNDZWSaQAYHckg Message-ID: <928CFBE8E7CB0040959E56B4EA41A77E9271804B@irsmsx504.ger.corp.intel.com> References: <20090402145455.597376000@intel.com> <20090402145702.669790000@intel.com> <20090402184514.GC843@elte.hu> In-Reply-To: <20090402184514.GC843@elte.hu> 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: 2703 Lines: 84 >-----Original Message----- >From: Ingo Molnar [mailto:mingo@elte.hu] >Sent: Thursday, April 02, 2009 8:45 PM >To: Metzger, Markus T >Cc: tglx@linutronix.de; hpa@zytor.com; markus.t.metzger@gmail.com; roland@redhat.com; >eranian@googlemail.com; oleg@redhat.com; Villacis, Juan; ak@linux.jf.intel.com; linux- >kernel@vger.kernel.org >Subject: Re: [patch 01/18] x86, bts: fix race when bts tracer is removed > > >* markus.t.metzger@intel.com wrote: > >> +static inline void ds_take_timestamp(struct ds_context *context, >> + enum bts_qualifier qualifier, >> + struct task_struct *task) >> +{ >> + struct bts_tracer *tracer = context->bts_master; >> + barrier(); > >why the barrier()? See http://lkml.org/lkml/2009/3/31/544 Oleg: "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)." >> + >> + if (tracer && (tracer->flags & BTS_TIMESTAMPS)) { >> + struct bts_struct ts = { >> + .qualifier = qualifier, >> + .variant.timestamp.jiffies = jiffies_64, >> + .variant.timestamp.pid = task->pid >> + }; >> + bts_write(tracer, &ts); >> + } > >Why do we have .variant.timestamp.pid ? A PID is not a timestamp. It >might be .event.jiffies and .event.pid perhaps. OK. >Also, the whole function could be cleaned up by: > > 1) returning early if !tracer || !(tracer->flags & BTS_TIMESTAMPS). > > 2) Doing a cleaner initialization - something like: > >struct bts_struct ts = { > .qualifier = qualifier, > .variant.event.jiffies = jiffies_64, > .variant.event.pid = task->pid >}; > >Also, raw use of jiffies_64 is buggy and racy. Why does this use >jiffies to begin with - why not some finer grained time? What would be a good time to use? thanks, 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/