Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764382AbZDCL30 (ORCPT ); Fri, 3 Apr 2009 07:29:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761863AbZDCL3Q (ORCPT ); Fri, 3 Apr 2009 07:29:16 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:43070 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754390AbZDCL3P (ORCPT ); Fri, 3 Apr 2009 07:29:15 -0400 Date: Fri, 3 Apr 2009 13:29:00 +0200 From: Ingo Molnar 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 Message-ID: <20090403112900.GD31399@elte.hu> References: <20090402145455.597376000@intel.com> <20090402145702.669790000@intel.com> <20090402184514.GC843@elte.hu> <928CFBE8E7CB0040959E56B4EA41A77E9271804B@irsmsx504.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <928CFBE8E7CB0040959E56B4EA41A77E9271804B@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=3.2.5 -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: 1875 Lines: 55 * Metzger, Markus T wrote: > >-----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)." Please convert this piece of non-trivial information into a small two-sentence blurb and put it into a comment block. > >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? ktime_get() would be the primary candidate. (Or, perhaps, if performance is really an issue then trace_clock() or trace_clock_global().) 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/