Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757509AbZDBSps (ORCPT ); Thu, 2 Apr 2009 14:45:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753548AbZDBSpi (ORCPT ); Thu, 2 Apr 2009 14:45:38 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:36565 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750923AbZDBSph (ORCPT ); Thu, 2 Apr 2009 14:45:37 -0400 Date: Thu, 2 Apr 2009 20:45:14 +0200 From: Ingo Molnar To: markus.t.metzger@intel.com Cc: tglx@linutronix.de, hpa@zytor.com, markus.t.metzger@gmail.com, roland@redhat.com, eranian@googlemail.com, oleg@redhat.com, juan.villacis@intel.com, 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: <20090402184514.GC843@elte.hu> References: <20090402145455.597376000@intel.com> <20090402145702.669790000@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090402145702.669790000@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: 1352 Lines: 46 * 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()? > + > + 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. 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? 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/