Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932186AbZDCLcs (ORCPT ); Fri, 3 Apr 2009 07:32:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761120AbZDCLci (ORCPT ); Fri, 3 Apr 2009 07:32:38 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:43775 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758912AbZDCLch (ORCPT ); Fri, 3 Apr 2009 07:32:37 -0400 Date: Fri, 3 Apr 2009 13:32:19 +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 04/18] x86, bts: wait until traced task has been scheduled out Message-ID: <20090403113219.GF31399@elte.hu> References: <20090402145455.597376000@intel.com> <20090402145709.422226000@intel.com> <20090402191730.GD843@elte.hu> <928CFBE8E7CB0040959E56B4EA41A77E92718054@irsmsx504.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <928CFBE8E7CB0040959E56B4EA41A77E92718054@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: 3043 Lines: 79 * Metzger, Markus T wrote: > >-----Original Message----- > >From: Ingo Molnar [mailto:mingo@elte.hu] > >Sent: Thursday, April 02, 2009 9:18 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 04/18] x86, bts: wait until traced task has been scheduled out > > > > > >* markus.t.metzger@intel.com wrote: > > > >> In order to stop branch tracing for a running task, we need to > >> first clear the branch tracing control bits before we may free the > >> tracing buffer. If the traced task is running, the cpu might still > >> trace that task after the branch trace control bits have cleared. > >> > >> Wait until the traced task has been scheduled out before > >> proceeding. > >> > >> A similar problem affects the task debug store context. We first > >> remove the context, then we need to wait until the task has been > >> scheduled out before we can free the context memory. > >> > >> > >> Reviewed-by: Oleg Nesterov > >> Signed-off-by: Markus Metzger > >> --- > >> arch/x86/kernel/ds.c | 40 40 + 0 - 0 ! > >> 1 file changed, 40 insertions(+) > >> > >> Index: b/arch/x86/kernel/ds.c > >> =================================================================== > >> --- a/arch/x86/kernel/ds.c > >> +++ b/arch/x86/kernel/ds.c > >> @@ -250,6 +250,40 @@ static DEFINE_PER_CPU(struct ds_context > >> #define system_context per_cpu(system_context_array, smp_processor_id()) > >> > >> > >> +/* > >> + * Wait for the traced task to unschedule. > >> + * > >> + * This guarantees that the bts trace configuration has been > >> + * synchronized with the cpu executing the task. > >> + */ > >> +static void wait_to_unschedule(struct task_struct *task) > >> +{ > > > >this should be in sched.c and task_is_running() should not be > >exported from there. > > > >I.e. your original patch which i objected to is probably the right > >one, but should be named something like "task_wait_context_switch()" > >- which signals its purpose: that it is to wait for the task to > >context-switch at least once, so that its ptrace state is installed > >(or deinstalled) for sure. > > OK. > > I'll move it to sched.c. > > In that case, I would use task_running() without holding the rq > lock, since we don't really care whether we read an old value or > not. Would that be OK with you? i'd have to see that in full context - reading non-locked results can in essence result in stale old values being read out, regardless of current reality. task_running() is normally used within the rq lock. 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/