Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762039AbZDBO6n (ORCPT ); Thu, 2 Apr 2009 10:58:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1761276AbZDBO5S (ORCPT ); Thu, 2 Apr 2009 10:57:18 -0400 Received: from mga03.intel.com ([143.182.124.21]:52235 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760989AbZDBO5R (ORCPT ); Thu, 2 Apr 2009 10:57:17 -0400 Content-Type: multipart/mixed; boundary="===============0508950418==" MIME-Version: 1.0 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.39,314,1235980800"; d="scan'208";a="127093752" Message-Id: <20090402145709.422226000@intel.com> References: <20090402145455.597376000@intel.com> User-Agent: quilt/0.46-1 Date: Thu, 02 Apr 2009 16:54:59 +0200 From: markus.t.metzger@intel.com To: mingo@elte.hu, tglx@linutronix.de, hpa@zytor.com Cc: 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, Markus Metzger Subject: [patch 04/18] x86, bts: wait until traced task has been scheduled out Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3622 Lines: 119 --===============0508950418== MIME-Version: 1.0 Content-Disposition: inline; filename=tip.master.ds.wait_task_inactive.patch 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) +{ + unsigned long nvcsw; + unsigned long nivcsw; + + if (!task) + return; + + if (task == current) + return; + + nvcsw = task->nvcsw; + nivcsw = task->nivcsw; + for (;;) { + if (!task_is_running(task)) + break; + /* + * The switch count is incremented before the actual + * context switch. We thus wait for two switches to be + * sure at least one completed. + */ + if ((task->nvcsw - nvcsw) > 1) + break; + if ((task->nivcsw - nivcsw) > 1) + break; + } +} + static inline struct ds_context *ds_get_context(struct task_struct *task) { struct ds_context **p_context = @@ -321,6 +355,9 @@ static inline void ds_put_context(struct spin_unlock_irqrestore(&ds_lock, irq); + /* The context might still be in use for context switching. */ + wait_to_unschedule(context->task); + kfree(context); } @@ -789,6 +826,9 @@ void ds_release_bts(struct bts_tracer *t WARN_ON_ONCE(tracer->ds.context->bts_master != tracer); tracer->ds.context->bts_master = NULL; + /* Make sure tracing stopped and the tracer is not in use. */ + wait_to_unschedule(tracer->ds.context->task); + put_tracer(tracer->ds.context->task); ds_put_context(tracer->ds.context); -- --===============0508950418== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline --------------------------------------------------------------------- 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. --===============0508950418==-- -- 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/