Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753608AbZFFJZK (ORCPT ); Sat, 6 Jun 2009 05:25:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751740AbZFFJZA (ORCPT ); Sat, 6 Jun 2009 05:25:00 -0400 Received: from www.tglx.de ([62.245.132.106]:54243 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751462AbZFFJY7 (ORCPT ); Sat, 6 Jun 2009 05:24:59 -0400 Date: Sat, 6 Jun 2009 11:24:50 +0200 (CEST) From: Thomas Gleixner To: Feng Tang cc: mingo@elte.hu, linux-kernel@vger.kernel.org Subject: Re: [PATCH] tick: add check for the existence of broadcast clock event device In-Reply-To: <20090605112711.67e7d5cb@feng-desktop> Message-ID: References: <20090605112711.67e7d5cb@feng-desktop> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1716 Lines: 48 On Fri, 5 Jun 2009, Feng Tang wrote: > >From 2f076e1867c8bbb145b74d289358174644d9fed8 Mon Sep 17 00:00:00 2001 > From: Feng Tang > Date: Fri, 5 Jun 2009 10:36:15 +0800 > Subject: [PATCH] tick: add check for the existence of broadcast clock event device > > Some platform may have no broadcast clock event device, as it use always-on > external timers for per-cpu timer and has no extra one for broadcast device. > This check will secure the access to bc device when system get some boradcast > on/off and enter/exit message > > Signed-off-by: Feng Tang > --- > kernel/time/tick-broadcast.c | 8 +++++++- > 1 files changed, 7 insertions(+), 1 deletions(-) > > diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c > index 118a3b3..110e0bc 100644 > --- a/kernel/time/tick-broadcast.c > +++ b/kernel/time/tick-broadcast.c > @@ -214,10 +214,13 @@ static void tick_do_broadcast_on_off(void *why) > > spin_lock_irqsave(&tick_broadcast_lock, flags); > > + bc = tick_broadcast_device.evtdev; > + if (!bc) > + goto out; > + This check is not necessary because we check whether the percpu device is affected by the stops in C3 madness _before_ we touch the broadcast device. if (!dev || !(dev->features & CLOCK_EVT_FEAT_C3STOP)) got out; If your percpu devices are always on (not affected by C3 stop) then you never dereference bc. So why do we need an extra check for !bc ? Thanks, tglx -- 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/