From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yong Zhang Subject: Re: [PATCH] fix BUG using smp_processor_id() in touch_nmi_watchdog and touch_softlockup_watchdog Date: Fri, 20 Aug 2010 23:02:31 +0800 Message-ID: <20100820150231.GA8628@zhy> References: <20100817083945.GA12022@swordfish.minsk.epam.com> <20100817092407.GB12022@swordfish.minsk.epam.com> <20100817103948.GA5352@swordfish.minsk.epam.com> <20100817131320.GX4879@redhat.com> <20100818024802.GA24748@nowhere> <20100818130156.43a183d9.akpm@linux-foundation.org> <20100820025749.GB4879@redhat.com> Reply-To: Yong Zhang Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Received: from mail-gy0-f174.google.com ([209.85.160.174]:41695 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752200Ab0HTPCl (ORCPT ); Fri, 20 Aug 2010 11:02:41 -0400 Content-Disposition: inline In-Reply-To: <20100820025749.GB4879@redhat.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Don Zickus Cc: Andrew Morton , Frederic Weisbecker , Len Brown , Sergey Senozhatsky , Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, Andy Grover On Thu, Aug 19, 2010 at 10:57:49PM -0400, Don Zickus wrote: > On Wed, Aug 18, 2010 at 01:01:56PM -0700, Andrew Morton wrote: > > The surprise new requirement that touch_nmi_watchdog() be called from > > non-preemptible code does seem to make sense IMO. It's hard to see why > > anyone would be touching the watchdog unless he's spinning in irqs-off > > code. Except, of course, when we have a utility function which can be > > called from wither irqs-on or irqs-off: acpi_os_stall(). > > > > That being said, it's not good to introduce new API requirements by > > accident! An audit of all callers should first be performed, at least. > > > > > > The surprise new requirement that touch_softlockup_watchdog() be called > > from non-preemptible code doesn't make sense IMO. If I have a piece of > > code in the kernel which I expect to sit in TASK_UNINTERRUPTIBLE state > > for three minutes waiting for my egg to boil, I should be able to do > > that and I should be able to touch the softlockup detector without > > needing to go non-preemptible. > > Ok, so here is my patch that syncs the touch_*_watchdog back in line with > the old semantics. Hopefully this will undo any harm I caused. > > ------------cut -->--------------------------- > > >From b372e821c804982438db090db6b4a2f753c78091 Mon Sep 17 00:00:00 2001 > From: Don Zickus > Date: Thu, 19 Aug 2010 22:48:26 -0400 > Subject: [PATCH] [lockup detector] sync touch_*_watchdog back to old semantics > > During my rewrite, the semantics of touch_nmi_watchdog and > touch_softlockup_watchdog changed enough to break some drivers > (mostly over preemptable regions). > > This change brings those touch_*_watchdog functions back in line > to how they used to work. This one looks good to me. Thank you Don. -Yong > > Signed-off-by: Don Zickus > --- > kernel/watchdog.c | 17 ++++++++++++----- > 1 files changed, 12 insertions(+), 5 deletions(-) > > diff --git a/kernel/watchdog.c b/kernel/watchdog.c > index 613bc1f..99e35a2 100644 > --- a/kernel/watchdog.c > +++ b/kernel/watchdog.c > @@ -122,7 +122,7 @@ static void __touch_watchdog(void) > > void touch_softlockup_watchdog(void) > { > - __get_cpu_var(watchdog_touch_ts) = 0; > + __raw_get_cpu_var(watchdog_touch_ts) = 0; > } > EXPORT_SYMBOL(touch_softlockup_watchdog); > > @@ -142,7 +142,14 @@ void touch_all_softlockup_watchdogs(void) > #ifdef CONFIG_HARDLOCKUP_DETECTOR > void touch_nmi_watchdog(void) > { > - __get_cpu_var(watchdog_nmi_touch) = true; > + if (watchdog_enabled) { > + unsigned cpu; > + > + for_each_present_cpu(cpu) { > + if (per_cpu(watchdog_nmi_touch, cpu) != true) > + per_cpu(watchdog_nmi_touch, cpu) = true; > + } > + } > touch_softlockup_watchdog(); > } > EXPORT_SYMBOL(touch_nmi_watchdog); > @@ -430,6 +437,9 @@ static int watchdog_enable(int cpu) > wake_up_process(p); > } > > + /* if any cpu succeeds, watchdog is considered enabled for the system */ > + watchdog_enabled = 1; > + > return 0; > } > > @@ -452,9 +462,6 @@ static void watchdog_disable(int cpu) > per_cpu(softlockup_watchdog, cpu) = NULL; > kthread_stop(p); > } > - > - /* if any cpu succeeds, watchdog is considered enabled for the system */ > - watchdog_enabled = 1; > } > > static void watchdog_enable_all_cpus(void) > -- > 1.7.2.1