Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751608Ab0HTC6q (ORCPT ); Thu, 19 Aug 2010 22:58:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:18709 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751242Ab0HTC6n (ORCPT ); Thu, 19 Aug 2010 22:58:43 -0400 Date: Thu, 19 Aug 2010 22:57:49 -0400 From: Don Zickus To: Andrew Morton Cc: Frederic Weisbecker , Len Brown , Sergey Senozhatsky , Yong Zhang , Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, Andy Grover Subject: Re: [PATCH] fix BUG using smp_processor_id() in touch_nmi_watchdog and touch_softlockup_watchdog Message-ID: <20100820025749.GB4879@redhat.com> References: <20100817025954.GA12366@nowhere> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100818130156.43a183d9.akpm@linux-foundation.org> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3299 Lines: 98 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. 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 -- 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/