From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761075Ab2D0STn (ORCPT ); Fri, 27 Apr 2012 14:19:43 -0400 Received: from mail-qa0-f74.google.com ([209.85.216.74]:43500 "EHLO mail-qa0-f74.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760965Ab2D0STj (ORCPT ); Fri, 27 Apr 2012 14:19:39 -0400 From: Sameer Nanda To: mingo@redhat.com, peterz@infradead.org, len.brown@intel.com, pavel@ucw.cz, rjw@sisk.pl, akpm@linux-foundation.org, dzickus@redhat.com, msb@chromium.org Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, olofj@chromium.org, Sameer Nanda Subject: [PATCH] watchdog: fix for lockup detector breakage on resume Date: Fri, 27 Apr 2012 11:10:40 -0700 Message-Id: <1335550240-17765-1-git-send-email-snanda@chromium.org> X-Mailer: git-send-email 1.7.7.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On the suspend/resume path the boot CPU does not go though an offline->online transition. This breaks the NMI detector post-resume since it depends on PMU state that is lost when the system gets suspended. Fix this by forcing a CPU offline->online transition for the lockup detector on the boot CPU during resume. Signed-off-by: Sameer Nanda --- To provide more context, we enable NMI watchdog on Chrome OS. We have seen several reports of systems freezing up completely which indicated that the NMI watchdog was not firing for some reason. Debugging further, we found a simple way of repro'ing system freezes -- issuing the command 'tasket 1 sh -c "echo nmilockup > /proc/breakme"' after the system has been suspended/resumed one or more times. With this patch in place, the system freeze result in panics, as expected. These panics provide a nice stack trace for us to debug the actual issue causing the freeze. include/linux/sched.h | 4 ++++ kernel/power/suspend.c | 3 +++ kernel/watchdog.c | 16 ++++++++++++++++ 3 files changed, 23 insertions(+), 0 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 81a173c..118cc38 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -317,6 +317,7 @@ extern int proc_dowatchdog_thresh(struct ctl_table *table, int write, size_t *lenp, loff_t *ppos); extern unsigned int softlockup_panic; void lockup_detector_init(void); +void lockup_detector_bootcpu_resume(void); #else static inline void touch_softlockup_watchdog(void) { @@ -330,6 +331,9 @@ static inline void touch_all_softlockup_watchdogs(void) static inline void lockup_detector_init(void) { } +static inline void lockup_detector_bootcpu_resume(void) +{ +} #endif #ifdef CONFIG_DETECT_HUNG_TASK diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c index 396d262..0d262a8 100644 --- a/kernel/power/suspend.c +++ b/kernel/power/suspend.c @@ -177,6 +177,9 @@ static int suspend_enter(suspend_state_t state, bool *wakeup) arch_suspend_enable_irqs(); BUG_ON(irqs_disabled()); + /* Kick the lockup detector */ + lockup_detector_bootcpu_resume(); + Enable_cpus: enable_nonboot_cpus(); diff --git a/kernel/watchdog.c b/kernel/watchdog.c index df30ee0..dd2ac93 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -585,6 +585,22 @@ static struct notifier_block __cpuinitdata cpu_nfb = { .notifier_call = cpu_callback }; +void lockup_detector_bootcpu_resume(void) +{ + void *cpu = (void *)(long)smp_processor_id(); + + /* + * On the suspend/resume path the boot CPU does not go though the + * offline->online transition. This breaks the NMI detector post + * resume. Force an offline->online transition for the boot CPU on + * resume. + */ + cpu_callback(&cpu_nfb, CPU_DEAD, cpu); + cpu_callback(&cpu_nfb, CPU_ONLINE, cpu); + + return; +} + void __init lockup_detector_init(void) { void *cpu = (void *)(long)smp_processor_id(); -- 1.7.7.3