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Date: Thu, 16 Jan 2020 19:17:02 +0100 From: Thomas Gleixner <tglx@...utronix.de> To: Robert Richter <rrichter@...vell.com> Cc: Waiman Long <longman@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, Ingo Molnar <mingo@...nel.org>, "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>, Mike Rapoport <rppt@...ux.ibm.com>, Kees Cook <keescook@...omium.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Petr Mladek <pmladek@...e.com> Subject: [PATCH] watchdog/softlockup: Enforce that timestamp is valid on boot Robert reported that during boot the watchdog timestamp is set to 0 for one second which is the indicator for a watchdog reset. The reason for this is that the timestamp is in seconds and the time is taken from sched clock and divided by ~1e9. sched clock starts at 0 which means that for the first second during boot the watchdog timestamp is 0, i.e. reset. Use ULONG_MAX as the reset indicator value so the watchdog works correctly right from the start. ULONG_MAX would only conflict with a real timestamp if the system reaches an uptime of 136 years on 32bit and almost eternity on 64bit. Reported-by: Robert Richter <rrichter@...vell.com> Signed-off-by: Thomas Gleixner <tglx@...utronix.de> --- kernel/watchdog.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -161,6 +161,8 @@ static void lockup_detector_update_enabl #ifdef CONFIG_SOFTLOCKUP_DETECTOR +#define SOFTLOCKUP_RESET ULONG_MAX + /* Global variables, exported for sysctl */ unsigned int __read_mostly softlockup_panic = CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE; @@ -272,7 +274,7 @@ notrace void touch_softlockup_watchdog_s * Preemption can be enabled. It doesn't matter which CPU's timestamp * gets zeroed here, so use the raw_ operation. */ - raw_cpu_write(watchdog_touch_ts, 0); + raw_cpu_write(watchdog_touch_ts, SOFTLOCKUP_RESET); } notrace void touch_softlockup_watchdog(void) @@ -296,14 +298,14 @@ void touch_all_softlockup_watchdogs(void * the softlockup check. */ for_each_cpu(cpu, &watchdog_allowed_mask) - per_cpu(watchdog_touch_ts, cpu) = 0; + per_cpu(watchdog_touch_ts, cpu) = SOFTLOCKUP_RESET; wq_watchdog_touch(-1); } void touch_softlockup_watchdog_sync(void) { __this_cpu_write(softlockup_touch_sync, true); - __this_cpu_write(watchdog_touch_ts, 0); + __this_cpu_write(watchdog_touch_ts, SOFTLOCKUP_RESET); } static int is_softlockup(unsigned long touch_ts) @@ -379,7 +381,7 @@ static enum hrtimer_restart watchdog_tim /* .. and repeat */ hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period)); - if (touch_ts == 0) { + if (touch_ts == SOFTLOCKUP_RESET) { if (unlikely(__this_cpu_read(softlockup_touch_sync))) { /* * If the time stamp was touched atomically
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