linux-kernel - Re: [PATCH] softlockup: stop spurious softlockup messages due to overflow

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Date:	Mon, 15 Mar 2010 15:29:48 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Colin Ian King <colin.king@...onical.com>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] softlockup: stop spurious softlockup messages due to
 overflow

Le lundi 15 mars 2010 à 14:01 +0000, Colin Ian King a écrit :
> Ensure additions on touch_ts do not overflow.  This can occur when
> the top 32 bits of the TSC reach 0xffffffff causing additions to
> touch_ts to overflow and this in turn generates spurious softlockup
> warnings.
> 
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  kernel/softlockup.c |    6 +++---
>  1 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/softlockup.c b/kernel/softlockup.c
> index 0d4c789..90d9aa0 100644
> --- a/kernel/softlockup.c
> +++ b/kernel/softlockup.c
> @@ -111,10 +111,10 @@ int proc_dosoftlockup_thresh(struct ctl_table *table, int write,
>  void softlockup_tick(void)
>  {
>  	int this_cpu = smp_processor_id();
> -	unsigned long touch_ts = per_cpu(softlockup_touch_ts, this_cpu);
> +	unsigned long long touch_ts = per_cpu(softlockup_touch_ts, this_cpu);
>  	unsigned long print_ts;
>  	struct pt_regs *regs = get_irq_regs();
> -	unsigned long now;
> +	unsigned long long now;
>  
>  	/* Is detection switched off? */
>  	if (!per_cpu(softlockup_watchdog, this_cpu) || softlockup_thresh <= 0) {
> @@ -165,7 +165,7 @@ void softlockup_tick(void)
>  	per_cpu(softlockup_print_ts, this_cpu) = touch_ts;
>  
>  	spin_lock(&print_lock);
> -	printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %lus! [%s:%d]\n",
> +	printk(KERN_ERR "BUG: soft lockup - CPU#%d stuck for %llus! [%s:%d]\n",
>  			this_cpu, now - touch_ts,
>  			current->comm, task_pid_nr(current));
>  	print_modules();

This looks wrong, touch_ts is a long, not a long long.

You probably want to change the comparisons instead.

if (now > touch_ts + softlockup_thresh/2)
	wake_up_process(per_cpu(softlockup_watchdog, this_cpu));
if (now <= (touch_ts + softlockup_thresh))
	return;
	
->

if ((long)(now - touch_ts) > softlockup_thresh/2)
	wake_up_process(per_cpu(softlockup_watchdog, this_cpu));
if ((long)(now - touch_ts) <= softlockup_thresh))
	return;

Or use standard time_after()/time_before() macros.


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