Re: [PATCH] fix potential jiffies overflow

[Andrew Morton <akpm@osdl.org>]

Atsushi Nemoto <anemo@mba.ocn.ne.jp> wrote:
>
> >>>>> On Thu, 2 Mar 2006 10:43:12 -0600, "Ram Gupta" <ram.gupta5@gmail.com> said:
> >> I found i386 timer_resume is updating jiffies, not jiffies_64.  It
> >> looks there is a potential overflow problem.  Is this a correct
> >> fix?
> 
> ram> The 64-bit jiffies value is not atomic. You need to hold
> ram> xtime_lock to read it.
> 
> OK, and I guess wall_jiffies also needs xtime_lock.
> 
> 
> I found i386 timer_resume is updating jiffies, not jiffies_64.  It
> looks there is a potential overflow problem.  And jiffies_64 and
> wall_jiffies should be protected by xtime_lock.
> 
> Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
> 
> diff --git a/arch/i386/kernel/time.c b/arch/i386/kernel/time.c
> index a14d594..9d30747 100644
> --- a/arch/i386/kernel/time.c
> +++ b/arch/i386/kernel/time.c
> @@ -412,9 +412,9 @@ static int timer_resume(struct sys_devic
>  	write_seqlock_irqsave(&xtime_lock, flags);
>  	xtime.tv_sec = sec;
>  	xtime.tv_nsec = 0;
> -	write_sequnlock_irqrestore(&xtime_lock, flags);
> -	jiffies += sleep_length;
> +	jiffies_64 += sleep_length;
>  	wall_jiffies += sleep_length;
> +	write_sequnlock_irqrestore(&xtime_lock, flags);
>  	if (last_timer->resume)
>  		last_timer->resume();
>  	cur_timer = last_timer;

Thanks, that looks like 2.6.16 material.

What happens if the machine slept for more than 49.7 days?