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Date: Thu, 2 Mar 2006 10:43:12 -0600
From: "Ram Gupta" <ram.gupta5@gmail.com>
To: "Atsushi Nemoto" <anemo@mba.ocn.ne.jp>
Subject: Re: [PATCH] fix potential jiffies overflow
Cc: linux-kernel@vger.kernel.org, akpm@osdl.org
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On 3/2/06, Atsushi Nemoto <anemo@mba.ocn.ne.jp> wrote:
> I found i386 timer_resume is updating jiffies, not jiffies_64.  It
> looks there is a potential overflow problem.  Is this a correct fix?
>
> 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..e4ed172 100644
> --- a/arch/i386/kernel/time.c
> +++ b/arch/i386/kernel/time.c
> @@ -413,7 +413,7 @@ static int timer_resume(struct sys_devic
>         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;
>         if (last_timer->resume)
>                 last_timer->resume();


The 64-bit jiffies value is not atomic. You need to hold xtime_lock to read it.