linux-kernel - Re: [PATCH] Fix fixpoint divide exception in acct_update

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Date:	Mon, 9 Mar 2009 15:01:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	torvalds@...ux-foundation.org, elendil@...net.nl,
	schwidefsky@...ibm.com, linux-kernel@...r.kernel.org,
	stable@...nel.org
Subject: Re: [PATCH] Fix fixpoint divide exception in acct_update_integrals

On Mon, 9 Mar 2009 13:31:59 +0100
Heiko Carstens <heiko.carstens@...ibm.com> wrote:

> ...
>
> --- linux-2.6.orig/kernel/tsacct.c
> +++ linux-2.6/kernel/tsacct.c
> @@ -122,8 +122,10 @@ void acct_update_integrals(struct task_s
>  	if (likely(tsk->mm)) {
>  		cputime_t time, dtime;
>  		struct timeval value;
> +		unsigned long flags;
>  		u64 delta;
>  
> +		local_irq_save(flags);
>  		time = tsk->stime + tsk->utime;
>  		dtime = cputime_sub(time, tsk->acct_timexpd);
>  		jiffies_to_timeval(cputime_to_jiffies(dtime), &value);
> @@ -131,10 +133,12 @@ void acct_update_integrals(struct task_s
>  		delta = delta * USEC_PER_SEC + value.tv_usec;
>  
>  		if (delta == 0)
> -			return;
> +			goto out;
>  		tsk->acct_timexpd = time;
>  		tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm);
>  		tsk->acct_vm_mem1 += delta * tsk->mm->total_vm;
> +	out:
> +		local_irq_restore(flags);
>  	}
>  }
>  

hrm, so we use local-interrupt protection for <something>.

I wonder what we can do to reduce the probability of bugs of this
nature being introduced in the future?

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