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Subject: Re: [PATCH 2/2] posix-timers: fix RLIMIT_CPU &&
 setitimer(CPUCLOCK_PROF)
From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>, Peter Lojkin <ia6432@inbox.ru>,
       Roland McGrath <roland@redhat.com>, linux-kernel@vger.kernel.org,
       stable@kernel.org
In-Reply-To: <20090327000610.GA10108@redhat.com>
References: <20090327000610.GA10108@redhat.com>
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Date: Sat, 28 Mar 2009 00:59:28 +0100
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On Fri, 2009-03-27 at 01:06 +0100, Oleg Nesterov wrote:
> update_rlimit_cpu() tries to optimize out set_process_cpu_timer() in case
> when we already have CPUCLOCK_PROF timer which should expire first. But it
> uses cputime_lt() instead of cputime_gt().
> 
> Test case:
> 
> 	int main(void)
> 	{
> 		struct itimerval it = {
> 			.it_value = { .tv_sec = 1000 },
> 		};
> 
> 		assert(!setitimer(ITIMER_PROF, &it, NULL));
> 
> 		struct rlimit rl = {
> 			.rlim_cur = 1,
> 			.rlim_max = 1,
> 		};
> 
> 		assert(!setrlimit(RLIMIT_CPU, &rl));
> 
> 		for (;;)
> 			;
> 
> 		return 0;
> 	}
> 
> Without this patch, the task is not killed as RLIMIT_CPU demands.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Nice catch,

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>

> --- 6.29/kernel/posix-cpu-timers.c~2_UPDATE_RLIM	2009-03-23 18:13:57.000000000 +0100
> +++ 6.29/kernel/posix-cpu-timers.c	2009-03-27 00:45:31.000000000 +0100
> @@ -18,7 +18,7 @@ void update_rlimit_cpu(unsigned long rli
>  
>  	cputime = secs_to_cputime(rlim_new);
>  	if (cputime_eq(current->signal->it_prof_expires, cputime_zero) ||
> -	    cputime_lt(current->signal->it_prof_expires, cputime)) {
> +	    cputime_gt(current->signal->it_prof_expires, cputime)) {
>  		spin_lock_irq(&current->sighand->siglock);
>  		set_process_cpu_timer(current, CPUCLOCK_PROF, &cputime, NULL);
>  		spin_unlock_irq(&current->sighand->siglock);
>