Re: [PATCH 1/2] posix-timers: fix RLIMIT_CPU && fork()

[Peter Zijlstra <peterz@infradead.org>]

On Fri, 2009-03-27 at 01:06 +0100, Oleg Nesterov wrote:
> See http://bugzilla.kernel.org/show_bug.cgi?id=12911
> 
> copy_signal() copies signal->rlim, but RLIMIT_CPU is "lost". Because
> posix_cpu_timers_init_group() sets cputime_expires.prof_exp = 0 and thus
> fastpath_timer_check() returns false unless we have other expired cpu timers.
> 
> Change copy_signal() to set cputime_expires.prof_exp if we have RLIMIT_CPU.
> Also, set cputimer.running = 1 in that case. This is not strictly necessary,
> but imho makes sense.

The other site that enables is also syncs the timer with the clock, but
since we're doing clone_signal, I presume there isn't much of a thread
group to sync to anyway.

Looks good, thanks for looking into this.

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

> Reported-by: Peter Lojkin <ia6432@inbox.ru>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> 
> --- 6.29/kernel/fork.c~1_FORK	2009-03-23 18:14:34.000000000 +0100
> +++ 6.29/kernel/fork.c	2009-03-27 00:25:52.000000000 +0100
> @@ -808,6 +808,12 @@ static void posix_cpu_timers_init_group(
>  	sig->cputime_expires.virt_exp = cputime_zero;
>  	sig->cputime_expires.sched_exp = 0;
>  
> +	if (sig->rlim[RLIMIT_CPU].rlim_cur != RLIM_INFINITY) {
> +		sig->cputime_expires.prof_exp =
> +			secs_to_cputime(sig->rlim[RLIMIT_CPU].rlim_cur);
> +		sig->cputimer.running = 1;
> +	}
> +
>  	/* The timer lists. */
>  	INIT_LIST_HEAD(&sig->cpu_timers[0]);
>  	INIT_LIST_HEAD(&sig->cpu_timers[1]);
> @@ -823,11 +829,8 @@ static int copy_signal(unsigned long clo
>  		atomic_inc(&current->signal->live);
>  		return 0;
>  	}
> -	sig = kmem_cache_alloc(signal_cachep, GFP_KERNEL);
> -
> -	if (sig)
> -		posix_cpu_timers_init_group(sig);
>  
> +	sig = kmem_cache_alloc(signal_cachep, GFP_KERNEL);
>  	tsk->signal = sig;
>  	if (!sig)
>  		return -ENOMEM;
> @@ -865,6 +868,8 @@ static int copy_signal(unsigned long clo
>  	memcpy(sig->rlim, current->signal->rlim, sizeof sig->rlim);
>  	task_unlock(current->group_leader);
>  
> +	posix_cpu_timers_init_group(sig);
> +
>  	acct_init_pacct(&sig->pacct);
>  
>  	tty_audit_fork(sig);
>