Re: [patch 2/2] sched: Protect sched_rr_get_param access to task->sched_class

[Peter Zijlstra <peterz@infradead.org>]

On Tue, 2009-12-08 at 20:24 +0000, Thomas Gleixner wrote:
> plain text document attachment
> (sched-fix-sched-get-rr-param-race.patch)
> sched_rr_get_param calls task->sched_class->get_rr_interval(task)
> without protection against a concurrent sched_setscheduler() call
> which modifies task->sched_class.
> 
> Serialize the access with task_rq_lock(task);
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  kernel/sched.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> Index: linux-2.6-tip/kernel/sched.c
> ===================================================================
> --- linux-2.6-tip.orig/kernel/sched.c
> +++ linux-2.6-tip/kernel/sched.c
> @@ -6887,6 +6887,8 @@ SYSCALL_DEFINE2(sched_rr_get_interval, p
>  {
>  	struct task_struct *p;
>  	unsigned int time_slice;
> +	unsigned long flags;
> +	struct rq *rq;
>  	int retval;
>  	struct timespec t;
>  
> @@ -6903,7 +6905,9 @@ SYSCALL_DEFINE2(sched_rr_get_interval, p
>  	if (retval)
>  		goto out_unlock;
>  
> +	rq = task_rq_lock(p, &flags);
>  	time_slice = p->sched_class->get_rr_interval(p);
> +	task_rq_unlock(rq, &flags);
>  
>  	read_unlock(&tasklist_lock);
>  	jiffies_to_timespec(time_slice, &t);
> 

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