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Date: Sun, 25 Jun 2006 04:50:45 +0400
From: Oleg Nesterov <oleg@tv-sign.ru>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@osdl.org>,
       linux-kernel@vger.kernel.org
Subject: Re: [patch 1/3] Drop tasklist lock in do_sched_setscheduler
Message-ID: <20060625005045.GA155@oleg>
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Thomas Gleixner wrote:
>
> There is no need to hold tasklist_lock across the setscheduler call, when we
> pin the task structure with get_task_struct(). Interrupts are disabled in 
> setscheduler anyway and the permission checks do not need interrupts disabled.
>
> --- linux-2.6.17-mm.orig/kernel/sched.c	2006-06-22 10:26:11.000000000 +0200
> +++ linux-2.6.17-mm/kernel/sched.c	2006-06-22 10:26:11.000000000 +0200
> @@ -4140,8 +4140,10 @@
>  		read_unlock_irq(&tasklist_lock);
>  		return -ESRCH;
>  	}
> -	retval = sched_setscheduler(p, policy, &lparam);
> +	get_task_struct(p);
>  	read_unlock_irq(&tasklist_lock);
> +	retval = sched_setscheduler(p, policy, &lparam);
> +	put_task_struct(p);
>  	return retval;
>  }

But we don't need read_lock(tasklist) and get_task_struct(p) at all?

rcu_read_lock/rcu_read_unlock is enough, no?

Oleg.