Re: [patch 1/3] Drop tasklist lock in do_sched_setscheduler

[Thomas Gleixner <tglx@linutronix.de>]

On Sun, 2006-06-25 at 04:50 +0400, Oleg Nesterov wrote:
> 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?

Probably yes, did not think about that

	tglx