linux-kernel - Re: [PATCH] sched: remove rcu_read_lock from wake

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Date:	Tue, 07 Jun 2011 19:29:23 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: remove rcu_read_lock from wake_affine

On Tue, 2011-06-07 at 10:26 -0700, Paul E. McKenney wrote:
> 
> Nikunj, one such approach is is "WARN_ON_ONCE(!rcu_read_lock_held())".
> 
> This will complain if this function is called without an rcu_read_lock()
> in effect, but only if CONFIG_PROVE_RCU=y.

rcu_lockdep_assert(rcu_read_lock_held()) would be nicer, however, since
the below:

> > >  static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
> > >  {
> > >     s64 this_load, load;
> > > @@ -1481,7 +1482,6 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
> > >      * effect of the currently running task from the load
> > >      * of the current CPU:
> > >      */
> > > -   rcu_read_lock();
> > >     if (sync) {
> > >             tg = task_group(current);
> > >             weight = current->se.load.weight; 

task_group() has an rcu_dereference_check() in, its really not needed,
the thing will yell if we get this wrong.
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