Re: [PATCH] sched: remove rcu_read_lock from wake_affine

[Peter Zijlstra <peterz@infradead.org>]

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.