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SubjectRe: [PATCH] sched: remove rcu_read_lock from wake_affine
On Tue, Jun 07, 2011 at 12:26:51PM +0200, Peter Zijlstra wrote:
> On Tue, 2011-06-07 at 15:43 +0530, Nikunj A. Dadhania wrote:
> > wake_affine is called from one path: select_task_rq_fair, which already has
> > rcu read lock held.
> >
> > Signed-off-by: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>
> > ---
> > kernel/sched_fair.c | 3 +--
> > 1 files changed, 1 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> > index 354e26b..0bfec93 100644
> > --- a/kernel/sched_fair.c
> > +++ b/kernel/sched_fair.c
> > @@ -1461,6 +1461,7 @@ static inline unsigned long effective_load(struct task_group *tg, int cpu,
> >
> > #endif
> >
> > +/* Assumes rcu_read_lock is held */
>
> Not a big fan of such comments, esp with CONFIG_PROVE_RCU its better to
> use those facilities, which is to say: if we're missing a
> rcu_read_lock() the thing will yell bloody murder.

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.

Thanx, Paul

> > 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;
> > @@ -1517,7 +1517,6 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
> > balanced = this_eff_load <= prev_eff_load;
> > } else
> > balanced = true;
> > - rcu_read_unlock();
> >
> > /*
> > * If the currently running task will sleep within
> >
>
> OK, took the patch and removed the comment, thanks!
> --
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