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SubjectRe: [PATCH tip/core/urgent 1/3] rcu: fix lockdep splat in wake_affine()
On Wed, Jun 16, 2010 at 08:23:11AM +0200, Peter Zijlstra wrote:
> On Tue, 2010-06-15 at 15:29 -0700, Paul E. McKenney wrote:
> > From: Daniel J Blueman <daniel.blueman@gmail.com>
> >
> > With 2.6.35-rc1 and your patch in the context below, we still see
> > "include/linux/cgroup.h:534 invoked rcu_dereference_check() without
> > protection!", so need this additional patch:
> >
> > Acquire read-side RCU lock around task_group() calls, addressing
> > "include/linux/cgroup.h:534 invoked rcu_dereference_check() without
> > protection!" warning.
>
> Uhm,. this is all just slapping in rcu_read_lock() to make the warning
> go away, without explanation of what and why.
>
> Its not obvious what the races is, nor how its handled.

Please let me know if my explanation in a recent email covers this.
If so, I will add it to the commit log. If not, well, back to the
drawing board, I guess. ;-)

Thanx, Paul

> > Signed-off-by: Daniel J Blueman <daniel.blueman@gmail.com>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > ---
> > kernel/sched_fair.c | 2 ++
> > 1 files changed, 2 insertions(+), 0 deletions(-)
> >
> > diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
> > index eed35ed..ca56133 100644
> > --- a/kernel/sched_fair.c
> > +++ b/kernel/sched_fair.c
> > @@ -1240,6 +1240,7 @@ 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;
> > @@ -1249,6 +1250,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
> > }
> >
> > tg = task_group(p);
> > + rcu_read_unlock();
> > weight = p->se.load.weight;
> >
> > /*
>
>


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