On Fri, Aug 31, 2012 at 11:34:31AM -0700, Josh Triplett wrote:
> On Thu, Aug 30, 2012 at 11:56:26AM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paul.mcken...@linaro.org>
> >
> > The use of raw_local_irq_save() is unnecessary, given that local_irq_save()
> > really does disable interrupts. Also, it appears to interfere with lockdep.
> > Therefore, this commit moves to local_irq_save().
>
> It looks like the non-raw versions also include tracing, which typically
> has recursive dependency problems with RCU. Can all of these call sites
> safely call into tracing without recursing back into RCU?
The rcu_trace_sub_qlen() version is the most suspicious, but it is the
one that Fengguang found to be causing the problem:
https://lkml.org/lkml/2012/8/21/551
Thanx, Paul
> - Josh Triplett
>
> > Reported-by: Fengguang Wu <fengguang...@intel.com>
> > Signed-off-by: Paul E. McKenney <paul.mcken...@linaro.org>
> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> > Tested-by: Fengguang Wu <fengguang...@intel.com>
> > ---
> > kernel/rcutiny_plugin.h | 10 +++++-----
> > 1 files changed, 5 insertions(+), 5 deletions(-)
> >
> > diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h
> > index 918fd1e..3d01902 100644
> > --- a/kernel/rcutiny_plugin.h
> > +++ b/kernel/rcutiny_plugin.h
> > @@ -278,7 +278,7 @@ static int rcu_boost(void)
> > rcu_preempt_ctrlblk.exp_tasks == NULL)
> > return 0; /* Nothing to boost. */
> >
> > - raw_local_irq_save(flags);
> > + local_irq_save(flags);
> >
> > /*
> > * Recheck with irqs disabled: all tasks in need of boosting
> > @@ -287,7 +287,7 @@ static int rcu_boost(void)
> > */
> > if (rcu_preempt_ctrlblk.boost_tasks == NULL &&
> > rcu_preempt_ctrlblk.exp_tasks == NULL) {
> > - raw_local_irq_restore(flags);
> > + local_irq_restore(flags);
> > return 0;
> > }
> >
> > @@ -317,7 +317,7 @@ static int rcu_boost(void)
> > t = container_of(tb, struct task_struct, rcu_node_entry);
> > rt_mutex_init_proxy_locked(&mtx, t);
> > t->rcu_boost_mutex = &mtx;
> > - raw_local_irq_restore(flags);
> > + local_irq_restore(flags);
> > rt_mutex_lock(&mtx);
> > rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
> >
> > @@ -991,9 +991,9 @@ static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp,
> > int n)
> > {
> > unsigned long flags;
> >
> > - raw_local_irq_save(flags);
> > + local_irq_save(flags);
> > rcp->qlen -= n;
> > - raw_local_irq_restore(flags);
> > + local_irq_restore(flags);
> > }
> >
> > /*
> > --
> > 1.7.8
> >
>
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