Messages in this thread | | | Date | Mon, 5 Dec 2011 18:12:27 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC tip/core/rcu 7/7] rcu: Quiet RCU-lockdep warnings involving interrupt disabling |
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On Tue, Dec 06, 2011 at 09:26:35AM +0800, Yong Zhang wrote: > On Mon, Dec 05, 2011 at 08:45:05AM -0800, Paul E. McKenney wrote: > > On Mon, Dec 05, 2011 at 05:19:24PM +0800, Yong Zhang wrote: > > > On Sat, Dec 03, 2011 at 10:34:42AM -0800, Paul E. McKenney wrote: > > > > From: Yong Zhang <yong.zhang0@gmail.com> > > > > > > > > RCU-lockdep will issue warnings given the following use pattern: > > > > > > > > rcu_read_lock(); > > > > local_irq_disable(); > > > > rcu_read_unlock(); > > > > local_irq_enable(); > > > > > > > > However, this use pattern is legal except for the scheduler's runqueue > > > > and priority-inheritance locks (and any other locks that the scheduler > > > > might use during priority-inheritance operations). > > > > > > > > Signed-off-by: Yong Zhang <yong.zhang0@gmail.com> > > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > > > --- > > > > kernel/rcutree_plugin.h | 8 ++++++-- > > > > 1 files changed, 6 insertions(+), 2 deletions(-) > > > > > > > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > > > > index 8cd9efe..2020e8a 100644 > > > > --- a/kernel/rcutree_plugin.h > > > > +++ b/kernel/rcutree_plugin.h > > > > @@ -401,8 +401,11 @@ static noinline void rcu_read_unlock_special(struct task_struct *t) > > > > > > > > #ifdef CONFIG_RCU_BOOST > > > > /* Unboost if we were boosted. */ > > > > - if (rbmp) > > > > + if (rbmp) { > > > > + local_irq_save(flags); > > > > rt_mutex_unlock(rbmp); > > > > + local_irq_restore(flags); > > > > + } > > > > #endif /* #ifdef CONFIG_RCU_BOOST */ > > > > > > > > /* > > > > @@ -1233,9 +1236,10 @@ static int rcu_boost(struct rcu_node *rnp) > > > > lockdep_set_class_and_name(&mtx.wait_lock, &rcu_boost_class, > > > > "rcu_boost_mutex"); > > > > t->rcu_boost_mutex = &mtx; > > > > - raw_spin_unlock_irqrestore(&rnp->lock, flags); > > > > + raw_spin_unlock(&rnp->lock); /* rrupts remain disabled. */ > > > > rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ > > > > rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ > > > > > > We permit rt_mutex_unlock() to be call with irq disabled, > > > but rt_mutex_lock() is still not allowed. So this usage > > > is not legal now. > > > > Even after commit #5342e269b has been applied? > > Yeah, because we call might_sleep() in rt_mutex_lock() unconditionally. > But in this case the 'BUG: sleeping function called from invalid context > at *' is obviously false positive. > > Maybe we could teach might_sleep() about this special case?
That sounds very good to me!
Thanx, Paul
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