On Wed, Jul 19, 2017 at 03:43:07PM +0200, Frederic Weisbecker wrote:
> On Wed, Jul 12, 2017 at 08:56:51AM -0700, Paul E. McKenney wrote:
> > On Wed, Jul 12, 2017 at 01:54:51PM +0200, Peter Zijlstra wrote:
> > > On Tue, Jul 11, 2017 at 11:09:31AM -0700, Paul E. McKenney wrote:
> > > > On Tue, Jul 11, 2017 at 06:34:22PM +0200, Peter Zijlstra wrote:
> > >
> > > > > But I think we can at the very least do this; it only gets called from
> > > > > kernel/sched/idle.c and both callsites have IRQs explicitly disabled
> > > > > by
> > > > > that point.
> > > > >
> > > > >
> > > > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > > > index 51d4c3acf32d..dccf2dc8155a 100644
> > > > > --- a/kernel/rcu/tree.c
> > > > > +++ b/kernel/rcu/tree.c
> > > > > @@ -843,13 +843,8 @@ static void rcu_eqs_enter(bool user)
> > > > > */
> > > > > void rcu_idle_enter(void)
> > > > > {
> > > > > - unsigned long flags;
> > > > > -
> > > > > - local_irq_save(flags);
> > > >
> > > > With this addition, I am all for it:
> > > >
> > > > RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_idle_enter() invoked with irqs
> > > > enabled!!!");
> > > >
> > > > If you are OK with this addition, may I please have your Signed-off-by?
> > >
> > > Sure,
> > >
> > > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> >
> > Very good, I have queued the patch below. I left out the removal of
> > the export as I need to work out why the export was there. If it turns
> > out not to be needed, I will remove the related ones as well.
> >
> > Fair enough?
> >
> > Thanx, Paul
> >
> > ------------------------------------------------------------------------
> >
> > commit 95f3e587ce6388028a51f0c852800fca944e7032
> > Author: Peter Zijlstra (Intel) <pet...@infradead.org>
> > Date: Wed Jul 12 07:59:54 2017 -0700
> >
> > rcu: Make rcu_idle_enter() rely on callers disabling irqs
> >
> > All callers to rcu_idle_enter() have irqs disabled, so there is no
> > point in rcu_idle_enter disabling them again. This commit therefore
> > replaces the irq disabling with a RCU_LOCKDEP_WARN().
> >
> > Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> >
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 6de6b1c5ee53..c78b076653ce 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -840,11 +840,8 @@ static void rcu_eqs_enter(bool user)
> > */
> > void rcu_idle_enter(void)
> > {
> > - unsigned long flags;
> > -
> > - local_irq_save(flags);
> > + RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_idle_enter() invoked with irqs
> > enabled!!!");
>
> Nice! I really need to make that LOCKDEP_ASSERT_IRQS_DISABLED() patchset
> because there
> are many places where either we have WARN_ON_ONCE(!irqs_disabled()) or we
> need it but we were too
> shy to do it for performance reason.
If you create it, let me know, I could switch to it.
Thanx, Paul
> > rcu_eqs_enter(false);
> > - local_irq_restore(flags);
> > }
> > EXPORT_SYMBOL_GPL(rcu_idle_enter);
> >
> >
>
