Re: [PATCH 2/3] rcu: Equip sleepable RCU with lockdep dependency graph checks

[Boqun Feng <boqun.feng@gmail.com>]

On Fri, Jan 13, 2023 at 09:03:30PM +0800, Hillf Danton wrote:
> On 12 Jan 2023 22:59:54 -0800 Boqun Feng <boqun.feng@gmail.com>
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -1267,6 +1267,8 @@ static void __synchronize_srcu(struct srcu_struct *ssp, bool do_norm)
> >  {
> >  	struct rcu_synchronize rcu;
> >  
> > +	srcu_lock_sync(&ssp->dep_map);
> > +
> >  	RCU_LOCKDEP_WARN(lockdep_is_held(ssp) ||
> >  			 lock_is_held(&rcu_bh_lock_map) ||
> >  			 lock_is_held(&rcu_lock_map) ||
> > -- 
> > 2.38.1
> 
> The following deadlock is able to escape srcu_lock_sync() because the
> __lock_release folded in sync leaves one lock on the sync side.
> 
> 	cpu9		cpu0
> 	---		---
> 	lock A		srcu_lock_acquire(&ssp->dep_map);
> 	srcu_lock_sync(&ssp->dep_map);
> 			lock A

But isn't it just the srcu_mutex_ABBA test case in patch #3, and my run
of lockdep selftest shows we can catch it. Anything subtle I'm missing?

Regards,
Boqun