On 13 Jan 2023 09:58:10 -0800 Boqun Feng <boqun.feng@xxxxxxxxx>
> 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@xxxxxxxxx>
> > > --- 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?
I am leaning to not call it ABBA deadlock, because B is unlocked.
task X task Y
--- ---
lock A
lock B
lock B
unlock B
wait_for_completion E
lock A
complete E
And no deadlock should be detected/caught after B goes home.
