Re: [PATCH 3/3] rcu: Report callbacks enqueued on offline CPU blind spot

[Paul E. McKenney]

On Tue, Oct 08, 2024 at 07:03:50PM -0700, Paul E. McKenney wrote:
> On Wed, Oct 02, 2024 at 05:00:03PM +0200, Frederic Weisbecker wrote:
> > Le Wed, Oct 02, 2024 at 04:57:38PM +0200, Frederic Weisbecker a écrit :
> > > Callbacks enqueued after rcutree_report_cpu_dead() fall into RCU barrier
> > > blind spot. Report any potential misuse.
> > > 
> > > Reported-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > > Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
> > > ---
> > >  kernel/rcu/tree.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index a60616e69b66..36070b6bf4a1 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -3084,8 +3084,11 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
> > >  	head->func = func;
> > >  	head->next = NULL;
> > >  	kasan_record_aux_stack_noalloc(head);
> > > +
> > >  	local_irq_save(flags);
> > >  	rdp = this_cpu_ptr(&rcu_data);
> > > +	RCU_LOCKDEP_WARN(rcu_rdp_cpu_online(rdp), "Callback enqueued on offline
> > > CPU!");
> > 
> > This should be !rcu_rdp_cpu_online(rdp)
> > 
> > Sigh...
> 
> I am pulling this in for testing with this change, thank you!

And:

Tested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

> 							Thanx, Paul
> 
> > > +
> > >  	lazy = lazy_in && !rcu_async_should_hurry();
> > >  
> > >  	/* Add the callback to our list. */
> > > -- 
> > > 2.46.0
> > > 
> > > 
>