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

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Message-ID: <084a9230-c272-49c8-9c67-6c51b595f6e2@paulmck-laptop>
Date: Wed, 9 Oct 2024 08:13:33 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Frederic Weisbecker <frederic@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Boqun Feng <boqun.feng@...il.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	Neeraj Upadhyay <neeraj.upadhyay@....com>,
	Uladzislau Rezki <urezki@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>, rcu <rcu@...r.kernel.org>
Subject: Re: [PATCH 3/3] rcu: Report callbacks enqueued on offline CPU blind
 spot

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@...nel.org>
> > > Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
> > > ---
> > >  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@...nel.org>

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