Re: [PATCH v2 1/5] rcu-tasks: Track barrier callbacks in debugobjects

[Paul E. McKenney]

On Sun, Nov 08, 2026 at 07:02:37PM -0500, Joel Fernandes wrote:
> rcu_tasks_invoke_cbs() now unqueues each callback from debugobjects.
> However, rcu_barrier_tasks_generic() inserts its per-CPU barrier heads
> directly with rcu_segcblist_entrain(), bypassing the queue hook in
> call_rcu_tasks_generic(). This produces active_state and deactivate
> warnings for untracked objects when a barrier callback runs.
> 
> Activate each barrier head before entrainment and undo that activation
> when there are no callbacks to entrain behind. Successful entrainment
> is balanced by the invocation path, as for ordinary callbacks.
> 
> The existing n_barrier_cbs=2 torture test reproduces the warnings before
> this change and completes without them afterwards.
> 
> This fixes patch "rcu-tasks: Detect duplicate callback enqueue".
> 
> Cc: Kunwu Chan <kunwu.chan@xxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Signed-off-by: Joel Fernandes <joelagnelf@xxxxxxxxxx>

This looks good to me, but I strongly suggest squashing it into the
original patch for bisectability.  With appropriate attribution,
of course.

							Thanx, Paul

> ---
>  kernel/rcu/tasks.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index d5d060a5c4b6..a20db323612b 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -470,9 +470,12 @@ static void __maybe_unused rcu_barrier_tasks_generic(struct rcu_tasks *rtp)
>  			break;
>  		rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu);
>  		rtpcp->barrier_q_head.func = rcu_barrier_tasks_generic_cb;
> +		debug_rcu_head_queue(&rtpcp->barrier_q_head);
>  		raw_spin_lock_irqsave_rcu_node(rtpcp, flags);
>  		if (rcu_segcblist_entrain(&rtpcp->cblist, &rtpcp->barrier_q_head))
>  			atomic_inc(&rtp->barrier_q_count);
> +		else
> +			debug_rcu_head_unqueue(&rtpcp->barrier_q_head);
>  		raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
>  	}
>  	if (atomic_sub_and_test(2, &rtp->barrier_q_count))
> -- 
> 2.54.0
>