Re: [PATCH] rcu-tasks: Track barrier callbacks in debugobjects

[Bradley Morgan <brads@mainlining.org>]

On 4 November 2026 15:30:45 GMT, Joel Fernandes <joelagnelf@nvidia.com>
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@gmail.com>
>Cc: Paul E. McKenney <paulmck@kernel.org>

Thanks,

Reviewed-by: Bradley Morgan <brads@mainlining.org>

>Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
>---
> 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
>+		

Wow!
	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))
>

--- Thanks!