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

[KunWu Chan]

Hi Joel,

I ran into the same warnings while testing rcutorture changes on top
of my earlier series,
so thanks for posting the fix.

Verified on x86_64 with torture_type=tasks object_debug=1 n_barrier_cbs=2:

Without the patch, each barrier round triggers:
ODEBUG: active_state not available (active state 0) object:
(____ptrval____) object type: rcu_head hint: 0x0

With the patch applied, the warnings are gone, and 300+ barrier rounds
complete cleanly.

I'd like to include this as the first patch in my follow-up series,
since the new
rcutorture tasks coverage depends on it. Please let me know if that's an issue.

Tested-by:  Kunwu Chan <chentao@xxxxxxxxxx>
Reviewed-by: Kunwu Chan <chentao@xxxxxxxxxx>

Thanks,
Kunwu

On Wed, Nov 4, 2026 at 11:31 PM Joel Fernandes <joelagnelf@xxxxxxxxxx> 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>
> ---
>  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
>