Re: [PATCH 9/9] rcu-tasks: Detect duplicate callback enqueue

[Paul E. McKenney]

On Fri, Oct 23, 2026 at 06:18:41PM +0800, Kunwu Chan wrote:
> Detect duplicate callback enqueue attempts in the generic
> RCU Tasks callback registration path.
> 
> Signed-off-by: Kunwu Chan <chentao@xxxxxxxxxx>

And the same questions for this patch as well.  ;-)

							Thanx, Paul

> ---
>  kernel/rcu/tasks.h | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> index 5d7f234795b4..49b716feb31d 100644
> --- a/kernel/rcu/tasks.h
> +++ b/kernel/rcu/tasks.h
> @@ -6,6 +6,7 @@
>   */
>  
>  #ifdef CONFIG_TASKS_RCU_GENERIC
> +#include <linux/mm.h>
>  #include "rcu_segcblist.h"
>  
>  ////////////////////////////////////////////////////////////////////////
> @@ -339,9 +340,12 @@ static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp)
>  }
>  
>  // Enqueue a callback for the specified flavor of Tasks RCU.
> +static void rcu_tasks_leak_callback(struct rcu_head *rhp) { }
> +
>  static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
>  				   struct rcu_tasks *rtp)
>  {
> +	static atomic_t doublefrees;
>  	int chosen_cpu;
>  	unsigned long flags;
>  	bool havekthread = smp_load_acquire(&rtp->kthread_ptr);
> @@ -358,6 +362,16 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
>  	if (WARN_ON_ONCE(!func))
>  		return;
>  
> +	if (debug_rcu_head_queue(rhp)) {
> +		if (atomic_inc_return(&doublefrees) < 4) {
> +			pr_err("%s(): Duplicate call_rcu_%s() CB %p->%pS()\n",
> +			       __func__, rtp->name, rhp, rhp->func);
> +			mem_dump_obj(rhp);
> +		}
> +		WRITE_ONCE(rhp->func, rcu_tasks_leak_callback);
> +		return;
> +	}
> +
>  	rhp->next = NULL;
>  	rhp->func = func;
>  	local_irq_save(flags);
> @@ -586,6 +600,7 @@ static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu
>  	raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
>  	len = rcl.len;
>  	for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) {
> +		debug_rcu_head_unqueue(rhp);
>  		debug_rcu_head_callback(rhp);
>  		local_bh_disable();
>  		rhp->func(rhp);
> -- 
> 2.43.0
>