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

[KunWu Chan]

On Sat, Oct 24, 2026 at 3:31 AM Paul E. McKenney <paulmck@xxxxxxxxxx> wrote:
>
> 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.  ;-)

Same changes applied: pr_err_ratelimited() and dump_stack.

Thanks,
Kunwu

>
>                                                         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
> >