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

[Paul E. McKenney]

On Mon, Oct 26, 2026 at 10:36:02AM +0800, KunWu Chan wrote:
> 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.

Very good, thank you!

							Thanx, Paul

> 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
> > >