Re: [PATCH] rcu/tasks: Use static per cpu work_struct for Tasks Rude grace periods

["Zqiang" <qiang.zhang@linux.dev>]

> 
> On Sat, Oct 17, 2026 at 12:33:13PM +0000, Bradley Morgan wrote:
> 
> > 
> > Zqiang caught a snafu in the rude grace period, if a too small grace
> >  period was reached, a UAF could occur. However, his patch used
> >  a WARN_ONCE() on schedule_on_each_cpu() OOM failures, which would not
> >  have handled the failure properly.
> >  
> >  Instead of throwing a warning or relying on dynamic alloc_percpu(), replace
> >  the dynamic allocation with static per cpu work_struct instances. Using
> >  schedule_work_on() and flush_work() keeps everything in task context,
> >  guarantees the required context switch on every online CPU, and stays
> >  zero allocation so it cannot fail under OOM.
> >  
> >  Suggested-by: Zqiang <qiang.zhang@linux.dev>
> >  Signed-off-by: Bradley Morgan <brads@mainlining.org>
> > 
> Sorry, Bradley, but no, absolutely not.
> 
> Because this not taking a suggestion, but is instead *exactly* Zqiang's
> patch. We do not commit plagiarism in the Linux-kernel community.
> 
> Zqiang, please submit a proper patch with appropriate credit to Bradley.
> The obvious approach would be to following his example, that is, to
> credit him using Suggested-by, but Reported-by or a sentence calling out
> his feedback in the commit log would suffice. However, I will defer to
> your best judgment.

Thanks, Paul

I will resend it as v2 and add Bradley as Suggested-by.

Thanks
Zqiang


> 
>  Thanx, Paul
> 
> > 
> > ---
> >  kernel/rcu/tasks.h | 16 +++++++++++++++-
> >  1 file changed, 15 insertions(+), 1 deletion(-)
> >  
> >  diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> >  index 627295396cd9..f81c0ea0b92a 100644
> >  --- a/kernel/rcu/tasks.h
> >  +++ b/kernel/rcu/tasks.h
> >  @@ -1348,11 +1348,25 @@ static void rcu_tasks_be_rude(struct work_struct *work)
> >  {
> >  }
> >  
> >  +static DEFINE_PER_CPU(struct work_struct, tasks_rude_work);
> >  +
> >  // Wait for one rude RCU-tasks grace period.
> >  static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp)
> >  {
> >  + int cpu;
> >  +
> >  + guard(cpus_read_lock)();
> >  rtp->n_ipis += cpumask_weight(cpu_online_mask);
> >  - schedule_on_each_cpu(rcu_tasks_be_rude);
> >  +
> >  + for_each_online_cpu(cpu) {
> >  + struct work_struct *work = &per_cpu(tasks_rude_work, cpu);
> >  +
> >  + INIT_WORK(work, rcu_tasks_be_rude);
> >  + schedule_work_on(cpu, work);
> >  + }
> >  +
> >  + for_each_online_cpu(cpu)
> >  + flush_work(&per_cpu(tasks_rude_work, cpu));
> >  }
> >  
> >  static void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func);
> >  -- 
> >  2.53.0
> >
>