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 <[email protected]>
> Signed-off-by: Bradley Morgan <[email protected]>
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.
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
