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

[Bradley Morgan <brads@mainlining.org>]

On 17 October 2026 18:55:37 BST, "Paul E. McKenney" <paulmck@kernel.org>
wrote:
>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.

Apologies, I must've misunderstood..
:(

>
>							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

--- Thanks!
"I'm not a very positive person" - Linus torvalds