Re: [PATCH] rcu-tasks: Warn on too-short RCU Tasks Rude grace period

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

> 
> > 
> > On Oct 15, 2026, at 5:46 AM, Zqiang <qiang.zhang@linux.dev> wrote:
> >  
> >  The RCU Tasks Rude grace period is implemented by invoking the
> >  schedule_on_each_cpu() with an empty work function, which forces
> >  a context switch on every online CPU and guarantees that all
> >  rude-tasks read-side critical sections have completed. However,
> >  schedule_on_each_cpu() can fail (via alloc_percpu() returning
> >  -ENOMEM) and returns immediately, in which case those context
> >  switches never happen, too-short grace period happen.
> >  
> >  This commit therefore wraps the schedule_on_each_cpu() call in
> >  WARN_ONCE() so that this failure is reported as a "Too-short
> >  grace period" warning.
> >  
> >  Signed-off-by: Zqiang <qiang.zhang@linux.dev>
> >  ---
> >  kernel/rcu/tasks.h | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >  
> >  diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
> >  index fcac7361ec51..91c25717402e 100644
> >  --- a/kernel/rcu/tasks.h
> >  +++ b/kernel/rcu/tasks.h
> >  @@ -1361,7 +1361,8 @@ static void rcu_tasks_be_rude(struct work_struct *work)
> >  static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp)
> >  {
> >  rtp->n_ipis += cpumask_weight(cpu_online_mask);
> >  - schedule_on_each_cpu(rcu_tasks_be_rude);
> >  + WARN_ONCE(schedule_on_each_cpu(rcu_tasks_be_rude),
> >  + "%s: Too-short grace period, OOM is now expected behavior!!!\n", rtp->name);
> > 
> Is that the best error message? OOM is expected when grace periods do not conclude.
> 

Hi, Joel

I will resend v2, use DEFINE_PER_CPU() to replace alloc_percpu() to allocate work_struct objects.

Thanks
Zqiang

> Thanks.
> 
> > 
> > }
> >  
> >  static void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t func);
> >  --
> >  2.17.1
> >
>