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

[Joel Fernandes]

On Sun, Oct 18, 2026 at 02:51:18AM +0000, Zqiang wrote:
> > 
> > > 
> > > On Oct 15, 2026, at 5:46 AM, Zqiang <qiang.zhang@xxxxxxxxx> 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@xxxxxxxxx>
> > >  ---
> > >  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.

Thank you! Looking forward to it,

Joel Fernandes