> > On 15 October 2026 10:46:19 BST, Zqiang <[email protected]> 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. > > > NAK, this seems like a edge case, and potentially panicking the system > with panic on oops doesn't seem right to me, because we would reserve that > for when something definitely goes really wrong and we need to notify > the user. > > I don't believe this patch should go in for this reason, it's a heavy edge > case, that doesn't *have* nessesarily need to be accounted for.
Indeed, this is a rare event, so I use WARN_ONCE() to mark it, the WARN_ONCE() not panicking system unless you set warn_on_oops true, this can help us troubleshoot UAF issues caused by a too short tasks-rude grace period. or maybe we can use DEFINE_PER_CPU(struct work_struct, rude_work) to replace alloc_percpu(struct work_struct) queue to all online CPUs. Anyway, Thank you for your reply. I would also like to hear the opinions of others. Thanks Zqiang > > Zqiang, have you reproduced this OOM on your own system, if so, could you > tell me more details, you may turn my frown into a smiley face ;) > > > > > Signed-off-by: Zqiang <[email protected]> > > --- > > 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); > > > Good message, makes sense. But I don't think this is right, see above. > > > > > } > > > > static void call_rcu_tasks_rude(struct rcu_head *rhp, rcu_callback_t > > func); > > > --- Thanks! > "I'm not a very positive person" - Linus torvalds >
