> > Le Thu, Oct 03, 2024 at 10:01:57PM +0800, Z qiang a écrit : > > When the rcuoc kthreads process rcu callback, before invoke > > rcu_segcblist_add_len(&rdp->cblist, -count), > > the rcu_barrier() can insert rcu_barrier_callback() func to offline > > cpu rdp's->list. > > Excellent analysis! Indeed we can have: > > CPU 0 CPU 1 CPU 2 > ----- ----- ------- > > // deoffload // nocb_cb_wait // rcutorture > rcu_barrier() > rcu_segcblist_entrain() > rcu_segcblist_add_len(1); > rcu_do_batch() > rcu_barrier_callback() > rcu_barrier() > // still see len == 1 > rcu_segcblist_entrain() > rcu_segcblist_add_len(1); > // decrement len > rcu_segcblist_add_len(-1); > kthread_parkme() > // Warn because there is > // still a pending barrier > WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist)); > > > And the worst is that the second rcu_barrier() is ignored. > > > > > 6,5408,150692937,-,caller=T453;rcu: rcu_callback func: rcu_barrier_callback > > > > Maybe we can wait until rcu_segcblist_n_cbs(&rdp->cblist) return zero > > and then invoke kthread_parkme() in rcuoc kthreads. > > > Any thoughts ? > > Sounds good, or simply make sure that rdp->nocb_cb_sleep == false before > parking? Since kthread_park() should only be called after rcu_barrier() and > then rdp->nocb_cb_sleep shouldn't be set to true as long as there is a pending > one? Well we can also add a WARN_ON_ONCE(rcu_segcblist_n_cbs(&rdp->cblist)) > before calling kthread_park(). > > Would you like to send the fix? I will update and send the fix :) . Thanks Zqiang > > Thanks.
