> On Jan 14, 2026, at 12:32 PM, Joel Fernandes <[email protected]> wrote: > To be sure we have no rcog wake ups that were lost, add a warning > to cover the case where the rdp is overloaded with callbacks but > no wake up was attempted. > > [applied Frederic's adjustment to clearing of nocb_gp_handling flag]
Frederic, Is it possible for you to do a quick review of these last few? They're mostly simple. It would be great if we can pick it for this upcoming merge window. Thanks! - Joel > > Signed-off-by: Joel Fernandes <[email protected]> > --- > kernel/rcu/tree.c | 4 ++++ > kernel/rcu/tree.h | 1 + > kernel/rcu/tree_nocb.h | 11 ++++++++++- > 3 files changed, 15 insertions(+), 1 deletion(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 2921ffb19939..958b61be87ea 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -3767,6 +3767,10 @@ static void rcu_barrier_entrain(struct rcu_data *rdp) > debug_rcu_head_unqueue(&rdp->barrier_head); > rcu_barrier_trace(TPS("IRQNQ"), -1, rcu_state.barrier_sequence); > } > +#ifdef CONFIG_RCU_NOCB_CPU > + /* wake_nocb implies all CBs queued before were bypass/lazy. */ > + WARN_ON_ONCE(wake_nocb && !rdp->nocb_gp_handling); > +#endif > rcu_nocb_unlock(rdp); > if (wake_nocb) > wake_nocb_gp(rdp); > diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h > index 7dfc57e9adb1..af1d065e3215 100644 > --- a/kernel/rcu/tree.h > +++ b/kernel/rcu/tree.h > @@ -257,6 +257,7 @@ struct rcu_data { > unsigned long nocb_gp_loops; /* # passes through wait code. */ > struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */ > bool nocb_cb_sleep; /* Is the nocb CB thread asleep? */ > + bool nocb_gp_handling; /* Is rcuog handling this rdp? */ > struct task_struct *nocb_cb_kthread; > struct list_head nocb_head_rdp; /* > * Head of rcu_data list in wakeup chain, > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > index f525e4f7985b..acca24670a8c 100644 > --- a/kernel/rcu/tree_nocb.h > +++ b/kernel/rcu/tree_nocb.h > @@ -546,6 +546,7 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, > bool was_alldone, > lazy_len = READ_ONCE(rdp->lazy_len); > if (was_alldone) { > rdp->qlen_last_fqs_check = len; > + rdp->nocb_gp_handling = true; > rcu_nocb_unlock(rdp); > // Only lazy CBs in bypass list > if (lazy_len && bypass_len == lazy_len) { > @@ -563,7 +564,8 @@ static void __call_rcu_nocb_wake(struct rcu_data *rdp, > bool was_alldone, > > return; > } else if (len > rdp->qlen_last_fqs_check + qhimark) { > - /* ... or if many callbacks queued. */ > + /* Callback overload condition. */ > + WARN_ON_ONCE(!rdp->nocb_gp_handling); > rdp->qlen_last_fqs_check = len; > j = jiffies; > if (j != rdp->nocb_gp_adv_time && > @@ -732,6 +734,12 @@ static void nocb_gp_wait(struct rcu_data *my_rdp) > needwait_gp = true; > trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, > TPS("NeedWaitGP")); > + } else if (!rcu_cblist_n_cbs(&rdp->nocb_bypass)) { > + /* > + * No pending callbacks and no bypass callbacks. > + * The rcuog kthread is done handling this rdp. > + */ > + rdp->nocb_gp_handling = false; > } > if (rcu_segcblist_ready_cbs(&rdp->cblist)) { > needwake = rdp->nocb_cb_sleep; > @@ -1254,6 +1262,7 @@ lazy_rcu_shrink_scan(struct shrinker *shrink, struct > shrink_control *sc) > continue; > } > rcu_nocb_try_flush_bypass(rdp, jiffies); > + rdp->nocb_gp_handling = true; > rcu_nocb_unlock_irqrestore(rdp, flags); > wake_nocb_gp(rdp); > sc->nr_to_scan -= _count; > -- > 2.34.1
