Le Wed, Jun 24, 2026 at 06:23:52AM -0700, Puranjay Mohan a écrit :
> Even when rcu_pending() triggers rcu_core(), the normal callback
> advancement path through note_gp_changes() -> __note_gp_changes() bails
> out when rdp->gp_seq == rnp->gp_seq (no normal GP change). Since
> expedited GPs do not update rnp->gp_seq, rcu_advance_cbs() is never
> called and callbacks remain stuck in RCU_WAIT_TAIL.
>
> Add a direct callback advancement block in rcu_core() that checks for GP
> completion via rcu_segcblist_nextgp() combined with
> poll_state_synchronize_rcu_full(). When detected, trylock rnp and call
> rcu_advance_cbs() to move completed callbacks to RCU_DONE_TAIL. Wake the
> GP kthread if rcu_advance_cbs() requests a new grace period.
>
> Uses trylock to avoid adding contention on rnp->lock. If the lock is
> contended, callbacks will be advanced on the next tick.
>
> Reviewed-by: Paul E. McKenney <[email protected]>
> Signed-off-by: Puranjay Mohan <[email protected]>
> ---
> kernel/rcu/tree.c | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index b01d7bf6b57b1..f42e01ef479c4 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2891,6 +2891,23 @@ static __latent_entropy void rcu_core(void)
> /* Update RCU state based on any recent quiescent states. */
> rcu_check_quiescent_state(rdp);
>
> + /* Advance callbacks if an expedited GP has completed. */
> + if (!rcu_rdp_is_offloaded(rdp) &&
> rcu_segcblist_is_enabled(&rdp->cblist)) {
> + struct rcu_gp_seq gp_state;
> +
> + if (rcu_segcblist_nextgp(&rdp->cblist, &gp_state) &&
> + poll_state_synchronize_rcu_full(&gp_state)) {
> + guard(irqsave)();
> + if (raw_spin_trylock_rcu_node(rnp)) {
> + bool needwake = rcu_advance_cbs(rnp, rdp);
> +
> + raw_spin_unlock_rcu_node(rnp);
> + if (needwake)
> + rcu_gp_kthread_wake();
> + }
> + }
> + }
Should that go as an improvement to note_gp_changes() instead?
Thanks.
> +
> /* No grace period and unregistered callbacks? */
> if (!rcu_gp_in_progress() &&
> rcu_segcblist_is_enabled(&rdp->cblist) &&
> !rcu_rdp_is_offloaded(rdp)) {
> --
> 2.53.0-Meta
>
--
Frederic Weisbecker
SUSE Labs
