[tip: core/rcu] rcu: Make show_rcu_gp_kthreads() dump rcu_node structures blocking GP

[tip-bot2 for Paul E. McKenney]

The following commit has been merged into the core/rcu branch of tip:

Commit-ID:     b15805013b441b13fcf6e402c03421c03edb79c6
Gitweb:        https://git.kernel.org/tip/b15805013b441b13fcf6e402c03421c03edb79c6
Author:        Paul E. McKenney <paulmck@xxxxxxxxxx>
AuthorDate:    Wed, 07 Apr 2021 15:14:01 -07:00
Committer:     Paul E. McKenney <paulmck@xxxxxxxxxx>
CommitterDate: Mon, 10 May 2021 16:22:54 -07:00

rcu: Make show_rcu_gp_kthreads() dump rcu_node structures blocking GP

Currently, show_rcu_gp_kthreads() only dumps rcu_node structures that
have outdated ideas of the current grace-period number.  This commit
also dumps those that are in any way blocking the current grace period.
This helps diagnose RCU priority boosting failures.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/tree_stall.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index c1f8386..e6bd518 100644
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -746,8 +746,9 @@ void show_rcu_gp_kthreads(void)
 		data_race(rcu_state.gp_max),
 		data_race(rcu_state.gp_flags));
 	rcu_for_each_node_breadth_first(rnp) {
-		if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq),
-				 READ_ONCE(rnp->gp_seq_needed)))
+		if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), READ_ONCE(rnp->gp_seq_needed)) &&
+		    !data_race(rnp->qsmask) && !data_race(rnp->boost_tasks) &&
+		    !data_race(rnp->exp_tasks) && !data_race(rnp->gp_tasks))
 			continue;
 		pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld ->qsmask %#lx %c%c%c%c ->n_boosts %ld\n",
 			rnp->grplo, rnp->grphi,