rcu: Detect stalls caused by failure to propagate up rcu_node tree

If all CPUs have passed through quiescent states, then stalls might be
due to starvation of the grace-period kthread or to failure to propagate
the quiescent states up the rcu_node combining tree.  The current stall
warning messages do not differentiate, so this commit adds a printout
of the root rcu_node structure's ->qsmask field.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 98da632d1d49..3b7e4133ca99 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1196,9 +1196,10 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
                 } else {
                         j = jiffies;
                         gpa = ACCESS_ONCE(rsp->gp_activity);
-                        pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld\n",
+                        pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
                                rsp->name, j - gpa, j, gpa,
-                               jiffies_till_next_fqs);
+                               jiffies_till_next_fqs,
+                               rcu_get_root(rsp)->qsmask);
                         /* In this case, the current CPU might be at fault. */
                         sched_show_task(current);
                 }