rcu: Summarize expedited RCU CPU stall warnings during CSD-lock stalls

During CSD-lock stalls, the additional information output by expedited
RCU CPU stall warnings is usually redundant, flooding the console for
not good reason.  However, this has been the way things work for a few
years.  This commit therefore uses rcutree.csd_lock_suppress_rcu_stall
kernel boot parameter that causes expedited RCU CPU stall warnings to
be abbreviated to a single line when there is at least one CPU that has
been stuck waiting for CSD lock for more than five seconds.

Signed-off-by: Paul E. McKenney <[email protected]>
Signed-off-by: Neeraj Upadhyay <[email protected]>

Author: paulmckrcu

kernel/rcu/tree_exp.h

@@ -553,6 +553,10 @@ static void synchronize_rcu_expedited_stall(unsigned long jiffies_start, unsigne
 	struct rcu_node *rnp;
 	struct rcu_node *rnp_root = rcu_get_root();
 
+	if (READ_ONCE(csd_lock_suppress_rcu_stall) && csd_lock_is_stuck()) {
+		pr_err("INFO: %s detected expedited stalls, but suppressed full report due to a stuck CSD-lock.\n", rcu_state.name);
+		return;
+	}
 	pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {", rcu_state.name);
 	ndetected = 0;
 	rcu_for_each_leaf_node(rnp) {