[PATCH rcu 18/18] rcu: Print human-readable message for schedule() in RCU reader

[Paul E. McKenney]

The WARN_ON_ONCE() invocation within the CONFIG_PREEMPT=y version of
rcu_note_context_switch() triggers when there is a voluntary context
switch in an RCU read-side critical section, but there is quite a gap
between the output of that WARN_ON_ONCE() and this RCU-usage error.
This commit therefore converts the WARN_ON_ONCE() to a WARN_ONCE()
that explicitly describes the problem in its message.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/tree_plugin.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 83a702a4e2963..e8b45ab72a799 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -346,7 +346,7 @@ void rcu_note_context_switch(bool preempt)
 
 	trace_rcu_utilization(TPS("Start context switch"));
 	lockdep_assert_irqs_disabled();
-	WARN_ON_ONCE(!preempt && rcu_preempt_depth() > 0);
+	WARN_ONCE(!preempt && rcu_preempt_depth() > 0, "Voluntary context switch within RCU read-side critical section!");
 	if (rcu_preempt_depth() > 0 &&
 	    !t->rcu_read_unlock_special.b.blocked) {
 
-- 
2.31.1.189.g2e36527f23