[PATCH tip/core/rcu 4/4] rcu: Eliminate BUG_ON() for kernel/rcu/update.c

[Paul E. McKenney]

The update.c file has a number of calls to BUG_ON(), which panics the
kernel, which is not a good strategy for devices (like embedded) that
don't have a way to capture console output.  This commit therefore
converts these BUG_ON() calls to WARN_ON_ONCE() and WARN_ONCE().

Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxx>
---
 kernel/rcu/update.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index f203b94f6b5b..cb26de25658a 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -822,7 +822,8 @@ static int __init rcu_spawn_tasks_kthread(void)
 	struct task_struct *t;
 
 	t = kthread_run(rcu_tasks_kthread, NULL, "rcu_tasks_kthread");
-	BUG_ON(IS_ERR(t));
+	if (WARN_ONCE(IS_ERR(t), "%s: Could not start Tasks-RCU grace-period kthread, OOM is now expected behavior\n", __func__))
+		return 0;
 	smp_mb(); /* Ensure others see full kthread. */
 	WRITE_ONCE(rcu_tasks_kthread_ptr, t);
 	return 0;
-- 
2.17.1