linux-kernel - [PATCH tip/core/rcu 4/4] rcu: Eliminate BUG

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Date:   Sun, 11 Nov 2018 11:32:17 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH tip/core/rcu 4/4] rcu: Eliminate BUG_ON() for kernel/rcu/update.c

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@...ux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
---
 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