rcu: Eliminate BUG_ON() for kernel/rcu/tree.c

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

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 121f833..bdb6659 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2826,7 +2826,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func, int cpu, bool lazy)
                 * Very early boot, before rcu_init().  Initialize if needed
                 * and then drop through to queue the callback.
                 */
-               BUG_ON(cpu != -1);
+               WARN_ON_ONCE(cpu != -1);
                WARN_ON_ONCE(!rcu_is_watching());
                if (rcu_segcblist_empty(&rdp->cblist))
                        rcu_segcblist_init(&rdp->cblist);
@@ -3485,7 +3485,8 @@ static int __init rcu_spawn_gp_kthread(void)
 
        rcu_scheduler_fully_active = 1;
        t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name);
-       BUG_ON(IS_ERR(t));
+       if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__))
+               return 0;
        rnp = rcu_get_root();
        raw_spin_lock_irqsave_rcu_node(rnp, flags);
        rcu_state.gp_kthread = t;