[PATCH tip/core/rcu 17/17] rcu: Add check for CPUs going offline with callbacks queued

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

From: "Paul E. McKenney" <paul.mckenney@linaro.org>

If a CPU goes offline with callbacks queued, those callbacks might be
indefinitely postponed, which can result in a system hang.  This commit
therefore inserts warnings for this condition.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutree.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index c0cc41f..f849202 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1506,6 +1506,9 @@ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
 		raw_spin_unlock_irqrestore(&rnp->lock, flags);
 	if (need_report & RCU_OFL_TASKS_EXP_GP)
 		rcu_report_exp_rnp(rsp, rnp, true);
+	WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
+		  "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
+		  cpu, rdp->qlen, rdp->nxtlist);
 }
 
 #else /* #ifdef CONFIG_HOTPLUG_CPU */
-- 
1.7.8