rcu: Introduce check for callback list/count mismatch

The recent bug that introduced the RCU callback list/count mismatch
showed the need for a diagnostic to check for this, which this commit
adds.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 95c7b61e77e4..4154c9567a6d 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1612,6 +1612,7 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
                 rdp->n_force_qs_snap = rsp->n_force_qs;
         } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
                 rdp->qlen_last_fqs_check = rdp->qlen;
+        WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
 
         local_irq_restore(flags);