[PATCH tip/core/rcu 21/22] EXP rcu: Add checks for setting ->gp_flags

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

The ->gp_flags pointer must not be set unless the current rcu_node structure
is waiting on at least one quiescent state.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c        | 2 ++
 kernel/rcu/tree.h        | 1 +
 kernel/rcu/tree_plugin.h | 6 +++++-
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 3bfd1519d378..d275c49aa0e8 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2419,6 +2419,7 @@ rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
 			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
 			return;
 		}
+		rnp->completedqs = rnp->gpnum;
 		mask = rnp->grpmask;
 		if (rnp->parent == NULL) {
 
@@ -4035,6 +4036,7 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 						   &rcu_fqs_class[i], fqs[i]);
 			rnp->gpnum = rsp->gpnum;
 			rnp->completed = rsp->completed;
+			rnp->completedqs = rsp->completed;
 			rnp->qsmask = 0;
 			rnp->qsmaskinit = 0;
 			rnp->grplo = j * cpustride;
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index 23ae7c00d3c5..f03da0b091fb 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -79,6 +79,7 @@ struct rcu_node {
 	unsigned long completed; /* Last GP completed for this node. */
 				/*  This will either be equal to or one */
 				/*  behind the root rcu_node's gpnum. */
+	unsigned long completedqs; /* All QSes done for this node. */
 	unsigned long qsmask;	/* CPUs or groups that need to switch in */
 				/*  order for current grace period to proceed.*/
 				/*  In leaf rcu_node, each bit corresponds to */
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 429f9358d0b6..8014a09a5c9b 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -260,8 +260,10 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
 	 * ->exp_tasks pointers, respectively, to reference the newly
 	 * blocked tasks.
 	 */
-	if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD))
+	if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD)) {
 		rnp->gp_tasks = &t->rcu_node_entry;
+		WARN_ON_ONCE(rnp->completedqs == rnp->gpnum);
+	}
 	if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
 		rnp->exp_tasks = &t->rcu_node_entry;
 	WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
@@ -535,6 +537,8 @@ void rcu_read_unlock_special(struct task_struct *t)
 		WARN_ON_ONCE(rnp != t->rcu_blocked_node);
 		WARN_ON_ONCE(!rcu_is_leaf_node(rnp));
 		empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
+		WARN_ON_ONCE(rnp->completedqs == rnp->gpnum &&
+			     (!empty_norm || rnp->qsmask));
 		empty_exp = sync_rcu_preempt_exp_done(rnp);
 		smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
 		np = rcu_next_node_entry(t, rnp);
-- 
2.5.2