[PATCH 05/10] rcu: Limit rcu_state::levelcnt[] to RCU_NUM_LVLS items

From: Alexander Gordeev
Date: Mon Mar 09 2015 - 04:36:23 EST

Variable rcu_num_lvls is limited by RCU_NUM_LVLS macro.
In turn, rcu_state::levelcnt[] array is never accessed
beyond rcu_num_lvls. Thus, rcu_state::levelcnt[] is safe
to limit to RCU_NUM_LVLS items.

Since rcu_num_lvls could be changed during boot (as result
of rcutree.rcu_fanout_leaf kernel parameter update) one might
assume a new value could overflow the value of RCU_NUM_LVLS.
However, that is not the case, since leaf-level fanout is only
permitted to increase, resulting in rcu_num_lvls possibly to

Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Alexander Gordeev <agordeev@xxxxxxxxxx>
kernel/rcu/tree.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index dd5ce40..f358a83 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -421,7 +421,7 @@ do { \
struct rcu_state {
struct rcu_node node[NUM_RCU_NODES]; /* Hierarchy. */
struct rcu_node *level[RCU_NUM_LVLS]; /* Hierarchy levels. */
- u32 levelcnt[MAX_RCU_LVLS + 1]; /* # nodes in each level. */
+ u32 levelcnt[RCU_NUM_LVLS]; /* # nodes in each level. */
u8 levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
u8 flavor_mask; /* bit in flavor mask. */
struct rcu_data __percpu *rda; /* pointer of percu rcu_data. */

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