Commit a6d77081 authored Jun 03, 2015 by Alexander Gordeev Committed by Paul E. McKenney Jul 15, 2015

rcu: Limit rcu_state::levelcnt[] to RCU_NUM_LVLS items



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
decrease.

Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent 9618138b

kernel/rcu/tree.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -443,7 +443,7 @@ 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. */