Commit 032dfc87 authored Jul 09, 2015 by Alexander Gordeev Committed by Paul E. McKenney Jul 17, 2015

rcu: Shut up bogus gcc array bounds warning



Because gcc does not realize a loop would not be entered ever
(i.e. in case of rcu_num_lvls == 1):

  for (i = 1; i < rcu_num_lvls; i++)
	  rsp->level[i] = rsp->level[i - 1] + levelcnt[i - 1];

some compiler (pre- 5.x?) versions give a bogus warning:

  kernel/rcu/tree.c: In function ‘rcu_init_one.isra.55’:
  kernel/rcu/tree.c:4108:13: warning: array subscript is above array bounds [-Warray-bounds]
     rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
               ^
Fix that warning by adding an extra item to rcu_state::level[]
array. Once the bogus warning is fixed in gcc and kernel drops
support of older versions, the dummy item may be removed from
the array.

Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Suggested-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

parent 42621697

kernel/rcu/tree.h

+3 −1

Original line number	Diff line number	Diff line
		@@ -443,7 +443,9 @@ do { \
		*/
		struct rcu_state {
		struct rcu_node node[NUM_RCU_NODES]; /* Hierarchy. */
		struct rcu_node level[RCU_NUM_LVLS]; / Hierarchy levels. */
		struct rcu_node *level[RCU_NUM_LVLS + 1];
		/* Hierarchy levels (+1 to */
		/* shut bogus gcc warning) */
		u8 flavor_mask; /* bit in flavor mask. */
		struct rcu_data __percpu rda; / pointer of percu rcu_data. */
		void (call)(struct rcu_head head, /* call_rcu() flavor. */