rcu: Make RCU able to tolerate undefined CONFIG_RCU_FANOUT

This commit introduces an RCU_FANOUT C-preprocessor macro so that RCU will
build even when CONFIG_RCU_FANOUT is undefined.  The RCU_FANOUT macro is
set to the value of CONFIG_RCU_FANOUT when defined, otherwise it is set
to 32 for 32-bit systems and 64 for 64-bit systems.  This commit then
makes CONFIG_RCU_FANOUT depend on CONFIG_RCU_EXPERT, so that Kconfig
users won't be asked about CONFIG_RCU_FANOUT unless they want to be.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Pranith Kumar <bobby.prani@gmail.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 1bc14c670641..ba3f8d59d948 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3971,7 +3971,7 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp)
         if (rcu_fanout_exact) {
                 rsp->levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
                 for (i = rcu_num_lvls - 2; i >= 0; i--)
-                        rsp->levelspread[i] = CONFIG_RCU_FANOUT;
+                        rsp->levelspread[i] = RCU_FANOUT;
         } else {
                 int ccur;
                 int cprv;
@@ -4111,7 +4111,7 @@ static void __init rcu_init_geometry(void)
         rcu_capacity[0] = 1;
         rcu_capacity[1] = rcu_fanout_leaf;
         for (i = 2; i <= MAX_RCU_LVLS; i++)
-                rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT;
+                rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
 
         /*
          * The boot-time rcu_fanout_leaf parameter is only permitted