rcu: Make RCU able to tolerate undefined CONFIG_RCU_FANOUT_LEAF

This commit introduces an RCU_FANOUT_LEAF C-preprocessor macro so
that RCU will build even when CONFIG_RCU_FANOUT_LEAF is undefined.
The RCU_FANOUT_LEAF macro is set to the value of CONFIG_RCU_FANOUT_LEAF
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_LEAF depend
on CONFIG_RCU_EXPERT, so that Kconfig users won't be asked about
CONFIG_RCU_FANOUT_LEAF 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, 4 insertions, 4 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ba3f8d59d948..1edd11298224 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -119,8 +119,8 @@ module_param(dump_tree, bool, 0444);
 /* Control rcu_node-tree auto-balancing at boot time. */
 static bool rcu_fanout_exact;
 module_param(rcu_fanout_exact, bool, 0444);
-/* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
-static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF;
+/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
+static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
 module_param(rcu_fanout_leaf, int, 0444);
 int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
 static int num_rcu_lvl[] = {  /* Number of rcu_nodes at specified level. */
@@ -4097,7 +4097,7 @@ static void __init rcu_init_geometry(void)
                 jiffies_till_next_fqs = d;
 
         /* If the compile-time values are accurate, just leave. */
-        if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
+        if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
             nr_cpu_ids == NR_CPUS)
                 return;
         pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
@@ -4121,7 +4121,7 @@ static void __init rcu_init_geometry(void)
          * the configured number of CPUs.  Complain and fall back to the
          * compile-time values if these limits are exceeded.
          */
-        if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF ||
+        if (rcu_fanout_leaf < RCU_FANOUT_LEAF ||
             rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
             n > rcu_capacity[MAX_RCU_LVLS]) {
                 WARN_ON(1);