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, 3 insertions, 3 deletions

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index d7e505970f24..713503853841 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -76,10 +76,10 @@ static void __init rcu_bootup_announce_oddness(void)
                 pr_info("\tAdditional per-CPU info printed with stalls.\n");
         if (NUM_RCU_LVL_4 != 0)
                 pr_info("\tFour-level hierarchy is enabled.\n");
-        if (CONFIG_RCU_FANOUT_LEAF != 16)
+        if (RCU_FANOUT_LEAF != 16)
                 pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
-                        CONFIG_RCU_FANOUT_LEAF);
-        if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
+                        RCU_FANOUT_LEAF);
+        if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
                 pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
         if (nr_cpu_ids != NR_CPUS)
                 pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);