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>

diff --git a/init/Kconfig b/init/Kconfig
index fd2d4fb..7817600 100644 (file)
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -603,7 +603,7 @@ config RCU_FANOUT_LEAF
        int "Tree-based hierarchical RCU leaf-level fanout value"
        range 2 64 if 64BIT
        range 2 32 if !64BIT
-       depends on TREE_RCU || PREEMPT_RCU
+       depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
        default 16
        help
          This option controls the leaf-level fanout of hierarchical

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ba3f8d5..1edd112 100644 (file)
--- 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);

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index ac3020f..7d949c1 100644 (file)
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -48,7 +48,17 @@
 # endif
 #endif /* #else #ifdef CONFIG_RCU_FANOUT */
 
-#define RCU_FANOUT_1         (CONFIG_RCU_FANOUT_LEAF)
+#ifdef CONFIG_RCU_FANOUT_LEAF
+#define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF
+#else /* #ifdef CONFIG_RCU_FANOUT_LEAF */
+# ifdef CONFIG_64BIT
+# define RCU_FANOUT_LEAF 64
+# else
+# define RCU_FANOUT_LEAF 32
+# endif
+#endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */
+
+#define RCU_FANOUT_1         (RCU_FANOUT_LEAF)
 #define RCU_FANOUT_2         (RCU_FANOUT_1 * RCU_FANOUT)
 #define RCU_FANOUT_3         (RCU_FANOUT_2 * RCU_FANOUT)
 #define RCU_FANOUT_4         (RCU_FANOUT_3 * RCU_FANOUT)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index d7e5059..7135038 100644 (file)
--- 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);