rcu: Conditionally build CPU-hotplug teardown callbacks

Among the three CPU-hotplug teardown RCU callbacks, two of them early
exit if CONFIG_HOTPLUG_CPU=n, and one is left unchanged. In any case
all of them have an implementation when CONFIG_HOTPLUG_CPU=n.

Align instead with the common way to deal with CPU-hotplug teardown
callbacks and provide a proper stub when they are not supported.

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index 153cfc7bbffd630eea1d30c4f9ef0f4536d8a508..46875c4e9f56a07a67dfa6abbe2e957d1a2abf59 100644 (file)
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -110,9 +110,16 @@ void rcu_all_qs(void);
 /* RCUtree hotplug events */
 int rcutree_prepare_cpu(unsigned int cpu);
 int rcutree_online_cpu(unsigned int cpu);
-int rcutree_offline_cpu(unsigned int cpu);
+void rcu_cpu_starting(unsigned int cpu);
+
+#ifdef CONFIG_HOTPLUG_CPU
 int rcutree_dead_cpu(unsigned int cpu);
 int rcutree_dying_cpu(unsigned int cpu);
-void rcu_cpu_starting(unsigned int cpu);
+int rcutree_offline_cpu(unsigned int cpu);
+#else
+#define rcutree_dead_cpu NULL
+#define rcutree_dying_cpu NULL
+#define rcutree_offline_cpu NULL
+#endif
 
 #endif /* __LINUX_RCUTREE_H */

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 2e1e7eadf2cc7384add995c7fc8d8b746962097e..f9c6b2680cbb5959ad512b699d31aeeba900375b 100644 (file)
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -4237,25 +4237,6 @@ static bool rcu_init_invoked(void)
        return !!rcu_state.n_online_cpus;
 }
 
-/*
- * Near the end of the offline process.  Trace the fact that this CPU
- * is going offline.
- */
-int rcutree_dying_cpu(unsigned int cpu)
-{
-       bool blkd;
-       struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
-       struct rcu_node *rnp = rdp->mynode;
-
-       if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
-               return 0;
-
-       blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask);
-       trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
-                              blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));
-       return 0;
-}
-
 /*
  * All CPUs for the specified rcu_node structure have gone offline,
  * and all tasks that were preempted within an RCU read-side critical
@@ -4301,23 +4282,6 @@ static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
        }
 }
 
-/*
- * The CPU has been completely removed, and some other CPU is reporting
- * this fact from process context.  Do the remainder of the cleanup.
- * There can only be one CPU hotplug operation at a time, so no need for
- * explicit locking.
- */
-int rcutree_dead_cpu(unsigned int cpu)
-{
-       if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
-               return 0;
-
-       WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);
-       // Stop-machine done, so allow nohz_full to disable tick.
-       tick_dep_clear(TICK_DEP_BIT_RCU);
-       return 0;
-}
-
 /*
  * Propagate ->qsinitmask bits up the rcu_node tree to account for the
  * first CPU in a given leaf rcu_node structure coming online.  The caller
@@ -4470,29 +4434,6 @@ int rcutree_online_cpu(unsigned int cpu)
        return 0;
 }
 
-/*
- * Near the beginning of the process.  The CPU is still very much alive
- * with pretty much all services enabled.
- */
-int rcutree_offline_cpu(unsigned int cpu)
-{
-       unsigned long flags;
-       struct rcu_data *rdp;
-       struct rcu_node *rnp;
-
-       rdp = per_cpu_ptr(&rcu_data, cpu);
-       rnp = rdp->mynode;
-       raw_spin_lock_irqsave_rcu_node(rnp, flags);
-       rnp->ffmask &= ~rdp->grpmask;
-       raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
-
-       rcutree_affinity_setting(cpu, cpu);
-
-       // nohz_full CPUs need the tick for stop-machine to work quickly
-       tick_dep_set(TICK_DEP_BIT_RCU);
-       return 0;
-}
-
 /*
  * Mark the specified CPU as being online so that subsequent grace periods
  * (both expedited and normal) will wait on it.  Note that this means that
@@ -4646,7 +4587,60 @@ void rcutree_migrate_callbacks(int cpu)
                  cpu, rcu_segcblist_n_cbs(&rdp->cblist),
                  rcu_segcblist_first_cb(&rdp->cblist));
 }
-#endif
+
+/*
+ * The CPU has been completely removed, and some other CPU is reporting
+ * this fact from process context.  Do the remainder of the cleanup.
+ * There can only be one CPU hotplug operation at a time, so no need for
+ * explicit locking.
+ */
+int rcutree_dead_cpu(unsigned int cpu)
+{
+       WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1);
+       // Stop-machine done, so allow nohz_full to disable tick.
+       tick_dep_clear(TICK_DEP_BIT_RCU);
+       return 0;
+}
+
+/*
+ * Near the end of the offline process.  Trace the fact that this CPU
+ * is going offline.
+ */
+int rcutree_dying_cpu(unsigned int cpu)
+{
+       bool blkd;
+       struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
+       struct rcu_node *rnp = rdp->mynode;
+
+       blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask);
+       trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq),
+                              blkd ? TPS("cpuofl-bgp") : TPS("cpuofl"));
+       return 0;
+}
+
+/*
+ * Near the beginning of the process.  The CPU is still very much alive
+ * with pretty much all services enabled.
+ */
+int rcutree_offline_cpu(unsigned int cpu)
+{
+       unsigned long flags;
+       struct rcu_data *rdp;
+       struct rcu_node *rnp;
+
+       rdp = per_cpu_ptr(&rcu_data, cpu);
+       rnp = rdp->mynode;
+       raw_spin_lock_irqsave_rcu_node(rnp, flags);
+       rnp->ffmask &= ~rdp->grpmask;
+       raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
+
+       rcutree_affinity_setting(cpu, cpu);
+
+       // nohz_full CPUs need the tick for stop-machine to work quickly
+       tick_dep_set(TICK_DEP_BIT_RCU);
+       return 0;
+}
+#endif /* #ifdef CONFIG_HOTPLUG_CPU */
 
 /*
  * On non-huge systems, use expedited RCU grace periods to make suspend