rcu: Define rcu_all_qs() only in !PREEMPT builds

Now that rcu_all_qs() is used only in !PREEMPT builds, move it to
tree_plugin.h so that it is defined only in those builds.  This in
turn means that rcu_momentary_dyntick_idle() is only used in !PREEMPT
builds, but it is simply marked __maybe_unused in order to keep it
near the rest of the dyntick-idle code.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index cd4c1b979446..7add1c297500 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -948,6 +948,45 @@ static void rcu_qs(void)
 }
 
 /*
+ * Register an urgently needed quiescent state.  If there is an
+ * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
+ * dyntick-idle quiescent state visible to other CPUs, which will in
+ * some cases serve for expedited as well as normal grace periods.
+ * Either way, register a lightweight quiescent state.
+ *
+ * The barrier() calls are redundant in the common case when this is
+ * called externally, but just in case this is called from within this
+ * file.
+ *
+ */
+void rcu_all_qs(void)
+{
+	unsigned long flags;
+
+	if (!raw_cpu_read(rcu_dynticks.rcu_urgent_qs))
+		return;
+	preempt_disable();
+	/* Load rcu_urgent_qs before other flags. */
+	if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
+		preempt_enable();
+		return;
+	}
+	this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
+	barrier(); /* Avoid RCU read-side critical sections leaking down. */
+	if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
+		local_irq_save(flags);
+		rcu_momentary_dyntick_idle();
+		local_irq_restore(flags);
+	}
+	if (unlikely(raw_cpu_read(rcu_data.cpu_no_qs.b.exp)))
+		rcu_qs();
+	this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
+	barrier(); /* Avoid RCU read-side critical sections leaking up. */
+	preempt_enable();
+}
+EXPORT_SYMBOL_GPL(rcu_all_qs);
+
+/*
  * Note a PREEMPT=n context switch.  The caller must have disabled interrupts.
  */
 void rcu_note_context_switch(bool preempt)