rcu: Move expedited code from tree_plugin.h to tree_exp.h
People have been having some difficulty finding their way around the
RCU code. This commit therefore pulls some of the expedited grace-period
code from tree_plugin.h to a new tree_exp.h file. This commit is strictly
code movement.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index db0909c..00a02a2 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -562,3 +562,97 @@
rcu_exp_wait_wake(rsp, s);
}
EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
+
+#ifdef CONFIG_PREEMPT_RCU
+
+/*
+ * Remote handler for smp_call_function_single(). If there is an
+ * RCU read-side critical section in effect, request that the
+ * next rcu_read_unlock() record the quiescent state up the
+ * ->expmask fields in the rcu_node tree. Otherwise, immediately
+ * report the quiescent state.
+ */
+static void sync_rcu_exp_handler(void *info)
+{
+ struct rcu_data *rdp;
+ struct rcu_state *rsp = info;
+ struct task_struct *t = current;
+
+ /*
+ * Within an RCU read-side critical section, request that the next
+ * rcu_read_unlock() report. Unless this RCU read-side critical
+ * section has already blocked, in which case it is already set
+ * up for the expedited grace period to wait on it.
+ */
+ if (t->rcu_read_lock_nesting > 0 &&
+ !t->rcu_read_unlock_special.b.blocked) {
+ t->rcu_read_unlock_special.b.exp_need_qs = true;
+ return;
+ }
+
+ /*
+ * We are either exiting an RCU read-side critical section (negative
+ * values of t->rcu_read_lock_nesting) or are not in one at all
+ * (zero value of t->rcu_read_lock_nesting). Or we are in an RCU
+ * read-side critical section that blocked before this expedited
+ * grace period started. Either way, we can immediately report
+ * the quiescent state.
+ */
+ rdp = this_cpu_ptr(rsp->rda);
+ rcu_report_exp_rdp(rsp, rdp, true);
+}
+
+/**
+ * synchronize_rcu_expedited - Brute-force RCU grace period
+ *
+ * Wait for an RCU-preempt grace period, but expedite it. The basic
+ * idea is to IPI all non-idle non-nohz online CPUs. The IPI handler
+ * checks whether the CPU is in an RCU-preempt critical section, and
+ * if so, it sets a flag that causes the outermost rcu_read_unlock()
+ * to report the quiescent state. On the other hand, if the CPU is
+ * not in an RCU read-side critical section, the IPI handler reports
+ * the quiescent state immediately.
+ *
+ * Although this is a greate improvement over previous expedited
+ * implementations, it is still unfriendly to real-time workloads, so is
+ * thus not recommended for any sort of common-case code. In fact, if
+ * you are using synchronize_rcu_expedited() in a loop, please restructure
+ * your code to batch your updates, and then Use a single synchronize_rcu()
+ * instead.
+ */
+void synchronize_rcu_expedited(void)
+{
+ struct rcu_state *rsp = rcu_state_p;
+ unsigned long s;
+
+ /* If expedited grace periods are prohibited, fall back to normal. */
+ if (rcu_gp_is_normal()) {
+ wait_rcu_gp(call_rcu);
+ return;
+ }
+
+ s = rcu_exp_gp_seq_snap(rsp);
+ if (exp_funnel_lock(rsp, s))
+ return; /* Someone else did our work for us. */
+
+ /* Initialize the rcu_node tree in preparation for the wait. */
+ sync_rcu_exp_select_cpus(rsp, sync_rcu_exp_handler);
+
+ /* Wait for ->blkd_tasks lists to drain, then wake everyone up. */
+ rcu_exp_wait_wake(rsp, s);
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+#else /* #ifdef CONFIG_PREEMPT_RCU */
+
+/*
+ * Wait for an rcu-preempt grace period, but make it happen quickly.
+ * But because preemptible RCU does not exist, map to rcu-sched.
+ */
+void synchronize_rcu_expedited(void)
+{
+ synchronize_sched_expedited();
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
+
+#endif /* #else #ifdef CONFIG_PREEMPT_RCU */