1 files changed, 185 insertions, 0 deletions
diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
new file mode 100644
index 000000000..aa897c3f2
--- /dev/null
+++ b/kernel/rcu/tiny.c
@@ -0,0 +1,185 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
+ *
+ * Copyright IBM Corporation, 2008
+ *
+ * Author: Paul E. McKenney <paulmck@linux.ibm.com>
+ *
+ * For detailed explanation of Read-Copy Update mechanism see -
+ *		Documentation/RCU
+ */
+#include <linux/completion.h>
+#include <linux/interrupt.h>
+#include <linux/notifier.h>
+#include <linux/rcupdate_wait.h>
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/mutex.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/init.h>
+#include <linux/time.h>
+#include <linux/cpu.h>
+#include <linux/prefetch.h>
+#include <linux/slab.h>
+#include <linux/mm.h>
+
+#include "rcu.h"
+
+/* Global control variables for rcupdate callback mechanism. */
+struct rcu_ctrlblk {
+	struct rcu_head *rcucblist;	/* List of pending callbacks (CBs). */
+	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */
+	struct rcu_head **curtail;	/* ->next pointer of last CB. */
+};
+
+/* Definition for rcupdate control block. */
+static struct rcu_ctrlblk rcu_ctrlblk = {
+	.donetail	= &rcu_ctrlblk.rcucblist,
+	.curtail	= &rcu_ctrlblk.rcucblist,
+};
+
+void rcu_barrier(void)
+{
+	wait_rcu_gp(call_rcu);
+}
+EXPORT_SYMBOL(rcu_barrier);
+
+/* Record an rcu quiescent state.  */
+void rcu_qs(void)
+{
+	unsigned long flags;
+
+	local_irq_save(flags);
+	if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
+		rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
+		raise_softirq_irqoff(RCU_SOFTIRQ);
+	}
+	local_irq_restore(flags);
+}
+
+/*
+ * Check to see if the scheduling-clock interrupt came from an extended
+ * quiescent state, and, if so, tell RCU about it.  This function must
+ * be called from hardirq context.  It is normally called from the
+ * scheduling-clock interrupt.
+ */
+void rcu_sched_clock_irq(int user)
+{
+	if (user) {
+		rcu_qs();
+	} else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
+		set_tsk_need_resched(current);
+		set_preempt_need_resched();
+	}
+}
+
+/*
+ * Reclaim the specified callback, either by invoking it for non-kfree cases or
+ * freeing it directly (for kfree). Return true if kfreeing, false otherwise.
+ */
+static inline bool rcu_reclaim_tiny(struct rcu_head *head)
+{
+	rcu_callback_t f;
+	unsigned long offset = (unsigned long)head->func;
+
+	rcu_lock_acquire(&rcu_callback_map);
+	if (__is_kvfree_rcu_offset(offset)) {
+		trace_rcu_invoke_kvfree_callback("", head, offset);
+		kvfree((void *)head - offset);
+		rcu_lock_release(&rcu_callback_map);
+		return true;
+	}
+
+	trace_rcu_invoke_callback("", head);
+	f = head->func;
+	WRITE_ONCE(head->func, (rcu_callback_t)0L);
+	f(head);
+	rcu_lock_release(&rcu_callback_map);
+	return false;
+}
+
+/* Invoke the RCU callbacks whose grace period has elapsed.  */
+static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
+{
+	struct rcu_head *next, *list;
+	unsigned long flags;
+
+	/* Move the ready-to-invoke callbacks to a local list. */
+	local_irq_save(flags);
+	if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
+		/* No callbacks ready, so just leave. */
+		local_irq_restore(flags);
+		return;
+	}
+	list = rcu_ctrlblk.rcucblist;
+	rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
+	*rcu_ctrlblk.donetail = NULL;
+	if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
+		rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
+	rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
+	local_irq_restore(flags);
+
+	/* Invoke the callbacks on the local list. */
+	while (list) {
+		next = list->next;
+		prefetch(next);
+		debug_rcu_head_unqueue(list);
+		local_bh_disable();
+		rcu_reclaim_tiny(list);
+		local_bh_enable();
+		list = next;
+	}
+}
+
+/*
+ * Wait for a grace period to elapse.  But it is illegal to invoke
+ * synchronize_rcu() from within an RCU read-side critical section.
+ * Therefore, any legal call to synchronize_rcu() is a quiescent
+ * state, and so on a UP system, synchronize_rcu() need do nothing.
+ * (But Lai Jiangshan points out the benefits of doing might_sleep()
+ * to reduce latency.)
+ *
+ * Cool, huh?  (Due to Josh Triplett.)
+ */
+void synchronize_rcu(void)
+{
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
+			 lock_is_held(&rcu_lock_map) ||
+			 lock_is_held(&rcu_sched_lock_map),
+			 "Illegal synchronize_rcu() in RCU read-side critical section");
+}
+EXPORT_SYMBOL_GPL(synchronize_rcu);
+
+/*
+ * Post an RCU callback to be invoked after the end of an RCU grace
+ * period.  But since we have but one CPU, that would be after any
+ * quiescent state.
+ */
+void call_rcu(struct rcu_head *head, rcu_callback_t func)
+{
+	unsigned long flags;
+
+	debug_rcu_head_queue(head);
+	head->func = func;
+	head->next = NULL;
+
+	local_irq_save(flags);
+	*rcu_ctrlblk.curtail = head;
+	rcu_ctrlblk.curtail = &head->next;
+	local_irq_restore(flags);
+
+	if (unlikely(is_idle_task(current))) {
+		/* force scheduling for rcu_qs() */
+		resched_cpu(0);
+	}
+}
+EXPORT_SYMBOL_GPL(call_rcu);
+
+void __init rcu_init(void)
+{
+	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
+	rcu_early_boot_tests();
+	srcu_init();
+}