1// SPDX-License-Identifier: GPL-2.0+
  2/*
  3 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
  4 *
  5 * Copyright IBM Corporation, 2008
  6 *
  7 * Author: Paul E. McKenney <paulmck@linux.ibm.com>
  8 *
  9 * For detailed explanation of Read-Copy Update mechanism see -
 10 *		Documentation/RCU
 11 */
 12#include <linux/completion.h>
 13#include <linux/interrupt.h>
 14#include <linux/notifier.h>
 15#include <linux/rcupdate_wait.h>
 16#include <linux/kernel.h>
 17#include <linux/export.h>
 18#include <linux/mutex.h>
 19#include <linux/sched.h>
 20#include <linux/types.h>
 21#include <linux/init.h>
 22#include <linux/time.h>
 23#include <linux/cpu.h>
 24#include <linux/prefetch.h>
 25
 26#include "rcu.h"
 27
 28/* Global control variables for rcupdate callback mechanism. */
 29struct rcu_ctrlblk {
 30	struct rcu_head *rcucblist;	/* List of pending callbacks (CBs). */
 31	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */
 32	struct rcu_head **curtail;	/* ->next pointer of last CB. */
 33};
 34
 35/* Definition for rcupdate control block. */
 36static struct rcu_ctrlblk rcu_ctrlblk = {
 37	.donetail	= &rcu_ctrlblk.rcucblist,
 38	.curtail	= &rcu_ctrlblk.rcucblist,
 39};
 40
 41void rcu_barrier(void)
 42{
 43	wait_rcu_gp(call_rcu);
 44}
 45EXPORT_SYMBOL(rcu_barrier);
 46
 47/* Record an rcu quiescent state.  */
 48void rcu_qs(void)
 49{
 50	unsigned long flags;
 51
 52	local_irq_save(flags);
 53	if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
 54		rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
 55		raise_softirq_irqoff(RCU_SOFTIRQ);
 56	}
 57	local_irq_restore(flags);
 58}
 59
 60/*
 61 * Check to see if the scheduling-clock interrupt came from an extended
 62 * quiescent state, and, if so, tell RCU about it.  This function must
 63 * be called from hardirq context.  It is normally called from the
 64 * scheduling-clock interrupt.
 65 */
 66void rcu_sched_clock_irq(int user)
 67{
 68	if (user) {
 69		rcu_qs();
 70	} else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
 71		set_tsk_need_resched(current);
 72		set_preempt_need_resched();
 73	}
 74}
 75
 76/* Invoke the RCU callbacks whose grace period has elapsed.  */
 77static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
 78{
 79	struct rcu_head *next, *list;
 80	unsigned long flags;
 81
 82	/* Move the ready-to-invoke callbacks to a local list. */
 83	local_irq_save(flags);
 84	if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
 85		/* No callbacks ready, so just leave. */
 86		local_irq_restore(flags);
 87		return;
 88	}
 89	list = rcu_ctrlblk.rcucblist;
 90	rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
 91	*rcu_ctrlblk.donetail = NULL;
 92	if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
 93		rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
 94	rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
 95	local_irq_restore(flags);
 96
 97	/* Invoke the callbacks on the local list. */
 98	while (list) {
 99		next = list->next;
100		prefetch(next);
101		debug_rcu_head_unqueue(list);
102		local_bh_disable();
103		__rcu_reclaim("", list);
104		local_bh_enable();
105		list = next;
106	}
107}
108
109/*
110 * Wait for a grace period to elapse.  But it is illegal to invoke
111 * synchronize_rcu() from within an RCU read-side critical section.
112 * Therefore, any legal call to synchronize_rcu() is a quiescent
113 * state, and so on a UP system, synchronize_rcu() need do nothing.
114 * (But Lai Jiangshan points out the benefits of doing might_sleep()
115 * to reduce latency.)
116 *
117 * Cool, huh?  (Due to Josh Triplett.)
118 */
119void synchronize_rcu(void)
120{
121	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
122			 lock_is_held(&rcu_lock_map) ||
123			 lock_is_held(&rcu_sched_lock_map),
124			 "Illegal synchronize_rcu() in RCU read-side critical section");
125}
126EXPORT_SYMBOL_GPL(synchronize_rcu);
127
128/*
129 * Post an RCU callback to be invoked after the end of an RCU grace
130 * period.  But since we have but one CPU, that would be after any
131 * quiescent state.
132 */
133void call_rcu(struct rcu_head *head, rcu_callback_t func)
134{
135	unsigned long flags;
136
137	debug_rcu_head_queue(head);
138	head->func = func;
139	head->next = NULL;
140
141	local_irq_save(flags);
142	*rcu_ctrlblk.curtail = head;
143	rcu_ctrlblk.curtail = &head->next;
144	local_irq_restore(flags);
145
146	if (unlikely(is_idle_task(current))) {
147		/* force scheduling for rcu_qs() */
148		resched_cpu(0);
149	}
150}
151EXPORT_SYMBOL_GPL(call_rcu);
152
153void __init rcu_init(void)
154{
155	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
156	rcu_early_boot_tests();
157	srcu_init();
158}