tiny.c

  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#include <linux/slab.h>
 26#include <linux/mm.h>
 27
 28#include "rcu.h"
 29
 30/* Global control variables for rcupdate callback mechanism. */
 31struct rcu_ctrlblk {
 32	struct rcu_head *rcucblist;	/* List of pending callbacks (CBs). */
 33	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */
 34	struct rcu_head **curtail;	/* ->next pointer of last CB. */
 35	unsigned long gp_seq;		/* Grace-period counter. */
 36};
 37
 38/* Definition for rcupdate control block. */
 39static struct rcu_ctrlblk rcu_ctrlblk = {
 40	.donetail	= &rcu_ctrlblk.rcucblist,
 41	.curtail	= &rcu_ctrlblk.rcucblist,
 42	.gp_seq		= 0 - 300UL,
 43};
 44
 45void rcu_barrier(void)
 46{
 47	wait_rcu_gp(call_rcu_hurry);
 48}
 49EXPORT_SYMBOL(rcu_barrier);
 50
 51/* Record an rcu quiescent state.  */
 52void rcu_qs(void)
 53{
 54	unsigned long flags;
 55
 56	local_irq_save(flags);
 57	if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
 58		rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
 59		raise_softirq_irqoff(RCU_SOFTIRQ);
 60	}
 61	WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2);
 62	local_irq_restore(flags);
 63}
 64
 65/*
 66 * Check to see if the scheduling-clock interrupt came from an extended
 67 * quiescent state, and, if so, tell RCU about it.  This function must
 68 * be called from hardirq context.  It is normally called from the
 69 * scheduling-clock interrupt.
 70 */
 71void rcu_sched_clock_irq(int user)
 72{
 73	if (user)
 74		rcu_qs();
 75	else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail)
 76		set_need_resched_current();
 77}
 78
 79/*
 80 * Reclaim the specified callback, either by invoking it for non-kfree cases or
 81 * freeing it directly (for kfree). Return true if kfreeing, false otherwise.
 82 */
 83static inline bool rcu_reclaim_tiny(struct rcu_head *head)
 84{
 85	rcu_callback_t f;
 86
 87	rcu_lock_acquire(&rcu_callback_map);
 88
 89	trace_rcu_invoke_callback("", head);
 90	f = head->func;
 91	debug_rcu_head_callback(head);
 92	WRITE_ONCE(head->func, (rcu_callback_t)0L);
 93	f(head);
 94	rcu_lock_release(&rcu_callback_map);
 95	return false;
 96}
 97
 98/* Invoke the RCU callbacks whose grace period has elapsed.  */
 99static __latent_entropy void rcu_process_callbacks(void)
100{
101	struct rcu_head *next, *list;
102	unsigned long flags;
103
104	/* Move the ready-to-invoke callbacks to a local list. */
105	local_irq_save(flags);
106	if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
107		/* No callbacks ready, so just leave. */
108		local_irq_restore(flags);
109		return;
110	}
111	list = rcu_ctrlblk.rcucblist;
112	rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
113	*rcu_ctrlblk.donetail = NULL;
114	if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
115		rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
116	rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
117	local_irq_restore(flags);
118
119	/* Invoke the callbacks on the local list. */
120	while (list) {
121		next = list->next;
122		prefetch(next);
123		debug_rcu_head_unqueue(list);
124		rcu_reclaim_tiny(list);
125		list = next;
126	}
127}
128
129/*
130 * Wait for a grace period to elapse.  But it is illegal to invoke
131 * synchronize_rcu() from within an RCU read-side critical section.
132 * Therefore, any legal call to synchronize_rcu() is a quiescent state,
133 * and so on a UP system, synchronize_rcu() need do nothing, other than
134 * let the polled APIs know that another grace period elapsed.
135 *
136 * (But Lai Jiangshan points out the benefits of doing might_sleep()
137 * to reduce latency.)
138 *
139 * Cool, huh?  (Due to Josh Triplett.)
140 */
141void synchronize_rcu(void)
142{
143	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
144			 lock_is_held(&rcu_lock_map) ||
145			 lock_is_held(&rcu_sched_lock_map),
146			 "Illegal synchronize_rcu() in RCU read-side critical section");
147	preempt_disable();
148	WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2);
149	preempt_enable();
150}
151EXPORT_SYMBOL_GPL(synchronize_rcu);
152
153/*
154 * Post an RCU callback to be invoked after the end of an RCU grace
155 * period.  But since we have but one CPU, that would be after any
156 * quiescent state.
157 */
158void call_rcu(struct rcu_head *head, rcu_callback_t func)
159{
160	static atomic_t doublefrees;
161	unsigned long flags;
162
163	if (debug_rcu_head_queue(head)) {
164		if (atomic_inc_return(&doublefrees) < 4) {
165			pr_err("%s(): Double-freed CB %p->%pS()!!!  ", __func__, head, head->func);
166			mem_dump_obj(head);
167		}
168		return;
169	}
170
171	head->func = func;
172	head->next = NULL;
173
174	local_irq_save(flags);
175	*rcu_ctrlblk.curtail = head;
176	rcu_ctrlblk.curtail = &head->next;
177	local_irq_restore(flags);
178
179	if (unlikely(is_idle_task(current))) {
180		/* force scheduling for rcu_qs() */
181		resched_cpu(0);
182	}
183}
184EXPORT_SYMBOL_GPL(call_rcu);
185
186/*
187 * Store a grace-period-counter "cookie".  For more information,
188 * see the Tree RCU header comment.
189 */
190void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
191{
192	rgosp->rgos_norm = RCU_GET_STATE_COMPLETED;
193}
194EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full);
195
196/*
197 * Return a grace-period-counter "cookie".  For more information,
198 * see the Tree RCU header comment.
199 */
200unsigned long get_state_synchronize_rcu(void)
201{
202	return READ_ONCE(rcu_ctrlblk.gp_seq);
203}
204EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
205
206/*
207 * Return a grace-period-counter "cookie" and ensure that a future grace
208 * period completes.  For more information, see the Tree RCU header comment.
209 */
210unsigned long start_poll_synchronize_rcu(void)
211{
212	unsigned long gp_seq = get_state_synchronize_rcu();
213
214	if (unlikely(is_idle_task(current))) {
215		/* force scheduling for rcu_qs() */
216		resched_cpu(0);
217	}
218	return gp_seq;
219}
220EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
221
222/*
223 * Return true if the grace period corresponding to oldstate has completed
224 * and false otherwise.  For more information, see the Tree RCU header
225 * comment.
226 */
227bool poll_state_synchronize_rcu(unsigned long oldstate)
228{
229	return oldstate == RCU_GET_STATE_COMPLETED || READ_ONCE(rcu_ctrlblk.gp_seq) != oldstate;
230}
231EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
232
233#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST)
234unsigned long long rcutorture_gather_gp_seqs(void)
235{
236	return READ_ONCE(rcu_ctrlblk.gp_seq) & 0xffffULL;
237}
238EXPORT_SYMBOL_GPL(rcutorture_gather_gp_seqs);
239
240void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t len)
241{
242	snprintf(cp, len, "g%04llx", seqs & 0xffffULL);
243}
244EXPORT_SYMBOL_GPL(rcutorture_format_gp_seqs);
245#endif
246
247void __init rcu_init(void)
248{
249	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
250	rcu_early_boot_tests();
251	tasks_cblist_init_generic();
252}