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. */
31 struct 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. */
39 static struct rcu_ctrlblk rcu_ctrlblk = {
40 	.donetail	= &rcu_ctrlblk.rcucblist,
41 	.curtail	= &rcu_ctrlblk.rcucblist,
42 	.gp_seq		= 0 - 300UL,
43 };
44 
45 void rcu_barrier(void)
46 {
47 	wait_rcu_gp(call_rcu_hurry);
48 }
49 EXPORT_SYMBOL(rcu_barrier);
50 
51 /* Record an rcu quiescent state.  */
52 void 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  */
71 void rcu_sched_clock_irq(int user)
72 {
73 	if (user) {
74 		rcu_qs();
75 	} else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
76 		set_tsk_need_resched(current);
77 		set_preempt_need_resched();
78 	}
79 }
80 
81 /*
82  * Reclaim the specified callback, either by invoking it for non-kfree cases or
83  * freeing it directly (for kfree). Return true if kfreeing, false otherwise.
84  */
85 static inline bool rcu_reclaim_tiny(struct rcu_head *head)
86 {
87 	rcu_callback_t f;
88 
89 	rcu_lock_acquire(&rcu_callback_map);
90 
91 	trace_rcu_invoke_callback("", head);
92 	f = head->func;
93 	debug_rcu_head_callback(head);
94 	WRITE_ONCE(head->func, (rcu_callback_t)0L);
95 	f(head);
96 	rcu_lock_release(&rcu_callback_map);
97 	return false;
98 }
99 
100 /* Invoke the RCU callbacks whose grace period has elapsed.  */
101 static __latent_entropy void rcu_process_callbacks(void)
102 {
103 	struct rcu_head *next, *list;
104 	unsigned long flags;
105 
106 	/* Move the ready-to-invoke callbacks to a local list. */
107 	local_irq_save(flags);
108 	if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
109 		/* No callbacks ready, so just leave. */
110 		local_irq_restore(flags);
111 		return;
112 	}
113 	list = rcu_ctrlblk.rcucblist;
114 	rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
115 	*rcu_ctrlblk.donetail = NULL;
116 	if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
117 		rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
118 	rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
119 	local_irq_restore(flags);
120 
121 	/* Invoke the callbacks on the local list. */
122 	while (list) {
123 		next = list->next;
124 		prefetch(next);
125 		debug_rcu_head_unqueue(list);
126 		rcu_reclaim_tiny(list);
127 		list = next;
128 	}
129 }
130 
131 /*
132  * Wait for a grace period to elapse.  But it is illegal to invoke
133  * synchronize_rcu() from within an RCU read-side critical section.
134  * Therefore, any legal call to synchronize_rcu() is a quiescent state,
135  * and so on a UP system, synchronize_rcu() need do nothing, other than
136  * let the polled APIs know that another grace period elapsed.
137  *
138  * (But Lai Jiangshan points out the benefits of doing might_sleep()
139  * to reduce latency.)
140  *
141  * Cool, huh?  (Due to Josh Triplett.)
142  */
143 void synchronize_rcu(void)
144 {
145 	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
146 			 lock_is_held(&rcu_lock_map) ||
147 			 lock_is_held(&rcu_sched_lock_map),
148 			 "Illegal synchronize_rcu() in RCU read-side critical section");
149 	preempt_disable();
150 	WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2);
151 	preempt_enable();
152 }
153 EXPORT_SYMBOL_GPL(synchronize_rcu);
154 
155 /*
156  * Post an RCU callback to be invoked after the end of an RCU grace
157  * period.  But since we have but one CPU, that would be after any
158  * quiescent state.
159  */
160 void call_rcu(struct rcu_head *head, rcu_callback_t func)
161 {
162 	static atomic_t doublefrees;
163 	unsigned long flags;
164 
165 	if (debug_rcu_head_queue(head)) {
166 		if (atomic_inc_return(&doublefrees) < 4) {
167 			pr_err("%s(): Double-freed CB %p->%pS()!!!  ", __func__, head, head->func);
168 			mem_dump_obj(head);
169 		}
170 		return;
171 	}
172 
173 	head->func = func;
174 	head->next = NULL;
175 
176 	local_irq_save(flags);
177 	*rcu_ctrlblk.curtail = head;
178 	rcu_ctrlblk.curtail = &head->next;
179 	local_irq_restore(flags);
180 
181 	if (unlikely(is_idle_task(current))) {
182 		/* force scheduling for rcu_qs() */
183 		resched_cpu(0);
184 	}
185 }
186 EXPORT_SYMBOL_GPL(call_rcu);
187 
188 /*
189  * Store a grace-period-counter "cookie".  For more information,
190  * see the Tree RCU header comment.
191  */
192 void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp)
193 {
194 	rgosp->rgos_norm = RCU_GET_STATE_COMPLETED;
195 }
196 EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full);
197 
198 /*
199  * Return a grace-period-counter "cookie".  For more information,
200  * see the Tree RCU header comment.
201  */
202 unsigned long get_state_synchronize_rcu(void)
203 {
204 	return READ_ONCE(rcu_ctrlblk.gp_seq);
205 }
206 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
207 
208 /*
209  * Return a grace-period-counter "cookie" and ensure that a future grace
210  * period completes.  For more information, see the Tree RCU header comment.
211  */
212 unsigned long start_poll_synchronize_rcu(void)
213 {
214 	unsigned long gp_seq = get_state_synchronize_rcu();
215 
216 	if (unlikely(is_idle_task(current))) {
217 		/* force scheduling for rcu_qs() */
218 		resched_cpu(0);
219 	}
220 	return gp_seq;
221 }
222 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
223 
224 /*
225  * Return true if the grace period corresponding to oldstate has completed
226  * and false otherwise.  For more information, see the Tree RCU header
227  * comment.
228  */
229 bool poll_state_synchronize_rcu(unsigned long oldstate)
230 {
231 	return oldstate == RCU_GET_STATE_COMPLETED || READ_ONCE(rcu_ctrlblk.gp_seq) != oldstate;
232 }
233 EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
234 
235 #if IS_ENABLED(CONFIG_RCU_TORTURE_TEST)
236 unsigned long long rcutorture_gather_gp_seqs(void)
237 {
238 	return READ_ONCE(rcu_ctrlblk.gp_seq) & 0xffffULL;
239 }
240 EXPORT_SYMBOL_GPL(rcutorture_gather_gp_seqs);
241 
242 void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t len)
243 {
244 	snprintf(cp, len, "g%04llx", seqs & 0xffffULL);
245 }
246 EXPORT_SYMBOL_GPL(rcutorture_format_gp_seqs);
247 #endif
248 
249 void __init rcu_init(void)
250 {
251 	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
252 	rcu_early_boot_tests();
253 	tasks_cblist_init_generic();
254 }
255