Merge tag 'riscv-for-linus-5.18-mw0' of git://git.kernel.org/pub/scm/linux/kernel...
[linux-2.6-microblaze.git] / kernel / rcu / 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. */
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);
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 + 1);
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         unsigned long offset = (unsigned long)head->func;
89
90         rcu_lock_acquire(&rcu_callback_map);
91         if (__is_kvfree_rcu_offset(offset)) {
92                 trace_rcu_invoke_kvfree_callback("", head, offset);
93                 kvfree((void *)head - offset);
94                 rcu_lock_release(&rcu_callback_map);
95                 return true;
96         }
97
98         trace_rcu_invoke_callback("", head);
99         f = head->func;
100         WRITE_ONCE(head->func, (rcu_callback_t)0L);
101         f(head);
102         rcu_lock_release(&rcu_callback_map);
103         return false;
104 }
105
106 /* Invoke the RCU callbacks whose grace period has elapsed.  */
107 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
108 {
109         struct rcu_head *next, *list;
110         unsigned long flags;
111
112         /* Move the ready-to-invoke callbacks to a local list. */
113         local_irq_save(flags);
114         if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
115                 /* No callbacks ready, so just leave. */
116                 local_irq_restore(flags);
117                 return;
118         }
119         list = rcu_ctrlblk.rcucblist;
120         rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
121         *rcu_ctrlblk.donetail = NULL;
122         if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
123                 rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
124         rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
125         local_irq_restore(flags);
126
127         /* Invoke the callbacks on the local list. */
128         while (list) {
129                 next = list->next;
130                 prefetch(next);
131                 debug_rcu_head_unqueue(list);
132                 local_bh_disable();
133                 rcu_reclaim_tiny(list);
134                 local_bh_enable();
135                 list = next;
136         }
137 }
138
139 /*
140  * Wait for a grace period to elapse.  But it is illegal to invoke
141  * synchronize_rcu() from within an RCU read-side critical section.
142  * Therefore, any legal call to synchronize_rcu() is a quiescent
143  * state, and so on a UP system, synchronize_rcu() need do nothing.
144  * (But Lai Jiangshan points out the benefits of doing might_sleep()
145  * to reduce latency.)
146  *
147  * Cool, huh?  (Due to Josh Triplett.)
148  */
149 void synchronize_rcu(void)
150 {
151         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
152                          lock_is_held(&rcu_lock_map) ||
153                          lock_is_held(&rcu_sched_lock_map),
154                          "Illegal synchronize_rcu() in RCU read-side critical section");
155 }
156 EXPORT_SYMBOL_GPL(synchronize_rcu);
157
158 /*
159  * Post an RCU callback to be invoked after the end of an RCU grace
160  * period.  But since we have but one CPU, that would be after any
161  * quiescent state.
162  */
163 void call_rcu(struct rcu_head *head, rcu_callback_t func)
164 {
165         unsigned long flags;
166
167         debug_rcu_head_queue(head);
168         head->func = func;
169         head->next = NULL;
170
171         local_irq_save(flags);
172         *rcu_ctrlblk.curtail = head;
173         rcu_ctrlblk.curtail = &head->next;
174         local_irq_restore(flags);
175
176         if (unlikely(is_idle_task(current))) {
177                 /* force scheduling for rcu_qs() */
178                 resched_cpu(0);
179         }
180 }
181 EXPORT_SYMBOL_GPL(call_rcu);
182
183 /*
184  * Return a grace-period-counter "cookie".  For more information,
185  * see the Tree RCU header comment.
186  */
187 unsigned long get_state_synchronize_rcu(void)
188 {
189         return READ_ONCE(rcu_ctrlblk.gp_seq);
190 }
191 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
192
193 /*
194  * Return a grace-period-counter "cookie" and ensure that a future grace
195  * period completes.  For more information, see the Tree RCU header comment.
196  */
197 unsigned long start_poll_synchronize_rcu(void)
198 {
199         unsigned long gp_seq = get_state_synchronize_rcu();
200
201         if (unlikely(is_idle_task(current))) {
202                 /* force scheduling for rcu_qs() */
203                 resched_cpu(0);
204         }
205         return gp_seq;
206 }
207 EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
208
209 /*
210  * Return true if the grace period corresponding to oldstate has completed
211  * and false otherwise.  For more information, see the Tree RCU header
212  * comment.
213  */
214 bool poll_state_synchronize_rcu(unsigned long oldstate)
215 {
216         return READ_ONCE(rcu_ctrlblk.gp_seq) != oldstate;
217 }
218 EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
219
220 void __init rcu_init(void)
221 {
222         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
223         rcu_early_boot_tests();
224 }