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1/* SPDX-License-Identifier: GPL-2.0+ */
2/*
3 * RCU segmented callback lists
4 *
5 * This seemingly RCU-private file must be available to SRCU users
6 * because the size of the TREE SRCU srcu_struct structure depends
7 * on these definitions.
8 *
9 * Copyright IBM Corporation, 2017
10 *
11 * Authors: Paul E. McKenney <paulmck@linux.net.ibm.com>
12 */
13
14#ifndef __INCLUDE_LINUX_RCU_SEGCBLIST_H
15#define __INCLUDE_LINUX_RCU_SEGCBLIST_H
16
17#include <linux/types.h>
18#include <linux/atomic.h>
19
20/* Simple unsegmented callback lists. */
21struct rcu_cblist {
22 struct rcu_head *head;
23 struct rcu_head **tail;
24 long len;
25};
26
27#define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
28
29/* Complicated segmented callback lists. ;-) */
30
31/*
32 * Index values for segments in rcu_segcblist structure.
33 *
34 * The segments are as follows:
35 *
36 * [head, *tails[RCU_DONE_TAIL]):
37 * Callbacks whose grace period has elapsed, and thus can be invoked.
38 * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
39 * Callbacks waiting for the current GP from the current CPU's viewpoint.
40 * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
41 * Callbacks that arrived before the next GP started, again from
42 * the current CPU's viewpoint. These can be handled by the next GP.
43 * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
44 * Callbacks that might have arrived after the next GP started.
45 * There is some uncertainty as to when a given GP starts and
46 * ends, but a CPU knows the exact times if it is the one starting
47 * or ending the GP. Other CPUs know that the previous GP ends
48 * before the next one starts.
49 *
50 * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
51 * empty.
52 *
53 * The ->gp_seq[] array contains the grace-period number at which the
54 * corresponding segment of callbacks will be ready to invoke. A given
55 * element of this array is meaningful only when the corresponding segment
56 * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
57 * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
58 * not yet been assigned a grace-period number).
59 */
60#define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */
61#define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */
62#define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */
63#define RCU_NEXT_TAIL 3
64#define RCU_CBLIST_NSEGS 4
65
66struct rcu_segcblist {
67 struct rcu_head *head;
68 struct rcu_head **tails[RCU_CBLIST_NSEGS];
69 unsigned long gp_seq[RCU_CBLIST_NSEGS];
70#ifdef CONFIG_RCU_NOCB_CPU
71 atomic_long_t len;
72#else
73 long len;
74#endif
75 u8 enabled;
76 u8 offloaded;
77};
78
79#define RCU_SEGCBLIST_INITIALIZER(n) \
80{ \
81 .head = NULL, \
82 .tails[RCU_DONE_TAIL] = &n.head, \
83 .tails[RCU_WAIT_TAIL] = &n.head, \
84 .tails[RCU_NEXT_READY_TAIL] = &n.head, \
85 .tails[RCU_NEXT_TAIL] = &n.head, \
86}
87
88#endif /* __INCLUDE_LINUX_RCU_SEGCBLIST_H */