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1/*
2 * RCU segmented callback lists
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
17 *
18 * Copyright IBM Corporation, 2017
19 *
20 * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
21 */
22
23#ifndef __INCLUDE_LINUX_RCU_SEGCBLIST_H
24#define __INCLUDE_LINUX_RCU_SEGCBLIST_H
25
26/* Simple unsegmented callback lists. */
27struct rcu_cblist {
28 struct rcu_head *head;
29 struct rcu_head **tail;
30 long len;
31 long len_lazy;
32};
33
34#define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
35
36/* Complicated segmented callback lists. ;-) */
37
38/*
39 * Index values for segments in rcu_segcblist structure.
40 *
41 * The segments are as follows:
42 *
43 * [head, *tails[RCU_DONE_TAIL]):
44 * Callbacks whose grace period has elapsed, and thus can be invoked.
45 * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
46 * Callbacks waiting for the current GP from the current CPU's viewpoint.
47 * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
48 * Callbacks that arrived before the next GP started, again from
49 * the current CPU's viewpoint. These can be handled by the next GP.
50 * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
51 * Callbacks that might have arrived after the next GP started.
52 * There is some uncertainty as to when a given GP starts and
53 * ends, but a CPU knows the exact times if it is the one starting
54 * or ending the GP. Other CPUs know that the previous GP ends
55 * before the next one starts.
56 *
57 * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
58 * empty.
59 *
60 * The ->gp_seq[] array contains the grace-period number at which the
61 * corresponding segment of callbacks will be ready to invoke. A given
62 * element of this array is meaningful only when the corresponding segment
63 * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
64 * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
65 * not yet been assigned a grace-period number).
66 */
67#define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */
68#define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */
69#define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */
70#define RCU_NEXT_TAIL 3
71#define RCU_CBLIST_NSEGS 4
72
73struct rcu_segcblist {
74 struct rcu_head *head;
75 struct rcu_head **tails[RCU_CBLIST_NSEGS];
76 unsigned long gp_seq[RCU_CBLIST_NSEGS];
77 long len;
78 long len_lazy;
79};
80
81#define RCU_SEGCBLIST_INITIALIZER(n) \
82{ \
83 .head = NULL, \
84 .tails[RCU_DONE_TAIL] = &n.head, \
85 .tails[RCU_WAIT_TAIL] = &n.head, \
86 .tails[RCU_NEXT_READY_TAIL] = &n.head, \
87 .tails[RCU_NEXT_TAIL] = &n.head, \
88}
89
90#endif /* __INCLUDE_LINUX_RCU_SEGCBLIST_H */