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. */
21 struct rcu_cblist {
22 struct rcu_head *head;
23 struct rcu_head **tail;
24 long len;
25 long len_lazy;
26 };
27
28 #define RCU_CBLIST_INITIALIZER(n) { .head = NULL, .tail = &n.head }
29
30 /* Complicated segmented callback lists. ;-) */
31
32 /*
33 * Index values for segments in rcu_segcblist structure.
34 *
35 * The segments are as follows:
36 *
37 * [head, *tails[RCU_DONE_TAIL]):
38 * Callbacks whose grace period has elapsed, and thus can be invoked.
39 * [*tails[RCU_DONE_TAIL], *tails[RCU_WAIT_TAIL]):
40 * Callbacks waiting for the current GP from the current CPU's viewpoint.
41 * [*tails[RCU_WAIT_TAIL], *tails[RCU_NEXT_READY_TAIL]):
42 * Callbacks that arrived before the next GP started, again from
43 * the current CPU's viewpoint. These can be handled by the next GP.
44 * [*tails[RCU_NEXT_READY_TAIL], *tails[RCU_NEXT_TAIL]):
45 * Callbacks that might have arrived after the next GP started.
46 * There is some uncertainty as to when a given GP starts and
47 * ends, but a CPU knows the exact times if it is the one starting
48 * or ending the GP. Other CPUs know that the previous GP ends
49 * before the next one starts.
50 *
51 * Note that RCU_WAIT_TAIL cannot be empty unless RCU_NEXT_READY_TAIL is also
52 * empty.
53 *
54 * The ->gp_seq[] array contains the grace-period number at which the
55 * corresponding segment of callbacks will be ready to invoke. A given
56 * element of this array is meaningful only when the corresponding segment
57 * is non-empty, and it is never valid for RCU_DONE_TAIL (whose callbacks
58 * are already ready to invoke) or for RCU_NEXT_TAIL (whose callbacks have
59 * not yet been assigned a grace-period number).
60 */
61 #define RCU_DONE_TAIL 0 /* Also RCU_WAIT head. */
62 #define RCU_WAIT_TAIL 1 /* Also RCU_NEXT_READY head. */
63 #define RCU_NEXT_READY_TAIL 2 /* Also RCU_NEXT head. */
64 #define RCU_NEXT_TAIL 3
65 #define RCU_CBLIST_NSEGS 4
66
67 struct rcu_segcblist {
68 struct rcu_head *head;
69 struct rcu_head **tails[RCU_CBLIST_NSEGS];
70 unsigned long gp_seq[RCU_CBLIST_NSEGS];
71 #ifdef CONFIG_RCU_NOCB_CPU
72 atomic_long_t len;
73 #else
74 long len;
75 #endif
76 long len_lazy;
77 u8 enabled;
78 u8 offloaded;
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 */