1 /*
2 * Sleepable Read-Copy Update mechanism for mutual exclusion,
3 * tiny variant.
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, you can access it online at
17 * http://www.gnu.org/licenses/gpl-2.0.html.
18 *
19 * Copyright (C) IBM Corporation, 2017
20 *
21 * Author: Paul McKenney <paulmck@us.ibm.com>
22 */
23
24 #ifndef _LINUX_SRCU_TINY_H
25 #define _LINUX_SRCU_TINY_H
26
27 #include <linux/swait.h>
28
29 struct srcu_struct {
30 short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */
31 short srcu_idx; /* Current reader array element. */
32 u8 srcu_gp_running; /* GP workqueue running? */
33 u8 srcu_gp_waiting; /* GP waiting for readers? */
34 struct swait_queue_head srcu_wq;
35 /* Last srcu_read_unlock() wakes GP. */
36 struct rcu_head *srcu_cb_head; /* Pending callbacks: Head. */
37 struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
38 struct work_struct srcu_work; /* For driving grace periods. */
39 #ifdef CONFIG_DEBUG_LOCK_ALLOC
40 struct lockdep_map dep_map;
41 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
42 };
43
44 void srcu_drive_gp(struct work_struct *wp);
45
46 #define __SRCU_STRUCT_INIT(name, __ignored) \
47 { \
48 .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \
49 .srcu_cb_tail = &name.srcu_cb_head, \
50 .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
51 __SRCU_DEP_MAP_INIT(name) \
52 }
53
54 /*
55 * This odd _STATIC_ arrangement is needed for API compatibility with
56 * Tree SRCU, which needs some per-CPU data.
57 */
58 #define DEFINE_SRCU(name) \
59 struct srcu_struct name = __SRCU_STRUCT_INIT(name, name)
60 #define DEFINE_STATIC_SRCU(name) \
61 static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name)
62
63 void synchronize_srcu(struct srcu_struct *sp);
64
65 /*
66 * Counts the new reader in the appropriate per-CPU element of the
67 * srcu_struct. Can be invoked from irq/bh handlers, but the matching
68 * __srcu_read_unlock() must be in the same handler instance. Returns an
69 * index that must be passed to the matching srcu_read_unlock().
70 */
__srcu_read_lock(struct srcu_struct * sp)71 static inline int __srcu_read_lock(struct srcu_struct *sp)
72 {
73 int idx;
74
75 idx = READ_ONCE(sp->srcu_idx);
76 WRITE_ONCE(sp->srcu_lock_nesting[idx], sp->srcu_lock_nesting[idx] + 1);
77 return idx;
78 }
79
synchronize_srcu_expedited(struct srcu_struct * sp)80 static inline void synchronize_srcu_expedited(struct srcu_struct *sp)
81 {
82 synchronize_srcu(sp);
83 }
84
srcu_barrier(struct srcu_struct * sp)85 static inline void srcu_barrier(struct srcu_struct *sp)
86 {
87 synchronize_srcu(sp);
88 }
89
90 /* Defined here to avoid size increase for non-torture kernels. */
srcu_torture_stats_print(struct srcu_struct * sp,char * tt,char * tf)91 static inline void srcu_torture_stats_print(struct srcu_struct *sp,
92 char *tt, char *tf)
93 {
94 int idx;
95
96 idx = READ_ONCE(sp->srcu_idx) & 0x1;
97 pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd)\n",
98 tt, tf, idx,
99 READ_ONCE(sp->srcu_lock_nesting[!idx]),
100 READ_ONCE(sp->srcu_lock_nesting[idx]));
101 }
102
103 #endif
104