1 /* SPDX-License-Identifier: GPL-2.0+ */
2 /*
3 * Sleepable Read-Copy Update mechanism for mutual exclusion,
4 * tiny variant.
5 *
6 * Copyright (C) IBM Corporation, 2017
7 *
8 * Author: Paul McKenney <paulmck@linux.ibm.com>
9 */
10
11 #ifndef _LINUX_SRCU_TINY_H
12 #define _LINUX_SRCU_TINY_H
13
14 #include <linux/swait.h>
15
16 struct srcu_struct {
17 short srcu_lock_nesting[2]; /* srcu_read_lock() nesting depth. */
18 u8 srcu_gp_running; /* GP workqueue running? */
19 u8 srcu_gp_waiting; /* GP waiting for readers? */
20 unsigned long srcu_idx; /* Current reader array element in bit 0x2. */
21 unsigned long srcu_idx_max; /* Furthest future srcu_idx request. */
22 struct swait_queue_head srcu_wq;
23 /* Last srcu_read_unlock() wakes GP. */
24 struct rcu_head *srcu_cb_head; /* Pending callbacks: Head. */
25 struct rcu_head **srcu_cb_tail; /* Pending callbacks: Tail. */
26 struct work_struct srcu_work; /* For driving grace periods. */
27 #ifdef CONFIG_DEBUG_LOCK_ALLOC
28 struct lockdep_map dep_map;
29 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
30 };
31
32 void srcu_drive_gp(struct work_struct *wp);
33
34 #define __SRCU_STRUCT_INIT(name, __ignored, ___ignored) \
35 { \
36 .srcu_wq = __SWAIT_QUEUE_HEAD_INITIALIZER(name.srcu_wq), \
37 .srcu_cb_tail = &name.srcu_cb_head, \
38 .srcu_work = __WORK_INITIALIZER(name.srcu_work, srcu_drive_gp), \
39 __SRCU_DEP_MAP_INIT(name) \
40 }
41
42 /*
43 * This odd _STATIC_ arrangement is needed for API compatibility with
44 * Tree SRCU, which needs some per-CPU data.
45 */
46 #define DEFINE_SRCU(name) \
47 struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name)
48 #define DEFINE_STATIC_SRCU(name) \
49 static struct srcu_struct name = __SRCU_STRUCT_INIT(name, name, name)
50
51 // Dummy structure for srcu_notifier_head.
52 struct srcu_usage { };
53 #define __SRCU_USAGE_INIT(name) { }
54
55 void synchronize_srcu(struct srcu_struct *ssp);
56
57 /*
58 * Counts the new reader in the appropriate per-CPU element of the
59 * srcu_struct. Can be invoked from irq/bh handlers, but the matching
60 * __srcu_read_unlock() must be in the same handler instance. Returns an
61 * index that must be passed to the matching srcu_read_unlock().
62 */
63 static inline int __srcu_read_lock(struct srcu_struct *ssp)
64 {
65 int idx;
66
67 preempt_disable(); // Needed for PREEMPT_AUTO
68 idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
69 WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
70 preempt_enable();
71 return idx;
72 }
73
74 static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
75 {
76 synchronize_srcu(ssp);
77 }
78
79 static inline void srcu_barrier(struct srcu_struct *ssp)
80 {
81 synchronize_srcu(ssp);
82 }
83
84 /* Defined here to avoid size increase for non-torture kernels. */
85 static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
86 char *tt, char *tf)
87 {
88 int idx;
89
90 idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1;
91 pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd) gp: %lu->%lu\n",
92 tt, tf, idx,
93 data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
94 data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])),
95 data_race(READ_ONCE(ssp->srcu_idx)),
96 data_race(READ_ONCE(ssp->srcu_idx_max)));
97 }
98
99 #endif
100
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