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  */
__srcu_read_lock(struct srcu_struct * ssp)63 static inline int __srcu_read_lock(struct srcu_struct *ssp)
64 {
65 	int idx;
66 
67 	idx = ((READ_ONCE(ssp->srcu_idx) + 1) & 0x2) >> 1;
68 	WRITE_ONCE(ssp->srcu_lock_nesting[idx], READ_ONCE(ssp->srcu_lock_nesting[idx]) + 1);
69 	return idx;
70 }
71 
synchronize_srcu_expedited(struct srcu_struct * ssp)72 static inline void synchronize_srcu_expedited(struct srcu_struct *ssp)
73 {
74 	synchronize_srcu(ssp);
75 }
76 
srcu_barrier(struct srcu_struct * ssp)77 static inline void srcu_barrier(struct srcu_struct *ssp)
78 {
79 	synchronize_srcu(ssp);
80 }
81 
82 /* Defined here to avoid size increase for non-torture kernels. */
srcu_torture_stats_print(struct srcu_struct * ssp,char * tt,char * tf)83 static inline void srcu_torture_stats_print(struct srcu_struct *ssp,
84 					    char *tt, char *tf)
85 {
86 	int idx;
87 
88 	idx = ((data_race(READ_ONCE(ssp->srcu_idx)) + 1) & 0x2) >> 1;
89 	pr_alert("%s%s Tiny SRCU per-CPU(idx=%d): (%hd,%hd) gp: %lu->%lu\n",
90 		 tt, tf, idx,
91 		 data_race(READ_ONCE(ssp->srcu_lock_nesting[!idx])),
92 		 data_race(READ_ONCE(ssp->srcu_lock_nesting[idx])),
93 		 data_race(READ_ONCE(ssp->srcu_idx)),
94 		 data_race(READ_ONCE(ssp->srcu_idx_max)));
95 }
96 
97 #endif
98