1 /* SPDX-License-Identifier: GPL-2.0+ */
2 /*
3  * RCU-based infrastructure for lightweight reader-writer locking
4  *
5  * Copyright (c) 2015, Red Hat, Inc.
6  *
7  * Author: Oleg Nesterov <oleg@redhat.com>
8  */
9 
10 #ifndef _LINUX_RCU_SYNC_H_
11 #define _LINUX_RCU_SYNC_H_
12 
13 #include <linux/wait.h>
14 #include <linux/rcupdate.h>
15 
16 /* Structure to mediate between updaters and fastpath-using readers.  */
17 struct rcu_sync {
18 	int			gp_state;
19 	int			gp_count;
20 	wait_queue_head_t	gp_wait;
21 
22 	struct rcu_head		cb_head;
23 };
24 
25 /**
26  * rcu_sync_is_idle() - Are readers permitted to use their fastpaths?
27  * @rsp: Pointer to rcu_sync structure to use for synchronization
28  *
29  * Returns true if readers are permitted to use their fastpaths.  Must be
30  * invoked within some flavor of RCU read-side critical section.
31  */
rcu_sync_is_idle(struct rcu_sync * rsp)32 static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
33 {
34 	RCU_LOCKDEP_WARN(!rcu_read_lock_any_held(),
35 			 "suspicious rcu_sync_is_idle() usage");
36 	return !READ_ONCE(rsp->gp_state); /* GP_IDLE */
37 }
38 
39 extern void rcu_sync_init(struct rcu_sync *);
40 extern void rcu_sync_enter_start(struct rcu_sync *);
41 extern void rcu_sync_enter(struct rcu_sync *);
42 extern void rcu_sync_exit(struct rcu_sync *);
43 extern void rcu_sync_dtor(struct rcu_sync *);
44 
45 #define __RCU_SYNC_INITIALIZER(name) {					\
46 		.gp_state = 0,						\
47 		.gp_count = 0,						\
48 		.gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait),	\
49 	}
50 
51 #define	DEFINE_RCU_SYNC(name)	\
52 	struct rcu_sync name = __RCU_SYNC_INITIALIZER(name)
53 
54 #endif /* _LINUX_RCU_SYNC_H_ */
55