1 /*
2  * Sleepable Read-Copy Update mechanism for mutual exclusion
3  *
4  * This program is free software; you can redistribute it and/or modify
5  * it under the terms of the GNU General Public License as published by
6  * the Free Software Foundation; either version 2 of the License, or
7  * (at your option) any later version.
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * You should have received a copy of the GNU General Public License
15  * along with this program; if not, write to the Free Software
16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17  *
18  * Copyright (C) IBM Corporation, 2006
19  *
20  * Author: Paul McKenney <paulmck@us.ibm.com>
21  *
22  * For detailed explanation of Read-Copy Update mechanism see -
23  * 		Documentation/RCU/ *.txt
24  *
25  */
26 
27 #ifndef _LINUX_SRCU_H
28 #define _LINUX_SRCU_H
29 
30 #include <linux/mutex.h>
31 #include <linux/rcupdate.h>
32 
33 struct srcu_struct_array {
34 	int c[2];
35 };
36 
37 struct srcu_struct {
38 	int completed;
39 	struct srcu_struct_array __percpu *per_cpu_ref;
40 	struct mutex mutex;
41 #ifdef CONFIG_DEBUG_LOCK_ALLOC
42 	struct lockdep_map dep_map;
43 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
44 };
45 
46 #ifndef CONFIG_PREEMPT
47 #define srcu_barrier() barrier()
48 #else /* #ifndef CONFIG_PREEMPT */
49 #define srcu_barrier()
50 #endif /* #else #ifndef CONFIG_PREEMPT */
51 
52 #ifdef CONFIG_DEBUG_LOCK_ALLOC
53 
54 int __init_srcu_struct(struct srcu_struct *sp, const char *name,
55 		       struct lock_class_key *key);
56 
57 #define init_srcu_struct(sp) \
58 ({ \
59 	static struct lock_class_key __srcu_key; \
60 	\
61 	__init_srcu_struct((sp), #sp, &__srcu_key); \
62 })
63 
64 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
65 
66 int init_srcu_struct(struct srcu_struct *sp);
67 
68 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
69 
70 void cleanup_srcu_struct(struct srcu_struct *sp);
71 int __srcu_read_lock(struct srcu_struct *sp) __acquires(sp);
72 void __srcu_read_unlock(struct srcu_struct *sp, int idx) __releases(sp);
73 void synchronize_srcu(struct srcu_struct *sp);
74 void synchronize_srcu_expedited(struct srcu_struct *sp);
75 long srcu_batches_completed(struct srcu_struct *sp);
76 
77 #ifdef CONFIG_DEBUG_LOCK_ALLOC
78 
79 /**
80  * srcu_read_lock_held - might we be in SRCU read-side critical section?
81  *
82  * If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an SRCU
83  * read-side critical section.  In absence of CONFIG_DEBUG_LOCK_ALLOC,
84  * this assumes we are in an SRCU read-side critical section unless it can
85  * prove otherwise.
86  *
87  * Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
88  * and while lockdep is disabled.
89  *
90  * Note that if the CPU is in the idle loop from an RCU point of view
91  * (ie: that we are in the section between rcu_idle_enter() and
92  * rcu_idle_exit()) then srcu_read_lock_held() returns false even if
93  * the CPU did an srcu_read_lock().  The reason for this is that RCU
94  * ignores CPUs that are in such a section, considering these as in
95  * extended quiescent state, so such a CPU is effectively never in an
96  * RCU read-side critical section regardless of what RCU primitives it
97  * invokes.  This state of affairs is required --- we need to keep an
98  * RCU-free window in idle where the CPU may possibly enter into low
99  * power mode. This way we can notice an extended quiescent state to
100  * other CPUs that started a grace period. Otherwise we would delay any
101  * grace period as long as we run in the idle task.
102  *
103  * Similarly, we avoid claiming an SRCU read lock held if the current
104  * CPU is offline.
105  */
srcu_read_lock_held(struct srcu_struct * sp)106 static inline int srcu_read_lock_held(struct srcu_struct *sp)
107 {
108 	if (!debug_lockdep_rcu_enabled())
109 		return 1;
110 	if (rcu_is_cpu_idle())
111 		return 0;
112 	if (!rcu_lockdep_current_cpu_online())
113 		return 0;
114 	return lock_is_held(&sp->dep_map);
115 }
116 
117 #else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
118 
srcu_read_lock_held(struct srcu_struct * sp)119 static inline int srcu_read_lock_held(struct srcu_struct *sp)
120 {
121 	return 1;
122 }
123 
124 #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
125 
126 /**
127  * srcu_dereference_check - fetch SRCU-protected pointer for later dereferencing
128  * @p: the pointer to fetch and protect for later dereferencing
129  * @sp: pointer to the srcu_struct, which is used to check that we
130  *	really are in an SRCU read-side critical section.
131  * @c: condition to check for update-side use
132  *
133  * If PROVE_RCU is enabled, invoking this outside of an RCU read-side
134  * critical section will result in an RCU-lockdep splat, unless @c evaluates
135  * to 1.  The @c argument will normally be a logical expression containing
136  * lockdep_is_held() calls.
137  */
138 #define srcu_dereference_check(p, sp, c) \
139 	__rcu_dereference_check((p), srcu_read_lock_held(sp) || (c), __rcu)
140 
141 /**
142  * srcu_dereference - fetch SRCU-protected pointer for later dereferencing
143  * @p: the pointer to fetch and protect for later dereferencing
144  * @sp: pointer to the srcu_struct, which is used to check that we
145  *	really are in an SRCU read-side critical section.
146  *
147  * Makes rcu_dereference_check() do the dirty work.  If PROVE_RCU
148  * is enabled, invoking this outside of an RCU read-side critical
149  * section will result in an RCU-lockdep splat.
150  */
151 #define srcu_dereference(p, sp) srcu_dereference_check((p), (sp), 0)
152 
153 /**
154  * srcu_read_lock - register a new reader for an SRCU-protected structure.
155  * @sp: srcu_struct in which to register the new reader.
156  *
157  * Enter an SRCU read-side critical section.  Note that SRCU read-side
158  * critical sections may be nested.  However, it is illegal to
159  * call anything that waits on an SRCU grace period for the same
160  * srcu_struct, whether directly or indirectly.  Please note that
161  * one way to indirectly wait on an SRCU grace period is to acquire
162  * a mutex that is held elsewhere while calling synchronize_srcu() or
163  * synchronize_srcu_expedited().
164  *
165  * Note that srcu_read_lock() and the matching srcu_read_unlock() must
166  * occur in the same context, for example, it is illegal to invoke
167  * srcu_read_unlock() in an irq handler if the matching srcu_read_lock()
168  * was invoked in process context.
169  */
srcu_read_lock(struct srcu_struct * sp)170 static inline int srcu_read_lock(struct srcu_struct *sp) __acquires(sp)
171 {
172 	int retval = __srcu_read_lock(sp);
173 
174 	rcu_lock_acquire(&(sp)->dep_map);
175 	rcu_lockdep_assert(!rcu_is_cpu_idle(),
176 			   "srcu_read_lock() used illegally while idle");
177 	return retval;
178 }
179 
180 /**
181  * srcu_read_unlock - unregister a old reader from an SRCU-protected structure.
182  * @sp: srcu_struct in which to unregister the old reader.
183  * @idx: return value from corresponding srcu_read_lock().
184  *
185  * Exit an SRCU read-side critical section.
186  */
srcu_read_unlock(struct srcu_struct * sp,int idx)187 static inline void srcu_read_unlock(struct srcu_struct *sp, int idx)
188 	__releases(sp)
189 {
190 	rcu_lockdep_assert(!rcu_is_cpu_idle(),
191 			   "srcu_read_unlock() used illegally while idle");
192 	rcu_lock_release(&(sp)->dep_map);
193 	__srcu_read_unlock(sp, idx);
194 }
195 
196 /**
197  * srcu_read_lock_raw - register a new reader for an SRCU-protected structure.
198  * @sp: srcu_struct in which to register the new reader.
199  *
200  * Enter an SRCU read-side critical section.  Similar to srcu_read_lock(),
201  * but avoids the RCU-lockdep checking.  This means that it is legal to
202  * use srcu_read_lock_raw() in one context, for example, in an exception
203  * handler, and then have the matching srcu_read_unlock_raw() in another
204  * context, for example in the task that took the exception.
205  *
206  * However, the entire SRCU read-side critical section must reside within a
207  * single task.  For example, beware of using srcu_read_lock_raw() in
208  * a device interrupt handler and srcu_read_unlock() in the interrupted
209  * task:  This will not work if interrupts are threaded.
210  */
srcu_read_lock_raw(struct srcu_struct * sp)211 static inline int srcu_read_lock_raw(struct srcu_struct *sp)
212 {
213 	unsigned long flags;
214 	int ret;
215 
216 	local_irq_save(flags);
217 	ret =  __srcu_read_lock(sp);
218 	local_irq_restore(flags);
219 	return ret;
220 }
221 
222 /**
223  * srcu_read_unlock_raw - unregister reader from an SRCU-protected structure.
224  * @sp: srcu_struct in which to unregister the old reader.
225  * @idx: return value from corresponding srcu_read_lock_raw().
226  *
227  * Exit an SRCU read-side critical section without lockdep-RCU checking.
228  * See srcu_read_lock_raw() for more details.
229  */
srcu_read_unlock_raw(struct srcu_struct * sp,int idx)230 static inline void srcu_read_unlock_raw(struct srcu_struct *sp, int idx)
231 {
232 	unsigned long flags;
233 
234 	local_irq_save(flags);
235 	__srcu_read_unlock(sp, idx);
236 	local_irq_restore(flags);
237 }
238 
239 #endif
240