FreeBSD/Linux Kernel Cross Reference
sys/sys/sx.h
1 /*-
2 * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
3 * Copyright (c) 2001 Jason Evans <jasone@freebsd.org>
4 * All rights reserved.
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice(s), this list of conditions and the following disclaimer as
11 * the first lines of this file unmodified other than the possible
12 * addition of one or more copyright notices.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice(s), this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
18 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
19 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
20 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
21 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
22 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
23 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
24 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
27 * DAMAGE.
28 *
29 * $FreeBSD$
30 */
31
32 #ifndef _SYS_SX_H_
33 #define _SYS_SX_H_
34
35 #include <sys/_lock.h>
36 #include <sys/_sx.h>
37 #include <sys/lock_profile.h>
38
39 #ifdef _KERNEL
40 #include <machine/atomic.h>
41 #endif
42
43 /*
44 * In general, the sx locks and rwlocks use very similar algorithms.
45 * The main difference in the implementations is how threads are
46 * blocked when a lock is unavailable. For this, sx locks use sleep
47 * queues which do not support priority propagation, and rwlocks use
48 * turnstiles which do.
49 *
50 * The sx_lock field consists of several fields. The low bit
51 * indicates if the lock is locked with a shared or exclusive lock. A
52 * value of 0 indicates an exclusive lock, and a value of 1 indicates
53 * a shared lock. Bit 1 is a boolean indicating if there are any
54 * threads waiting for a shared lock. Bit 2 is a boolean indicating
55 * if there are any threads waiting for an exclusive lock. Bit 3 is a
56 * boolean indicating if an exclusive lock is recursively held. The
57 * rest of the variable's definition is dependent on the value of the
58 * first bit. For an exclusive lock, it is a pointer to the thread
59 * holding the lock, similar to the mtx_lock field of mutexes. For
60 * shared locks, it is a count of read locks that are held.
61 *
62 * When the lock is not locked by any thread, it is encoded as a
63 * shared lock with zero waiters.
64 *
65 * A note about memory barriers. Exclusive locks need to use the same
66 * memory barriers as mutexes: _acq when acquiring an exclusive lock
67 * and _rel when releasing an exclusive lock. On the other side,
68 * shared lock needs to use an _acq barrier when acquiring the lock
69 * but, since they don't update any locked data, no memory barrier is
70 * needed when releasing a shared lock.
71 */
72
73 #define SX_LOCK_SHARED 0x01
74 #define SX_LOCK_SHARED_WAITERS 0x02
75 #define SX_LOCK_EXCLUSIVE_WAITERS 0x04
76 #define SX_LOCK_RECURSED 0x08
77 #define SX_LOCK_FLAGMASK \
78 (SX_LOCK_SHARED | SX_LOCK_SHARED_WAITERS | \
79 SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_RECURSED)
80
81 #define SX_OWNER(x) ((x) & ~SX_LOCK_FLAGMASK)
82 #define SX_SHARERS_SHIFT 4
83 #define SX_SHARERS(x) (SX_OWNER(x) >> SX_SHARERS_SHIFT)
84 #define SX_SHARERS_LOCK(x) \
85 ((x) << SX_SHARERS_SHIFT | SX_LOCK_SHARED)
86 #define SX_ONE_SHARER (1 << SX_SHARERS_SHIFT)
87
88 #define SX_LOCK_UNLOCKED SX_SHARERS_LOCK(0)
89 #define SX_LOCK_DESTROYED \
90 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)
91
92 #ifdef _KERNEL
93
94 /*
95 * Function prototipes. Routines that start with an underscore are not part
96 * of the public interface and are wrappered with a macro.
97 */
98 void sx_sysinit(void *arg);
99 void sx_init(struct sx *sx, const char *description);
100 void sx_init_flags(struct sx *sx, const char *description, int opts);
101 void sx_destroy(struct sx *sx);
102 int sx_sleep(void *ident, struct sx *sx, int priority, const char *wmesg,
103 int timo);
104 int _sx_slock(struct sx *sx, int opts, const char *file, int line);
105 int _sx_xlock(struct sx *sx, int opts, const char *file, int line);
106 int _sx_try_slock(struct sx *sx, const char *file, int line);
107 int _sx_try_xlock(struct sx *sx, const char *file, int line);
108 void _sx_sunlock(struct sx *sx, const char *file, int line);
109 void _sx_xunlock(struct sx *sx, const char *file, int line);
110 int _sx_try_upgrade(struct sx *sx, const char *file, int line);
111 void _sx_downgrade(struct sx *sx, const char *file, int line);
112 int _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts,
113 const char *file, int line);
114 int _sx_slock_hard(struct sx *sx, int opts, const char *file, int line);
115 void _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int
116 line);
117 void _sx_sunlock_hard(struct sx *sx, const char *file, int line);
118 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
119 void _sx_assert(struct sx *sx, int what, const char *file, int line);
120 #endif
121 #ifdef DDB
122 int sx_chain(struct thread *td, struct thread **ownerp);
123 #endif
124
125 struct sx_args {
126 struct sx *sa_sx;
127 const char *sa_desc;
128 };
129
130 #define SX_SYSINIT(name, sxa, desc) \
131 static struct sx_args name##_args = { \
132 (sxa), \
133 (desc) \
134 }; \
135 SYSINIT(name##_sx_sysinit, SI_SUB_LOCK, SI_ORDER_MIDDLE, \
136 sx_sysinit, &name##_args); \
137 SYSUNINIT(name##_sx_sysuninit, SI_SUB_LOCK, SI_ORDER_MIDDLE, \
138 sx_destroy, (sxa))
139
140 /*
141 * Full lock operations that are suitable to be inlined in non-debug kernels.
142 * If the lock can't be acquired or released trivially then the work is
143 * deferred to 'tougher' functions.
144 */
145
146 /* Acquire an exclusive lock. */
147 static __inline int
148 __sx_xlock(struct sx *sx, struct thread *td, int opts, const char *file,
149 int line)
150 {
151 uintptr_t tid = (uintptr_t)td;
152 int error = 0;
153
154 if (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
155 error = _sx_xlock_hard(sx, tid, opts, file, line);
156 else
157 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, file,
158 line);
159
160 return (error);
161 }
162
163 /* Release an exclusive lock. */
164 static __inline void
165 __sx_xunlock(struct sx *sx, struct thread *td, const char *file, int line)
166 {
167 uintptr_t tid = (uintptr_t)td;
168
169 if (!atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
170 _sx_xunlock_hard(sx, tid, file, line);
171 }
172
173 /* Acquire a shared lock. */
174 static __inline int
175 __sx_slock(struct sx *sx, int opts, const char *file, int line)
176 {
177 uintptr_t x = sx->sx_lock;
178 int error = 0;
179
180 if (!(x & SX_LOCK_SHARED) ||
181 !atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER))
182 error = _sx_slock_hard(sx, opts, file, line);
183 #ifdef LOCK_PROFILING_SHARED
184 else if (SX_SHARERS(x) == 0)
185 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, file,
186 line);
187 #endif
188
189 return (error);
190 }
191
192 /*
193 * Release a shared lock. We can just drop a single shared lock so
194 * long as we aren't trying to drop the last shared lock when other
195 * threads are waiting for an exclusive lock. This takes advantage of
196 * the fact that an unlocked lock is encoded as a shared lock with a
197 * count of 0.
198 */
199 static __inline void
200 __sx_sunlock(struct sx *sx, const char *file, int line)
201 {
202 uintptr_t x = sx->sx_lock;
203
204 if (x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS) ||
205 !atomic_cmpset_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER))
206 _sx_sunlock_hard(sx, file, line);
207 }
208
209 /*
210 * Public interface for lock operations.
211 */
212 #ifndef LOCK_DEBUG
213 #error "LOCK_DEBUG not defined, include <sys/lock.h> before <sys/sx.h>"
214 #endif
215 #if (LOCK_DEBUG > 0) || defined(SX_NOINLINE)
216 #define sx_xlock(sx) (void)_sx_xlock((sx), 0, LOCK_FILE, LOCK_LINE)
217 #define sx_xlock_sig(sx) \
218 _sx_xlock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
219 #define sx_xunlock(sx) _sx_xunlock((sx), LOCK_FILE, LOCK_LINE)
220 #define sx_slock(sx) (void)_sx_slock((sx), 0, LOCK_FILE, LOCK_LINE)
221 #define sx_slock_sig(sx) \
222 _sx_slock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
223 #define sx_sunlock(sx) _sx_sunlock((sx), LOCK_FILE, LOCK_LINE)
224 #else
225 #define sx_xlock(sx) \
226 (void)__sx_xlock((sx), curthread, 0, LOCK_FILE, LOCK_LINE)
227 #define sx_xlock_sig(sx) \
228 __sx_xlock((sx), curthread, SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
229 #define sx_xunlock(sx) \
230 __sx_xunlock((sx), curthread, LOCK_FILE, LOCK_LINE)
231 #define sx_slock(sx) (void)__sx_slock((sx), 0, LOCK_FILE, LOCK_LINE)
232 #define sx_slock_sig(sx) \
233 __sx_slock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
234 #define sx_sunlock(sx) __sx_sunlock((sx), LOCK_FILE, LOCK_LINE)
235 #endif /* LOCK_DEBUG > 0 || SX_NOINLINE */
236 #define sx_try_slock(sx) _sx_try_slock((sx), LOCK_FILE, LOCK_LINE)
237 #define sx_try_xlock(sx) _sx_try_xlock((sx), LOCK_FILE, LOCK_LINE)
238 #define sx_try_upgrade(sx) _sx_try_upgrade((sx), LOCK_FILE, LOCK_LINE)
239 #define sx_downgrade(sx) _sx_downgrade((sx), LOCK_FILE, LOCK_LINE)
240
241 /*
242 * Return a pointer to the owning thread if the lock is exclusively
243 * locked.
244 */
245 #define sx_xholder(sx) \
246 ((sx)->sx_lock & SX_LOCK_SHARED ? NULL : \
247 (struct thread *)SX_OWNER((sx)->sx_lock))
248
249 #define sx_xlocked(sx) \
250 (((sx)->sx_lock & ~(SX_LOCK_FLAGMASK & ~SX_LOCK_SHARED)) == \
251 (uintptr_t)curthread)
252
253 #define sx_unlock(sx) do { \
254 if (sx_xlocked(sx)) \
255 sx_xunlock(sx); \
256 else \
257 sx_sunlock(sx); \
258 } while (0)
259
260 /*
261 * Options passed to sx_init_flags().
262 */
263 #define SX_DUPOK 0x01
264 #define SX_NOPROFILE 0x02
265 #define SX_NOWITNESS 0x04
266 #define SX_QUIET 0x08
267 #define SX_ADAPTIVESPIN 0x10
268 #define SX_RECURSE 0x20
269
270 /*
271 * Options passed to sx_*lock_hard().
272 */
273 #define SX_INTERRUPTIBLE 0x40
274
275 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
276 #define SA_LOCKED LA_LOCKED
277 #define SA_SLOCKED LA_SLOCKED
278 #define SA_XLOCKED LA_XLOCKED
279 #define SA_UNLOCKED LA_UNLOCKED
280 #define SA_RECURSED LA_RECURSED
281 #define SA_NOTRECURSED LA_NOTRECURSED
282
283 /* Backwards compatability. */
284 #define SX_LOCKED LA_LOCKED
285 #define SX_SLOCKED LA_SLOCKED
286 #define SX_XLOCKED LA_XLOCKED
287 #define SX_UNLOCKED LA_UNLOCKED
288 #define SX_RECURSED LA_RECURSED
289 #define SX_NOTRECURSED LA_NOTRECURSED
290 #endif
291
292 #ifdef INVARIANTS
293 #define sx_assert(sx, what) _sx_assert((sx), (what), LOCK_FILE, LOCK_LINE)
294 #else
295 #define sx_assert(sx, what)
296 #endif
297
298 #endif /* _KERNEL */
299
300 #endif /* !_SYS_SX_H_ */
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