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 #define sx_init(sx, desc) sx_init_flags((sx), (desc), 0)
100 void sx_init_flags(struct sx *sx, const char *description, int opts);
101 void sx_destroy(struct sx *sx);
102 int _sx_slock(struct sx *sx, int opts, const char *file, int line);
103 int _sx_xlock(struct sx *sx, int opts, const char *file, int line);
104 int _sx_try_slock(struct sx *sx, const char *file, int line);
105 int _sx_try_xlock(struct sx *sx, const char *file, int line);
106 void _sx_sunlock(struct sx *sx, const char *file, int line);
107 void _sx_xunlock(struct sx *sx, const char *file, int line);
108 int _sx_try_upgrade(struct sx *sx, const char *file, int line);
109 void _sx_downgrade(struct sx *sx, const char *file, int line);
110 int _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts,
111 const char *file, int line);
112 int _sx_slock_hard(struct sx *sx, int opts, const char *file, int line);
113 void _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int
114 line);
115 void _sx_sunlock_hard(struct sx *sx, const char *file, int line);
116 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
117 void _sx_assert(struct sx *sx, int what, const char *file, int line);
118 #endif
119 #ifdef DDB
120 int sx_chain(struct thread *td, struct thread **ownerp);
121 #endif
122
123 struct sx_args {
124 struct sx *sa_sx;
125 const char *sa_desc;
126 };
127
128 #define SX_SYSINIT(name, sxa, desc) \
129 static struct sx_args name##_args = { \
130 (sxa), \
131 (desc) \
132 }; \
133 SYSINIT(name##_sx_sysinit, SI_SUB_LOCK, SI_ORDER_MIDDLE, \
134 sx_sysinit, &name##_args); \
135 SYSUNINIT(name##_sx_sysuninit, SI_SUB_LOCK, SI_ORDER_MIDDLE, \
136 sx_destroy, (sxa))
137
138 /*
139 * Full lock operations that are suitable to be inlined in non-debug kernels.
140 * If the lock can't be acquired or released trivially then the work is
141 * deferred to 'tougher' functions.
142 */
143
144 /* Acquire an exclusive lock. */
145 static __inline int
146 __sx_xlock(struct sx *sx, struct thread *td, int opts, const char *file,
147 int line)
148 {
149 uintptr_t tid = (uintptr_t)td;
150 int error = 0;
151
152 if (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
153 error = _sx_xlock_hard(sx, tid, opts, file, line);
154 else
155 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, file,
156 line);
157
158 return (error);
159 }
160
161 /* Release an exclusive lock. */
162 static __inline void
163 __sx_xunlock(struct sx *sx, struct thread *td, const char *file, int line)
164 {
165 uintptr_t tid = (uintptr_t)td;
166
167 if (!atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
168 _sx_xunlock_hard(sx, tid, file, line);
169 }
170
171 /* Acquire a shared lock. */
172 static __inline int
173 __sx_slock(struct sx *sx, int opts, const char *file, int line)
174 {
175 uintptr_t x = sx->sx_lock;
176 int error = 0;
177
178 if (!(x & SX_LOCK_SHARED) ||
179 !atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER))
180 error = _sx_slock_hard(sx, opts, file, line);
181 #ifdef LOCK_PROFILING_SHARED
182 else if (SX_SHARERS(x) == 0)
183 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, file,
184 line);
185 #endif
186
187 return (error);
188 }
189
190 /*
191 * Release a shared lock. We can just drop a single shared lock so
192 * long as we aren't trying to drop the last shared lock when other
193 * threads are waiting for an exclusive lock. This takes advantage of
194 * the fact that an unlocked lock is encoded as a shared lock with a
195 * count of 0.
196 */
197 static __inline void
198 __sx_sunlock(struct sx *sx, const char *file, int line)
199 {
200 uintptr_t x = sx->sx_lock;
201
202 if (x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS) ||
203 !atomic_cmpset_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER))
204 _sx_sunlock_hard(sx, file, line);
205 }
206
207 /*
208 * Public interface for lock operations.
209 */
210 #ifndef LOCK_DEBUG
211 #error "LOCK_DEBUG not defined, include <sys/lock.h> before <sys/sx.h>"
212 #endif
213 #if (LOCK_DEBUG > 0) || defined(SX_NOINLINE)
214 #define sx_xlock(sx) (void)_sx_xlock((sx), 0, LOCK_FILE, LOCK_LINE)
215 #define sx_xlock_sig(sx) \
216 _sx_xlock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
217 #define sx_xunlock(sx) _sx_xunlock((sx), LOCK_FILE, LOCK_LINE)
218 #define sx_slock(sx) (void)_sx_slock((sx), 0, LOCK_FILE, LOCK_LINE)
219 #define sx_slock_sig(sx) \
220 _sx_slock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
221 #define sx_sunlock(sx) _sx_sunlock((sx), LOCK_FILE, LOCK_LINE)
222 #else
223 #define sx_xlock(sx) \
224 (void)__sx_xlock((sx), curthread, 0, LOCK_FILE, LOCK_LINE)
225 #define sx_xlock_sig(sx) \
226 __sx_xlock((sx), curthread, SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
227 #define sx_xunlock(sx) \
228 __sx_xunlock((sx), curthread, LOCK_FILE, LOCK_LINE)
229 #define sx_slock(sx) (void)__sx_slock((sx), 0, LOCK_FILE, LOCK_LINE)
230 #define sx_slock_sig(sx) \
231 __sx_slock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE)
232 #define sx_sunlock(sx) __sx_sunlock((sx), LOCK_FILE, LOCK_LINE)
233 #endif /* LOCK_DEBUG > 0 || SX_NOINLINE */
234 #define sx_try_slock(sx) _sx_try_slock((sx), LOCK_FILE, LOCK_LINE)
235 #define sx_try_xlock(sx) _sx_try_xlock((sx), LOCK_FILE, LOCK_LINE)
236 #define sx_try_upgrade(sx) _sx_try_upgrade((sx), LOCK_FILE, LOCK_LINE)
237 #define sx_downgrade(sx) _sx_downgrade((sx), LOCK_FILE, LOCK_LINE)
238
239 /*
240 * Return a pointer to the owning thread if the lock is exclusively
241 * locked.
242 */
243 #define sx_xholder(sx) \
244 ((sx)->sx_lock & SX_LOCK_SHARED ? NULL : \
245 (struct thread *)SX_OWNER((sx)->sx_lock))
246
247 #define sx_xlocked(sx) \
248 (((sx)->sx_lock & ~(SX_LOCK_FLAGMASK & ~SX_LOCK_SHARED)) == \
249 (uintptr_t)curthread)
250
251 #define sx_unlock(sx) do { \
252 if (sx_xlocked(sx)) \
253 sx_xunlock(sx); \
254 else \
255 sx_sunlock(sx); \
256 } while (0)
257
258 #define sx_sleep(chan, sx, pri, wmesg, timo) \
259 _sleep((chan), &(sx)->lock_object, (pri), (wmesg), (timo))
260
261 /*
262 * Options passed to sx_init_flags().
263 */
264 #define SX_DUPOK 0x01
265 #define SX_NOPROFILE 0x02
266 #define SX_NOWITNESS 0x04
267 #define SX_QUIET 0x08
268 #define SX_ADAPTIVESPIN 0x10
269 #define SX_RECURSE 0x20
270
271 /*
272 * Options passed to sx_*lock_hard().
273 */
274 #define SX_INTERRUPTIBLE 0x40
275
276 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
277 #define SA_LOCKED LA_LOCKED
278 #define SA_SLOCKED LA_SLOCKED
279 #define SA_XLOCKED LA_XLOCKED
280 #define SA_UNLOCKED LA_UNLOCKED
281 #define SA_RECURSED LA_RECURSED
282 #define SA_NOTRECURSED LA_NOTRECURSED
283
284 /* Backwards compatability. */
285 #define SX_LOCKED LA_LOCKED
286 #define SX_SLOCKED LA_SLOCKED
287 #define SX_XLOCKED LA_XLOCKED
288 #define SX_UNLOCKED LA_UNLOCKED
289 #define SX_RECURSED LA_RECURSED
290 #define SX_NOTRECURSED LA_NOTRECURSED
291 #endif
292
293 #ifdef INVARIANTS
294 #define sx_assert(sx, what) _sx_assert((sx), (what), LOCK_FILE, LOCK_LINE)
295 #else
296 #define sx_assert(sx, what)
297 #endif
298
299 #endif /* _KERNEL */
300
301 #endif /* !_SYS_SX_H_ */
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