2 * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
3 * Copyright (c) 2001 Jason Evans <jasone@freebsd.org>
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
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.
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
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35 #include <sys/_lock.h>
40 #include <sys/lock_profile.h>
41 #include <sys/lockstat.h>
42 #include <machine/atomic.h>
46 * In general, the sx locks and rwlocks use very similar algorithms.
47 * The main difference in the implementations is how threads are
48 * blocked when a lock is unavailable. For this, sx locks use sleep
49 * queues which do not support priority propagation, and rwlocks use
50 * turnstiles which do.
52 * The sx_lock field consists of several fields. The low bit
53 * indicates if the lock is locked with a shared or exclusive lock. A
54 * value of 0 indicates an exclusive lock, and a value of 1 indicates
55 * a shared lock. Bit 1 is a boolean indicating if there are any
56 * threads waiting for a shared lock. Bit 2 is a boolean indicating
57 * if there are any threads waiting for an exclusive lock. Bit 3 is a
58 * boolean indicating if an exclusive lock is recursively held. The
59 * rest of the variable's definition is dependent on the value of the
60 * first bit. For an exclusive lock, it is a pointer to the thread
61 * holding the lock, similar to the mtx_lock field of mutexes. For
62 * shared locks, it is a count of read locks that are held.
64 * When the lock is not locked by any thread, it is encoded as a
65 * shared lock with zero waiters.
68 #define SX_LOCK_SHARED 0x01
69 #define SX_LOCK_SHARED_WAITERS 0x02
70 #define SX_LOCK_EXCLUSIVE_WAITERS 0x04
71 #define SX_LOCK_RECURSED 0x08
72 #define SX_LOCK_FLAGMASK \
73 (SX_LOCK_SHARED | SX_LOCK_SHARED_WAITERS | \
74 SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_RECURSED)
76 #define SX_OWNER(x) ((x) & ~SX_LOCK_FLAGMASK)
77 #define SX_SHARERS_SHIFT 4
78 #define SX_SHARERS(x) (SX_OWNER(x) >> SX_SHARERS_SHIFT)
79 #define SX_SHARERS_LOCK(x) \
80 ((x) << SX_SHARERS_SHIFT | SX_LOCK_SHARED)
81 #define SX_ONE_SHARER (1 << SX_SHARERS_SHIFT)
83 #define SX_LOCK_UNLOCKED SX_SHARERS_LOCK(0)
84 #define SX_LOCK_DESTROYED \
85 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)
89 #define sx_recurse lock_object.lo_data
92 * Function prototipes. Routines that start with an underscore are not part
93 * of the public interface and are wrappered with a macro.
95 void sx_sysinit(void *arg);
96 #define sx_init(sx, desc) sx_init_flags((sx), (desc), 0)
97 void sx_init_flags(struct sx *sx, const char *description, int opts);
98 void sx_destroy(struct sx *sx);
99 int sx_try_slock_(struct sx *sx, const char *file, int line);
100 int sx_try_xlock_(struct sx *sx, const char *file, int line);
101 int sx_try_upgrade_(struct sx *sx, const char *file, int line);
102 void sx_downgrade_(struct sx *sx, const char *file, int line);
103 int _sx_slock(struct sx *sx, int opts, const char *file, int line);
104 int _sx_xlock(struct sx *sx, int opts, const char *file, int line);
105 void _sx_sunlock(struct sx *sx, const char *file, int line);
106 void _sx_xunlock(struct sx *sx, const char *file, int line);
107 int _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts,
108 const char *file, int line);
109 int _sx_slock_hard(struct sx *sx, int opts, const char *file, int line);
110 void _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int
112 void _sx_sunlock_hard(struct sx *sx, const char *file, int line);
113 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
114 void _sx_assert(const struct sx *sx, int what, const char *file, int line);
117 int sx_chain(struct thread *td, struct thread **ownerp);
126 #define SX_SYSINIT_FLAGS(name, sxa, desc, flags) \
127 static struct sx_args name##_args = { \
132 SYSINIT(name##_sx_sysinit, SI_SUB_LOCK, SI_ORDER_MIDDLE, \
133 sx_sysinit, &name##_args); \
134 SYSUNINIT(name##_sx_sysuninit, SI_SUB_LOCK, SI_ORDER_MIDDLE, \
137 #define SX_SYSINIT(name, sxa, desc) SX_SYSINIT_FLAGS(name, sxa, desc, 0)
140 * Full lock operations that are suitable to be inlined in non-debug kernels.
141 * If the lock can't be acquired or released trivially then the work is
142 * deferred to 'tougher' functions.
145 /* Acquire an exclusive lock. */
147 __sx_xlock(struct sx *sx, struct thread *td, int opts, const char *file,
150 uintptr_t tid = (uintptr_t)td;
153 if (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
154 error = _sx_xlock_hard(sx, tid, opts, file, line);
156 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
157 0, 0, file, line, LOCKSTAT_WRITER);
162 /* Release an exclusive lock. */
164 __sx_xunlock(struct sx *sx, struct thread *td, const char *file, int line)
166 uintptr_t tid = (uintptr_t)td;
168 if (sx->sx_recurse == 0)
169 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx,
171 if (!atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
172 _sx_xunlock_hard(sx, tid, file, line);
175 /* Acquire a shared lock. */
177 __sx_slock(struct sx *sx, int opts, const char *file, int line)
179 uintptr_t x = sx->sx_lock;
182 if (!(x & SX_LOCK_SHARED) ||
183 !atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER))
184 error = _sx_slock_hard(sx, opts, file, line);
186 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
187 0, 0, file, line, LOCKSTAT_READER);
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
200 __sx_sunlock(struct sx *sx, const char *file, int line)
202 uintptr_t x = sx->sx_lock;
204 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER);
205 if (x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS) ||
206 !atomic_cmpset_rel_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER))
207 _sx_sunlock_hard(sx, file, line);
211 * Public interface for lock operations.
214 #error "LOCK_DEBUG not defined, include <sys/lock.h> before <sys/sx.h>"
216 #if (LOCK_DEBUG > 0) || defined(SX_NOINLINE)
217 #define sx_xlock_(sx, file, line) \
218 (void)_sx_xlock((sx), 0, (file), (line))
219 #define sx_xlock_sig_(sx, file, line) \
220 _sx_xlock((sx), SX_INTERRUPTIBLE, (file), (line))
221 #define sx_xunlock_(sx, file, line) \
222 _sx_xunlock((sx), (file), (line))
223 #define sx_slock_(sx, file, line) \
224 (void)_sx_slock((sx), 0, (file), (line))
225 #define sx_slock_sig_(sx, file, line) \
226 _sx_slock((sx), SX_INTERRUPTIBLE, (file) , (line))
227 #define sx_sunlock_(sx, file, line) \
228 _sx_sunlock((sx), (file), (line))
230 #define sx_xlock_(sx, file, line) \
231 (void)__sx_xlock((sx), curthread, 0, (file), (line))
232 #define sx_xlock_sig_(sx, file, line) \
233 __sx_xlock((sx), curthread, SX_INTERRUPTIBLE, (file), (line))
234 #define sx_xunlock_(sx, file, line) \
235 __sx_xunlock((sx), curthread, (file), (line))
236 #define sx_slock_(sx, file, line) \
237 (void)__sx_slock((sx), 0, (file), (line))
238 #define sx_slock_sig_(sx, file, line) \
239 __sx_slock((sx), SX_INTERRUPTIBLE, (file), (line))
240 #define sx_sunlock_(sx, file, line) \
241 __sx_sunlock((sx), (file), (line))
242 #endif /* LOCK_DEBUG > 0 || SX_NOINLINE */
243 #define sx_try_slock(sx) sx_try_slock_((sx), LOCK_FILE, LOCK_LINE)
244 #define sx_try_xlock(sx) sx_try_xlock_((sx), LOCK_FILE, LOCK_LINE)
245 #define sx_try_upgrade(sx) sx_try_upgrade_((sx), LOCK_FILE, LOCK_LINE)
246 #define sx_downgrade(sx) sx_downgrade_((sx), LOCK_FILE, LOCK_LINE)
248 #define sx_assert_(sx, what, file, line) \
249 _sx_assert((sx), (what), (file), (line))
251 #define sx_assert_(sx, what, file, line) (void)0
254 #define sx_xlock(sx) sx_xlock_((sx), LOCK_FILE, LOCK_LINE)
255 #define sx_xlock_sig(sx) sx_xlock_sig_((sx), LOCK_FILE, LOCK_LINE)
256 #define sx_xunlock(sx) sx_xunlock_((sx), LOCK_FILE, LOCK_LINE)
257 #define sx_slock(sx) sx_slock_((sx), LOCK_FILE, LOCK_LINE)
258 #define sx_slock_sig(sx) sx_slock_sig_((sx), LOCK_FILE, LOCK_LINE)
259 #define sx_sunlock(sx) sx_sunlock_((sx), LOCK_FILE, LOCK_LINE)
260 #define sx_assert(sx, what) sx_assert_((sx), (what), __FILE__, __LINE__)
263 * Return a pointer to the owning thread if the lock is exclusively
266 #define sx_xholder(sx) \
267 ((sx)->sx_lock & SX_LOCK_SHARED ? NULL : \
268 (struct thread *)SX_OWNER((sx)->sx_lock))
270 #define sx_xlocked(sx) \
271 (((sx)->sx_lock & ~(SX_LOCK_FLAGMASK & ~SX_LOCK_SHARED)) == \
272 (uintptr_t)curthread)
274 #define sx_unlock_(sx, file, line) do { \
275 if (sx_xlocked(sx)) \
276 sx_xunlock_(sx, file, line); \
278 sx_sunlock_(sx, file, line); \
281 #define sx_unlock(sx) sx_unlock_((sx), LOCK_FILE, LOCK_LINE)
283 #define sx_sleep(chan, sx, pri, wmesg, timo) \
284 _sleep((chan), &(sx)->lock_object, (pri), (wmesg), \
285 tick_sbt * (timo), 0, C_HARDCLOCK)
288 * Options passed to sx_init_flags().
290 #define SX_DUPOK 0x01
291 #define SX_NOPROFILE 0x02
292 #define SX_NOWITNESS 0x04
293 #define SX_QUIET 0x08
294 #define SX_NOADAPTIVE 0x10
295 #define SX_RECURSE 0x20
299 * Options passed to sx_*lock_hard().
301 #define SX_INTERRUPTIBLE 0x40
303 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
304 #define SA_LOCKED LA_LOCKED
305 #define SA_SLOCKED LA_SLOCKED
306 #define SA_XLOCKED LA_XLOCKED
307 #define SA_UNLOCKED LA_UNLOCKED
308 #define SA_RECURSED LA_RECURSED
309 #define SA_NOTRECURSED LA_NOTRECURSED
311 /* Backwards compatability. */
312 #define SX_LOCKED LA_LOCKED
313 #define SX_SLOCKED LA_SLOCKED
314 #define SX_XLOCKED LA_XLOCKED
315 #define SX_UNLOCKED LA_UNLOCKED
316 #define SX_RECURSED LA_RECURSED
317 #define SX_NOTRECURSED LA_NOTRECURSED
322 #endif /* !_SYS_SX_H_ */