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
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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.
67 * A note about memory barriers. Exclusive locks need to use the same
68 * memory barriers as mutexes: _acq when acquiring an exclusive lock
69 * and _rel when releasing an exclusive lock. On the other side,
70 * shared lock needs to use an _acq barrier when acquiring the lock
71 * but, since they don't update any locked data, no memory barrier is
72 * needed when releasing a shared lock.
75 #define SX_LOCK_SHARED 0x01
76 #define SX_LOCK_SHARED_WAITERS 0x02
77 #define SX_LOCK_EXCLUSIVE_WAITERS 0x04
78 #define SX_LOCK_RECURSED 0x08
79 #define SX_LOCK_FLAGMASK \
80 (SX_LOCK_SHARED | SX_LOCK_SHARED_WAITERS | \
81 SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_RECURSED)
83 #define SX_OWNER(x) ((x) & ~SX_LOCK_FLAGMASK)
84 #define SX_SHARERS_SHIFT 4
85 #define SX_SHARERS(x) (SX_OWNER(x) >> SX_SHARERS_SHIFT)
86 #define SX_SHARERS_LOCK(x) \
87 ((x) << SX_SHARERS_SHIFT | SX_LOCK_SHARED)
88 #define SX_ONE_SHARER (1 << SX_SHARERS_SHIFT)
90 #define SX_LOCK_UNLOCKED SX_SHARERS_LOCK(0)
91 #define SX_LOCK_DESTROYED \
92 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)
97 * Function prototipes. Routines that start with an underscore are not part
98 * of the public interface and are wrappered with a macro.
100 void sx_sysinit(void *arg);
101 #define sx_init(sx, desc) sx_init_flags((sx), (desc), 0)
102 void sx_init_flags(struct sx *sx, const char *description, int opts);
103 void sx_destroy(struct sx *sx);
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
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);
122 int sx_chain(struct thread *td, struct thread **ownerp);
130 #define SX_SYSINIT(name, sxa, desc) \
131 static struct sx_args name##_args = { \
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, \
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.
146 /* Acquire an exclusive lock. */
148 __sx_xlock(struct sx *sx, struct thread *td, int opts, const char *file,
151 uintptr_t tid = (uintptr_t)td;
154 if (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
155 error = _sx_xlock_hard(sx, tid, opts, file, line);
157 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE,
158 sx, 0, 0, file, line);
163 /* Release an exclusive lock. */
165 __sx_xunlock(struct sx *sx, struct thread *td, const char *file, int line)
167 uintptr_t tid = (uintptr_t)td;
169 if (!atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
170 _sx_xunlock_hard(sx, tid, file, line);
173 /* Acquire a shared lock. */
175 __sx_slock(struct sx *sx, int opts, const char *file, int line)
177 uintptr_t x = sx->sx_lock;
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);
184 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx, 0,
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
198 __sx_sunlock(struct sx *sx, const char *file, int line)
200 uintptr_t x = sx->sx_lock;
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);
208 * Public interface for lock operations.
211 #error "LOCK_DEBUG not defined, include <sys/lock.h> before <sys/sx.h>"
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)
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)
240 * Return a pointer to the owning thread if the lock is exclusively
243 #define sx_xholder(sx) \
244 ((sx)->sx_lock & SX_LOCK_SHARED ? NULL : \
245 (struct thread *)SX_OWNER((sx)->sx_lock))
247 #define sx_xlocked(sx) \
248 (((sx)->sx_lock & ~(SX_LOCK_FLAGMASK & ~SX_LOCK_SHARED)) == \
249 (uintptr_t)curthread)
251 #define sx_unlock(sx) do { \
252 if (sx_xlocked(sx)) \
258 #define sx_sleep(chan, sx, pri, wmesg, timo) \
259 _sleep((chan), &(sx)->lock_object, (pri), (wmesg), (timo))
262 * Options passed to sx_init_flags().
264 #define SX_DUPOK 0x01
265 #define SX_NOPROFILE 0x02
266 #define SX_NOWITNESS 0x04
267 #define SX_QUIET 0x08
268 #define SX_NOADAPTIVE 0x10
269 #define SX_RECURSE 0x20
272 * Options passed to sx_*lock_hard().
274 #define SX_INTERRUPTIBLE 0x40
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
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
294 #define sx_assert(sx, what) _sx_assert((sx), (what), LOCK_FILE, LOCK_LINE)
296 #define sx_assert(sx, what) (void)0
301 #endif /* !_SYS_SX_H_ */