2 * Copyright (c) 2005 Jeffrey M. Hsu. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 * 3. Neither the name of The DragonFly Project nor the names of its
16 * contributors may be used to endorse or promote products derived
17 * from this software without specific, prior written permission.
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
21 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
22 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
23 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
24 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
25 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
26 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
27 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
28 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
29 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 #ifndef _SYS_SPINLOCK2_H_
34 #define _SYS_SPINLOCK2_H_
38 #error "This file should not be included by userland programs."
43 #include <sys/systm.h>
45 #ifndef _SYS_THREAD2_H_
46 #include <sys/thread2.h>
48 #ifndef _SYS_GLOBALDATA_H_
49 #include <sys/globaldata.h>
51 #include <machine/atomic.h>
52 #include <machine/cpufunc.h>
54 extern struct spinlock pmap_spin;
56 int spin_trylock_contested(struct spinlock *spin);
57 void _spin_lock_contested(struct spinlock *spin, const char *ident, int count);
58 void _spin_lock_shared_contested(struct spinlock *spin, const char *ident);
60 #define spin_lock(spin) _spin_lock(spin, __func__)
61 #define spin_lock_quick(spin) _spin_lock_quick(spin, __func__)
62 #define spin_lock_shared(spin) _spin_lock_shared(spin, __func__)
63 #define spin_lock_shared_quick(spin) _spin_lock_shared_quick(spin, __func__)
66 * Attempt to obtain an exclusive spinlock. Returns FALSE on failure,
69 static __inline boolean_t
70 spin_trylock(struct spinlock *spin)
72 globaldata_t gd = mycpu;
74 ++gd->gd_curthread->td_critcount;
77 if (atomic_cmpset_int(&spin->counta, 0, 1) == 0)
78 return (spin_trylock_contested(spin));
81 for (i = 0; i < SPINLOCK_DEBUG_ARRAY_SIZE; i++) {
82 if (gd->gd_curthread->td_spinlock_stack_id[i] == 0) {
83 gd->gd_curthread->td_spinlock_stack_id[i] = 1;
84 gd->gd_curthread->td_spinlock_stack[i] = spin;
85 gd->gd_curthread->td_spinlock_caller_pc[i] =
86 __builtin_return_address(0);
95 * Return TRUE if the spinlock is held (we can't tell by whom, though)
98 spin_held(struct spinlock *spin)
100 return((spin->counta & ~SPINLOCK_SHARED) != 0);
104 * Obtain an exclusive spinlock and return. It is possible for the
105 * SPINLOCK_SHARED bit to already be set, in which case the contested
106 * code is called to fix it up.
109 _spin_lock_quick(globaldata_t gd, struct spinlock *spin, const char *ident)
113 ++gd->gd_curthread->td_critcount;
117 count = atomic_fetchadd_int(&spin->counta, 1);
118 if (__predict_false(count != 0)) {
119 _spin_lock_contested(spin, ident, count);
123 for (i = 0; i < SPINLOCK_DEBUG_ARRAY_SIZE; i++) {
124 if (gd->gd_curthread->td_spinlock_stack_id[i] == 0) {
125 gd->gd_curthread->td_spinlock_stack_id[i] = 1;
126 gd->gd_curthread->td_spinlock_stack[i] = spin;
127 gd->gd_curthread->td_spinlock_caller_pc[i] =
128 __builtin_return_address(0);
136 _spin_lock(struct spinlock *spin, const char *ident)
138 _spin_lock_quick(mycpu, spin, ident);
142 * Release an exclusive spinlock. We can just do this passively, only
143 * ensuring that our spinlock count is left intact until the mutex is
147 spin_unlock_quick(globaldata_t gd, struct spinlock *spin)
151 for (i = 0; i < SPINLOCK_DEBUG_ARRAY_SIZE; i++) {
152 if ((gd->gd_curthread->td_spinlock_stack_id[i] == 1) &&
153 (gd->gd_curthread->td_spinlock_stack[i] == spin)) {
154 gd->gd_curthread->td_spinlock_stack_id[i] = 0;
155 gd->gd_curthread->td_spinlock_stack[i] = NULL;
156 gd->gd_curthread->td_spinlock_caller_pc[i] = NULL;
162 * Don't use a locked instruction here. To reduce latency we avoid
163 * reading spin->counta prior to writing to it.
166 KKASSERT(spin->counta != 0);
169 atomic_add_int(&spin->counta, -1);
172 KKASSERT(gd->gd_spinlocks > 0);
176 --gd->gd_curthread->td_critcount;
180 spin_unlock(struct spinlock *spin)
182 spin_unlock_quick(mycpu, spin);
186 * Shared spinlock. Acquire a count, if SPINLOCK_SHARED is not already
187 * set then try a trivial conversion and drop into the contested code if
188 * the trivial cocnversion fails. The SHARED bit is 'cached' when lock
189 * counts go to 0 so the critical path is typically just the fetchadd.
191 * WARNING! Due to the way exclusive conflict resolution works, we cannot
192 * just unconditionally set the SHARED bit on previous-count == 0.
193 * Doing so will interfere with the exclusive contended code.
196 _spin_lock_shared_quick(globaldata_t gd, struct spinlock *spin,
201 ++gd->gd_curthread->td_critcount;
205 counta = atomic_fetchadd_int(&spin->counta, 1);
206 if (__predict_false((counta & SPINLOCK_SHARED) == 0)) {
208 !atomic_cmpset_int(&spin->counta, 1, SPINLOCK_SHARED | 1)) {
209 _spin_lock_shared_contested(spin, ident);
214 for (i = 0; i < SPINLOCK_DEBUG_ARRAY_SIZE; i++) {
215 if (gd->gd_curthread->td_spinlock_stack_id[i] == 0) {
216 gd->gd_curthread->td_spinlock_stack_id[i] = 1;
217 gd->gd_curthread->td_spinlock_stack[i] = spin;
218 gd->gd_curthread->td_spinlock_caller_pc[i] =
219 __builtin_return_address(0);
227 * Unlock a shared lock. For convenience we allow the last transition
228 * to be to (SPINLOCK_SHARED|0), leaving the SPINLOCK_SHARED bit set
229 * with a count to 0 which will optimize the next shared lock obtained.
231 * WARNING! In order to implement shared and exclusive spinlocks, an
232 * exclusive request will convert a multiply-held shared lock
233 * to exclusive and wait for shared holders to unlock. So keep
234 * in mind that as of now the spinlock could actually be in an
238 spin_unlock_shared_quick(globaldata_t gd, struct spinlock *spin)
242 for (i = 0; i < SPINLOCK_DEBUG_ARRAY_SIZE; i++) {
243 if ((gd->gd_curthread->td_spinlock_stack_id[i] == 1) &&
244 (gd->gd_curthread->td_spinlock_stack[i] == spin)) {
245 gd->gd_curthread->td_spinlock_stack_id[i] = 0;
246 gd->gd_curthread->td_spinlock_stack[i] = NULL;
247 gd->gd_curthread->td_spinlock_caller_pc[i] = NULL;
253 KKASSERT(spin->counta != 0);
256 atomic_add_int(&spin->counta, -1);
259 KKASSERT(gd->gd_spinlocks > 0);
263 --gd->gd_curthread->td_critcount;
267 _spin_lock_shared(struct spinlock *spin, const char *ident)
269 _spin_lock_shared_quick(mycpu, spin, ident);
273 spin_unlock_shared(struct spinlock *spin)
275 spin_unlock_shared_quick(mycpu, spin);
279 spin_init(struct spinlock *spin, const char *descr __unused)
289 spin_uninit(struct spinlock *spin)
295 #endif /* _SYS_SPINLOCK2_H_ */