mutex.h revision 1.6 
1/*	$NetBSD: mutex.h,v 1.6 2007/11/21 10:19:08 yamt Exp $	*/
2
3/*-
4 * Copyright (c) 2002, 2007 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Jason R. Thorpe and Andrew Doran.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 3. All advertising materials mentioning features or use of this software
19 *    must display the following acknowledgement:
20 *	This product includes software developed by the NetBSD
21 *	Foundation, Inc. and its contributors.
22 * 4. Neither the name of The NetBSD Foundation nor the names of its
23 *    contributors may be used to endorse or promote products derived
24 *    from this software without specific prior written permission.
25 *
26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
29 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
36 * POSSIBILITY OF SUCH DAMAGE.
37 */
38
39#ifndef _SPARC_MUTEX_H_
40#define	_SPARC_MUTEX_H_
41
42/*
43 * There sparc mutex implementation is troublesome, because sparc (v7 and
44 * v8) lacks a compare-and-set operation, yet there are many SMP sparc
45 * machines in circulation.  SMP for spin mutexes is easy - we don't need
46 * to know who owns the lock.  For adaptive mutexes, we need an aditional
47 * interlock.
48 *
49 * The locked byte set by the sparc 'ldstub' instruction is 0xff.  sparc
50 * kernels are always loaded above 0xe0000000, and the low 5 bits of any
51 * "struct lwp *" are always zero.  So, to record the lock owner, we only
52 * need 23 bits of space.  mtxa_owner contains the mutex owner's address
53 * shifted right by 5: the top three bits of which will always be 0xe,
54 * overlapping with the interlock at the top byte, which is always 0xff
55 * when the mutex is held.
56 *
57 * For a mutex acquisition, the owner field is set in two steps: first,
58 * acquire the interlock (top byte), and second OR in the owner's address.
59 * Once the owner field is non zero, it will appear that the mutex is held,
60 * by which LWP it does not matter: other LWPs competing for the lock will
61 * fall through to mutex_vector_enter(), and either spin or sleep.
62 *
63 * As a result there is no space for a waiters bit in the owner field.  No
64 * problem, because it would be hard to synchronise using one without a CAS
65 * operation.  Note that in order to do unlocked release of adaptive
66 * mutexes, we need the effect of MUTEX_SET_WAITERS() to be immediatley
67 * visible on the bus.  So, adaptive mutexes share the spin lock byte with
68 * spin mutexes (set with ldstub), but it is not treated as a lock in its
69 * own right, rather as a flag that can be atomically set or cleared.
70 *
71 * When releasing an adaptive mutex, we first clear the owners field, and
72 * then check to see if the waiters byte is set.  This ensures that there
73 * will always be someone to wake any sleeping waiters up (even it the mutex
74 * is acquired immediately after we release it, or if we are preempted
75 * immediatley after clearing the owners field).  The setting or clearing of
76 * the waiters byte is serialized by the turnstile chain lock associated
77 * with the mutex.
78 *
79 * See comments in kern_mutex.c about releasing adaptive mutexes without
80 * an interlocking step.
81 */
82
83#ifndef __MUTEX_PRIVATE
84
85struct kmutex {
86	uintptr_t	mtx_pad1;
87	uint32_t	mtx_pad2;
88};
89
90#else	/* __MUTEX_PRIVATE */
91
92struct kmutex {
93	union {
94		/* Adaptive mutex */
95		volatile uintptr_t	mtxu_owner;		/* 0-3 */
96		__cpu_simple_lock_t	mtxu_interlock;		/* 0 */
97
98		/* Spin mutex. */
99		struct {
100			uint8_t			mtxs_dummy;	/* 0 */
101			uint8_t			mtxs_unused1;	/* 1 */
102			ipl_cookie_t		mtxs_ipl;	/* 2 */
103			uint8_t			mtxs_unused2;	/* 3 */
104		} s;
105	} u;
106	__cpu_simple_lock_t	mtx_lock;			/* 4 */
107	uint8_t			mtx_dodebug;			/* 5 */
108	uint8_t			mtx_isspin;			/* 6 */
109	uint8_t			mtx_pad[1];			/* 7 */
110};
111
112#define	__HAVE_MUTEX_STUBS	1
113#if 0 /* does not work for MP yet */
114#define	__HAVE_SPIN_MUTEX_STUBS	1
115#endif
116
117#define	mtx_owner	u.mtxu_owner
118#define	mtx_interlock	u.mtxu_interlock
119#define	mtx_dummy	u.s.mtxs_dummy
120#define	mtx_ipl		u.s.mtxs_ipl
121
122static inline uintptr_t
123MUTEX_OWNER(uintptr_t owner)
124{
125	return owner << 5;
126}
127
128static inline int
129MUTEX_OWNED(uintptr_t owner)
130{
131	return owner != 0;
132}
133
134static inline int
135MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner)
136{
137	(void)__cpu_simple_lock_try(&mtx->mtx_lock);
138 	return mtx->mtx_owner != 0;
139}
140
141static inline int
142MUTEX_HAS_WAITERS(volatile kmutex_t *mtx)
143{
144	if (mtx->mtx_owner == 0)
145		return 0;
146	return mtx->mtx_lock == __SIMPLELOCK_LOCKED;
147}
148
149static inline void
150MUTEX_INITIALIZE_SPIN(kmutex_t *mtx, bool dodebug, int ipl)
151{
152	mtx->mtx_dodebug = dodebug;
153	mtx->mtx_isspin = 1;
154	mtx->mtx_ipl = makeiplcookie(ipl);
155	mtx->mtx_interlock = __SIMPLELOCK_LOCKED;
156	__cpu_simple_lock_init(&mtx->mtx_lock);
157}
158
159static inline void
160MUTEX_INITIALIZE_ADAPTIVE(kmutex_t *mtx, bool dodebug)
161{
162	mtx->mtx_dodebug = dodebug;
163	mtx->mtx_isspin = 0;
164	__cpu_simple_lock_init(&mtx->mtx_lock);
165}
166
167static inline void
168MUTEX_DESTROY(kmutex_t *mtx)
169{
170	mtx->mtx_owner = (uintptr_t)-1L;
171}
172
173static inline bool
174MUTEX_DEBUG_P(kmutex_t *mtx)
175{
176	return mtx->mtx_dodebug != 0;
177}
178
179static inline int
180MUTEX_SPIN_P(volatile kmutex_t *mtx)
181{
182	return mtx->mtx_isspin != 0;
183}
184
185static inline int
186MUTEX_ADAPTIVE_P(volatile kmutex_t *mtx)
187{
188	return mtx->mtx_isspin == 0;
189}
190
191static inline int
192MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
193{
194	if (!__cpu_simple_lock_try(&mtx->mtx_interlock))
195		return 0;
196	mtx->mtx_owner = (curthread >> 5) | 0xf8000000;
197	return 1;
198}
199
200static inline void
201MUTEX_RELEASE(kmutex_t *mtx)
202{
203	mtx->mtx_owner = 0;
204	__cpu_simple_unlock(&mtx->mtx_lock);
205}
206
207static inline void
208MUTEX_CLEAR_WAITERS(kmutex_t *mtx)
209{
210	__cpu_simple_unlock(&mtx->mtx_lock);
211}
212
213#endif	/* __MUTEX_PRIVATE */
214
215#endif /* _SPARC_MUTEX_H_ */
216