mutex.h revision 1.7 
1/*	$NetBSD: mutex.h,v 1.7 2008/01/02 11:48:28 ad 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
92#include <machine/lock.h>
93
94struct kmutex {
95	union {
96		/* Adaptive mutex */
97		volatile uintptr_t	mtxu_owner;		/* 0-3 */
98		__cpu_simple_lock_t	mtxu_interlock;		/* 0 */
99
100		/* Spin mutex. */
101		struct {
102			uint8_t			mtxs_dummy;	/* 0 */
103			uint8_t			mtxs_unused1;	/* 1 */
104			ipl_cookie_t		mtxs_ipl;	/* 2 */
105			uint8_t			mtxs_unused2;	/* 3 */
106		} s;
107	} u;
108	__cpu_simple_lock_t	mtx_lock;			/* 4 */
109	uint8_t			mtx_dodebug;			/* 5 */
110	uint8_t			mtx_isspin;			/* 6 */
111	uint8_t			mtx_pad[1];			/* 7 */
112};
113
114#define	__HAVE_MUTEX_STUBS	1
115#if 0 /* does not work for MP yet */
116#define	__HAVE_SPIN_MUTEX_STUBS	1
117#endif
118
119#define	mtx_owner	u.mtxu_owner
120#define	mtx_interlock	u.mtxu_interlock
121#define	mtx_dummy	u.s.mtxs_dummy
122#define	mtx_ipl		u.s.mtxs_ipl
123
124static inline uintptr_t
125MUTEX_OWNER(uintptr_t owner)
126{
127	return owner << 5;
128}
129
130static inline int
131MUTEX_OWNED(uintptr_t owner)
132{
133	return owner != 0;
134}
135
136static inline int
137MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner)
138{
139	(void)__cpu_simple_lock_try(&mtx->mtx_lock);
140 	return mtx->mtx_owner != 0;
141}
142
143static inline int
144MUTEX_HAS_WAITERS(volatile kmutex_t *mtx)
145{
146	if (mtx->mtx_owner == 0)
147		return 0;
148	return mtx->mtx_lock == __SIMPLELOCK_LOCKED;
149}
150
151static inline void
152MUTEX_INITIALIZE_SPIN(kmutex_t *mtx, bool dodebug, int ipl)
153{
154	mtx->mtx_dodebug = dodebug;
155	mtx->mtx_isspin = 1;
156	mtx->mtx_ipl = makeiplcookie(ipl);
157	mtx->mtx_interlock = __SIMPLELOCK_LOCKED;
158	__cpu_simple_lock_init(&mtx->mtx_lock);
159}
160
161static inline void
162MUTEX_INITIALIZE_ADAPTIVE(kmutex_t *mtx, bool dodebug)
163{
164	mtx->mtx_dodebug = dodebug;
165	mtx->mtx_isspin = 0;
166	__cpu_simple_lock_init(&mtx->mtx_lock);
167}
168
169static inline void
170MUTEX_DESTROY(kmutex_t *mtx)
171{
172	mtx->mtx_owner = (uintptr_t)-1L;
173}
174
175static inline bool
176MUTEX_DEBUG_P(kmutex_t *mtx)
177{
178	return mtx->mtx_dodebug != 0;
179}
180
181static inline int
182MUTEX_SPIN_P(volatile kmutex_t *mtx)
183{
184	return mtx->mtx_isspin != 0;
185}
186
187static inline int
188MUTEX_ADAPTIVE_P(volatile kmutex_t *mtx)
189{
190	return mtx->mtx_isspin == 0;
191}
192
193static inline int
194MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
195{
196	if (!__cpu_simple_lock_try(&mtx->mtx_interlock))
197		return 0;
198	mtx->mtx_owner = (curthread >> 5) | 0xf8000000;
199	return 1;
200}
201
202static inline void
203MUTEX_RELEASE(kmutex_t *mtx)
204{
205	mtx->mtx_owner = 0;
206	__cpu_simple_unlock(&mtx->mtx_lock);
207}
208
209static inline void
210MUTEX_CLEAR_WAITERS(kmutex_t *mtx)
211{
212	__cpu_simple_unlock(&mtx->mtx_lock);
213}
214
215#endif	/* __MUTEX_PRIVATE */
216
217#endif /* _SPARC_MUTEX_H_ */
218