mutex.h revision 1.9 
1/*	$NetBSD: mutex.h,v 1.9 2007/11/21 10:19:09 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 _VAX_MUTEX_H_
40#define	_VAX_MUTEX_H_
41
42/*
43 * The VAX mutex implementation is troublesome, because the VAX architecture
44 * lacks a compare-and-set operation, yet there are many SMP VAX
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.  However, since we know that owners will be kernel addresses
48 * and all kernel addresses have the high bit set, we can use the high bit
49 * as an interlock.
50 *
51 * So we test the high bit with BBSSI and if clear
52 * kernels are always loaded above 0xe0000000, and the low 5 bits of any
53 * "struct lwp *" are always zero.  So, to record the lock owner, we only
54 * need 23 bits of space.  mtxa_owner contains the mutex owner's address
55 * shifted right by 5: the top three bits of which will always be 0xe,
56 * overlapping with the interlock at the top byte, which is always 0xff
57 * when the mutex is held.
58 *
59 * For a mutex acquisition, the owner field is set in two steps: first,
60 * acquire the interlock (top bit), and second OR in the owner's address.
61 * Once the owner field is non zero, it will appear that the mutex is held,
62 * by which LWP it does not matter: other LWPs competing for the lock will
63 * fall through to mutex_vector_enter(), and either spin or sleep.
64 *
65 * As a result there is no space for a waiters bit in the owner field.  No
66 * problem, because it would be hard to synchronise using one without a CAS
67 * operation.  Note that in order to do unlocked release of adaptive
68 * mutexes, we need the effect of MUTEX_SET_WAITERS() to be immediatley
69 * visible on the bus.  So, adaptive mutexes share the spin lock byte with
70 * spin mutexes (set with bb{cc,ss}i), but it is not treated as a lock in its
71 * own right, rather as a flag that can be atomically set or cleared.
72 *
73 * When releasing an adaptive mutex, we first clear the owners field, and
74 * then check to see if the waiters byte is set.  This ensures that there
75 * will always be someone to wake any sleeping waiters up (even it the mutex
76 * is acquired immediately after we release it, or if we are preempted
77 * immediatley after clearing the owners field).  The setting or clearing of
78 * the waiters byte is serialized by the turnstile chain lock associated
79 * with the mutex.
80 *
81 * See comments in kern_mutex.c about releasing adaptive mutexes without
82 * an interlocking step.
83 */
84
85#ifndef LOCKDEBUG
86#define	MUTEX_COUNT_BIAS		1
87#endif
88
89#ifndef __MUTEX_PRIVATE
90
91struct kmutex {
92	uintptr_t	mtx_pad1;
93	uint32_t	mtx_pad2;
94};
95
96#else	/* __MUTEX_PRIVATE */
97
98struct kmutex {
99	/* Adaptive mutex */
100	union {
101		volatile uintptr_t	u_owner;		/* 0-3 */
102		struct {
103			uint8_t			s_dummylo;	/* 0 */
104			__cpu_simple_lock_t	s_lock;		/* 1 */
105			ipl_cookie_t		s_ipl;		/* 2 */
106			uint8_t			s_dummyhi;	/* 3 */
107		} u_s;
108	} mtx_u;
109	uint32_t			mtx_flags;		/* 4-7 */
110};
111#define	mtx_owner	mtx_u.u_owner
112#define	mtx_lock	mtx_u.u_s.s_lock
113#define	mtx_ipl		mtx_u.u_s.s_ipl
114
115#define	__HAVE_MUTEX_STUBS		1
116#define	__HAVE_SPIN_MUTEX_STUBS		1
117
118static inline uintptr_t
119MUTEX_OWNER(uintptr_t owner)
120{
121	return owner & ~1;
122}
123
124static inline bool
125MUTEX_OWNED(uintptr_t owner)
126{
127	return owner != 0;
128}
129
130static inline bool
131MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner)
132{
133	mtx->mtx_owner |= 1;
134 	return (mtx->mtx_owner & ~1) != 0;
135}
136
137static inline bool
138MUTEX_HAS_WAITERS(volatile kmutex_t *mtx)
139{
140	return (mtx->mtx_owner & 1) != 0;
141}
142
143static inline void
144MUTEX_CLEAR_WAITERS(volatile kmutex_t *mtx)
145{
146	mtx->mtx_owner &= ~1;
147}
148
149static inline void
150MUTEX_INITIALIZE_SPIN(kmutex_t *mtx, bool dodebug, int ipl)
151{
152	mtx->mtx_flags = (dodebug << 1) | 1;
153	mtx->mtx_owner = 0x80000000;
154	mtx->mtx_ipl = makeiplcookie(ipl);
155	mtx->mtx_lock = 0;
156}
157
158static inline void
159MUTEX_INITIALIZE_ADAPTIVE(kmutex_t *mtx, bool dodebug)
160{
161	mtx->mtx_flags = (dodebug << 1);
162	mtx->mtx_ipl = makeiplcookie(-1);
163	mtx->mtx_owner = 0;
164}
165
166static inline void
167MUTEX_DESTROY(kmutex_t *mtx)
168{
169	mtx->mtx_owner = (uintptr_t)-1L;
170	mtx->mtx_flags = 0xdeadface << 1;
171}
172
173static inline bool
174MUTEX_DEBUG_P(volatile kmutex_t *mtx)
175{
176	return mtx->mtx_flags >> 1;
177}
178
179static inline bool
180MUTEX_SPIN_P(volatile kmutex_t *mtx)
181{
182	return (mtx->mtx_flags & 1) != 0;
183}
184
185static inline bool
186MUTEX_ADAPTIVE_P(volatile kmutex_t *mtx)
187{
188	return (mtx->mtx_flags & 1) == 0;
189}
190
191static inline bool
192MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
193{
194	int rv;
195	__asm __volatile(
196		"clrl %1;"
197		"bbssi $31,%0,1f;"
198		"incl %1;"
199		"insv %2,$0,$31,%0;"
200		"1:"
201	    : "=m"(mtx->mtx_owner), "=r"(rv)
202	    : "g"(curthread));
203	return rv;
204}
205
206static inline void
207MUTEX_RELEASE(kmutex_t *mtx)
208{
209	__asm __volatile(
210		"insv $0,$0,$31,%0;"
211		"bbcci $31,%0,1f;"
212		"1:"
213	   : "=m" (mtx->mtx_owner));
214}
215
216#endif	/* __MUTEX_PRIVATE */
217
218#endif /* _VAX_MUTEX_H_ */
219