2 * $FreeBSD: src/sys/i386/i386/mplock.s,v 1.29.2.2 2000/05/16 06:58:06 dillon Exp $
3 * $DragonFly: src/sys/i386/i386/Attic/mplock.s,v 1.15 2004/11/20 20:50:33 dillon Exp $
5 * Copyright (c) 2003,2004 The DragonFly Project. All rights reserved.
7 * This code is derived from software contributed to The DragonFly Project
8 * by Matthew Dillon <dillon@backplane.com>
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in
18 * the documentation and/or other materials provided with the
20 * 3. Neither the name of The DragonFly Project nor the names of its
21 * contributors may be used to endorse or promote products derived
22 * from this software without specific, prior written permission.
24 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
25 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
26 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
27 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
28 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
29 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
30 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
31 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
32 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
33 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
34 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
37 * DragonFly MPLOCK operation
39 * Each thread has an MP lock count, td_mpcount, and there is a shared
40 * global called mp_lock. mp_lock is the physical MP lock and contains either
41 * -1 or the cpuid of the cpu owning the lock. The count is *NOT* integrated
42 * into mp_lock but instead resides in each thread td_mpcount.
44 * When obtaining or releasing the MP lock the td_mpcount is PREDISPOSED
45 * to the desired count *PRIOR* to operating on the mp_lock itself. MP
46 * lock operations can occur outside a critical section with interrupts
47 * enabled with the provisio (which the routines below handle) that an
48 * interrupt may come along and preempt us, racing our cmpxchgl instruction
49 * to perform the operation we have requested by pre-dispoing td_mpcount.
51 * Additionally, the LWKT threading system manages the MP lock and
52 * lwkt_switch(), in particular, may be called after pre-dispoing td_mpcount
53 * to handle 'blocking' on the MP lock.
56 * Recoded from the FreeBSD original:
57 * ----------------------------------------------------------------------------
58 * "THE BEER-WARE LICENSE" (Revision 42):
59 * <phk@FreeBSD.org> wrote this file. As long as you retain this notice you
60 * can do whatever you want with this stuff. If we meet some day, and you think
61 * this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
62 * ----------------------------------------------------------------------------
65 #include <machine/asmacros.h>
66 #include <machine/smptests.h> /** GRAB_LOPRIO */
67 #include <machine/apicreg.h>
72 * YYY Debugging only. Define this to be paranoid about invalidating the
73 * TLB when we get giant.
75 #undef PARANOID_INVLTLB
82 .long -1 /* initialized to not held */
89 * Note on cmpxchgl... exchanges ecx with mem if mem matches eax.
90 * Z=1 (jz) on success. A lock prefix is required for MP.
92 NON_GPROF_ENTRY(cpu_get_initial_mplock)
93 movl PCPU(curthread),%ecx
94 movl $1,TD_MPCOUNT(%ecx) /* curthread has mpcount of 1 */
95 movl $0,mp_lock /* owned by cpu 0 */
99 * cpu_try_mplock() returns non-zero on success, 0 on failure. It
100 * only adjusts mp_lock, it does not touch td_mpcount. Callers
101 * should always increment td_mpcount *before* trying to acquire
102 * the actual lock, predisposing td_mpcount to the desired state of
105 * NOTE! Only call cpu_try_mplock() inside a critical section. If
106 * you don't an interrupt can come along and get and release
107 * the lock before our cmpxchgl instruction, causing us to fail
108 * but resulting in the lock being held by our cpu.
110 NON_GPROF_ENTRY(cpu_try_mplock)
111 movl PCPU(cpuid),%ecx
113 lock cmpxchgl %ecx,mp_lock /* ecx<->mem if eax matches */
115 #ifdef PARANOID_INVLTLB
116 movl %cr3,%eax; movl %eax,%cr3 /* YYY check and remove */
125 * get_mplock() Obtains the MP lock and may switch away if it cannot
126 * get it. This routine may be called WITHOUT a critical section
127 * and with cpu interrupts enabled.
129 * To handle races in a sane fashion we predispose TD_MPCOUNT,
130 * which prevents us from losing the lock in a race if we already
131 * have it or happen to get it. It also means that we might get
132 * the lock in an interrupt race before we have a chance to execute
133 * our cmpxchgl instruction, so we have to handle that case.
134 * Fortunately simply calling lwkt_switch() handles the situation
135 * for us and also 'blocks' us until the MP lock can be obtained.
137 NON_GPROF_ENTRY(get_mplock)
138 movl PCPU(cpuid),%ecx
139 movl PCPU(curthread),%edx
140 incl TD_MPCOUNT(%edx) /* predispose */
143 NON_GPROF_RET /* success! */
146 * We don't already own the mp_lock, use cmpxchgl to try to get
151 lock cmpxchgl %ecx,mp_lock
153 #ifdef PARANOID_INVLTLB
154 movl %cr3,%eax; movl %eax,%cr3 /* YYY check and remove */
156 NON_GPROF_RET /* success */
159 * Failure, but we could end up owning mp_lock anyway due to
160 * an interrupt race. lwkt_switch() will clean up the mess
161 * and 'block' until the mp_lock is obtained.
167 movl PCPU(cpuid),%eax /* failure */
174 cmpl $0,panicstr /* don't double panic */
180 * try_mplock() attempts to obtain the MP lock. 1 is returned on
181 * success, 0 on failure. We do not have to be in a critical section
182 * and interrupts are almost certainly enabled.
184 * We must pre-dispose TD_MPCOUNT in order to deal with races in
188 NON_GPROF_ENTRY(try_mplock)
189 movl PCPU(cpuid),%ecx
190 movl PCPU(curthread),%edx
191 incl TD_MPCOUNT(%edx) /* pre-dispose for race */
193 je 1f /* trivial success */
195 lock cmpxchgl %ecx,mp_lock
200 #ifdef PARANOID_INVLTLB
201 movl %cr3,%eax; movl %eax,%cr3 /* YYY check and remove */
204 movl $1,%eax /* success (cmpxchgl good!) */
208 * The cmpxchgl failed but we might have raced. Undo the mess by
209 * predispoing TD_MPCOUNT and then checking. If TD_MPCOUNT is
210 * still non-zero we don't care what state the lock is in (since
211 * we obviously didn't own it above), just return failure even if
212 * we won the lock in an interrupt race. If TD_MPCOUNT is zero
213 * make sure we don't own the lock in case we did win it in a race.
216 decl TD_MPCOUNT(%edx)
217 cmpl $0,TD_MPCOUNT(%edx)
219 movl PCPU(cpuid),%eax
221 lock cmpxchgl %ecx,mp_lock
227 * rel_mplock() releases a previously obtained MP lock.
229 * In order to release the MP lock we pre-dispose TD_MPCOUNT for
230 * the release and basically repeat the release portion of try_mplock
233 NON_GPROF_ENTRY(rel_mplock)
234 movl PCPU(curthread),%edx
235 movl TD_MPCOUNT(%edx),%eax
241 movl %eax,TD_MPCOUNT(%edx)
244 movl PCPU(cpuid),%eax
246 lock cmpxchgl %ecx,mp_lock
265 .asciz "try/get_mplock(): already have lock! %d %p"
268 .asciz "try/get_mplock(): failed on count or switch %d %p"
271 .asciz "rel_mplock(): mpcount already 0 @ %p %p %p %p %p %p %p %p!"