sys/platform/vkernel/i386/mplock.s

   1 /*
   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/platform/vkernel/i386/mplock.s,v 1.2 2007/07/01 02:51:43 dillon Exp $
   4  *
   5  * Copyright (c) 2003,2004 The DragonFly Project.  All rights reserved.
   6  *
   7  * This code is derived from software contributed to The DragonFly Project
   8  * by Matthew Dillon <dillon@backplane.com>
   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  *
  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
  19  *    distribution.
  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.
  23  *
  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
  35  * SUCH DAMAGE.
  36  *
  37  *                              DragonFly MPLOCK operation
  38  *
  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.
  43  *
  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-disposing td_mpcount.
  50  *
  51  * Additionally, the LWKT threading system manages the MP lock and
  52  * lwkt_switch(), in particular, may be called after pre-disposing td_mpcount
  53  * to handle 'blocking' on the MP lock.
  54  *
  55  *
  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  * ----------------------------------------------------------------------------
  63  */
  64
  65 #include <machine/asmacros.h>
  66 #if 0
  67 #include <machine_base/apic/apicreg.h>
  68 #endif
  69
  70 #include "assym.s"
  71
  72 /*
  73  * YYY Debugging only.  Define this to be paranoid about invalidating the
  74  * TLB when we get giant.
  75  */
  76 #undef PARANOID_INVLTLB
  77
  78         .data
  79         ALIGN_DATA
  80 #ifdef SMP
  81         .globl  mp_lock
  82 mp_lock:
  83         .long   -1                      /* initialized to not held */
  84 #endif
  85
  86         .text
  87         SUPERALIGN_TEXT
  88
  89         /*
  90          * Note on cmpxchgl... exchanges ecx with mem if mem matches eax.
  91          * Z=1 (jz) on success.   A lock prefix is required for MP.
  92          */
  93 NON_GPROF_ENTRY(cpu_get_initial_mplock)
  94         movl    PCPU(curthread),%ecx
  95         movl    $1,TD_MPCOUNT(%ecx)     /* curthread has mpcount of 1 */
  96         movl    $0,mp_lock              /* owned by cpu 0 */
  97         NON_GPROF_RET
  98
  99         /*
 100          * cpu_try_mplock() returns non-zero on success, 0 on failure.  It
 101          * only adjusts mp_lock, it does not touch td_mpcount.  Callers
 102          * should always increment td_mpcount *before* trying to acquire
 103          * the actual lock, predisposing td_mpcount to the desired state of
 104          * the lock.
 105          *
 106          * NOTE! Only call cpu_try_mplock() inside a critical section.  If
 107          * you don't an interrupt can come along and get and release
 108          * the lock before our cmpxchgl instruction, causing us to fail
 109          * but resulting in the lock being held by our cpu.
 110          */
 111 NON_GPROF_ENTRY(cpu_try_mplock)
 112         movl    PCPU(cpuid),%ecx
 113         movl    $-1,%eax
 114         lock cmpxchgl %ecx,mp_lock      /* ecx<->mem if eax matches */
 115         jnz     1f
 116 #ifdef PARANOID_INVLTLB
 117         movl    %cr3,%eax; movl %eax,%cr3       /* YYY check and remove */
 118 #endif
 119         movl    $1,%eax
 120         NON_GPROF_RET
 121 1:
 122         subl    %eax,%eax
 123         NON_GPROF_RET
 124
 125         /*
 126          * get_mplock() Obtains the MP lock and may switch away if it cannot
 127          * get it.  This routine may be called WITHOUT a critical section
 128          * and with cpu interrupts enabled.
 129          *
 130          * To handle races in a sane fashion we predispose TD_MPCOUNT,
 131          * which prevents us from losing the lock in a race if we already
 132          * have it or happen to get it.  It also means that we might get
 133          * the lock in an interrupt race before we have a chance to execute
 134          * our cmpxchgl instruction, so we have to handle that case.
 135          * Fortunately simply calling lwkt_switch() handles the situation
 136          * for us and also 'blocks' us until the MP lock can be obtained.
 137          */
 138 NON_GPROF_ENTRY(get_mplock)
 139         movl    PCPU(cpuid),%ecx
 140         movl    PCPU(curthread),%edx
 141         incl    TD_MPCOUNT(%edx)        /* predispose */
 142         cmpl    %ecx,mp_lock
 143         jne     1f
 144         NON_GPROF_RET                   /* success! */
 145
 146         /*
 147          * We don't already own the mp_lock, use cmpxchgl to try to get
 148          * it.
 149          */
 150 1:
 151         movl    $-1,%eax
 152         lock cmpxchgl %ecx,mp_lock
 153         jnz     2f
 154         NON_GPROF_RET                   /* success */
 155
 156         /*
 157          * Failure, but we could end up owning mp_lock anyway due to
 158          * an interrupt race.  lwkt_switch() will clean up the mess
 159          * and 'block' until the mp_lock is obtained.
 160          *
 161          * Create a stack frame for the call so KTR logs the stack
 162          * backtrace properly.
 163          */
 164 2:
 165         pushl   %ebp
 166         movl    %esp,%ebp
 167         call    lwkt_mp_lock_contested
 168         popl    %ebp
 169 #ifdef INVARIANTS
 170         movl    PCPU(cpuid),%eax        /* failure */
 171         cmpl    %eax,mp_lock
 172         jne     4f
 173 #endif
 174         NON_GPROF_RET
 175 #ifdef INVARIANTS
 176 4:
 177         cmpl    $0,panicstr             /* don't double panic */
 178         je      badmp_get2
 179         NON_GPROF_RET
 180 #endif
 181
 182         /*
 183          * try_mplock() attempts to obtain the MP lock.  1 is returned on
 184          * success, 0 on failure.  We do not have to be in a critical section
 185          * and interrupts are almost certainly enabled.
 186          *
 187          * We must pre-dispose TD_MPCOUNT in order to deal with races in
 188          * a reasonable way.
 189          *
 190          */
 191 NON_GPROF_ENTRY(try_mplock)
 192         movl    PCPU(cpuid),%ecx
 193         movl    PCPU(curthread),%edx
 194         incl    TD_MPCOUNT(%edx)                /* pre-dispose for race */
 195         cmpl    %ecx,mp_lock
 196         je      1f                              /* trivial success */
 197         movl    $-1,%eax
 198         lock cmpxchgl %ecx,mp_lock
 199         jnz     2f
 200         /*
 201          * Success
 202          */
 203 #ifdef PARANOID_INVLTLB
 204         movl    %cr3,%eax; movl %eax,%cr3       /* YYY check and remove */
 205 #endif
 206 1:
 207         movl    $1,%eax                         /* success (cmpxchgl good!) */
 208         NON_GPROF_RET
 209
 210         /*
 211          * The cmpxchgl failed but we might have raced.  Undo the mess by
 212          * predispoing TD_MPCOUNT and then checking.  If TD_MPCOUNT is
 213          * still non-zero we don't care what state the lock is in (since
 214          * we obviously didn't own it above), just return failure even if
 215          * we won the lock in an interrupt race.  If TD_MPCOUNT is zero
 216          * make sure we don't own the lock in case we did win it in a race.
 217          */
 218 2:
 219         decl    TD_MPCOUNT(%edx)
 220         cmpl    $0,TD_MPCOUNT(%edx)
 221         jne     3f
 222         movl    PCPU(cpuid),%eax
 223         movl    $-1,%ecx
 224         lock cmpxchgl %ecx,mp_lock
 225 3:
 226         subl    %eax,%eax
 227         NON_GPROF_RET
 228
 229         /*
 230          * rel_mplock() releases a previously obtained MP lock.
 231          *
 232          * In order to release the MP lock we pre-dispose TD_MPCOUNT for
 233          * the release and basically repeat the release portion of try_mplock
 234          * above.
 235          */
 236 NON_GPROF_ENTRY(rel_mplock)
 237         movl    PCPU(curthread),%edx
 238         movl    TD_MPCOUNT(%edx),%eax
 239 #ifdef INVARIANTS
 240         cmpl    $0,%eax
 241         je      badmp_rel
 242 #endif
 243         subl    $1,%eax
 244         movl    %eax,TD_MPCOUNT(%edx)
 245         cmpl    $0,%eax
 246         jne     3f
 247         movl    PCPU(cpuid),%eax
 248         movl    $-1,%ecx
 249         lock cmpxchgl %ecx,mp_lock
 250 3:
 251         NON_GPROF_RET
 252
 253 #ifdef INVARIANTS
 254
 255 badmp_get:
 256         pushl   $bmpsw1
 257         call    panic
 258 badmp_get2:
 259         pushl   $bmpsw1a
 260         call    panic
 261 badmp_rel:
 262         pushl   $bmpsw2
 263         call    panic
 264
 265         .data
 266
 267 bmpsw1:
 268         .asciz  "try/get_mplock(): already have lock! %d %p"
 269
 270 bmpsw1a:
 271         .asciz  "try/get_mplock(): failed on count or switch %d %p"
 272
 273 bmpsw2:
 274         .asciz  "rel_mplock(): mpcount already 0 @ %p %p %p %p %p %p %p %p!"
 275
 276 #endif
 277