libexec/rtld-elf/rtld_lock.c

   1 /*-
   2  * Copyright 1999, 2000 John D. Polstra.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  16  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  17  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  18  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  19  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  20  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  21  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  *
  25  *      from: FreeBSD: src/libexec/rtld-elf/sparc64/lockdflt.c,v 1.3 2002/10/09
  26  * $FreeBSD$
  27  */
  28
  29 /*
  30  * Thread locking implementation for the dynamic linker.
  31  *
  32  * We use the "simple, non-scalable reader-preference lock" from:
  33  *
  34  *   J. M. Mellor-Crummey and M. L. Scott. "Scalable Reader-Writer
  35  *   Synchronization for Shared-Memory Multiprocessors." 3rd ACM Symp. on
  36  *   Principles and Practice of Parallel Programming, April 1991.
  37  *
  38  * In this algorithm the lock is a single word.  Its low-order bit is
  39  * set when a writer holds the lock.  The remaining high-order bits
  40  * contain a count of readers desiring the lock.  The algorithm requires
  41  * atomic "compare_and_store" and "add" operations, which we implement
  42  * using assembly language sequences in "rtld_start.S".
  43  */
  44
  45 #include <sys/param.h>
  46 #include <signal.h>
  47 #include <stdlib.h>
  48 #include <time.h>
  49
  50 #include <stdio.h>
  51 #include <sys/file.h>
  52
  53 #include "debug.h"
  54 #include "rtld.h"
  55 #include "rtld_machdep.h"
  56
  57 extern pid_t __sys_getpid(void);
  58
  59 #define WAFLAG          0x1     /* A writer holds the lock */
  60 #define RC_INCR         0x2     /* Adjusts count of readers desiring lock */
  61
  62 struct Struct_Lock {
  63         volatile u_int lock;
  64         int tid;                /* owner (exclusive) */
  65         int count;              /* recursion (exclusive) */
  66         sigset_t savesigmask;   /* first exclusive owner sets mask */
  67 } __cachealign;
  68
  69 #define cpu_ccfence()   __asm __volatile("" : : : "memory")
  70
  71 static sigset_t fullsigmask;
  72
  73 struct Struct_Lock phdr_lock;
  74 struct Struct_Lock bind_lock;
  75 struct Struct_Lock libc_lock;
  76
  77 rtld_lock_t     rtld_phdr_lock = &phdr_lock;
  78 rtld_lock_t     rtld_bind_lock = &bind_lock;
  79 rtld_lock_t     rtld_libc_lock = &libc_lock;
  80
  81 void
  82 rlock_acquire(rtld_lock_t lock, RtldLockState *state)
  83 {
  84         int v;
  85         int tid = 0;
  86
  87         v = lock->lock;
  88         cpu_ccfence();
  89         for (;;) {
  90                 if ((v & WAFLAG) == 0) {
  91                         if (atomic_fcmpset_int(&lock->lock, &v, v + RC_INCR)) {
  92                                 state->lockstate = RTLD_LOCK_RLOCKED;
  93                                 break;
  94                         }
  95                 } else {
  96                         if (tid == 0)
  97                                 tid = lwp_gettid();
  98                         if (lock->tid == tid) {
  99                                 ++lock->count;
 100                                 state->lockstate = RTLD_LOCK_WLOCKED;
 101                                 break;
 102                         }
 103                         umtx_sleep(&lock->lock, v, 0);
 104                         v = lock->lock;
 105                         cpu_ccfence();
 106                 }
 107         }
 108 }
 109
 110 void
 111 wlock_acquire(rtld_lock_t lock, RtldLockState *state)
 112 {
 113         sigset_t tmp_oldsigmask;
 114         int tid = lwp_gettid();
 115
 116         if (lock->tid == tid) {
 117                 ++lock->count;
 118                 state->lockstate = RTLD_LOCK_WLOCKED;
 119                 return;
 120         }
 121
 122         sigprocmask(SIG_BLOCK, &fullsigmask, &tmp_oldsigmask);
 123         for (;;) {
 124                 if (atomic_cmpset_acq_int(&lock->lock, 0, WAFLAG))
 125                         break;
 126                 umtx_sleep(&lock->lock, 0, 0);
 127         }
 128         lock->tid = tid;
 129         lock->count = 1;
 130         lock->savesigmask = tmp_oldsigmask;
 131         state->lockstate = RTLD_LOCK_WLOCKED;
 132 }
 133
 134 void
 135 lock_release(rtld_lock_t lock, RtldLockState *state)
 136 {
 137         sigset_t tmp_oldsigmask;
 138         int v;
 139
 140         if (state->lockstate == RTLD_LOCK_UNLOCKED)
 141                 return;
 142         if ((lock->lock & WAFLAG) == 0) {
 143                 v = atomic_fetchadd_int(&lock->lock, -RC_INCR) - RC_INCR;
 144                 if (v == 0)
 145                         umtx_wakeup(&lock->lock, 0);
 146         } else if (--lock->count == 0) {
 147                 tmp_oldsigmask = lock->savesigmask;
 148                 lock->tid = 0;
 149                 v = atomic_fetchadd_int(&lock->lock, -WAFLAG) - WAFLAG;
 150                 if (v == 0)
 151                         umtx_wakeup(&lock->lock, 0);
 152                 sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL);
 153         }
 154         state->lockstate = RTLD_LOCK_UNLOCKED;
 155 }
 156
 157 static
 158 void
 159 lock_reset(rtld_lock_t lock)
 160 {
 161         memset(lock, 0, sizeof(*lock));
 162 }
 163
 164 void
 165 lock_upgrade(rtld_lock_t lock, RtldLockState *state)
 166 {
 167         if (state == NULL)
 168                 return;
 169         if (state->lockstate == RTLD_LOCK_RLOCKED) {
 170                 lock_release(lock, state);
 171                 wlock_acquire(lock, state);
 172         }
 173 }
 174
 175 void
 176 lock_restart_for_upgrade(RtldLockState *state)
 177 {
 178         if (state == NULL)
 179                 return;
 180         switch (state->lockstate) {
 181         case RTLD_LOCK_UNLOCKED:
 182         case RTLD_LOCK_WLOCKED:
 183                 break;
 184         case RTLD_LOCK_RLOCKED:
 185                 siglongjmp(state->env, 1);
 186                 break;
 187         default:
 188                 assert(0);
 189         }
 190 }
 191
 192 void
 193 lockdflt_init(void)
 194 {
 195         /*
 196          * Construct a mask to block all signals except traps which might
 197          * conceivably be generated within the dynamic linker itself.
 198          */
 199         sigfillset(&fullsigmask);
 200         sigdelset(&fullsigmask, SIGILL);
 201         sigdelset(&fullsigmask, SIGTRAP);
 202         sigdelset(&fullsigmask, SIGABRT);
 203         sigdelset(&fullsigmask, SIGEMT);
 204         sigdelset(&fullsigmask, SIGFPE);
 205         sigdelset(&fullsigmask, SIGBUS);
 206         sigdelset(&fullsigmask, SIGSEGV);
 207         sigdelset(&fullsigmask, SIGSYS);
 208
 209         _rtld_thread_init(NULL);
 210 }
 211
 212 /*
 213  * (also called by pthreads)
 214  */
 215 void
 216 _rtld_thread_init(void *dummy __unused)
 217 {
 218         lock_reset(rtld_phdr_lock);
 219         lock_reset(rtld_bind_lock);
 220         lock_reset(rtld_libc_lock);
 221 }
 222
 223 static RtldLockState fork_states[3];
 224
 225 void
 226 _rtld_thread_prefork(void)
 227 {
 228         wlock_acquire(rtld_phdr_lock, &fork_states[0]);
 229         wlock_acquire(rtld_bind_lock, &fork_states[1]);
 230         wlock_acquire(rtld_libc_lock, &fork_states[2]);
 231 }
 232
 233 void
 234 _rtld_thread_postfork(void)
 235 {
 236         lock_release(rtld_libc_lock, &fork_states[2]);
 237         lock_release(rtld_bind_lock, &fork_states[1]);
 238         lock_release(rtld_phdr_lock, &fork_states[0]);
 239 }
 240
 241 void
 242 _rtld_thread_childfork(void)
 243 {
 244         sigset_t tmp_oldsigmask;
 245
 246         lock_reset(rtld_phdr_lock);
 247         lock_reset(rtld_bind_lock);
 248         tmp_oldsigmask = rtld_libc_lock->savesigmask;
 249         lock_reset(rtld_libc_lock);
 250         sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL);
 251 }