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 "debug.h"
  51 #include "rtld.h"
  52 #include "rtld_machdep.h"
  53
  54 #define WAFLAG          0x1     /* A writer holds the lock */
  55 #define RC_INCR         0x2     /* Adjusts count of readers desiring lock */
  56
  57 typedef struct Struct_Lock {
  58         volatile u_int lock;
  59         void *base;
  60 } Lock;
  61
  62 static sigset_t fullsigmask, oldsigmask;
  63 static int thread_flag;
  64
  65 static void *
  66 def_lock_create(void)
  67 {
  68     void *base;
  69     char *p;
  70     uintptr_t r;
  71     Lock *l;
  72
  73     /*
  74      * Arrange for the lock to occupy its own cache line.  First, we
  75      * optimistically allocate just a cache line, hoping that malloc
  76      * will give us a well-aligned block of memory.  If that doesn't
  77      * work, we allocate a larger block and take a well-aligned cache
  78      * line from it.
  79      */
  80     base = xmalloc(CACHE_LINE_SIZE);
  81     p = (char *)base;
  82     if ((uintptr_t)p % CACHE_LINE_SIZE != 0) {
  83         free(base);
  84         base = xmalloc(2 * CACHE_LINE_SIZE);
  85         p = (char *)base;
  86         if ((r = (uintptr_t)p % CACHE_LINE_SIZE) != 0)
  87             p += CACHE_LINE_SIZE - r;
  88     }
  89     l = (Lock *)p;
  90     l->base = base;
  91     l->lock = 0;
  92     return l;
  93 }
  94
  95 static void
  96 def_lock_destroy(void *lock)
  97 {
  98     Lock *l = (Lock *)lock;
  99
 100     free(l->base);
 101 }
 102
 103 static void
 104 def_rlock_acquire(void *lock)
 105 {
 106     Lock *l = (Lock *)lock;
 107
 108     atomic_add_acq_int(&l->lock, RC_INCR);
 109     while (l->lock & WAFLAG)
 110             ;   /* Spin */
 111 }
 112
 113 static void
 114 def_wlock_acquire(void *lock)
 115 {
 116     Lock *l = (Lock *)lock;
 117     sigset_t tmp_oldsigmask;
 118
 119     for ( ; ; ) {
 120         sigprocmask(SIG_BLOCK, &fullsigmask, &tmp_oldsigmask);
 121         if (atomic_cmpset_acq_int(&l->lock, 0, WAFLAG))
 122             break;
 123         sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL);
 124     }
 125     oldsigmask = tmp_oldsigmask;
 126 }
 127
 128 static void
 129 def_lock_release(void *lock)
 130 {
 131     Lock *l = (Lock *)lock;
 132
 133     if ((l->lock & WAFLAG) == 0)
 134         atomic_add_rel_int(&l->lock, -RC_INCR);
 135     else {
 136         atomic_add_rel_int(&l->lock, -WAFLAG);
 137         sigprocmask(SIG_SETMASK, &oldsigmask, NULL);
 138     }
 139 }
 140
 141 static int
 142 def_thread_set_flag(int mask)
 143 {
 144         int old_val = thread_flag;
 145         thread_flag |= mask;
 146         return (old_val);
 147 }
 148
 149 static int
 150 def_thread_clr_flag(int mask)
 151 {
 152         int old_val = thread_flag;
 153         thread_flag &= ~mask;
 154         return (old_val);
 155 }
 156
 157 /*
 158  * Public interface exposed to the rest of the dynamic linker.
 159  */
 160 static struct RtldLockInfo lockinfo;
 161 static struct RtldLockInfo deflockinfo;
 162
 163 static __inline int
 164 thread_mask_set(int mask)
 165 {
 166         return lockinfo.thread_set_flag(mask);
 167 }
 168
 169 static __inline void
 170 thread_mask_clear(int mask)
 171 {
 172         lockinfo.thread_clr_flag(mask);
 173 }
 174
 175 #define RTLD_LOCK_CNT   3
 176 struct rtld_lock {
 177         void    *handle;
 178         int      mask;
 179 } rtld_locks[RTLD_LOCK_CNT];
 180
 181 rtld_lock_t     rtld_bind_lock = &rtld_locks[0];
 182 rtld_lock_t     rtld_libc_lock = &rtld_locks[1];
 183 rtld_lock_t     rtld_phdr_lock = &rtld_locks[2];
 184
 185 void
 186 rlock_acquire(rtld_lock_t lock, RtldLockState *lockstate)
 187 {
 188
 189         if (lockstate == NULL)
 190                 return;
 191
 192         if (thread_mask_set(lock->mask) & lock->mask) {
 193                 dbg("rlock_acquire: recursed");
 194                 lockstate->lockstate = RTLD_LOCK_UNLOCKED;
 195                 return;
 196         }
 197         lockinfo.rlock_acquire(lock->handle);
 198         lockstate->lockstate = RTLD_LOCK_RLOCKED;
 199 }
 200
 201 void
 202 wlock_acquire(rtld_lock_t lock, RtldLockState *lockstate)
 203 {
 204
 205         if (lockstate == NULL)
 206                 return;
 207
 208         if (thread_mask_set(lock->mask) & lock->mask) {
 209                 dbg("wlock_acquire: recursed");
 210                 lockstate->lockstate = RTLD_LOCK_UNLOCKED;
 211                 return;
 212         }
 213         lockinfo.wlock_acquire(lock->handle);
 214         lockstate->lockstate = RTLD_LOCK_WLOCKED;
 215 }
 216
 217 void
 218 lock_release(rtld_lock_t lock, RtldLockState *lockstate)
 219 {
 220
 221         if (lockstate == NULL)
 222                 return;
 223
 224         switch (lockstate->lockstate) {
 225         case RTLD_LOCK_UNLOCKED:
 226                 break;
 227         case RTLD_LOCK_RLOCKED:
 228         case RTLD_LOCK_WLOCKED:
 229                 lockinfo.lock_release(lock->handle);
 230                 thread_mask_clear(lock->mask);
 231                 break;
 232         default:
 233                 assert(0);
 234         }
 235 }
 236
 237 void
 238 lock_upgrade(rtld_lock_t lock, RtldLockState *lockstate)
 239 {
 240
 241         if (lockstate == NULL)
 242                 return;
 243
 244         lock_release(lock, lockstate);
 245         wlock_acquire(lock, lockstate);
 246 }
 247
 248 void
 249 lock_restart_for_upgrade(RtldLockState *lockstate)
 250 {
 251
 252         if (lockstate == NULL)
 253                 return;
 254
 255         switch (lockstate->lockstate) {
 256         case RTLD_LOCK_UNLOCKED:
 257         case RTLD_LOCK_WLOCKED:
 258                 break;
 259         case RTLD_LOCK_RLOCKED:
 260                 siglongjmp(lockstate->env, 1);
 261                 break;
 262         default:
 263                 assert(0);
 264         }
 265 }
 266
 267 void
 268 lockdflt_init(void)
 269 {
 270     int i;
 271
 272     deflockinfo.rtli_version  = RTLI_VERSION;
 273     deflockinfo.lock_create   = def_lock_create;
 274     deflockinfo.lock_destroy  = def_lock_destroy;
 275     deflockinfo.rlock_acquire = def_rlock_acquire;
 276     deflockinfo.wlock_acquire = def_wlock_acquire;
 277     deflockinfo.lock_release  = def_lock_release;
 278     deflockinfo.thread_set_flag = def_thread_set_flag;
 279     deflockinfo.thread_clr_flag = def_thread_clr_flag;
 280     deflockinfo.at_fork = NULL;
 281
 282     for (i = 0; i < RTLD_LOCK_CNT; i++) {
 283             rtld_locks[i].mask   = (1 << i);
 284             rtld_locks[i].handle = NULL;
 285     }
 286
 287     memcpy(&lockinfo, &deflockinfo, sizeof(lockinfo));
 288     _rtld_thread_init(NULL);
 289     /*
 290      * Construct a mask to block all signals except traps which might
 291      * conceivably be generated within the dynamic linker itself.
 292      */
 293     sigfillset(&fullsigmask);
 294     sigdelset(&fullsigmask, SIGILL);
 295     sigdelset(&fullsigmask, SIGTRAP);
 296     sigdelset(&fullsigmask, SIGABRT);
 297     sigdelset(&fullsigmask, SIGEMT);
 298     sigdelset(&fullsigmask, SIGFPE);
 299     sigdelset(&fullsigmask, SIGBUS);
 300     sigdelset(&fullsigmask, SIGSEGV);
 301     sigdelset(&fullsigmask, SIGSYS);
 302 }
 303
 304 /*
 305  * Callback function to allow threads implementation to
 306  * register their own locking primitives if the default
 307  * one is not suitable.
 308  * The current context should be the only context
 309  * executing at the invocation time.
 310  */
 311 void
 312 _rtld_thread_init(struct RtldLockInfo *pli)
 313 {
 314         int flags, i;
 315         void *locks[RTLD_LOCK_CNT];
 316
 317         /* disable all locking while this function is running */
 318         flags = thread_mask_set(~0);
 319
 320         if (pli == NULL)
 321                 pli = &deflockinfo;
 322
 323
 324         for (i = 0; i < RTLD_LOCK_CNT; i++)
 325                 if ((locks[i] = pli->lock_create()) == NULL)
 326                         break;
 327
 328         if (i < RTLD_LOCK_CNT) {
 329                 while (--i >= 0)
 330                         pli->lock_destroy(locks[i]);
 331                 abort();
 332         }
 333
 334         for (i = 0; i < RTLD_LOCK_CNT; i++) {
 335                 if (rtld_locks[i].handle == NULL)
 336                         continue;
 337                 if (flags & rtld_locks[i].mask)
 338                         lockinfo.lock_release(rtld_locks[i].handle);
 339                 lockinfo.lock_destroy(rtld_locks[i].handle);
 340         }
 341
 342         for (i = 0; i < RTLD_LOCK_CNT; i++) {
 343                 rtld_locks[i].handle = locks[i];
 344                 if (flags & rtld_locks[i].mask)
 345                         pli->wlock_acquire(rtld_locks[i].handle);
 346         }
 347
 348         lockinfo.lock_create = pli->lock_create;
 349         lockinfo.lock_destroy = pli->lock_destroy;
 350         lockinfo.rlock_acquire = pli->rlock_acquire;
 351         lockinfo.wlock_acquire = pli->wlock_acquire;
 352         lockinfo.lock_release  = pli->lock_release;
 353         lockinfo.thread_set_flag = pli->thread_set_flag;
 354         lockinfo.thread_clr_flag = pli->thread_clr_flag;
 355         lockinfo.at_fork = pli->at_fork;
 356
 357         /* restore thread locking state, this time with new locks */
 358         thread_mask_clear(~0);
 359         thread_mask_set(flags);
 360         dbg("_rtld_thread_init: done");
 361 }