| 1 | /* |
| 2 | * Copyright (c) 1991 Regents of the University of California. |
| 3 | * All rights reserved. |
| 4 | * |
| 5 | * This code is derived from software contributed to Berkeley by |
| 6 | * The Mach Operating System project at Carnegie-Mellon University. |
| 7 | * |
| 8 | * Redistribution and use in source and binary forms, with or without |
| 9 | * modification, are permitted provided that the following conditions |
| 10 | * are met: |
| 11 | * 1. Redistributions of source code must retain the above copyright |
| 12 | * notice, this list of conditions and the following disclaimer. |
| 13 | * 2. Redistributions in binary form must reproduce the above copyright |
| 14 | * notice, this list of conditions and the following disclaimer in the |
| 15 | * documentation and/or other materials provided with the distribution. |
| 16 | * 3. All advertising materials mentioning features or use of this software |
| 17 | * must display the following acknowledgement: |
| 18 | * This product includes software developed by the University of |
| 19 | * California, Berkeley and its contributors. |
| 20 | * 4. Neither the name of the University nor the names of its contributors |
| 21 | * may be used to endorse or promote products derived from this software |
| 22 | * without specific prior written permission. |
| 23 | * |
| 24 | * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND |
| 25 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| 26 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| 27 | * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE |
| 28 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
| 29 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
| 30 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
| 31 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| 32 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY |
| 33 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| 34 | * SUCH DAMAGE. |
| 35 | * |
| 36 | * @(#)kern_lock.c 7.4 (Berkeley) 4/21/91 |
| 37 | * |
| 38 | * |
| 39 | * Copyright (c) 1987, 1990 Carnegie-Mellon University. |
| 40 | * All rights reserved. |
| 41 | * |
| 42 | * Authors: Avadis Tevanian, Jr., Michael Wayne Young |
| 43 | * |
| 44 | * Permission to use, copy, modify and distribute this software and |
| 45 | * its documentation is hereby granted, provided that both the copyright |
| 46 | * notice and this permission notice appear in all copies of the |
| 47 | * software, derivative works or modified versions, and any portions |
| 48 | * thereof, and that both notices appear in supporting documentation. |
| 49 | * |
| 50 | * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" |
| 51 | * CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND |
| 52 | * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. |
| 53 | * |
| 54 | * Carnegie Mellon requests users of this software to return to |
| 55 | * |
| 56 | * Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU |
| 57 | * School of Computer Science |
| 58 | * Carnegie Mellon University |
| 59 | * Pittsburgh PA 15213-3890 |
| 60 | * |
| 61 | * any improvements or extensions that they make and grant Carnegie the |
| 62 | * rights to redistribute these changes. |
| 63 | */ |
| 64 | |
| 65 | /* |
| 66 | * Locking primitives implementation |
| 67 | */ |
| 68 | |
| 69 | #include "param.h" |
| 70 | #include "vm_param.h" |
| 71 | #include "lock.h" |
| 72 | |
| 73 | /* XXX */ |
| 74 | #include "proc.h" |
| 75 | typedef int *thread_t; |
| 76 | #define current_thread() ((thread_t)&curproc->p_thread) |
| 77 | /* XXX */ |
| 78 | |
| 79 | #if NCPUS > 1 |
| 80 | |
| 81 | /* |
| 82 | * Module: lock |
| 83 | * Function: |
| 84 | * Provide reader/writer sychronization. |
| 85 | * Implementation: |
| 86 | * Simple interlock on a bit. Readers first interlock |
| 87 | * increment the reader count, then let go. Writers hold |
| 88 | * the interlock (thus preventing further readers), and |
| 89 | * wait for already-accepted readers to go away. |
| 90 | */ |
| 91 | |
| 92 | /* |
| 93 | * The simple-lock routines are the primitives out of which |
| 94 | * the lock package is built. The implementation is left |
| 95 | * to the machine-dependent code. |
| 96 | */ |
| 97 | |
| 98 | #ifdef notdef |
| 99 | /* |
| 100 | * A sample implementation of simple locks. |
| 101 | * assumes: |
| 102 | * boolean_t test_and_set(boolean_t *) |
| 103 | * indivisibly sets the boolean to TRUE |
| 104 | * and returns its old value |
| 105 | * and that setting a boolean to FALSE is indivisible. |
| 106 | */ |
| 107 | /* |
| 108 | * simple_lock_init initializes a simple lock. A simple lock |
| 109 | * may only be used for exclusive locks. |
| 110 | */ |
| 111 | |
| 112 | void simple_lock_init(l) |
| 113 | simple_lock_t l; |
| 114 | { |
| 115 | *(boolean_t *)l = FALSE; |
| 116 | } |
| 117 | |
| 118 | void simple_lock(l) |
| 119 | simple_lock_t l; |
| 120 | { |
| 121 | while (test_and_set((boolean_t *)l)) |
| 122 | continue; |
| 123 | } |
| 124 | |
| 125 | void simple_unlock(l) |
| 126 | simple_lock_t l; |
| 127 | { |
| 128 | *(boolean_t *)l = FALSE; |
| 129 | } |
| 130 | |
| 131 | boolean_t simple_lock_try(l) |
| 132 | simple_lock_t l; |
| 133 | { |
| 134 | return (!test_and_set((boolean_t *)l)); |
| 135 | } |
| 136 | #endif notdef |
| 137 | #endif NCPUS > 1 |
| 138 | |
| 139 | #if NCPUS > 1 |
| 140 | int lock_wait_time = 100; |
| 141 | #else NCPUS > 1 |
| 142 | |
| 143 | /* |
| 144 | * It is silly to spin on a uni-processor as if we |
| 145 | * thought something magical would happen to the |
| 146 | * want_write bit while we are executing. |
| 147 | */ |
| 148 | int lock_wait_time = 0; |
| 149 | #endif NCPUS > 1 |
| 150 | |
| 151 | |
| 152 | /* |
| 153 | * Routine: lock_init |
| 154 | * Function: |
| 155 | * Initialize a lock; required before use. |
| 156 | * Note that clients declare the "struct lock" |
| 157 | * variables and then initialize them, rather |
| 158 | * than getting a new one from this module. |
| 159 | */ |
| 160 | void lock_init(l, can_sleep) |
| 161 | lock_t l; |
| 162 | boolean_t can_sleep; |
| 163 | { |
| 164 | bzero(l, sizeof(lock_data_t)); |
| 165 | simple_lock_init(&l->interlock); |
| 166 | l->want_write = FALSE; |
| 167 | l->want_upgrade = FALSE; |
| 168 | l->read_count = 0; |
| 169 | l->can_sleep = can_sleep; |
| 170 | l->thread = (char *)-1; /* XXX */ |
| 171 | l->recursion_depth = 0; |
| 172 | } |
| 173 | |
| 174 | void lock_sleepable(l, can_sleep) |
| 175 | lock_t l; |
| 176 | boolean_t can_sleep; |
| 177 | { |
| 178 | simple_lock(&l->interlock); |
| 179 | l->can_sleep = can_sleep; |
| 180 | simple_unlock(&l->interlock); |
| 181 | } |
| 182 | |
| 183 | |
| 184 | /* |
| 185 | * Sleep locks. These use the same data structure and algorithm |
| 186 | * as the spin locks, but the process sleeps while it is waiting |
| 187 | * for the lock. These work on uniprocessor systems. |
| 188 | */ |
| 189 | |
| 190 | void lock_write(l) |
| 191 | register lock_t l; |
| 192 | { |
| 193 | register int i; |
| 194 | |
| 195 | simple_lock(&l->interlock); |
| 196 | |
| 197 | if (((thread_t)l->thread) == current_thread()) { |
| 198 | /* |
| 199 | * Recursive lock. |
| 200 | */ |
| 201 | l->recursion_depth++; |
| 202 | simple_unlock(&l->interlock); |
| 203 | return; |
| 204 | } |
| 205 | |
| 206 | /* |
| 207 | * Try to acquire the want_write bit. |
| 208 | */ |
| 209 | while (l->want_write) { |
| 210 | if ((i = lock_wait_time) > 0) { |
| 211 | simple_unlock(&l->interlock); |
| 212 | while (--i > 0 && l->want_write) |
| 213 | continue; |
| 214 | simple_lock(&l->interlock); |
| 215 | } |
| 216 | |
| 217 | if (l->can_sleep && l->want_write) { |
| 218 | l->waiting = TRUE; |
| 219 | thread_sleep((int) l, &l->interlock, FALSE); |
| 220 | simple_lock(&l->interlock); |
| 221 | } |
| 222 | } |
| 223 | l->want_write = TRUE; |
| 224 | |
| 225 | /* Wait for readers (and upgrades) to finish */ |
| 226 | |
| 227 | while ((l->read_count != 0) || l->want_upgrade) { |
| 228 | if ((i = lock_wait_time) > 0) { |
| 229 | simple_unlock(&l->interlock); |
| 230 | while (--i > 0 && (l->read_count != 0 || |
| 231 | l->want_upgrade)) |
| 232 | continue; |
| 233 | simple_lock(&l->interlock); |
| 234 | } |
| 235 | |
| 236 | if (l->can_sleep && (l->read_count != 0 || l->want_upgrade)) { |
| 237 | l->waiting = TRUE; |
| 238 | thread_sleep((int) l, &l->interlock, FALSE); |
| 239 | simple_lock(&l->interlock); |
| 240 | } |
| 241 | } |
| 242 | simple_unlock(&l->interlock); |
| 243 | } |
| 244 | |
| 245 | void lock_done(l) |
| 246 | register lock_t l; |
| 247 | { |
| 248 | simple_lock(&l->interlock); |
| 249 | |
| 250 | if (l->read_count != 0) |
| 251 | l->read_count--; |
| 252 | else |
| 253 | if (l->recursion_depth != 0) |
| 254 | l->recursion_depth--; |
| 255 | else |
| 256 | if (l->want_upgrade) |
| 257 | l->want_upgrade = FALSE; |
| 258 | else |
| 259 | l->want_write = FALSE; |
| 260 | |
| 261 | if (l->waiting) { |
| 262 | l->waiting = FALSE; |
| 263 | thread_wakeup((int) l); |
| 264 | } |
| 265 | simple_unlock(&l->interlock); |
| 266 | } |
| 267 | |
| 268 | void lock_read(l) |
| 269 | register lock_t l; |
| 270 | { |
| 271 | register int i; |
| 272 | |
| 273 | simple_lock(&l->interlock); |
| 274 | |
| 275 | if (((thread_t)l->thread) == current_thread()) { |
| 276 | /* |
| 277 | * Recursive lock. |
| 278 | */ |
| 279 | l->read_count++; |
| 280 | simple_unlock(&l->interlock); |
| 281 | return; |
| 282 | } |
| 283 | |
| 284 | while (l->want_write || l->want_upgrade) { |
| 285 | if ((i = lock_wait_time) > 0) { |
| 286 | simple_unlock(&l->interlock); |
| 287 | while (--i > 0 && (l->want_write || l->want_upgrade)) |
| 288 | continue; |
| 289 | simple_lock(&l->interlock); |
| 290 | } |
| 291 | |
| 292 | if (l->can_sleep && (l->want_write || l->want_upgrade)) { |
| 293 | l->waiting = TRUE; |
| 294 | thread_sleep((int) l, &l->interlock, FALSE); |
| 295 | simple_lock(&l->interlock); |
| 296 | } |
| 297 | } |
| 298 | |
| 299 | l->read_count++; |
| 300 | simple_unlock(&l->interlock); |
| 301 | } |
| 302 | |
| 303 | /* |
| 304 | * Routine: lock_read_to_write |
| 305 | * Function: |
| 306 | * Improves a read-only lock to one with |
| 307 | * write permission. If another reader has |
| 308 | * already requested an upgrade to a write lock, |
| 309 | * no lock is held upon return. |
| 310 | * |
| 311 | * Returns TRUE if the upgrade *failed*. |
| 312 | */ |
| 313 | boolean_t lock_read_to_write(l) |
| 314 | register lock_t l; |
| 315 | { |
| 316 | register int i; |
| 317 | |
| 318 | simple_lock(&l->interlock); |
| 319 | |
| 320 | l->read_count--; |
| 321 | |
| 322 | if (((thread_t)l->thread) == current_thread()) { |
| 323 | /* |
| 324 | * Recursive lock. |
| 325 | */ |
| 326 | l->recursion_depth++; |
| 327 | simple_unlock(&l->interlock); |
| 328 | return(FALSE); |
| 329 | } |
| 330 | |
| 331 | if (l->want_upgrade) { |
| 332 | /* |
| 333 | * Someone else has requested upgrade. |
| 334 | * Since we've released a read lock, wake |
| 335 | * him up. |
| 336 | */ |
| 337 | if (l->waiting) { |
| 338 | l->waiting = FALSE; |
| 339 | thread_wakeup((int) l); |
| 340 | } |
| 341 | |
| 342 | simple_unlock(&l->interlock); |
| 343 | return (TRUE); |
| 344 | } |
| 345 | |
| 346 | l->want_upgrade = TRUE; |
| 347 | |
| 348 | while (l->read_count != 0) { |
| 349 | if ((i = lock_wait_time) > 0) { |
| 350 | simple_unlock(&l->interlock); |
| 351 | while (--i > 0 && l->read_count != 0) |
| 352 | continue; |
| 353 | simple_lock(&l->interlock); |
| 354 | } |
| 355 | |
| 356 | if (l->can_sleep && l->read_count != 0) { |
| 357 | l->waiting = TRUE; |
| 358 | thread_sleep((int) l, &l->interlock, FALSE); |
| 359 | simple_lock(&l->interlock); |
| 360 | } |
| 361 | } |
| 362 | |
| 363 | simple_unlock(&l->interlock); |
| 364 | return (FALSE); |
| 365 | } |
| 366 | |
| 367 | void lock_write_to_read(l) |
| 368 | register lock_t l; |
| 369 | { |
| 370 | simple_lock(&l->interlock); |
| 371 | |
| 372 | l->read_count++; |
| 373 | if (l->recursion_depth != 0) |
| 374 | l->recursion_depth--; |
| 375 | else |
| 376 | if (l->want_upgrade) |
| 377 | l->want_upgrade = FALSE; |
| 378 | else |
| 379 | l->want_write = FALSE; |
| 380 | |
| 381 | if (l->waiting) { |
| 382 | l->waiting = FALSE; |
| 383 | thread_wakeup((int) l); |
| 384 | } |
| 385 | |
| 386 | simple_unlock(&l->interlock); |
| 387 | } |
| 388 | |
| 389 | |
| 390 | /* |
| 391 | * Routine: lock_try_write |
| 392 | * Function: |
| 393 | * Tries to get a write lock. |
| 394 | * |
| 395 | * Returns FALSE if the lock is not held on return. |
| 396 | */ |
| 397 | |
| 398 | boolean_t lock_try_write(l) |
| 399 | register lock_t l; |
| 400 | { |
| 401 | |
| 402 | simple_lock(&l->interlock); |
| 403 | |
| 404 | if (((thread_t)l->thread) == current_thread()) { |
| 405 | /* |
| 406 | * Recursive lock |
| 407 | */ |
| 408 | l->recursion_depth++; |
| 409 | simple_unlock(&l->interlock); |
| 410 | return(TRUE); |
| 411 | } |
| 412 | |
| 413 | if (l->want_write || l->want_upgrade || l->read_count) { |
| 414 | /* |
| 415 | * Can't get lock. |
| 416 | */ |
| 417 | simple_unlock(&l->interlock); |
| 418 | return(FALSE); |
| 419 | } |
| 420 | |
| 421 | /* |
| 422 | * Have lock. |
| 423 | */ |
| 424 | |
| 425 | l->want_write = TRUE; |
| 426 | simple_unlock(&l->interlock); |
| 427 | return(TRUE); |
| 428 | } |
| 429 | |
| 430 | /* |
| 431 | * Routine: lock_try_read |
| 432 | * Function: |
| 433 | * Tries to get a read lock. |
| 434 | * |
| 435 | * Returns FALSE if the lock is not held on return. |
| 436 | */ |
| 437 | |
| 438 | boolean_t lock_try_read(l) |
| 439 | register lock_t l; |
| 440 | { |
| 441 | simple_lock(&l->interlock); |
| 442 | |
| 443 | if (((thread_t)l->thread) == current_thread()) { |
| 444 | /* |
| 445 | * Recursive lock |
| 446 | */ |
| 447 | l->read_count++; |
| 448 | simple_unlock(&l->interlock); |
| 449 | return(TRUE); |
| 450 | } |
| 451 | |
| 452 | if (l->want_write || l->want_upgrade) { |
| 453 | simple_unlock(&l->interlock); |
| 454 | return(FALSE); |
| 455 | } |
| 456 | |
| 457 | l->read_count++; |
| 458 | simple_unlock(&l->interlock); |
| 459 | return(TRUE); |
| 460 | } |
| 461 | |
| 462 | /* |
| 463 | * Routine: lock_try_read_to_write |
| 464 | * Function: |
| 465 | * Improves a read-only lock to one with |
| 466 | * write permission. If another reader has |
| 467 | * already requested an upgrade to a write lock, |
| 468 | * the read lock is still held upon return. |
| 469 | * |
| 470 | * Returns FALSE if the upgrade *failed*. |
| 471 | */ |
| 472 | boolean_t lock_try_read_to_write(l) |
| 473 | register lock_t l; |
| 474 | { |
| 475 | |
| 476 | simple_lock(&l->interlock); |
| 477 | |
| 478 | if (((thread_t)l->thread) == current_thread()) { |
| 479 | /* |
| 480 | * Recursive lock |
| 481 | */ |
| 482 | l->read_count--; |
| 483 | l->recursion_depth++; |
| 484 | simple_unlock(&l->interlock); |
| 485 | return(TRUE); |
| 486 | } |
| 487 | |
| 488 | if (l->want_upgrade) { |
| 489 | simple_unlock(&l->interlock); |
| 490 | return(FALSE); |
| 491 | } |
| 492 | l->want_upgrade = TRUE; |
| 493 | l->read_count--; |
| 494 | |
| 495 | while (l->read_count != 0) { |
| 496 | l->waiting = TRUE; |
| 497 | thread_sleep((int) l, &l->interlock, FALSE); |
| 498 | simple_lock(&l->interlock); |
| 499 | } |
| 500 | |
| 501 | simple_unlock(&l->interlock); |
| 502 | return(TRUE); |
| 503 | } |
| 504 | |
| 505 | /* |
| 506 | * Allow a process that has a lock for write to acquire it |
| 507 | * recursively (for read, write, or update). |
| 508 | */ |
| 509 | void lock_set_recursive(l) |
| 510 | lock_t l; |
| 511 | { |
| 512 | simple_lock(&l->interlock); |
| 513 | if (!l->want_write) { |
| 514 | panic("lock_set_recursive: don't have write lock"); |
| 515 | } |
| 516 | l->thread = (char *) current_thread(); |
| 517 | simple_unlock(&l->interlock); |
| 518 | } |
| 519 | |
| 520 | /* |
| 521 | * Prevent a lock from being re-acquired. |
| 522 | */ |
| 523 | void lock_clear_recursive(l) |
| 524 | lock_t l; |
| 525 | { |
| 526 | simple_lock(&l->interlock); |
| 527 | if (((thread_t) l->thread) != current_thread()) { |
| 528 | panic("lock_clear_recursive: wrong thread"); |
| 529 | } |
| 530 | if (l->recursion_depth == 0) |
| 531 | l->thread = (char *)-1; /* XXX */ |
| 532 | simple_unlock(&l->interlock); |
| 533 | } |