| 1 | /* $NetBSD: kern_mutex.c,v 1.63 2016/07/07 06:55:43 msaitoh Exp $ */ |
| 2 | |
| 3 | /*- |
| 4 | * Copyright (c) 2002, 2006, 2007, 2008 The NetBSD Foundation, Inc. |
| 5 | * All rights reserved. |
| 6 | * |
| 7 | * This code is derived from software contributed to The NetBSD Foundation |
| 8 | * by Jason R. Thorpe and Andrew Doran. |
| 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 | * 1. Redistributions of source code must retain the above copyright |
| 14 | * notice, this list of conditions and the following disclaimer. |
| 15 | * 2. Redistributions in binary form must reproduce the above copyright |
| 16 | * notice, this list of conditions and the following disclaimer in the |
| 17 | * documentation and/or other materials provided with the distribution. |
| 18 | * |
| 19 | * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS |
| 20 | * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED |
| 21 | * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR |
| 22 | * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS |
| 23 | * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
| 24 | * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
| 25 | * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
| 26 | * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
| 27 | * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| 28 | * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE |
| 29 | * POSSIBILITY OF SUCH DAMAGE. |
| 30 | */ |
| 31 | |
| 32 | /* |
| 33 | * Kernel mutex implementation, modeled after those found in Solaris, |
| 34 | * a description of which can be found in: |
| 35 | * |
| 36 | * Solaris Internals: Core Kernel Architecture, Jim Mauro and |
| 37 | * Richard McDougall. |
| 38 | */ |
| 39 | |
| 40 | #define __MUTEX_PRIVATE |
| 41 | |
| 42 | #include <sys/cdefs.h> |
| 43 | __KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.63 2016/07/07 06:55:43 msaitoh Exp $" ); |
| 44 | |
| 45 | #include <sys/param.h> |
| 46 | #include <sys/atomic.h> |
| 47 | #include <sys/proc.h> |
| 48 | #include <sys/mutex.h> |
| 49 | #include <sys/sched.h> |
| 50 | #include <sys/sleepq.h> |
| 51 | #include <sys/systm.h> |
| 52 | #include <sys/lockdebug.h> |
| 53 | #include <sys/kernel.h> |
| 54 | #include <sys/intr.h> |
| 55 | #include <sys/lock.h> |
| 56 | #include <sys/types.h> |
| 57 | |
| 58 | #include <dev/lockstat.h> |
| 59 | |
| 60 | #include <machine/lock.h> |
| 61 | |
| 62 | /* |
| 63 | * When not running a debug kernel, spin mutexes are not much |
| 64 | * more than an splraiseipl() and splx() pair. |
| 65 | */ |
| 66 | |
| 67 | #if defined(DIAGNOSTIC) || defined(MULTIPROCESSOR) || defined(LOCKDEBUG) |
| 68 | #define FULL |
| 69 | #endif |
| 70 | |
| 71 | /* |
| 72 | * Debugging support. |
| 73 | */ |
| 74 | |
| 75 | #define MUTEX_WANTLOCK(mtx) \ |
| 76 | LOCKDEBUG_WANTLOCK(MUTEX_DEBUG_P(mtx), (mtx), \ |
| 77 | (uintptr_t)__builtin_return_address(0), 0) |
| 78 | #define MUTEX_LOCKED(mtx) \ |
| 79 | LOCKDEBUG_LOCKED(MUTEX_DEBUG_P(mtx), (mtx), NULL, \ |
| 80 | (uintptr_t)__builtin_return_address(0), 0) |
| 81 | #define MUTEX_UNLOCKED(mtx) \ |
| 82 | LOCKDEBUG_UNLOCKED(MUTEX_DEBUG_P(mtx), (mtx), \ |
| 83 | (uintptr_t)__builtin_return_address(0), 0) |
| 84 | #define MUTEX_ABORT(mtx, msg) \ |
| 85 | mutex_abort(mtx, __func__, msg) |
| 86 | |
| 87 | #if defined(LOCKDEBUG) |
| 88 | |
| 89 | #define MUTEX_DASSERT(mtx, cond) \ |
| 90 | do { \ |
| 91 | if (!(cond)) \ |
| 92 | MUTEX_ABORT(mtx, "assertion failed: " #cond); \ |
| 93 | } while (/* CONSTCOND */ 0); |
| 94 | |
| 95 | #else /* LOCKDEBUG */ |
| 96 | |
| 97 | #define MUTEX_DASSERT(mtx, cond) /* nothing */ |
| 98 | |
| 99 | #endif /* LOCKDEBUG */ |
| 100 | |
| 101 | #if defined(DIAGNOSTIC) |
| 102 | |
| 103 | #define MUTEX_ASSERT(mtx, cond) \ |
| 104 | do { \ |
| 105 | if (!(cond)) \ |
| 106 | MUTEX_ABORT(mtx, "assertion failed: " #cond); \ |
| 107 | } while (/* CONSTCOND */ 0) |
| 108 | |
| 109 | #else /* DIAGNOSTIC */ |
| 110 | |
| 111 | #define MUTEX_ASSERT(mtx, cond) /* nothing */ |
| 112 | |
| 113 | #endif /* DIAGNOSTIC */ |
| 114 | |
| 115 | /* |
| 116 | * Some architectures can't use __cpu_simple_lock as is so allow a way |
| 117 | * for them to use an alternate definition. |
| 118 | */ |
| 119 | #ifndef MUTEX_SPINBIT_LOCK_INIT |
| 120 | #define MUTEX_SPINBIT_LOCK_INIT(mtx) __cpu_simple_lock_init(&(mtx)->mtx_lock) |
| 121 | #endif |
| 122 | #ifndef MUTEX_SPINBIT_LOCKED_P |
| 123 | #define MUTEX_SPINBIT_LOCKED_P(mtx) __SIMPLELOCK_LOCKED_P(&(mtx)->mtx_lock) |
| 124 | #endif |
| 125 | #ifndef MUTEX_SPINBIT_LOCK_TRY |
| 126 | #define MUTEX_SPINBIT_LOCK_TRY(mtx) __cpu_simple_lock_try(&(mtx)->mtx_lock) |
| 127 | #endif |
| 128 | #ifndef MUTEX_SPINBIT_LOCK_UNLOCK |
| 129 | #define MUTEX_SPINBIT_LOCK_UNLOCK(mtx) __cpu_simple_unlock(&(mtx)->mtx_lock) |
| 130 | #endif |
| 131 | |
| 132 | #ifndef MUTEX_INITIALIZE_SPIN_IPL |
| 133 | #define MUTEX_INITIALIZE_SPIN_IPL(mtx, ipl) \ |
| 134 | ((mtx)->mtx_ipl = makeiplcookie((ipl))) |
| 135 | #endif |
| 136 | |
| 137 | /* |
| 138 | * Spin mutex SPL save / restore. |
| 139 | */ |
| 140 | |
| 141 | #define MUTEX_SPIN_SPLRAISE(mtx) \ |
| 142 | do { \ |
| 143 | struct cpu_info *x__ci; \ |
| 144 | int x__cnt, s; \ |
| 145 | s = splraiseipl(MUTEX_SPIN_IPL(mtx)); \ |
| 146 | x__ci = curcpu(); \ |
| 147 | x__cnt = x__ci->ci_mtx_count--; \ |
| 148 | __insn_barrier(); \ |
| 149 | if (x__cnt == 0) \ |
| 150 | x__ci->ci_mtx_oldspl = (s); \ |
| 151 | } while (/* CONSTCOND */ 0) |
| 152 | |
| 153 | #define MUTEX_SPIN_SPLRESTORE(mtx) \ |
| 154 | do { \ |
| 155 | struct cpu_info *x__ci = curcpu(); \ |
| 156 | int s = x__ci->ci_mtx_oldspl; \ |
| 157 | __insn_barrier(); \ |
| 158 | if (++(x__ci->ci_mtx_count) == 0) \ |
| 159 | splx(s); \ |
| 160 | } while (/* CONSTCOND */ 0) |
| 161 | |
| 162 | /* |
| 163 | * For architectures that provide 'simple' mutexes: they provide a |
| 164 | * CAS function that is either MP-safe, or does not need to be MP |
| 165 | * safe. Adaptive mutexes on these architectures do not require an |
| 166 | * additional interlock. |
| 167 | */ |
| 168 | |
| 169 | #ifdef __HAVE_SIMPLE_MUTEXES |
| 170 | |
| 171 | #define MUTEX_OWNER(owner) \ |
| 172 | (owner & MUTEX_THREAD) |
| 173 | #define MUTEX_HAS_WAITERS(mtx) \ |
| 174 | (((int)(mtx)->mtx_owner & MUTEX_BIT_WAITERS) != 0) |
| 175 | |
| 176 | #define MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug) \ |
| 177 | if (!dodebug) \ |
| 178 | (mtx)->mtx_owner |= MUTEX_BIT_NODEBUG; \ |
| 179 | do { \ |
| 180 | } while (/* CONSTCOND */ 0); |
| 181 | |
| 182 | #define MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl) \ |
| 183 | do { \ |
| 184 | (mtx)->mtx_owner = MUTEX_BIT_SPIN; \ |
| 185 | if (!dodebug) \ |
| 186 | (mtx)->mtx_owner |= MUTEX_BIT_NODEBUG; \ |
| 187 | MUTEX_INITIALIZE_SPIN_IPL((mtx), (ipl)); \ |
| 188 | MUTEX_SPINBIT_LOCK_INIT((mtx)); \ |
| 189 | } while (/* CONSTCOND */ 0) |
| 190 | |
| 191 | #define MUTEX_DESTROY(mtx) \ |
| 192 | do { \ |
| 193 | (mtx)->mtx_owner = MUTEX_THREAD; \ |
| 194 | } while (/* CONSTCOND */ 0); |
| 195 | |
| 196 | #define MUTEX_SPIN_P(mtx) \ |
| 197 | (((mtx)->mtx_owner & MUTEX_BIT_SPIN) != 0) |
| 198 | #define MUTEX_ADAPTIVE_P(mtx) \ |
| 199 | (((mtx)->mtx_owner & MUTEX_BIT_SPIN) == 0) |
| 200 | |
| 201 | #define MUTEX_DEBUG_P(mtx) (((mtx)->mtx_owner & MUTEX_BIT_NODEBUG) == 0) |
| 202 | #if defined(LOCKDEBUG) |
| 203 | #define MUTEX_OWNED(owner) (((owner) & ~MUTEX_BIT_NODEBUG) != 0) |
| 204 | #define MUTEX_INHERITDEBUG(n, o) (n) |= (o) & MUTEX_BIT_NODEBUG |
| 205 | #else /* defined(LOCKDEBUG) */ |
| 206 | #define MUTEX_OWNED(owner) ((owner) != 0) |
| 207 | #define MUTEX_INHERITDEBUG(n, o) /* nothing */ |
| 208 | #endif /* defined(LOCKDEBUG) */ |
| 209 | |
| 210 | static inline int |
| 211 | MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread) |
| 212 | { |
| 213 | int rv; |
| 214 | uintptr_t oldown = 0; |
| 215 | uintptr_t newown = curthread; |
| 216 | |
| 217 | MUTEX_INHERITDEBUG(oldown, mtx->mtx_owner); |
| 218 | MUTEX_INHERITDEBUG(newown, oldown); |
| 219 | rv = MUTEX_CAS(&mtx->mtx_owner, oldown, newown); |
| 220 | MUTEX_RECEIVE(mtx); |
| 221 | return rv; |
| 222 | } |
| 223 | |
| 224 | static inline int |
| 225 | MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner) |
| 226 | { |
| 227 | int rv; |
| 228 | rv = MUTEX_CAS(&mtx->mtx_owner, owner, owner | MUTEX_BIT_WAITERS); |
| 229 | MUTEX_RECEIVE(mtx); |
| 230 | return rv; |
| 231 | } |
| 232 | |
| 233 | static inline void |
| 234 | MUTEX_RELEASE(kmutex_t *mtx) |
| 235 | { |
| 236 | uintptr_t newown; |
| 237 | |
| 238 | MUTEX_GIVE(mtx); |
| 239 | newown = 0; |
| 240 | MUTEX_INHERITDEBUG(newown, mtx->mtx_owner); |
| 241 | mtx->mtx_owner = newown; |
| 242 | } |
| 243 | #endif /* __HAVE_SIMPLE_MUTEXES */ |
| 244 | |
| 245 | /* |
| 246 | * Patch in stubs via strong alias where they are not available. |
| 247 | */ |
| 248 | |
| 249 | #if defined(LOCKDEBUG) |
| 250 | #undef __HAVE_MUTEX_STUBS |
| 251 | #undef __HAVE_SPIN_MUTEX_STUBS |
| 252 | #endif |
| 253 | |
| 254 | #ifndef __HAVE_MUTEX_STUBS |
| 255 | __strong_alias(mutex_enter,mutex_vector_enter); |
| 256 | __strong_alias(mutex_exit,mutex_vector_exit); |
| 257 | #endif |
| 258 | |
| 259 | #ifndef __HAVE_SPIN_MUTEX_STUBS |
| 260 | __strong_alias(mutex_spin_enter,mutex_vector_enter); |
| 261 | __strong_alias(mutex_spin_exit,mutex_vector_exit); |
| 262 | #endif |
| 263 | |
| 264 | static void mutex_abort(kmutex_t *, const char *, const char *); |
| 265 | static void mutex_dump(volatile void *); |
| 266 | |
| 267 | lockops_t mutex_spin_lockops = { |
| 268 | "Mutex" , |
| 269 | LOCKOPS_SPIN, |
| 270 | mutex_dump |
| 271 | }; |
| 272 | |
| 273 | lockops_t mutex_adaptive_lockops = { |
| 274 | "Mutex" , |
| 275 | LOCKOPS_SLEEP, |
| 276 | mutex_dump |
| 277 | }; |
| 278 | |
| 279 | syncobj_t mutex_syncobj = { |
| 280 | SOBJ_SLEEPQ_SORTED, |
| 281 | turnstile_unsleep, |
| 282 | turnstile_changepri, |
| 283 | sleepq_lendpri, |
| 284 | (void *)mutex_owner, |
| 285 | }; |
| 286 | |
| 287 | /* |
| 288 | * mutex_dump: |
| 289 | * |
| 290 | * Dump the contents of a mutex structure. |
| 291 | */ |
| 292 | void |
| 293 | mutex_dump(volatile void *cookie) |
| 294 | { |
| 295 | volatile kmutex_t *mtx = cookie; |
| 296 | |
| 297 | printf_nolog("owner field : %#018lx wait/spin: %16d/%d\n" , |
| 298 | (long)MUTEX_OWNER(mtx->mtx_owner), MUTEX_HAS_WAITERS(mtx), |
| 299 | MUTEX_SPIN_P(mtx)); |
| 300 | } |
| 301 | |
| 302 | /* |
| 303 | * mutex_abort: |
| 304 | * |
| 305 | * Dump information about an error and panic the system. This |
| 306 | * generates a lot of machine code in the DIAGNOSTIC case, so |
| 307 | * we ask the compiler to not inline it. |
| 308 | */ |
| 309 | void __noinline |
| 310 | mutex_abort(kmutex_t *mtx, const char *func, const char *msg) |
| 311 | { |
| 312 | |
| 313 | LOCKDEBUG_ABORT(mtx, (MUTEX_SPIN_P(mtx) ? |
| 314 | &mutex_spin_lockops : &mutex_adaptive_lockops), func, msg); |
| 315 | } |
| 316 | |
| 317 | /* |
| 318 | * mutex_init: |
| 319 | * |
| 320 | * Initialize a mutex for use. Note that adaptive mutexes are in |
| 321 | * essence spin mutexes that can sleep to avoid deadlock and wasting |
| 322 | * CPU time. We can't easily provide a type of mutex that always |
| 323 | * sleeps - see comments in mutex_vector_enter() about releasing |
| 324 | * mutexes unlocked. |
| 325 | */ |
| 326 | void |
| 327 | mutex_init(kmutex_t *mtx, kmutex_type_t type, int ipl) |
| 328 | { |
| 329 | bool dodebug; |
| 330 | |
| 331 | memset(mtx, 0, sizeof(*mtx)); |
| 332 | |
| 333 | switch (type) { |
| 334 | case MUTEX_ADAPTIVE: |
| 335 | KASSERT(ipl == IPL_NONE); |
| 336 | break; |
| 337 | case MUTEX_DEFAULT: |
| 338 | case MUTEX_DRIVER: |
| 339 | if (ipl == IPL_NONE || ipl == IPL_SOFTCLOCK || |
| 340 | ipl == IPL_SOFTBIO || ipl == IPL_SOFTNET || |
| 341 | ipl == IPL_SOFTSERIAL) { |
| 342 | type = MUTEX_ADAPTIVE; |
| 343 | } else { |
| 344 | type = MUTEX_SPIN; |
| 345 | } |
| 346 | break; |
| 347 | default: |
| 348 | break; |
| 349 | } |
| 350 | |
| 351 | switch (type) { |
| 352 | case MUTEX_NODEBUG: |
| 353 | dodebug = LOCKDEBUG_ALLOC(mtx, NULL, |
| 354 | (uintptr_t)__builtin_return_address(0)); |
| 355 | MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl); |
| 356 | break; |
| 357 | case MUTEX_ADAPTIVE: |
| 358 | dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_adaptive_lockops, |
| 359 | (uintptr_t)__builtin_return_address(0)); |
| 360 | MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug); |
| 361 | break; |
| 362 | case MUTEX_SPIN: |
| 363 | dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_spin_lockops, |
| 364 | (uintptr_t)__builtin_return_address(0)); |
| 365 | MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl); |
| 366 | break; |
| 367 | default: |
| 368 | panic("mutex_init: impossible type" ); |
| 369 | break; |
| 370 | } |
| 371 | } |
| 372 | |
| 373 | /* |
| 374 | * mutex_destroy: |
| 375 | * |
| 376 | * Tear down a mutex. |
| 377 | */ |
| 378 | void |
| 379 | mutex_destroy(kmutex_t *mtx) |
| 380 | { |
| 381 | |
| 382 | if (MUTEX_ADAPTIVE_P(mtx)) { |
| 383 | MUTEX_ASSERT(mtx, !MUTEX_OWNED(mtx->mtx_owner) && |
| 384 | !MUTEX_HAS_WAITERS(mtx)); |
| 385 | } else { |
| 386 | MUTEX_ASSERT(mtx, !MUTEX_SPINBIT_LOCKED_P(mtx)); |
| 387 | } |
| 388 | |
| 389 | LOCKDEBUG_FREE(MUTEX_DEBUG_P(mtx), mtx); |
| 390 | MUTEX_DESTROY(mtx); |
| 391 | } |
| 392 | |
| 393 | #ifdef MULTIPROCESSOR |
| 394 | /* |
| 395 | * mutex_oncpu: |
| 396 | * |
| 397 | * Return true if an adaptive mutex owner is running on a CPU in the |
| 398 | * system. If the target is waiting on the kernel big lock, then we |
| 399 | * must release it. This is necessary to avoid deadlock. |
| 400 | */ |
| 401 | static bool |
| 402 | mutex_oncpu(uintptr_t owner) |
| 403 | { |
| 404 | struct cpu_info *ci; |
| 405 | lwp_t *l; |
| 406 | |
| 407 | KASSERT(kpreempt_disabled()); |
| 408 | |
| 409 | if (!MUTEX_OWNED(owner)) { |
| 410 | return false; |
| 411 | } |
| 412 | |
| 413 | /* |
| 414 | * See lwp_dtor() why dereference of the LWP pointer is safe. |
| 415 | * We must have kernel preemption disabled for that. |
| 416 | */ |
| 417 | l = (lwp_t *)MUTEX_OWNER(owner); |
| 418 | ci = l->l_cpu; |
| 419 | |
| 420 | if (ci && ci->ci_curlwp == l) { |
| 421 | /* Target is running; do we need to block? */ |
| 422 | return (ci->ci_biglock_wanted != l); |
| 423 | } |
| 424 | |
| 425 | /* Not running. It may be safe to block now. */ |
| 426 | return false; |
| 427 | } |
| 428 | #endif /* MULTIPROCESSOR */ |
| 429 | |
| 430 | /* |
| 431 | * mutex_vector_enter: |
| 432 | * |
| 433 | * Support routine for mutex_enter() that must handle all cases. In |
| 434 | * the LOCKDEBUG case, mutex_enter() is always aliased here, even if |
| 435 | * fast-path stubs are available. If a mutex_spin_enter() stub is |
| 436 | * not available, then it is also aliased directly here. |
| 437 | */ |
| 438 | void |
| 439 | mutex_vector_enter(kmutex_t *mtx) |
| 440 | { |
| 441 | uintptr_t owner, curthread; |
| 442 | turnstile_t *ts; |
| 443 | #ifdef MULTIPROCESSOR |
| 444 | u_int count; |
| 445 | #endif |
| 446 | LOCKSTAT_COUNTER(spincnt); |
| 447 | LOCKSTAT_COUNTER(slpcnt); |
| 448 | LOCKSTAT_TIMER(spintime); |
| 449 | LOCKSTAT_TIMER(slptime); |
| 450 | LOCKSTAT_FLAG(lsflag); |
| 451 | |
| 452 | /* |
| 453 | * Handle spin mutexes. |
| 454 | */ |
| 455 | if (MUTEX_SPIN_P(mtx)) { |
| 456 | #if defined(LOCKDEBUG) && defined(MULTIPROCESSOR) |
| 457 | u_int spins = 0; |
| 458 | #endif |
| 459 | MUTEX_SPIN_SPLRAISE(mtx); |
| 460 | MUTEX_WANTLOCK(mtx); |
| 461 | #ifdef FULL |
| 462 | if (MUTEX_SPINBIT_LOCK_TRY(mtx)) { |
| 463 | MUTEX_LOCKED(mtx); |
| 464 | return; |
| 465 | } |
| 466 | #if !defined(MULTIPROCESSOR) |
| 467 | MUTEX_ABORT(mtx, "locking against myself" ); |
| 468 | #else /* !MULTIPROCESSOR */ |
| 469 | |
| 470 | LOCKSTAT_ENTER(lsflag); |
| 471 | LOCKSTAT_START_TIMER(lsflag, spintime); |
| 472 | count = SPINLOCK_BACKOFF_MIN; |
| 473 | |
| 474 | /* |
| 475 | * Spin testing the lock word and do exponential backoff |
| 476 | * to reduce cache line ping-ponging between CPUs. |
| 477 | */ |
| 478 | do { |
| 479 | if (panicstr != NULL) |
| 480 | break; |
| 481 | while (MUTEX_SPINBIT_LOCKED_P(mtx)) { |
| 482 | SPINLOCK_BACKOFF(count); |
| 483 | #ifdef LOCKDEBUG |
| 484 | if (SPINLOCK_SPINOUT(spins)) |
| 485 | MUTEX_ABORT(mtx, "spinout" ); |
| 486 | #endif /* LOCKDEBUG */ |
| 487 | } |
| 488 | } while (!MUTEX_SPINBIT_LOCK_TRY(mtx)); |
| 489 | |
| 490 | if (count != SPINLOCK_BACKOFF_MIN) { |
| 491 | LOCKSTAT_STOP_TIMER(lsflag, spintime); |
| 492 | LOCKSTAT_EVENT(lsflag, mtx, |
| 493 | LB_SPIN_MUTEX | LB_SPIN, 1, spintime); |
| 494 | } |
| 495 | LOCKSTAT_EXIT(lsflag); |
| 496 | #endif /* !MULTIPROCESSOR */ |
| 497 | #endif /* FULL */ |
| 498 | MUTEX_LOCKED(mtx); |
| 499 | return; |
| 500 | } |
| 501 | |
| 502 | curthread = (uintptr_t)curlwp; |
| 503 | |
| 504 | MUTEX_DASSERT(mtx, MUTEX_ADAPTIVE_P(mtx)); |
| 505 | MUTEX_ASSERT(mtx, curthread != 0); |
| 506 | MUTEX_WANTLOCK(mtx); |
| 507 | |
| 508 | if (panicstr == NULL) { |
| 509 | LOCKDEBUG_BARRIER(&kernel_lock, 1); |
| 510 | } |
| 511 | |
| 512 | LOCKSTAT_ENTER(lsflag); |
| 513 | |
| 514 | /* |
| 515 | * Adaptive mutex; spin trying to acquire the mutex. If we |
| 516 | * determine that the owner is not running on a processor, |
| 517 | * then we stop spinning, and sleep instead. |
| 518 | */ |
| 519 | KPREEMPT_DISABLE(curlwp); |
| 520 | for (owner = mtx->mtx_owner;;) { |
| 521 | if (!MUTEX_OWNED(owner)) { |
| 522 | /* |
| 523 | * Mutex owner clear could mean two things: |
| 524 | * |
| 525 | * * The mutex has been released. |
| 526 | * * The owner field hasn't been set yet. |
| 527 | * |
| 528 | * Try to acquire it again. If that fails, |
| 529 | * we'll just loop again. |
| 530 | */ |
| 531 | if (MUTEX_ACQUIRE(mtx, curthread)) |
| 532 | break; |
| 533 | owner = mtx->mtx_owner; |
| 534 | continue; |
| 535 | } |
| 536 | if (__predict_false(panicstr != NULL)) { |
| 537 | KPREEMPT_ENABLE(curlwp); |
| 538 | return; |
| 539 | } |
| 540 | if (__predict_false(MUTEX_OWNER(owner) == curthread)) { |
| 541 | MUTEX_ABORT(mtx, "locking against myself" ); |
| 542 | } |
| 543 | #ifdef MULTIPROCESSOR |
| 544 | /* |
| 545 | * Check to see if the owner is running on a processor. |
| 546 | * If so, then we should just spin, as the owner will |
| 547 | * likely release the lock very soon. |
| 548 | */ |
| 549 | if (mutex_oncpu(owner)) { |
| 550 | LOCKSTAT_START_TIMER(lsflag, spintime); |
| 551 | count = SPINLOCK_BACKOFF_MIN; |
| 552 | do { |
| 553 | KPREEMPT_ENABLE(curlwp); |
| 554 | SPINLOCK_BACKOFF(count); |
| 555 | KPREEMPT_DISABLE(curlwp); |
| 556 | owner = mtx->mtx_owner; |
| 557 | } while (mutex_oncpu(owner)); |
| 558 | LOCKSTAT_STOP_TIMER(lsflag, spintime); |
| 559 | LOCKSTAT_COUNT(spincnt, 1); |
| 560 | if (!MUTEX_OWNED(owner)) |
| 561 | continue; |
| 562 | } |
| 563 | #endif |
| 564 | |
| 565 | ts = turnstile_lookup(mtx); |
| 566 | |
| 567 | /* |
| 568 | * Once we have the turnstile chain interlock, mark the |
| 569 | * mutex has having waiters. If that fails, spin again: |
| 570 | * chances are that the mutex has been released. |
| 571 | */ |
| 572 | if (!MUTEX_SET_WAITERS(mtx, owner)) { |
| 573 | turnstile_exit(mtx); |
| 574 | owner = mtx->mtx_owner; |
| 575 | continue; |
| 576 | } |
| 577 | |
| 578 | #ifdef MULTIPROCESSOR |
| 579 | /* |
| 580 | * mutex_exit() is permitted to release the mutex without |
| 581 | * any interlocking instructions, and the following can |
| 582 | * occur as a result: |
| 583 | * |
| 584 | * CPU 1: MUTEX_SET_WAITERS() CPU2: mutex_exit() |
| 585 | * ---------------------------- ---------------------------- |
| 586 | * .. acquire cache line |
| 587 | * .. test for waiters |
| 588 | * acquire cache line <- lose cache line |
| 589 | * lock cache line .. |
| 590 | * verify mutex is held .. |
| 591 | * set waiters .. |
| 592 | * unlock cache line .. |
| 593 | * lose cache line -> acquire cache line |
| 594 | * .. clear lock word, waiters |
| 595 | * return success |
| 596 | * |
| 597 | * There is another race that can occur: a third CPU could |
| 598 | * acquire the mutex as soon as it is released. Since |
| 599 | * adaptive mutexes are primarily spin mutexes, this is not |
| 600 | * something that we need to worry about too much. What we |
| 601 | * do need to ensure is that the waiters bit gets set. |
| 602 | * |
| 603 | * To allow the unlocked release, we need to make some |
| 604 | * assumptions here: |
| 605 | * |
| 606 | * o Release is the only non-atomic/unlocked operation |
| 607 | * that can be performed on the mutex. (It must still |
| 608 | * be atomic on the local CPU, e.g. in case interrupted |
| 609 | * or preempted). |
| 610 | * |
| 611 | * o At any given time, MUTEX_SET_WAITERS() can only ever |
| 612 | * be in progress on one CPU in the system - guaranteed |
| 613 | * by the turnstile chain lock. |
| 614 | * |
| 615 | * o No other operations other than MUTEX_SET_WAITERS() |
| 616 | * and release can modify a mutex with a non-zero |
| 617 | * owner field. |
| 618 | * |
| 619 | * o The result of a successful MUTEX_SET_WAITERS() call |
| 620 | * is an unbuffered write that is immediately visible |
| 621 | * to all other processors in the system. |
| 622 | * |
| 623 | * o If the holding LWP switches away, it posts a store |
| 624 | * fence before changing curlwp, ensuring that any |
| 625 | * overwrite of the mutex waiters flag by mutex_exit() |
| 626 | * completes before the modification of curlwp becomes |
| 627 | * visible to this CPU. |
| 628 | * |
| 629 | * o mi_switch() posts a store fence before setting curlwp |
| 630 | * and before resuming execution of an LWP. |
| 631 | * |
| 632 | * o _kernel_lock() posts a store fence before setting |
| 633 | * curcpu()->ci_biglock_wanted, and after clearing it. |
| 634 | * This ensures that any overwrite of the mutex waiters |
| 635 | * flag by mutex_exit() completes before the modification |
| 636 | * of ci_biglock_wanted becomes visible. |
| 637 | * |
| 638 | * We now post a read memory barrier (after setting the |
| 639 | * waiters field) and check the lock holder's status again. |
| 640 | * Some of the possible outcomes (not an exhaustive list): |
| 641 | * |
| 642 | * 1. The on-CPU check returns true: the holding LWP is |
| 643 | * running again. The lock may be released soon and |
| 644 | * we should spin. Importantly, we can't trust the |
| 645 | * value of the waiters flag. |
| 646 | * |
| 647 | * 2. The on-CPU check returns false: the holding LWP is |
| 648 | * not running. We now have the opportunity to check |
| 649 | * if mutex_exit() has blatted the modifications made |
| 650 | * by MUTEX_SET_WAITERS(). |
| 651 | * |
| 652 | * 3. The on-CPU check returns false: the holding LWP may |
| 653 | * or may not be running. It has context switched at |
| 654 | * some point during our check. Again, we have the |
| 655 | * chance to see if the waiters bit is still set or |
| 656 | * has been overwritten. |
| 657 | * |
| 658 | * 4. The on-CPU check returns false: the holding LWP is |
| 659 | * running on a CPU, but wants the big lock. It's OK |
| 660 | * to check the waiters field in this case. |
| 661 | * |
| 662 | * 5. The has-waiters check fails: the mutex has been |
| 663 | * released, the waiters flag cleared and another LWP |
| 664 | * now owns the mutex. |
| 665 | * |
| 666 | * 6. The has-waiters check fails: the mutex has been |
| 667 | * released. |
| 668 | * |
| 669 | * If the waiters bit is not set it's unsafe to go asleep, |
| 670 | * as we might never be awoken. |
| 671 | */ |
| 672 | if ((membar_consumer(), mutex_oncpu(owner)) || |
| 673 | (membar_consumer(), !MUTEX_HAS_WAITERS(mtx))) { |
| 674 | turnstile_exit(mtx); |
| 675 | owner = mtx->mtx_owner; |
| 676 | continue; |
| 677 | } |
| 678 | #endif /* MULTIPROCESSOR */ |
| 679 | |
| 680 | LOCKSTAT_START_TIMER(lsflag, slptime); |
| 681 | |
| 682 | turnstile_block(ts, TS_WRITER_Q, mtx, &mutex_syncobj); |
| 683 | |
| 684 | LOCKSTAT_STOP_TIMER(lsflag, slptime); |
| 685 | LOCKSTAT_COUNT(slpcnt, 1); |
| 686 | |
| 687 | owner = mtx->mtx_owner; |
| 688 | } |
| 689 | KPREEMPT_ENABLE(curlwp); |
| 690 | |
| 691 | LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SLEEP1, |
| 692 | slpcnt, slptime); |
| 693 | LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SPIN, |
| 694 | spincnt, spintime); |
| 695 | LOCKSTAT_EXIT(lsflag); |
| 696 | |
| 697 | MUTEX_DASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread); |
| 698 | MUTEX_LOCKED(mtx); |
| 699 | } |
| 700 | |
| 701 | /* |
| 702 | * mutex_vector_exit: |
| 703 | * |
| 704 | * Support routine for mutex_exit() that handles all cases. |
| 705 | */ |
| 706 | void |
| 707 | mutex_vector_exit(kmutex_t *mtx) |
| 708 | { |
| 709 | turnstile_t *ts; |
| 710 | uintptr_t curthread; |
| 711 | |
| 712 | if (MUTEX_SPIN_P(mtx)) { |
| 713 | #ifdef FULL |
| 714 | if (__predict_false(!MUTEX_SPINBIT_LOCKED_P(mtx))) { |
| 715 | if (panicstr != NULL) |
| 716 | return; |
| 717 | MUTEX_ABORT(mtx, "exiting unheld spin mutex" ); |
| 718 | } |
| 719 | MUTEX_UNLOCKED(mtx); |
| 720 | MUTEX_SPINBIT_LOCK_UNLOCK(mtx); |
| 721 | #endif |
| 722 | MUTEX_SPIN_SPLRESTORE(mtx); |
| 723 | return; |
| 724 | } |
| 725 | |
| 726 | if (__predict_false((uintptr_t)panicstr | cold)) { |
| 727 | MUTEX_UNLOCKED(mtx); |
| 728 | MUTEX_RELEASE(mtx); |
| 729 | return; |
| 730 | } |
| 731 | |
| 732 | curthread = (uintptr_t)curlwp; |
| 733 | MUTEX_DASSERT(mtx, curthread != 0); |
| 734 | MUTEX_ASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread); |
| 735 | MUTEX_UNLOCKED(mtx); |
| 736 | #if !defined(LOCKDEBUG) |
| 737 | __USE(curthread); |
| 738 | #endif |
| 739 | |
| 740 | #ifdef LOCKDEBUG |
| 741 | /* |
| 742 | * Avoid having to take the turnstile chain lock every time |
| 743 | * around. Raise the priority level to splhigh() in order |
| 744 | * to disable preemption and so make the following atomic. |
| 745 | */ |
| 746 | { |
| 747 | int s = splhigh(); |
| 748 | if (!MUTEX_HAS_WAITERS(mtx)) { |
| 749 | MUTEX_RELEASE(mtx); |
| 750 | splx(s); |
| 751 | return; |
| 752 | } |
| 753 | splx(s); |
| 754 | } |
| 755 | #endif |
| 756 | |
| 757 | /* |
| 758 | * Get this lock's turnstile. This gets the interlock on |
| 759 | * the sleep queue. Once we have that, we can clear the |
| 760 | * lock. If there was no turnstile for the lock, there |
| 761 | * were no waiters remaining. |
| 762 | */ |
| 763 | ts = turnstile_lookup(mtx); |
| 764 | |
| 765 | if (ts == NULL) { |
| 766 | MUTEX_RELEASE(mtx); |
| 767 | turnstile_exit(mtx); |
| 768 | } else { |
| 769 | MUTEX_RELEASE(mtx); |
| 770 | turnstile_wakeup(ts, TS_WRITER_Q, |
| 771 | TS_WAITERS(ts, TS_WRITER_Q), NULL); |
| 772 | } |
| 773 | } |
| 774 | |
| 775 | #ifndef __HAVE_SIMPLE_MUTEXES |
| 776 | /* |
| 777 | * mutex_wakeup: |
| 778 | * |
| 779 | * Support routine for mutex_exit() that wakes up all waiters. |
| 780 | * We assume that the mutex has been released, but it need not |
| 781 | * be. |
| 782 | */ |
| 783 | void |
| 784 | mutex_wakeup(kmutex_t *mtx) |
| 785 | { |
| 786 | turnstile_t *ts; |
| 787 | |
| 788 | ts = turnstile_lookup(mtx); |
| 789 | if (ts == NULL) { |
| 790 | turnstile_exit(mtx); |
| 791 | return; |
| 792 | } |
| 793 | MUTEX_CLEAR_WAITERS(mtx); |
| 794 | turnstile_wakeup(ts, TS_WRITER_Q, TS_WAITERS(ts, TS_WRITER_Q), NULL); |
| 795 | } |
| 796 | #endif /* !__HAVE_SIMPLE_MUTEXES */ |
| 797 | |
| 798 | /* |
| 799 | * mutex_owned: |
| 800 | * |
| 801 | * Return true if the current LWP (adaptive) or CPU (spin) |
| 802 | * holds the mutex. |
| 803 | */ |
| 804 | int |
| 805 | mutex_owned(kmutex_t *mtx) |
| 806 | { |
| 807 | |
| 808 | if (mtx == NULL) |
| 809 | return 0; |
| 810 | if (MUTEX_ADAPTIVE_P(mtx)) |
| 811 | return MUTEX_OWNER(mtx->mtx_owner) == (uintptr_t)curlwp; |
| 812 | #ifdef FULL |
| 813 | return MUTEX_SPINBIT_LOCKED_P(mtx); |
| 814 | #else |
| 815 | return 1; |
| 816 | #endif |
| 817 | } |
| 818 | |
| 819 | /* |
| 820 | * mutex_owner: |
| 821 | * |
| 822 | * Return the current owner of an adaptive mutex. Used for |
| 823 | * priority inheritance. |
| 824 | */ |
| 825 | lwp_t * |
| 826 | mutex_owner(kmutex_t *mtx) |
| 827 | { |
| 828 | |
| 829 | MUTEX_ASSERT(mtx, MUTEX_ADAPTIVE_P(mtx)); |
| 830 | return (struct lwp *)MUTEX_OWNER(mtx->mtx_owner); |
| 831 | } |
| 832 | |
| 833 | /* |
| 834 | * mutex_tryenter: |
| 835 | * |
| 836 | * Try to acquire the mutex; return non-zero if we did. |
| 837 | */ |
| 838 | int |
| 839 | mutex_tryenter(kmutex_t *mtx) |
| 840 | { |
| 841 | uintptr_t curthread; |
| 842 | |
| 843 | /* |
| 844 | * Handle spin mutexes. |
| 845 | */ |
| 846 | if (MUTEX_SPIN_P(mtx)) { |
| 847 | MUTEX_SPIN_SPLRAISE(mtx); |
| 848 | #ifdef FULL |
| 849 | if (MUTEX_SPINBIT_LOCK_TRY(mtx)) { |
| 850 | MUTEX_WANTLOCK(mtx); |
| 851 | MUTEX_LOCKED(mtx); |
| 852 | return 1; |
| 853 | } |
| 854 | MUTEX_SPIN_SPLRESTORE(mtx); |
| 855 | #else |
| 856 | MUTEX_WANTLOCK(mtx); |
| 857 | MUTEX_LOCKED(mtx); |
| 858 | return 1; |
| 859 | #endif |
| 860 | } else { |
| 861 | curthread = (uintptr_t)curlwp; |
| 862 | MUTEX_ASSERT(mtx, curthread != 0); |
| 863 | if (MUTEX_ACQUIRE(mtx, curthread)) { |
| 864 | MUTEX_WANTLOCK(mtx); |
| 865 | MUTEX_LOCKED(mtx); |
| 866 | MUTEX_DASSERT(mtx, |
| 867 | MUTEX_OWNER(mtx->mtx_owner) == curthread); |
| 868 | return 1; |
| 869 | } |
| 870 | } |
| 871 | |
| 872 | return 0; |
| 873 | } |
| 874 | |
| 875 | #if defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL) |
| 876 | /* |
| 877 | * mutex_spin_retry: |
| 878 | * |
| 879 | * Support routine for mutex_spin_enter(). Assumes that the caller |
| 880 | * has already raised the SPL, and adjusted counters. |
| 881 | */ |
| 882 | void |
| 883 | mutex_spin_retry(kmutex_t *mtx) |
| 884 | { |
| 885 | #ifdef MULTIPROCESSOR |
| 886 | u_int count; |
| 887 | LOCKSTAT_TIMER(spintime); |
| 888 | LOCKSTAT_FLAG(lsflag); |
| 889 | #ifdef LOCKDEBUG |
| 890 | u_int spins = 0; |
| 891 | #endif /* LOCKDEBUG */ |
| 892 | |
| 893 | MUTEX_WANTLOCK(mtx); |
| 894 | |
| 895 | LOCKSTAT_ENTER(lsflag); |
| 896 | LOCKSTAT_START_TIMER(lsflag, spintime); |
| 897 | count = SPINLOCK_BACKOFF_MIN; |
| 898 | |
| 899 | /* |
| 900 | * Spin testing the lock word and do exponential backoff |
| 901 | * to reduce cache line ping-ponging between CPUs. |
| 902 | */ |
| 903 | do { |
| 904 | if (panicstr != NULL) |
| 905 | break; |
| 906 | while (MUTEX_SPINBIT_LOCKED_P(mtx)) { |
| 907 | SPINLOCK_BACKOFF(count); |
| 908 | #ifdef LOCKDEBUG |
| 909 | if (SPINLOCK_SPINOUT(spins)) |
| 910 | MUTEX_ABORT(mtx, "spinout" ); |
| 911 | #endif /* LOCKDEBUG */ |
| 912 | } |
| 913 | } while (!MUTEX_SPINBIT_LOCK_TRY(mtx)); |
| 914 | |
| 915 | LOCKSTAT_STOP_TIMER(lsflag, spintime); |
| 916 | LOCKSTAT_EVENT(lsflag, mtx, LB_SPIN_MUTEX | LB_SPIN, 1, spintime); |
| 917 | LOCKSTAT_EXIT(lsflag); |
| 918 | |
| 919 | MUTEX_LOCKED(mtx); |
| 920 | #else /* MULTIPROCESSOR */ |
| 921 | MUTEX_ABORT(mtx, "locking against myself" ); |
| 922 | #endif /* MULTIPROCESSOR */ |
| 923 | } |
| 924 | #endif /* defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL) */ |
| 925 | |