1 /*- 2 * Copyright (c) 1982, 1986, 1990, 1991, 1993 3 * The Regents of the University of California. All rights reserved. 4 * (c) UNIX System Laboratories, Inc. 5 * All or some portions of this file are derived from material licensed 6 * to the University of California by American Telephone and Telegraph 7 * Co. or Unix System Laboratories, Inc. and are reproduced herein with 8 * the permission of UNIX System Laboratories, Inc. 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 * 4. Neither the name of the University nor the names of its contributors 19 * may be used to endorse or promote products derived from this software 20 * without specific prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32 * SUCH DAMAGE. 33 * 34 * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95 35 */ 36 37 #include <sys/cdefs.h> 38 __FBSDID("$FreeBSD$"); 39 40 #include "opt_kdtrace.h" 41 #include "opt_ktrace.h" 42 #include "opt_sched.h" 43 44 #include <sys/param.h> 45 #include <sys/systm.h> 46 #include <sys/condvar.h> 47 #include <sys/kdb.h> 48 #include <sys/kernel.h> 49 #include <sys/ktr.h> 50 #include <sys/lock.h> 51 #include <sys/mutex.h> 52 #include <sys/proc.h> 53 #include <sys/resourcevar.h> 54 #include <sys/sched.h> 55 #include <sys/sdt.h> 56 #include <sys/signalvar.h> 57 #include <sys/sleepqueue.h> 58 #include <sys/smp.h> 59 #include <sys/sx.h> 60 #include <sys/sysctl.h> 61 #include <sys/sysproto.h> 62 #include <sys/vmmeter.h> 63 #ifdef KTRACE 64 #include <sys/uio.h> 65 #include <sys/ktrace.h> 66 #endif 67 68 #include <machine/cpu.h> 69 70 #ifdef XEN 71 #include <vm/vm.h> 72 #include <vm/vm_param.h> 73 #include <vm/pmap.h> 74 #endif 75 76 #define KTDSTATE(td) \ 77 (((td)->td_inhibitors & TDI_SLEEPING) != 0 ? "sleep" : \ 78 ((td)->td_inhibitors & TDI_SUSPENDED) != 0 ? "suspended" : \ 79 ((td)->td_inhibitors & TDI_SWAPPED) != 0 ? "swapped" : \ 80 ((td)->td_inhibitors & TDI_LOCK) != 0 ? "blocked" : \ 81 ((td)->td_inhibitors & TDI_IWAIT) != 0 ? "iwait" : "yielding") 82 83 static void synch_setup(void *dummy); 84 SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup, 85 NULL); 86 87 int hogticks; 88 static uint8_t pause_wchan[MAXCPU]; 89 90 static struct callout loadav_callout; 91 92 struct loadavg averunnable = 93 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */ 94 /* 95 * Constants for averages over 1, 5, and 15 minutes 96 * when sampling at 5 second intervals. 97 */ 98 static fixpt_t cexp[3] = { 99 0.9200444146293232 * FSCALE, /* exp(-1/12) */ 100 0.9834714538216174 * FSCALE, /* exp(-1/60) */ 101 0.9944598480048967 * FSCALE, /* exp(-1/180) */ 102 }; 103 104 /* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */ 105 static int fscale __unused = FSCALE; 106 SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, ""); 107 108 static void loadav(void *arg); 109 110 SDT_PROVIDER_DECLARE(sched); 111 SDT_PROBE_DEFINE(sched, , , preempt, preempt); 112 113 /* 114 * These probes reference Solaris features that are not implemented in FreeBSD. 115 * Create the probes anyway for compatibility with existing D scripts; they'll 116 * just never fire. 117 */ 118 SDT_PROBE_DEFINE(sched, , , cpucaps_sleep, cpucaps-sleep); 119 SDT_PROBE_DEFINE(sched, , , cpucaps_wakeup, cpucaps-wakeup); 120 SDT_PROBE_DEFINE(sched, , , schedctl_nopreempt, schedctl-nopreempt); 121 SDT_PROBE_DEFINE(sched, , , schedctl_preempt, schedctl-preempt); 122 SDT_PROBE_DEFINE(sched, , , schedctl_yield, schedctl-yield); 123 124 static void 125 sleepinit(void *unused) 126 { 127 128 hogticks = (hz / 10) * 2; /* Default only. */ 129 init_sleepqueues(); 130 } 131 132 /* 133 * vmem tries to lock the sleepq mutexes when free'ing kva, so make sure 134 * it is available. 135 */ 136 SYSINIT(sleepinit, SI_SUB_KMEM, SI_ORDER_ANY, sleepinit, 0); 137 138 /* 139 * General sleep call. Suspends the current thread until a wakeup is 140 * performed on the specified identifier. The thread will then be made 141 * runnable with the specified priority. Sleeps at most sbt units of time 142 * (0 means no timeout). If pri includes the PCATCH flag, let signals 143 * interrupt the sleep, otherwise ignore them while sleeping. Returns 0 if 144 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a 145 * signal becomes pending, ERESTART is returned if the current system 146 * call should be restarted if possible, and EINTR is returned if the system 147 * call should be interrupted by the signal (return EINTR). 148 * 149 * The lock argument is unlocked before the caller is suspended, and 150 * re-locked before _sleep() returns. If priority includes the PDROP 151 * flag the lock is not re-locked before returning. 152 */ 153 int 154 _sleep(void *ident, struct lock_object *lock, int priority, 155 const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags) 156 { 157 struct thread *td; 158 struct proc *p; 159 struct lock_class *class; 160 uintptr_t lock_state; 161 int catch, pri, rval, sleepq_flags; 162 WITNESS_SAVE_DECL(lock_witness); 163 164 td = curthread; 165 p = td->td_proc; 166 #ifdef KTRACE 167 if (KTRPOINT(td, KTR_CSW)) 168 ktrcsw(1, 0, wmesg); 169 #endif 170 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, lock, 171 "Sleeping on \"%s\"", wmesg); 172 KASSERT(sbt != 0 || mtx_owned(&Giant) || lock != NULL, 173 ("sleeping without a lock")); 174 KASSERT(p != NULL, ("msleep1")); 175 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep")); 176 if (priority & PDROP) 177 KASSERT(lock != NULL && lock != &Giant.lock_object, 178 ("PDROP requires a non-Giant lock")); 179 if (lock != NULL) 180 class = LOCK_CLASS(lock); 181 else 182 class = NULL; 183 184 if (cold || SCHEDULER_STOPPED()) { 185 /* 186 * During autoconfiguration, just return; 187 * don't run any other threads or panic below, 188 * in case this is the idle thread and already asleep. 189 * XXX: this used to do "s = splhigh(); splx(safepri); 190 * splx(s);" to give interrupts a chance, but there is 191 * no way to give interrupts a chance now. 192 */ 193 if (lock != NULL && priority & PDROP) 194 class->lc_unlock(lock); 195 return (0); 196 } 197 catch = priority & PCATCH; 198 pri = priority & PRIMASK; 199 200 /* 201 * If we are already on a sleep queue, then remove us from that 202 * sleep queue first. We have to do this to handle recursive 203 * sleeps. 204 */ 205 if (TD_ON_SLEEPQ(td)) 206 sleepq_remove(td, td->td_wchan); 207 208 if ((uint8_t *)ident >= &pause_wchan[0] && 209 (uint8_t *)ident <= &pause_wchan[MAXCPU - 1]) 210 sleepq_flags = SLEEPQ_PAUSE; 211 else 212 sleepq_flags = SLEEPQ_SLEEP; 213 if (catch) 214 sleepq_flags |= SLEEPQ_INTERRUPTIBLE; 215 216 sleepq_lock(ident); 217 CTR5(KTR_PROC, "sleep: thread %ld (pid %ld, %s) on %s (%p)", 218 td->td_tid, p->p_pid, td->td_name, wmesg, ident); 219 220 if (lock == &Giant.lock_object) 221 mtx_assert(&Giant, MA_OWNED); 222 DROP_GIANT(); 223 if (lock != NULL && lock != &Giant.lock_object && 224 !(class->lc_flags & LC_SLEEPABLE)) { 225 WITNESS_SAVE(lock, lock_witness); 226 lock_state = class->lc_unlock(lock); 227 } else 228 /* GCC needs to follow the Yellow Brick Road */ 229 lock_state = -1; 230 231 /* 232 * We put ourselves on the sleep queue and start our timeout 233 * before calling thread_suspend_check, as we could stop there, 234 * and a wakeup or a SIGCONT (or both) could occur while we were 235 * stopped without resuming us. Thus, we must be ready for sleep 236 * when cursig() is called. If the wakeup happens while we're 237 * stopped, then td will no longer be on a sleep queue upon 238 * return from cursig(). 239 */ 240 sleepq_add(ident, lock, wmesg, sleepq_flags, 0); 241 if (sbt != 0) 242 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 243 if (lock != NULL && class->lc_flags & LC_SLEEPABLE) { 244 sleepq_release(ident); 245 WITNESS_SAVE(lock, lock_witness); 246 lock_state = class->lc_unlock(lock); 247 sleepq_lock(ident); 248 } 249 if (sbt != 0 && catch) 250 rval = sleepq_timedwait_sig(ident, pri); 251 else if (sbt != 0) 252 rval = sleepq_timedwait(ident, pri); 253 else if (catch) 254 rval = sleepq_wait_sig(ident, pri); 255 else { 256 sleepq_wait(ident, pri); 257 rval = 0; 258 } 259 #ifdef KTRACE 260 if (KTRPOINT(td, KTR_CSW)) 261 ktrcsw(0, 0, wmesg); 262 #endif 263 PICKUP_GIANT(); 264 if (lock != NULL && lock != &Giant.lock_object && !(priority & PDROP)) { 265 class->lc_lock(lock, lock_state); 266 WITNESS_RESTORE(lock, lock_witness); 267 } 268 return (rval); 269 } 270 271 int 272 msleep_spin_sbt(void *ident, struct mtx *mtx, const char *wmesg, 273 sbintime_t sbt, sbintime_t pr, int flags) 274 { 275 struct thread *td; 276 struct proc *p; 277 int rval; 278 WITNESS_SAVE_DECL(mtx); 279 280 td = curthread; 281 p = td->td_proc; 282 KASSERT(mtx != NULL, ("sleeping without a mutex")); 283 KASSERT(p != NULL, ("msleep1")); 284 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep")); 285 286 if (cold || SCHEDULER_STOPPED()) { 287 /* 288 * During autoconfiguration, just return; 289 * don't run any other threads or panic below, 290 * in case this is the idle thread and already asleep. 291 * XXX: this used to do "s = splhigh(); splx(safepri); 292 * splx(s);" to give interrupts a chance, but there is 293 * no way to give interrupts a chance now. 294 */ 295 return (0); 296 } 297 298 sleepq_lock(ident); 299 CTR5(KTR_PROC, "msleep_spin: thread %ld (pid %ld, %s) on %s (%p)", 300 td->td_tid, p->p_pid, td->td_name, wmesg, ident); 301 302 DROP_GIANT(); 303 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED); 304 WITNESS_SAVE(&mtx->lock_object, mtx); 305 mtx_unlock_spin(mtx); 306 307 /* 308 * We put ourselves on the sleep queue and start our timeout. 309 */ 310 sleepq_add(ident, &mtx->lock_object, wmesg, SLEEPQ_SLEEP, 0); 311 if (sbt != 0) 312 sleepq_set_timeout_sbt(ident, sbt, pr, flags); 313 314 /* 315 * Can't call ktrace with any spin locks held so it can lock the 316 * ktrace_mtx lock, and WITNESS_WARN considers it an error to hold 317 * any spin lock. Thus, we have to drop the sleepq spin lock while 318 * we handle those requests. This is safe since we have placed our 319 * thread on the sleep queue already. 320 */ 321 #ifdef KTRACE 322 if (KTRPOINT(td, KTR_CSW)) { 323 sleepq_release(ident); 324 ktrcsw(1, 0, wmesg); 325 sleepq_lock(ident); 326 } 327 #endif 328 #ifdef WITNESS 329 sleepq_release(ident); 330 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "Sleeping on \"%s\"", 331 wmesg); 332 sleepq_lock(ident); 333 #endif 334 if (sbt != 0) 335 rval = sleepq_timedwait(ident, 0); 336 else { 337 sleepq_wait(ident, 0); 338 rval = 0; 339 } 340 #ifdef KTRACE 341 if (KTRPOINT(td, KTR_CSW)) 342 ktrcsw(0, 0, wmesg); 343 #endif 344 PICKUP_GIANT(); 345 mtx_lock_spin(mtx); 346 WITNESS_RESTORE(&mtx->lock_object, mtx); 347 return (rval); 348 } 349 350 /* 351 * pause() delays the calling thread by the given number of system ticks. 352 * During cold bootup, pause() uses the DELAY() function instead of 353 * the tsleep() function to do the waiting. The "timo" argument must be 354 * greater than or equal to zero. A "timo" value of zero is equivalent 355 * to a "timo" value of one. 356 */ 357 int 358 pause_sbt(const char *wmesg, sbintime_t sbt, sbintime_t pr, int flags) 359 { 360 KASSERT(sbt >= 0, ("pause: timeout must be >= 0")); 361 362 /* silently convert invalid timeouts */ 363 if (sbt == 0) 364 sbt = tick_sbt; 365 366 if (cold) { 367 /* 368 * We delay one second at a time to avoid overflowing the 369 * system specific DELAY() function(s): 370 */ 371 while (sbt >= SBT_1S) { 372 DELAY(1000000); 373 sbt -= SBT_1S; 374 } 375 /* Do the delay remainder, if any */ 376 sbt = (sbt + SBT_1US - 1) / SBT_1US; 377 if (sbt > 0) 378 DELAY(sbt); 379 return (0); 380 } 381 return (_sleep(&pause_wchan[curcpu], NULL, 0, wmesg, sbt, pr, flags)); 382 } 383 384 /* 385 * Make all threads sleeping on the specified identifier runnable. 386 */ 387 void 388 wakeup(void *ident) 389 { 390 int wakeup_swapper; 391 392 sleepq_lock(ident); 393 wakeup_swapper = sleepq_broadcast(ident, SLEEPQ_SLEEP, 0, 0); 394 sleepq_release(ident); 395 if (wakeup_swapper) { 396 KASSERT(ident != &proc0, 397 ("wakeup and wakeup_swapper and proc0")); 398 kick_proc0(); 399 } 400 } 401 402 /* 403 * Make a thread sleeping on the specified identifier runnable. 404 * May wake more than one thread if a target thread is currently 405 * swapped out. 406 */ 407 void 408 wakeup_one(void *ident) 409 { 410 int wakeup_swapper; 411 412 sleepq_lock(ident); 413 wakeup_swapper = sleepq_signal(ident, SLEEPQ_SLEEP, 0, 0); 414 sleepq_release(ident); 415 if (wakeup_swapper) 416 kick_proc0(); 417 } 418 419 static void 420 kdb_switch(void) 421 { 422 thread_unlock(curthread); 423 kdb_backtrace(); 424 kdb_reenter(); 425 panic("%s: did not reenter debugger", __func__); 426 } 427 428 /* 429 * The machine independent parts of context switching. 430 */ 431 void 432 mi_switch(int flags, struct thread *newtd) 433 { 434 uint64_t runtime, new_switchtime; 435 struct thread *td; 436 struct proc *p; 437 438 td = curthread; /* XXX */ 439 THREAD_LOCK_ASSERT(td, MA_OWNED | MA_NOTRECURSED); 440 p = td->td_proc; /* XXX */ 441 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code")); 442 #ifdef INVARIANTS 443 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td)) 444 mtx_assert(&Giant, MA_NOTOWNED); 445 #endif 446 KASSERT(td->td_critnest == 1 || panicstr, 447 ("mi_switch: switch in a critical section")); 448 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0, 449 ("mi_switch: switch must be voluntary or involuntary")); 450 KASSERT(newtd != curthread, ("mi_switch: preempting back to ourself")); 451 452 /* 453 * Don't perform context switches from the debugger. 454 */ 455 if (kdb_active) 456 kdb_switch(); 457 if (SCHEDULER_STOPPED()) 458 return; 459 if (flags & SW_VOL) { 460 td->td_ru.ru_nvcsw++; 461 td->td_swvoltick = ticks; 462 } else 463 td->td_ru.ru_nivcsw++; 464 #ifdef SCHED_STATS 465 SCHED_STAT_INC(sched_switch_stats[flags & SW_TYPE_MASK]); 466 #endif 467 /* 468 * Compute the amount of time during which the current 469 * thread was running, and add that to its total so far. 470 */ 471 new_switchtime = cpu_ticks(); 472 runtime = new_switchtime - PCPU_GET(switchtime); 473 td->td_runtime += runtime; 474 td->td_incruntime += runtime; 475 PCPU_SET(switchtime, new_switchtime); 476 td->td_generation++; /* bump preempt-detect counter */ 477 PCPU_INC(cnt.v_swtch); 478 PCPU_SET(switchticks, ticks); 479 CTR4(KTR_PROC, "mi_switch: old thread %ld (td_sched %p, pid %ld, %s)", 480 td->td_tid, td->td_sched, p->p_pid, td->td_name); 481 #if (KTR_COMPILE & KTR_SCHED) != 0 482 if (TD_IS_IDLETHREAD(td)) 483 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "idle", 484 "prio:%d", td->td_priority); 485 else 486 KTR_STATE3(KTR_SCHED, "thread", sched_tdname(td), KTDSTATE(td), 487 "prio:%d", td->td_priority, "wmesg:\"%s\"", td->td_wmesg, 488 "lockname:\"%s\"", td->td_lockname); 489 #endif 490 SDT_PROBE0(sched, , , preempt); 491 #ifdef XEN 492 PT_UPDATES_FLUSH(); 493 #endif 494 sched_switch(td, newtd, flags); 495 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(td), "running", 496 "prio:%d", td->td_priority); 497 498 CTR4(KTR_PROC, "mi_switch: new thread %ld (td_sched %p, pid %ld, %s)", 499 td->td_tid, td->td_sched, p->p_pid, td->td_name); 500 501 /* 502 * If the last thread was exiting, finish cleaning it up. 503 */ 504 if ((td = PCPU_GET(deadthread))) { 505 PCPU_SET(deadthread, NULL); 506 thread_stash(td); 507 } 508 } 509 510 /* 511 * Change thread state to be runnable, placing it on the run queue if 512 * it is in memory. If it is swapped out, return true so our caller 513 * will know to awaken the swapper. 514 */ 515 int 516 setrunnable(struct thread *td) 517 { 518 519 THREAD_LOCK_ASSERT(td, MA_OWNED); 520 KASSERT(td->td_proc->p_state != PRS_ZOMBIE, 521 ("setrunnable: pid %d is a zombie", td->td_proc->p_pid)); 522 switch (td->td_state) { 523 case TDS_RUNNING: 524 case TDS_RUNQ: 525 return (0); 526 case TDS_INHIBITED: 527 /* 528 * If we are only inhibited because we are swapped out 529 * then arange to swap in this process. Otherwise just return. 530 */ 531 if (td->td_inhibitors != TDI_SWAPPED) 532 return (0); 533 /* FALLTHROUGH */ 534 case TDS_CAN_RUN: 535 break; 536 default: 537 printf("state is 0x%x", td->td_state); 538 panic("setrunnable(2)"); 539 } 540 if ((td->td_flags & TDF_INMEM) == 0) { 541 if ((td->td_flags & TDF_SWAPINREQ) == 0) { 542 td->td_flags |= TDF_SWAPINREQ; 543 return (1); 544 } 545 } else 546 sched_wakeup(td); 547 return (0); 548 } 549 550 /* 551 * Compute a tenex style load average of a quantity on 552 * 1, 5 and 15 minute intervals. 553 */ 554 static void 555 loadav(void *arg) 556 { 557 int i, nrun; 558 struct loadavg *avg; 559 560 nrun = sched_load(); 561 avg = &averunnable; 562 563 for (i = 0; i < 3; i++) 564 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] + 565 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT; 566 567 /* 568 * Schedule the next update to occur after 5 seconds, but add a 569 * random variation to avoid synchronisation with processes that 570 * run at regular intervals. 571 */ 572 callout_reset_sbt(&loadav_callout, 573 tick_sbt * (hz * 4 + (int)(random() % (hz * 2 + 1))), 0, 574 loadav, NULL, C_DIRECT_EXEC | C_HARDCLOCK); 575 } 576 577 /* ARGSUSED */ 578 static void 579 synch_setup(void *dummy) 580 { 581 callout_init(&loadav_callout, CALLOUT_MPSAFE); 582 583 /* Kick off timeout driven events by calling first time. */ 584 loadav(NULL); 585 } 586 587 int 588 should_yield(void) 589 { 590 591 return ((unsigned int)(ticks - curthread->td_swvoltick) >= hogticks); 592 } 593 594 void 595 maybe_yield(void) 596 { 597 598 if (should_yield()) 599 kern_yield(PRI_USER); 600 } 601 602 void 603 kern_yield(int prio) 604 { 605 struct thread *td; 606 607 td = curthread; 608 DROP_GIANT(); 609 thread_lock(td); 610 if (prio == PRI_USER) 611 prio = td->td_user_pri; 612 if (prio >= 0) 613 sched_prio(td, prio); 614 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 615 thread_unlock(td); 616 PICKUP_GIANT(); 617 } 618 619 /* 620 * General purpose yield system call. 621 */ 622 int 623 sys_yield(struct thread *td, struct yield_args *uap) 624 { 625 626 thread_lock(td); 627 if (PRI_BASE(td->td_pri_class) == PRI_TIMESHARE) 628 sched_prio(td, PRI_MAX_TIMESHARE); 629 mi_switch(SW_VOL | SWT_RELINQUISH, NULL); 630 thread_unlock(td); 631 td->td_retval[0] = 0; 632 return (0); 633 } 634