kern_synch.c revision 125162
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 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the University of 21 * California, Berkeley and its contributors. 22 * 4. Neither the name of the University nor the names of its contributors 23 * may be used to endorse or promote products derived from this software 24 * without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 27 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 28 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 29 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 30 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 31 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 32 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 33 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 34 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 35 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 36 * SUCH DAMAGE. 37 * 38 * @(#)kern_synch.c 8.9 (Berkeley) 5/19/95 39 */ 40 41#include <sys/cdefs.h> 42__FBSDID("$FreeBSD: head/sys/kern/kern_synch.c 125162 2004-01-28 20:44:41Z jhb $"); 43 44#include "opt_ddb.h" 45#include "opt_ktrace.h" 46 47#include <sys/param.h> 48#include <sys/systm.h> 49#include <sys/condvar.h> 50#include <sys/kernel.h> 51#include <sys/ktr.h> 52#include <sys/kthread.h> 53#include <sys/lock.h> 54#include <sys/mutex.h> 55#include <sys/proc.h> 56#include <sys/resourcevar.h> 57#include <sys/sched.h> 58#include <sys/signalvar.h> 59#include <sys/smp.h> 60#include <sys/sx.h> 61#include <sys/sysctl.h> 62#include <sys/sysproto.h> 63#include <sys/vmmeter.h> 64#ifdef DDB 65#include <ddb/ddb.h> 66#endif 67#ifdef KTRACE 68#include <sys/uio.h> 69#include <sys/ktrace.h> 70#endif 71 72#include <machine/cpu.h> 73 74static void synch_setup(void *dummy); 75SYSINIT(synch_setup, SI_SUB_KICK_SCHEDULER, SI_ORDER_FIRST, synch_setup, NULL) 76 77int hogticks; 78int lbolt; 79 80static struct callout lbolt_callout; 81 82struct loadavg averunnable = 83 { {0, 0, 0}, FSCALE }; /* load average, of runnable procs */ 84/* 85 * Constants for averages over 1, 5, and 15 minutes 86 * when sampling at 5 second intervals. 87 */ 88static fixpt_t cexp[3] = { 89 0.9200444146293232 * FSCALE, /* exp(-1/12) */ 90 0.9834714538216174 * FSCALE, /* exp(-1/60) */ 91 0.9944598480048967 * FSCALE, /* exp(-1/180) */ 92}; 93 94/* kernel uses `FSCALE', userland (SHOULD) use kern.fscale */ 95static int fscale __unused = FSCALE; 96SYSCTL_INT(_kern, OID_AUTO, fscale, CTLFLAG_RD, 0, FSCALE, ""); 97 98static void endtsleep(void *); 99static void loadav(void); 100static void loadav_thread(void *dummy); 101static void lboltcb(void *arg); 102 103/* 104 * We're only looking at 7 bits of the address; everything is 105 * aligned to 4, lots of things are aligned to greater powers 106 * of 2. Shift right by 8, i.e. drop the bottom 256 worth. 107 */ 108#define TABLESIZE 128 109static TAILQ_HEAD(slpquehead, thread) slpque[TABLESIZE]; 110#define LOOKUP(x) (((intptr_t)(x) >> 8) & (TABLESIZE - 1)) 111 112void 113sleepinit(void) 114{ 115 int i; 116 117 hogticks = (hz / 10) * 2; /* Default only. */ 118 for (i = 0; i < TABLESIZE; i++) 119 TAILQ_INIT(&slpque[i]); 120} 121 122/* 123 * General sleep call. Suspends the current process until a wakeup is 124 * performed on the specified identifier. The process will then be made 125 * runnable with the specified priority. Sleeps at most timo/hz seconds 126 * (0 means no timeout). If pri includes PCATCH flag, signals are checked 127 * before and after sleeping, else signals are not checked. Returns 0 if 128 * awakened, EWOULDBLOCK if the timeout expires. If PCATCH is set and a 129 * signal needs to be delivered, ERESTART is returned if the current system 130 * call should be restarted if possible, and EINTR is returned if the system 131 * call should be interrupted by the signal (return EINTR). 132 * 133 * The mutex argument is exited before the caller is suspended, and 134 * entered before msleep returns. If priority includes the PDROP 135 * flag the mutex is not entered before returning. 136 */ 137 138int 139msleep(ident, mtx, priority, wmesg, timo) 140 void *ident; 141 struct mtx *mtx; 142 int priority, timo; 143 const char *wmesg; 144{ 145 struct thread *td = curthread; 146 struct proc *p = td->td_proc; 147 int sig, catch = priority & PCATCH; 148 int rval = 0; 149 WITNESS_SAVE_DECL(mtx); 150 151#ifdef KTRACE 152 if (KTRPOINT(td, KTR_CSW)) 153 ktrcsw(1, 0); 154#endif 155 /* XXX: mtx == NULL ?? */ 156 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, &mtx->mtx_object, 157 "Sleeping on \"%s\"", wmesg); 158 KASSERT(timo != 0 || mtx_owned(&Giant) || mtx != NULL, 159 ("sleeping without a mutex")); 160 /* 161 * If we are capable of async syscalls and there isn't already 162 * another one ready to return, start a new thread 163 * and queue it as ready to run. Note that there is danger here 164 * because we need to make sure that we don't sleep allocating 165 * the thread (recursion here might be bad). 166 */ 167 mtx_lock_spin(&sched_lock); 168 if (p->p_flag & P_SA || p->p_numthreads > 1) { 169 /* 170 * Just don't bother if we are exiting 171 * and not the exiting thread or thread was marked as 172 * interrupted. 173 */ 174 if (catch) { 175 if ((p->p_flag & P_WEXIT) && p->p_singlethread != td) { 176 mtx_unlock_spin(&sched_lock); 177 return (EINTR); 178 } 179 if (td->td_flags & TDF_INTERRUPT) { 180 mtx_unlock_spin(&sched_lock); 181 return (td->td_intrval); 182 } 183 } 184 } 185 if (cold ) { 186 /* 187 * During autoconfiguration, just return; 188 * don't run any other procs or panic below, 189 * in case this is the idle process and already asleep. 190 * XXX: this used to do "s = splhigh(); splx(safepri); 191 * splx(s);" to give interrupts a chance, but there is 192 * no way to give interrupts a chance now. 193 */ 194 if (mtx != NULL && priority & PDROP) 195 mtx_unlock(mtx); 196 mtx_unlock_spin(&sched_lock); 197 return (0); 198 } 199 DROP_GIANT(); 200 if (mtx != NULL) { 201 mtx_assert(mtx, MA_OWNED | MA_NOTRECURSED); 202 WITNESS_SAVE(&mtx->mtx_object, mtx); 203 mtx_unlock(mtx); 204 if (priority & PDROP) 205 mtx = NULL; 206 } 207 KASSERT(p != NULL, ("msleep1")); 208 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("msleep")); 209 210 CTR5(KTR_PROC, "msleep: thread %p (pid %d, %s) on %s (%p)", 211 td, p->p_pid, p->p_comm, wmesg, ident); 212 213 td->td_wchan = ident; 214 td->td_wmesg = wmesg; 215 TAILQ_INSERT_TAIL(&slpque[LOOKUP(ident)], td, td_slpq); 216 TD_SET_ON_SLEEPQ(td); 217 if (timo) 218 callout_reset(&td->td_slpcallout, timo, endtsleep, td); 219 /* 220 * We put ourselves on the sleep queue and start our timeout 221 * before calling thread_suspend_check, as we could stop there, and 222 * a wakeup or a SIGCONT (or both) could occur while we were stopped. 223 * without resuming us, thus we must be ready for sleep 224 * when cursig is called. If the wakeup happens while we're 225 * stopped, td->td_wchan will be 0 upon return from cursig. 226 */ 227 if (catch) { 228 CTR3(KTR_PROC, "msleep caught: thread %p (pid %d, %s)", td, 229 p->p_pid, p->p_comm); 230 td->td_flags |= TDF_SINTR; 231 mtx_unlock_spin(&sched_lock); 232 PROC_LOCK(p); 233 mtx_lock(&p->p_sigacts->ps_mtx); 234 sig = cursig(td); 235 mtx_unlock(&p->p_sigacts->ps_mtx); 236 if (sig == 0 && thread_suspend_check(1)) 237 sig = SIGSTOP; 238 mtx_lock_spin(&sched_lock); 239 PROC_UNLOCK(p); 240 if (sig != 0) { 241 if (TD_ON_SLEEPQ(td)) 242 unsleep(td); 243 } else if (!TD_ON_SLEEPQ(td)) 244 catch = 0; 245 } else 246 sig = 0; 247 248 /* 249 * Let the scheduler know we're about to voluntarily go to sleep. 250 */ 251 sched_sleep(td, priority & PRIMASK); 252 253 if (TD_ON_SLEEPQ(td)) { 254 TD_SET_SLEEPING(td); 255 mi_switch(SW_VOL); 256 } 257 /* 258 * We're awake from voluntary sleep. 259 */ 260 CTR3(KTR_PROC, "msleep resume: thread %p (pid %d, %s)", td, p->p_pid, 261 p->p_comm); 262 KASSERT(TD_IS_RUNNING(td), ("running but not TDS_RUNNING")); 263 td->td_flags &= ~TDF_SINTR; 264 if (td->td_flags & TDF_TIMEOUT) { 265 td->td_flags &= ~TDF_TIMEOUT; 266 if (sig == 0) 267 rval = EWOULDBLOCK; 268 } else if (td->td_flags & TDF_TIMOFAIL) { 269 td->td_flags &= ~TDF_TIMOFAIL; 270 } else if (timo && callout_stop(&td->td_slpcallout) == 0) { 271 /* 272 * This isn't supposed to be pretty. If we are here, then 273 * the endtsleep() callout is currently executing on another 274 * CPU and is either spinning on the sched_lock or will be 275 * soon. If we don't synchronize here, there is a chance 276 * that this process may msleep() again before the callout 277 * has a chance to run and the callout may end up waking up 278 * the wrong msleep(). Yuck. 279 */ 280 TD_SET_SLEEPING(td); 281 mi_switch(SW_INVOL); 282 td->td_flags &= ~TDF_TIMOFAIL; 283 } 284 if ((td->td_flags & TDF_INTERRUPT) && (priority & PCATCH) && 285 (rval == 0)) { 286 rval = td->td_intrval; 287 } 288 mtx_unlock_spin(&sched_lock); 289 if (rval == 0 && catch) { 290 PROC_LOCK(p); 291 /* XXX: shouldn't we always be calling cursig()? */ 292 mtx_lock(&p->p_sigacts->ps_mtx); 293 if (sig != 0 || (sig = cursig(td))) { 294 if (SIGISMEMBER(p->p_sigacts->ps_sigintr, sig)) 295 rval = EINTR; 296 else 297 rval = ERESTART; 298 } 299 mtx_unlock(&p->p_sigacts->ps_mtx); 300 PROC_UNLOCK(p); 301 } 302#ifdef KTRACE 303 if (KTRPOINT(td, KTR_CSW)) 304 ktrcsw(0, 0); 305#endif 306 PICKUP_GIANT(); 307 if (mtx != NULL) { 308 mtx_lock(mtx); 309 WITNESS_RESTORE(&mtx->mtx_object, mtx); 310 } 311 return (rval); 312} 313 314/* 315 * Implement timeout for msleep(). 316 * 317 * If process hasn't been awakened (wchan non-zero), 318 * set timeout flag and undo the sleep. If proc 319 * is stopped, just unsleep so it will remain stopped. 320 * MP-safe, called without the Giant mutex. 321 */ 322static void 323endtsleep(arg) 324 void *arg; 325{ 326 register struct thread *td; 327 328 td = (struct thread *)arg; 329 CTR3(KTR_PROC, "endtsleep: thread %p (pid %d, %s)", 330 td, td->td_proc->p_pid, td->td_proc->p_comm); 331 mtx_lock_spin(&sched_lock); 332 /* 333 * This is the other half of the synchronization with msleep() 334 * described above. If the TDS_TIMEOUT flag is set, we lost the 335 * race and just need to put the process back on the runqueue. 336 */ 337 if (TD_ON_SLEEPQ(td)) { 338 TAILQ_REMOVE(&slpque[LOOKUP(td->td_wchan)], td, td_slpq); 339 TD_CLR_ON_SLEEPQ(td); 340 td->td_flags |= TDF_TIMEOUT; 341 td->td_wmesg = NULL; 342 } else 343 td->td_flags |= TDF_TIMOFAIL; 344 TD_CLR_SLEEPING(td); 345 setrunnable(td); 346 mtx_unlock_spin(&sched_lock); 347} 348 349/* 350 * Abort a thread, as if an interrupt had occured. Only abort 351 * interruptable waits (unfortunatly it isn't only safe to abort others). 352 * This is about identical to cv_abort(). 353 * Think about merging them? 354 * Also, whatever the signal code does... 355 */ 356void 357abortsleep(struct thread *td) 358{ 359 360 mtx_assert(&sched_lock, MA_OWNED); 361 /* 362 * If the TDF_TIMEOUT flag is set, just leave. A 363 * timeout is scheduled anyhow. 364 */ 365 if ((td->td_flags & (TDF_TIMEOUT | TDF_SINTR)) == TDF_SINTR) { 366 if (TD_ON_SLEEPQ(td)) { 367 unsleep(td); 368 TD_CLR_SLEEPING(td); 369 setrunnable(td); 370 } 371 } 372} 373 374/* 375 * Remove a process from its wait queue 376 */ 377void 378unsleep(struct thread *td) 379{ 380 381 mtx_lock_spin(&sched_lock); 382 if (TD_ON_SLEEPQ(td)) { 383 TAILQ_REMOVE(&slpque[LOOKUP(td->td_wchan)], td, td_slpq); 384 TD_CLR_ON_SLEEPQ(td); 385 td->td_wmesg = NULL; 386 } 387 mtx_unlock_spin(&sched_lock); 388} 389 390/* 391 * Make all processes sleeping on the specified identifier runnable. 392 */ 393void 394wakeup(ident) 395 register void *ident; 396{ 397 register struct slpquehead *qp; 398 register struct thread *td; 399 struct thread *ntd; 400 struct proc *p; 401 402 mtx_lock_spin(&sched_lock); 403 qp = &slpque[LOOKUP(ident)]; 404restart: 405 for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) { 406 ntd = TAILQ_NEXT(td, td_slpq); 407 if (td->td_wchan == ident) { 408 unsleep(td); 409 TD_CLR_SLEEPING(td); 410 setrunnable(td); 411 p = td->td_proc; 412 CTR3(KTR_PROC,"wakeup: thread %p (pid %d, %s)", 413 td, p->p_pid, p->p_comm); 414 goto restart; 415 } 416 } 417 mtx_unlock_spin(&sched_lock); 418} 419 420/* 421 * Make a process sleeping on the specified identifier runnable. 422 * May wake more than one process if a target process is currently 423 * swapped out. 424 */ 425void 426wakeup_one(ident) 427 register void *ident; 428{ 429 register struct proc *p; 430 register struct slpquehead *qp; 431 register struct thread *td; 432 struct thread *ntd; 433 434 mtx_lock_spin(&sched_lock); 435 qp = &slpque[LOOKUP(ident)]; 436 for (td = TAILQ_FIRST(qp); td != NULL; td = ntd) { 437 ntd = TAILQ_NEXT(td, td_slpq); 438 if (td->td_wchan == ident) { 439 unsleep(td); 440 TD_CLR_SLEEPING(td); 441 setrunnable(td); 442 p = td->td_proc; 443 CTR3(KTR_PROC,"wakeup1: thread %p (pid %d, %s)", 444 td, p->p_pid, p->p_comm); 445 break; 446 } 447 } 448 mtx_unlock_spin(&sched_lock); 449} 450 451/* 452 * The machine independent parts of mi_switch(). 453 */ 454void 455mi_switch(int flags) 456{ 457 struct bintime new_switchtime; 458 struct thread *td; 459 struct proc *p; 460 461 mtx_assert(&sched_lock, MA_OWNED | MA_NOTRECURSED); 462 td = curthread; /* XXX */ 463 p = td->td_proc; /* XXX */ 464 KASSERT(!TD_ON_RUNQ(td), ("mi_switch: called by old code")); 465#ifdef INVARIANTS 466 if (!TD_ON_LOCK(td) && !TD_IS_RUNNING(td)) 467 mtx_assert(&Giant, MA_NOTOWNED); 468#endif 469 KASSERT(td->td_critnest == 1, 470 ("mi_switch: switch in a critical section")); 471 KASSERT((flags & (SW_INVOL | SW_VOL)) != 0, 472 ("mi_switch: switch must be voluntary or involuntary")); 473 474 if (flags & SW_VOL) 475 p->p_stats->p_ru.ru_nvcsw++; 476 else 477 p->p_stats->p_ru.ru_nivcsw++; 478 /* 479 * Compute the amount of time during which the current 480 * process was running, and add that to its total so far. 481 */ 482 binuptime(&new_switchtime); 483 bintime_add(&p->p_runtime, &new_switchtime); 484 bintime_sub(&p->p_runtime, PCPU_PTR(switchtime)); 485 486 td->td_generation++; /* bump preempt-detect counter */ 487 488#ifdef DDB 489 /* 490 * Don't perform context switches from the debugger. 491 */ 492 if (db_active) { 493 mtx_unlock_spin(&sched_lock); 494 db_print_backtrace(); 495 db_error("Context switches not allowed in the debugger"); 496 } 497#endif 498 499 /* 500 * Check if the process exceeds its cpu resource allocation. If 501 * over max, arrange to kill the process in ast(). 502 */ 503 if (p->p_cpulimit != RLIM_INFINITY && 504 p->p_runtime.sec > p->p_cpulimit) { 505 p->p_sflag |= PS_XCPU; 506 td->td_flags |= TDF_ASTPENDING; 507 } 508 509 /* 510 * Finish up stats for outgoing thread. 511 */ 512 cnt.v_swtch++; 513 PCPU_SET(switchtime, new_switchtime); 514 PCPU_SET(switchticks, ticks); 515 CTR3(KTR_PROC, "mi_switch: old thread %p (pid %d, %s)", td, p->p_pid, 516 p->p_comm); 517 if (td->td_proc->p_flag & P_SA) 518 thread_switchout(td); 519 sched_switch(td); 520 521 CTR3(KTR_PROC, "mi_switch: new thread %p (pid %d, %s)", td, p->p_pid, 522 p->p_comm); 523 524 /* 525 * If the last thread was exiting, finish cleaning it up. 526 */ 527 if ((td = PCPU_GET(deadthread))) { 528 PCPU_SET(deadthread, NULL); 529 thread_stash(td); 530 } 531} 532 533/* 534 * Change process state to be runnable, 535 * placing it on the run queue if it is in memory, 536 * and awakening the swapper if it isn't in memory. 537 */ 538void 539setrunnable(struct thread *td) 540{ 541 struct proc *p; 542 543 p = td->td_proc; 544 mtx_assert(&sched_lock, MA_OWNED); 545 switch (p->p_state) { 546 case PRS_ZOMBIE: 547 panic("setrunnable(1)"); 548 default: 549 break; 550 } 551 switch (td->td_state) { 552 case TDS_RUNNING: 553 case TDS_RUNQ: 554 return; 555 case TDS_INHIBITED: 556 /* 557 * If we are only inhibited because we are swapped out 558 * then arange to swap in this process. Otherwise just return. 559 */ 560 if (td->td_inhibitors != TDI_SWAPPED) 561 return; 562 /* XXX: intentional fall-through ? */ 563 case TDS_CAN_RUN: 564 break; 565 default: 566 printf("state is 0x%x", td->td_state); 567 panic("setrunnable(2)"); 568 } 569 if ((p->p_sflag & PS_INMEM) == 0) { 570 if ((p->p_sflag & PS_SWAPPINGIN) == 0) { 571 p->p_sflag |= PS_SWAPINREQ; 572 wakeup(&proc0); 573 } 574 } else 575 sched_wakeup(td); 576} 577 578/* 579 * Compute a tenex style load average of a quantity on 580 * 1, 5 and 15 minute intervals. 581 * XXXKSE Needs complete rewrite when correct info is available. 582 * Completely Bogus.. only works with 1:1 (but compiles ok now :-) 583 */ 584static void 585loadav(void) 586{ 587 int i, nrun; 588 struct loadavg *avg; 589 struct proc *p; 590 struct thread *td; 591 592 avg = &averunnable; 593 sx_slock(&allproc_lock); 594 nrun = 0; 595 FOREACH_PROC_IN_SYSTEM(p) { 596 FOREACH_THREAD_IN_PROC(p, td) { 597 switch (td->td_state) { 598 case TDS_RUNQ: 599 case TDS_RUNNING: 600 if ((p->p_flag & P_NOLOAD) != 0) 601 goto nextproc; 602 nrun++; /* XXXKSE */ 603 default: 604 break; 605 } 606nextproc: 607 continue; 608 } 609 } 610 sx_sunlock(&allproc_lock); 611 for (i = 0; i < 3; i++) 612 avg->ldavg[i] = (cexp[i] * avg->ldavg[i] + 613 nrun * FSCALE * (FSCALE - cexp[i])) >> FSHIFT; 614} 615 616/* 617 * Main loop for a kthread that executes loadav() periodically. 618 */ 619static void 620loadav_thread(void *dummy) 621{ 622 struct proc *p; 623 int nowake; 624 625 p = curthread->td_proc; 626 PROC_LOCK(p); 627 p->p_flag |= P_NOLOAD; 628 PROC_UNLOCK(p); 629 for (;;) { 630 loadav(); 631 /* 632 * Schedule the next update to occur after 5 seconds, but 633 * add a random variation to avoid synchronisation with 634 * processes that run at regular intervals. 635 */ 636 tsleep(&nowake, curthread->td_priority, "-", hz * 4 + 637 (int)(random() % (hz * 2 + 1))); 638 } 639} 640 641static void 642lboltcb(void *arg) 643{ 644 wakeup(&lbolt); 645 callout_reset(&lbolt_callout, hz, lboltcb, NULL); 646} 647 648/* ARGSUSED */ 649static void 650synch_setup(dummy) 651 void *dummy; 652{ 653 callout_init(&lbolt_callout, CALLOUT_MPSAFE); 654 655 /* Kick off timeout driven events by calling first time. */ 656 lboltcb(NULL); 657 658 /* Kick off loadav kernel process. */ 659 kthread_create(loadav_thread, NULL, NULL, 0, 0, "loadav"); 660} 661 662/* 663 * General purpose yield system call 664 */ 665int 666yield(struct thread *td, struct yield_args *uap) 667{ 668 struct ksegrp *kg; 669 670 kg = td->td_ksegrp; 671 mtx_assert(&Giant, MA_NOTOWNED); 672 mtx_lock_spin(&sched_lock); 673 sched_prio(td, PRI_MAX_TIMESHARE); 674 mi_switch(SW_VOL); 675 mtx_unlock_spin(&sched_lock); 676 td->td_retval[0] = 0; 677 return (0); 678} 679