sys/kern/kern_thread.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   3  *
   4  * Copyright (C) 2001 Julian Elischer <julian@freebsd.org>.
   5  *  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice(s), this list of conditions and the following disclaimer as
  12  *    the first lines of this file unmodified other than the possible
  13  *    addition of one or more copyright notices.
  14  * 2. Redistributions in binary form must reproduce the above copyright
  15  *    notice(s), this list of conditions and the following disclaimer in the
  16  *    documentation and/or other materials provided with the distribution.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
  19  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  20  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  21  * DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
  22  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  23  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  24  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  25  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
  28  * DAMAGE.
  29  */
  30
  31 #include "opt_witness.h"
  32 #include "opt_hwpmc_hooks.h"
  33
  34 #include <sys/cdefs.h>
  35 __FBSDID("$FreeBSD$");
  36
  37 #include <sys/param.h>
  38 #include <sys/systm.h>
  39 #include <sys/kernel.h>
  40 #include <sys/lock.h>
  41 #include <sys/mutex.h>
  42 #include <sys/proc.h>
  43 #include <sys/epoch.h>
  44 #include <sys/rangelock.h>
  45 #include <sys/resourcevar.h>
  46 #include <sys/sdt.h>
  47 #include <sys/smp.h>
  48 #include <sys/sched.h>
  49 #include <sys/sleepqueue.h>
  50 #include <sys/selinfo.h>
  51 #include <sys/syscallsubr.h>
  52 #include <sys/sysent.h>
  53 #include <sys/turnstile.h>
  54 #include <sys/ktr.h>
  55 #include <sys/rwlock.h>
  56 #include <sys/umtx.h>
  57 #include <sys/vmmeter.h>
  58 #include <sys/cpuset.h>
  59 #ifdef  HWPMC_HOOKS
  60 #include <sys/pmckern.h>
  61 #endif
  62
  63 #include <security/audit/audit.h>
  64
  65 #include <vm/vm.h>
  66 #include <vm/vm_extern.h>
  67 #include <vm/uma.h>
  68 #include <sys/eventhandler.h>
  69
  70 /*
  71  * Asserts below verify the stability of struct thread and struct proc
  72  * layout, as exposed by KBI to modules.  On head, the KBI is allowed
  73  * to drift, change to the structures must be accompanied by the
  74  * assert update.
  75  *
  76  * On the stable branches after KBI freeze, conditions must not be
  77  * violated.  Typically new fields are moved to the end of the
  78  * structures.
  79  */
  80 #ifdef __amd64__
  81 _Static_assert(offsetof(struct thread, td_flags) == 0xfc,
  82     "struct thread KBI td_flags");
  83 _Static_assert(offsetof(struct thread, td_pflags) == 0x104,
  84     "struct thread KBI td_pflags");
  85 _Static_assert(offsetof(struct thread, td_frame) == 0x478,
  86     "struct thread KBI td_frame");
  87 _Static_assert(offsetof(struct thread, td_emuldata) == 0x690,
  88     "struct thread KBI td_emuldata");
  89 _Static_assert(offsetof(struct proc, p_flag) == 0xb0,
  90     "struct proc KBI p_flag");
  91 _Static_assert(offsetof(struct proc, p_pid) == 0xbc,
  92     "struct proc KBI p_pid");
  93 _Static_assert(offsetof(struct proc, p_filemon) == 0x3c8,
  94     "struct proc KBI p_filemon");
  95 _Static_assert(offsetof(struct proc, p_comm) == 0x3e0,
  96     "struct proc KBI p_comm");
  97 _Static_assert(offsetof(struct proc, p_emuldata) == 0x4c0,
  98     "struct proc KBI p_emuldata");
  99 #endif
 100 #ifdef __i386__
 101 _Static_assert(offsetof(struct thread, td_flags) == 0x98,
 102     "struct thread KBI td_flags");
 103 _Static_assert(offsetof(struct thread, td_pflags) == 0xa0,
 104     "struct thread KBI td_pflags");
 105 _Static_assert(offsetof(struct thread, td_frame) == 0x2f0,
 106     "struct thread KBI td_frame");
 107 _Static_assert(offsetof(struct thread, td_emuldata) == 0x338,
 108     "struct thread KBI td_emuldata");
 109 _Static_assert(offsetof(struct proc, p_flag) == 0x68,
 110     "struct proc KBI p_flag");
 111 _Static_assert(offsetof(struct proc, p_pid) == 0x74,
 112     "struct proc KBI p_pid");
 113 _Static_assert(offsetof(struct proc, p_filemon) == 0x278,
 114     "struct proc KBI p_filemon");
 115 _Static_assert(offsetof(struct proc, p_comm) == 0x28c,
 116     "struct proc KBI p_comm");
 117 _Static_assert(offsetof(struct proc, p_emuldata) == 0x318,
 118     "struct proc KBI p_emuldata");
 119 #endif
 120
 121 SDT_PROVIDER_DECLARE(proc);
 122 SDT_PROBE_DEFINE(proc, , , lwp__exit);
 123
 124 /*
 125  * thread related storage.
 126  */
 127 static uma_zone_t thread_zone;
 128
 129 TAILQ_HEAD(, thread) zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
 130 static struct mtx zombie_lock;
 131 MTX_SYSINIT(zombie_lock, &zombie_lock, "zombie lock", MTX_SPIN);
 132
 133 static void thread_zombie(struct thread *);
 134 static int thread_unsuspend_one(struct thread *td, struct proc *p,
 135     bool boundary);
 136
 137 #define TID_BUFFER_SIZE 1024
 138
 139 struct mtx tid_lock;
 140 static struct unrhdr *tid_unrhdr;
 141 static lwpid_t tid_buffer[TID_BUFFER_SIZE];
 142 static int tid_head, tid_tail;
 143 static MALLOC_DEFINE(M_TIDHASH, "tidhash", "thread hash");
 144
 145 struct  tidhashhead *tidhashtbl;
 146 u_long  tidhash;
 147 struct  rwlock tidhash_lock;
 148
 149 EVENTHANDLER_LIST_DEFINE(thread_ctor);
 150 EVENTHANDLER_LIST_DEFINE(thread_dtor);
 151 EVENTHANDLER_LIST_DEFINE(thread_init);
 152 EVENTHANDLER_LIST_DEFINE(thread_fini);
 153
 154 static lwpid_t
 155 tid_alloc(void)
 156 {
 157         lwpid_t tid;
 158
 159         tid = alloc_unr(tid_unrhdr);
 160         if (tid != -1)
 161                 return (tid);
 162         mtx_lock(&tid_lock);
 163         if (tid_head == tid_tail) {
 164                 mtx_unlock(&tid_lock);
 165                 return (-1);
 166         }
 167         tid = tid_buffer[tid_head];
 168         tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
 169         mtx_unlock(&tid_lock);
 170         return (tid);
 171 }
 172
 173 static void
 174 tid_free(lwpid_t tid)
 175 {
 176         lwpid_t tmp_tid = -1;
 177
 178         mtx_lock(&tid_lock);
 179         if ((tid_tail + 1) % TID_BUFFER_SIZE == tid_head) {
 180                 tmp_tid = tid_buffer[tid_head];
 181                 tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
 182         }
 183         tid_buffer[tid_tail] = tid;
 184         tid_tail = (tid_tail + 1) % TID_BUFFER_SIZE;
 185         mtx_unlock(&tid_lock);
 186         if (tmp_tid != -1)
 187                 free_unr(tid_unrhdr, tmp_tid);
 188 }
 189
 190 /*
 191  * Prepare a thread for use.
 192  */
 193 static int
 194 thread_ctor(void *mem, int size, void *arg, int flags)
 195 {
 196         struct thread   *td;
 197
 198         td = (struct thread *)mem;
 199         td->td_state = TDS_INACTIVE;
 200         td->td_lastcpu = td->td_oncpu = NOCPU;
 201
 202         td->td_tid = tid_alloc();
 203
 204         /*
 205          * Note that td_critnest begins life as 1 because the thread is not
 206          * running and is thereby implicitly waiting to be on the receiving
 207          * end of a context switch.
 208          */
 209         td->td_critnest = 1;
 210         td->td_lend_user_pri = PRI_MAX;
 211         EVENTHANDLER_DIRECT_INVOKE(thread_ctor, td);
 212 #ifdef AUDIT
 213         audit_thread_alloc(td);
 214 #endif
 215         umtx_thread_alloc(td);
 216         return (0);
 217 }
 218
 219 /*
 220  * Reclaim a thread after use.
 221  */
 222 static void
 223 thread_dtor(void *mem, int size, void *arg)
 224 {
 225         struct thread *td;
 226
 227         td = (struct thread *)mem;
 228
 229 #ifdef INVARIANTS
 230         /* Verify that this thread is in a safe state to free. */
 231         switch (td->td_state) {
 232         case TDS_INHIBITED:
 233         case TDS_RUNNING:
 234         case TDS_CAN_RUN:
 235         case TDS_RUNQ:
 236                 /*
 237                  * We must never unlink a thread that is in one of
 238                  * these states, because it is currently active.
 239                  */
 240                 panic("bad state for thread unlinking");
 241                 /* NOTREACHED */
 242         case TDS_INACTIVE:
 243                 break;
 244         default:
 245                 panic("bad thread state");
 246                 /* NOTREACHED */
 247         }
 248 #endif
 249 #ifdef AUDIT
 250         audit_thread_free(td);
 251 #endif
 252         /* Free all OSD associated to this thread. */
 253         osd_thread_exit(td);
 254         td_softdep_cleanup(td);
 255         MPASS(td->td_su == NULL);
 256
 257         EVENTHANDLER_DIRECT_INVOKE(thread_dtor, td);
 258         tid_free(td->td_tid);
 259 }
 260
 261 /*
 262  * Initialize type-stable parts of a thread (when newly created).
 263  */
 264 static int
 265 thread_init(void *mem, int size, int flags)
 266 {
 267         struct thread *td;
 268
 269         td = (struct thread *)mem;
 270
 271         td->td_sleepqueue = sleepq_alloc();
 272         td->td_turnstile = turnstile_alloc();
 273         td->td_rlqe = NULL;
 274         EVENTHANDLER_DIRECT_INVOKE(thread_init, td);
 275         umtx_thread_init(td);
 276         td->td_kstack = 0;
 277         td->td_sel = NULL;
 278         return (0);
 279 }
 280
 281 /*
 282  * Tear down type-stable parts of a thread (just before being discarded).
 283  */
 284 static void
 285 thread_fini(void *mem, int size)
 286 {
 287         struct thread *td;
 288
 289         td = (struct thread *)mem;
 290         EVENTHANDLER_DIRECT_INVOKE(thread_fini, td);
 291         rlqentry_free(td->td_rlqe);
 292         turnstile_free(td->td_turnstile);
 293         sleepq_free(td->td_sleepqueue);
 294         umtx_thread_fini(td);
 295         seltdfini(td);
 296 }
 297
 298 /*
 299  * For a newly created process,
 300  * link up all the structures and its initial threads etc.
 301  * called from:
 302  * {arch}/{arch}/machdep.c   {arch}_init(), init386() etc.
 303  * proc_dtor() (should go away)
 304  * proc_init()
 305  */
 306 void
 307 proc_linkup0(struct proc *p, struct thread *td)
 308 {
 309         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
 310         proc_linkup(p, td);
 311 }
 312
 313 void
 314 proc_linkup(struct proc *p, struct thread *td)
 315 {
 316
 317         sigqueue_init(&p->p_sigqueue, p);
 318         p->p_ksi = ksiginfo_alloc(1);
 319         if (p->p_ksi != NULL) {
 320                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
 321                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
 322         }
 323         LIST_INIT(&p->p_mqnotifier);
 324         p->p_numthreads = 0;
 325         thread_link(td, p);
 326 }
 327
 328 /*
 329  * Initialize global thread allocation resources.
 330  */
 331 void
 332 threadinit(void)
 333 {
 334
 335         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
 336
 337         /*
 338          * pid_max cannot be greater than PID_MAX.
 339          * leave one number for thread0.
 340          */
 341         tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
 342
 343         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
 344             thread_ctor, thread_dtor, thread_init, thread_fini,
 345             32 - 1, UMA_ZONE_NOFREE);
 346         tidhashtbl = hashinit(maxproc / 2, M_TIDHASH, &tidhash);
 347         rw_init(&tidhash_lock, "tidhash");
 348 }
 349
 350 /*
 351  * Place an unused thread on the zombie list.
 352  * Use the slpq as that must be unused by now.
 353  */
 354 void
 355 thread_zombie(struct thread *td)
 356 {
 357         mtx_lock_spin(&zombie_lock);
 358         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
 359         mtx_unlock_spin(&zombie_lock);
 360 }
 361
 362 /*
 363  * Release a thread that has exited after cpu_throw().
 364  */
 365 void
 366 thread_stash(struct thread *td)
 367 {
 368         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
 369         thread_zombie(td);
 370 }
 371
 372 /*
 373  * Reap zombie resources.
 374  */
 375 void
 376 thread_reap(void)
 377 {
 378         struct thread *td_first, *td_next;
 379
 380         /*
 381          * Don't even bother to lock if none at this instant,
 382          * we really don't care about the next instant.
 383          */
 384         if (!TAILQ_EMPTY(&zombie_threads)) {
 385                 mtx_lock_spin(&zombie_lock);
 386                 td_first = TAILQ_FIRST(&zombie_threads);
 387                 if (td_first)
 388                         TAILQ_INIT(&zombie_threads);
 389                 mtx_unlock_spin(&zombie_lock);
 390                 while (td_first) {
 391                         td_next = TAILQ_NEXT(td_first, td_slpq);
 392                         thread_cow_free(td_first);
 393                         thread_free(td_first);
 394                         td_first = td_next;
 395                 }
 396         }
 397 }
 398
 399 /*
 400  * Allocate a thread.
 401  */
 402 struct thread *
 403 thread_alloc(int pages)
 404 {
 405         struct thread *td;
 406
 407         thread_reap(); /* check if any zombies to get */
 408
 409         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
 410         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
 411         if (!vm_thread_new(td, pages)) {
 412                 uma_zfree(thread_zone, td);
 413                 return (NULL);
 414         }
 415         cpu_thread_alloc(td);
 416         return (td);
 417 }
 418
 419 int
 420 thread_alloc_stack(struct thread *td, int pages)
 421 {
 422
 423         KASSERT(td->td_kstack == 0,
 424             ("thread_alloc_stack called on a thread with kstack"));
 425         if (!vm_thread_new(td, pages))
 426                 return (0);
 427         cpu_thread_alloc(td);
 428         return (1);
 429 }
 430
 431 /*
 432  * Deallocate a thread.
 433  */
 434 void
 435 thread_free(struct thread *td)
 436 {
 437
 438         lock_profile_thread_exit(td);
 439         if (td->td_cpuset)
 440                 cpuset_rel(td->td_cpuset);
 441         td->td_cpuset = NULL;
 442         cpu_thread_free(td);
 443         if (td->td_kstack != 0)
 444                 vm_thread_dispose(td);
 445         callout_drain(&td->td_slpcallout);
 446         uma_zfree(thread_zone, td);
 447 }
 448
 449 void
 450 thread_cow_get_proc(struct thread *newtd, struct proc *p)
 451 {
 452
 453         PROC_LOCK_ASSERT(p, MA_OWNED);
 454         newtd->td_ucred = crhold(p->p_ucred);
 455         newtd->td_limit = lim_hold(p->p_limit);
 456         newtd->td_cowgen = p->p_cowgen;
 457 }
 458
 459 void
 460 thread_cow_get(struct thread *newtd, struct thread *td)
 461 {
 462
 463         newtd->td_ucred = crhold(td->td_ucred);
 464         newtd->td_limit = lim_hold(td->td_limit);
 465         newtd->td_cowgen = td->td_cowgen;
 466 }
 467
 468 void
 469 thread_cow_free(struct thread *td)
 470 {
 471
 472         if (td->td_ucred != NULL)
 473                 crfree(td->td_ucred);
 474         if (td->td_limit != NULL)
 475                 lim_free(td->td_limit);
 476 }
 477
 478 void
 479 thread_cow_update(struct thread *td)
 480 {
 481         struct proc *p;
 482         struct ucred *oldcred;
 483         struct plimit *oldlimit;
 484
 485         p = td->td_proc;
 486         oldcred = NULL;
 487         oldlimit = NULL;
 488         PROC_LOCK(p);
 489         if (td->td_ucred != p->p_ucred) {
 490                 oldcred = td->td_ucred;
 491                 td->td_ucred = crhold(p->p_ucred);
 492         }
 493         if (td->td_limit != p->p_limit) {
 494                 oldlimit = td->td_limit;
 495                 td->td_limit = lim_hold(p->p_limit);
 496         }
 497         td->td_cowgen = p->p_cowgen;
 498         PROC_UNLOCK(p);
 499         if (oldcred != NULL)
 500                 crfree(oldcred);
 501         if (oldlimit != NULL)
 502                 lim_free(oldlimit);
 503 }
 504
 505 /*
 506  * Discard the current thread and exit from its context.
 507  * Always called with scheduler locked.
 508  *
 509  * Because we can't free a thread while we're operating under its context,
 510  * push the current thread into our CPU's deadthread holder. This means
 511  * we needn't worry about someone else grabbing our context before we
 512  * do a cpu_throw().
 513  */
 514 void
 515 thread_exit(void)
 516 {
 517         uint64_t runtime, new_switchtime;
 518         struct thread *td;
 519         struct thread *td2;
 520         struct proc *p;
 521         int wakeup_swapper;
 522
 523         td = curthread;
 524         p = td->td_proc;
 525
 526         PROC_SLOCK_ASSERT(p, MA_OWNED);
 527         mtx_assert(&Giant, MA_NOTOWNED);
 528
 529         PROC_LOCK_ASSERT(p, MA_OWNED);
 530         KASSERT(p != NULL, ("thread exiting without a process"));
 531         CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
 532             (long)p->p_pid, td->td_name);
 533         SDT_PROBE0(proc, , , lwp__exit);
 534         KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
 535
 536         /*
 537          * drop FPU & debug register state storage, or any other
 538          * architecture specific resources that
 539          * would not be on a new untouched process.
 540          */
 541         cpu_thread_exit(td);
 542
 543         /*
 544          * The last thread is left attached to the process
 545          * So that the whole bundle gets recycled. Skip
 546          * all this stuff if we never had threads.
 547          * EXIT clears all sign of other threads when
 548          * it goes to single threading, so the last thread always
 549          * takes the short path.
 550          */
 551         if (p->p_flag & P_HADTHREADS) {
 552                 if (p->p_numthreads > 1) {
 553                         atomic_add_int(&td->td_proc->p_exitthreads, 1);
 554                         thread_unlink(td);
 555                         td2 = FIRST_THREAD_IN_PROC(p);
 556                         sched_exit_thread(td2, td);
 557
 558                         /*
 559                          * The test below is NOT true if we are the
 560                          * sole exiting thread. P_STOPPED_SINGLE is unset
 561                          * in exit1() after it is the only survivor.
 562                          */
 563                         if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 564                                 if (p->p_numthreads == p->p_suspcount) {
 565                                         thread_lock(p->p_singlethread);
 566                                         wakeup_swapper = thread_unsuspend_one(
 567                                                 p->p_singlethread, p, false);
 568                                         thread_unlock(p->p_singlethread);
 569                                         if (wakeup_swapper)
 570                                                 kick_proc0();
 571                                 }
 572                         }
 573
 574                         PCPU_SET(deadthread, td);
 575                 } else {
 576                         /*
 577                          * The last thread is exiting.. but not through exit()
 578                          */
 579                         panic ("thread_exit: Last thread exiting on its own");
 580                 }
 581         }
 582 #ifdef  HWPMC_HOOKS
 583         /*
 584          * If this thread is part of a process that is being tracked by hwpmc(4),
 585          * inform the module of the thread's impending exit.
 586          */
 587         if (PMC_PROC_IS_USING_PMCS(td->td_proc)) {
 588                 PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
 589                 PMC_CALL_HOOK_UNLOCKED(td, PMC_FN_THR_EXIT, NULL);
 590         } else if (PMC_SYSTEM_SAMPLING_ACTIVE())
 591                 PMC_CALL_HOOK_UNLOCKED(td, PMC_FN_THR_EXIT_LOG, NULL);
 592 #endif
 593         PROC_UNLOCK(p);
 594         PROC_STATLOCK(p);
 595         thread_lock(td);
 596         PROC_SUNLOCK(p);
 597
 598         /* Do the same timestamp bookkeeping that mi_switch() would do. */
 599         new_switchtime = cpu_ticks();
 600         runtime = new_switchtime - PCPU_GET(switchtime);
 601         td->td_runtime += runtime;
 602         td->td_incruntime += runtime;
 603         PCPU_SET(switchtime, new_switchtime);
 604         PCPU_SET(switchticks, ticks);
 605         VM_CNT_INC(v_swtch);
 606
 607         /* Save our resource usage in our process. */
 608         td->td_ru.ru_nvcsw++;
 609         ruxagg(p, td);
 610         rucollect(&p->p_ru, &td->td_ru);
 611         PROC_STATUNLOCK(p);
 612
 613         td->td_state = TDS_INACTIVE;
 614 #ifdef WITNESS
 615         witness_thread_exit(td);
 616 #endif
 617         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
 618         sched_throw(td);
 619         panic("I'm a teapot!");
 620         /* NOTREACHED */
 621 }
 622
 623 /*
 624  * Do any thread specific cleanups that may be needed in wait()
 625  * called with Giant, proc and schedlock not held.
 626  */
 627 void
 628 thread_wait(struct proc *p)
 629 {
 630         struct thread *td;
 631
 632         mtx_assert(&Giant, MA_NOTOWNED);
 633         KASSERT(p->p_numthreads == 1, ("multiple threads in thread_wait()"));
 634         KASSERT(p->p_exitthreads == 0, ("p_exitthreads leaking"));
 635         td = FIRST_THREAD_IN_PROC(p);
 636         /* Lock the last thread so we spin until it exits cpu_throw(). */
 637         thread_lock(td);
 638         thread_unlock(td);
 639         lock_profile_thread_exit(td);
 640         cpuset_rel(td->td_cpuset);
 641         td->td_cpuset = NULL;
 642         cpu_thread_clean(td);
 643         thread_cow_free(td);
 644         callout_drain(&td->td_slpcallout);
 645         thread_reap();  /* check for zombie threads etc. */
 646 }
 647
 648 /*
 649  * Link a thread to a process.
 650  * set up anything that needs to be initialized for it to
 651  * be used by the process.
 652  */
 653 void
 654 thread_link(struct thread *td, struct proc *p)
 655 {
 656
 657         /*
 658          * XXX This can't be enabled because it's called for proc0 before
 659          * its lock has been created.
 660          * PROC_LOCK_ASSERT(p, MA_OWNED);
 661          */
 662         td->td_state    = TDS_INACTIVE;
 663         td->td_proc     = p;
 664         td->td_flags    = TDF_INMEM;
 665
 666         LIST_INIT(&td->td_contested);
 667         LIST_INIT(&td->td_lprof[0]);
 668         LIST_INIT(&td->td_lprof[1]);
 669 #ifdef EPOCH_TRACE
 670         SLIST_INIT(&td->td_epochs);
 671 #endif
 672         sigqueue_init(&td->td_sigqueue, p);
 673         callout_init(&td->td_slpcallout, 1);
 674         TAILQ_INSERT_TAIL(&p->p_threads, td, td_plist);
 675         p->p_numthreads++;
 676 }
 677
 678 /*
 679  * Called from:
 680  *  thread_exit()
 681  */
 682 void
 683 thread_unlink(struct thread *td)
 684 {
 685         struct proc *p = td->td_proc;
 686
 687         PROC_LOCK_ASSERT(p, MA_OWNED);
 688 #ifdef EPOCH_TRACE
 689         MPASS(SLIST_EMPTY(&td->td_epochs));
 690 #endif
 691
 692         TAILQ_REMOVE(&p->p_threads, td, td_plist);
 693         p->p_numthreads--;
 694         /* could clear a few other things here */
 695         /* Must  NOT clear links to proc! */
 696 }
 697
 698 static int
 699 calc_remaining(struct proc *p, int mode)
 700 {
 701         int remaining;
 702
 703         PROC_LOCK_ASSERT(p, MA_OWNED);
 704         PROC_SLOCK_ASSERT(p, MA_OWNED);
 705         if (mode == SINGLE_EXIT)
 706                 remaining = p->p_numthreads;
 707         else if (mode == SINGLE_BOUNDARY)
 708                 remaining = p->p_numthreads - p->p_boundary_count;
 709         else if (mode == SINGLE_NO_EXIT || mode == SINGLE_ALLPROC)
 710                 remaining = p->p_numthreads - p->p_suspcount;
 711         else
 712                 panic("calc_remaining: wrong mode %d", mode);
 713         return (remaining);
 714 }
 715
 716 static int
 717 remain_for_mode(int mode)
 718 {
 719
 720         return (mode == SINGLE_ALLPROC ? 0 : 1);
 721 }
 722
 723 static int
 724 weed_inhib(int mode, struct thread *td2, struct proc *p)
 725 {
 726         int wakeup_swapper;
 727
 728         PROC_LOCK_ASSERT(p, MA_OWNED);
 729         PROC_SLOCK_ASSERT(p, MA_OWNED);
 730         THREAD_LOCK_ASSERT(td2, MA_OWNED);
 731
 732         wakeup_swapper = 0;
 733         switch (mode) {
 734         case SINGLE_EXIT:
 735                 if (TD_IS_SUSPENDED(td2))
 736                         wakeup_swapper |= thread_unsuspend_one(td2, p, true);
 737                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0)
 738                         wakeup_swapper |= sleepq_abort(td2, EINTR);
 739                 break;
 740         case SINGLE_BOUNDARY:
 741         case SINGLE_NO_EXIT:
 742                 if (TD_IS_SUSPENDED(td2) && (td2->td_flags & TDF_BOUNDARY) == 0)
 743                         wakeup_swapper |= thread_unsuspend_one(td2, p, false);
 744                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0)
 745                         wakeup_swapper |= sleepq_abort(td2, ERESTART);
 746                 break;
 747         case SINGLE_ALLPROC:
 748                 /*
 749                  * ALLPROC suspend tries to avoid spurious EINTR for
 750                  * threads sleeping interruptable, by suspending the
 751                  * thread directly, similarly to sig_suspend_threads().
 752                  * Since such sleep is not performed at the user
 753                  * boundary, TDF_BOUNDARY flag is not set, and TDF_ALLPROCSUSP
 754                  * is used to avoid immediate un-suspend.
 755                  */
 756                 if (TD_IS_SUSPENDED(td2) && (td2->td_flags & (TDF_BOUNDARY |
 757                     TDF_ALLPROCSUSP)) == 0)
 758                         wakeup_swapper |= thread_unsuspend_one(td2, p, false);
 759                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0) {
 760                         if ((td2->td_flags & TDF_SBDRY) == 0) {
 761                                 thread_suspend_one(td2);
 762                                 td2->td_flags |= TDF_ALLPROCSUSP;
 763                         } else {
 764                                 wakeup_swapper |= sleepq_abort(td2, ERESTART);
 765                         }
 766                 }
 767                 break;
 768         }
 769         return (wakeup_swapper);
 770 }
 771
 772 /*
 773  * Enforce single-threading.
 774  *
 775  * Returns 1 if the caller must abort (another thread is waiting to
 776  * exit the process or similar). Process is locked!
 777  * Returns 0 when you are successfully the only thread running.
 778  * A process has successfully single threaded in the suspend mode when
 779  * There are no threads in user mode. Threads in the kernel must be
 780  * allowed to continue until they get to the user boundary. They may even
 781  * copy out their return values and data before suspending. They may however be
 782  * accelerated in reaching the user boundary as we will wake up
 783  * any sleeping threads that are interruptable. (PCATCH).
 784  */
 785 int
 786 thread_single(struct proc *p, int mode)
 787 {
 788         struct thread *td;
 789         struct thread *td2;
 790         int remaining, wakeup_swapper;
 791
 792         td = curthread;
 793         KASSERT(mode == SINGLE_EXIT || mode == SINGLE_BOUNDARY ||
 794             mode == SINGLE_ALLPROC || mode == SINGLE_NO_EXIT,
 795             ("invalid mode %d", mode));
 796         /*
 797          * If allowing non-ALLPROC singlethreading for non-curproc
 798          * callers, calc_remaining() and remain_for_mode() should be
 799          * adjusted to also account for td->td_proc != p.  For now
 800          * this is not implemented because it is not used.
 801          */
 802         KASSERT((mode == SINGLE_ALLPROC && td->td_proc != p) ||
 803             (mode != SINGLE_ALLPROC && td->td_proc == p),
 804             ("mode %d proc %p curproc %p", mode, p, td->td_proc));
 805         mtx_assert(&Giant, MA_NOTOWNED);
 806         PROC_LOCK_ASSERT(p, MA_OWNED);
 807
 808         if ((p->p_flag & P_HADTHREADS) == 0 && mode != SINGLE_ALLPROC)
 809                 return (0);
 810
 811         /* Is someone already single threading? */
 812         if (p->p_singlethread != NULL && p->p_singlethread != td)
 813                 return (1);
 814
 815         if (mode == SINGLE_EXIT) {
 816                 p->p_flag |= P_SINGLE_EXIT;
 817                 p->p_flag &= ~P_SINGLE_BOUNDARY;
 818         } else {
 819                 p->p_flag &= ~P_SINGLE_EXIT;
 820                 if (mode == SINGLE_BOUNDARY)
 821                         p->p_flag |= P_SINGLE_BOUNDARY;
 822                 else
 823                         p->p_flag &= ~P_SINGLE_BOUNDARY;
 824         }
 825         if (mode == SINGLE_ALLPROC)
 826                 p->p_flag |= P_TOTAL_STOP;
 827         p->p_flag |= P_STOPPED_SINGLE;
 828         PROC_SLOCK(p);
 829         p->p_singlethread = td;
 830         remaining = calc_remaining(p, mode);
 831         while (remaining != remain_for_mode(mode)) {
 832                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
 833                         goto stopme;
 834                 wakeup_swapper = 0;
 835                 FOREACH_THREAD_IN_PROC(p, td2) {
 836                         if (td2 == td)
 837                                 continue;
 838                         thread_lock(td2);
 839                         td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
 840                         if (TD_IS_INHIBITED(td2)) {
 841                                 wakeup_swapper |= weed_inhib(mode, td2, p);
 842 #ifdef SMP
 843                         } else if (TD_IS_RUNNING(td2) && td != td2) {
 844                                 forward_signal(td2);
 845 #endif
 846                         }
 847                         thread_unlock(td2);
 848                 }
 849                 if (wakeup_swapper)
 850                         kick_proc0();
 851                 remaining = calc_remaining(p, mode);
 852
 853                 /*
 854                  * Maybe we suspended some threads.. was it enough?
 855                  */
 856                 if (remaining == remain_for_mode(mode))
 857                         break;
 858
 859 stopme:
 860                 /*
 861                  * Wake us up when everyone else has suspended.
 862                  * In the mean time we suspend as well.
 863                  */
 864                 thread_suspend_switch(td, p);
 865                 remaining = calc_remaining(p, mode);
 866         }
 867         if (mode == SINGLE_EXIT) {
 868                 /*
 869                  * Convert the process to an unthreaded process.  The
 870                  * SINGLE_EXIT is called by exit1() or execve(), in
 871                  * both cases other threads must be retired.
 872                  */
 873                 KASSERT(p->p_numthreads == 1, ("Unthreading with >1 threads"));
 874                 p->p_singlethread = NULL;
 875                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_HADTHREADS);
 876
 877                 /*
 878                  * Wait for any remaining threads to exit cpu_throw().
 879                  */
 880                 while (p->p_exitthreads != 0) {
 881                         PROC_SUNLOCK(p);
 882                         PROC_UNLOCK(p);
 883                         sched_relinquish(td);
 884                         PROC_LOCK(p);
 885                         PROC_SLOCK(p);
 886                 }
 887         } else if (mode == SINGLE_BOUNDARY) {
 888                 /*
 889                  * Wait until all suspended threads are removed from
 890                  * the processors.  The thread_suspend_check()
 891                  * increments p_boundary_count while it is still
 892                  * running, which makes it possible for the execve()
 893                  * to destroy vmspace while our other threads are
 894                  * still using the address space.
 895                  *
 896                  * We lock the thread, which is only allowed to
 897                  * succeed after context switch code finished using
 898                  * the address space.
 899                  */
 900                 FOREACH_THREAD_IN_PROC(p, td2) {
 901                         if (td2 == td)
 902                                 continue;
 903                         thread_lock(td2);
 904                         KASSERT((td2->td_flags & TDF_BOUNDARY) != 0,
 905                             ("td %p not on boundary", td2));
 906                         KASSERT(TD_IS_SUSPENDED(td2),
 907                             ("td %p is not suspended", td2));
 908                         thread_unlock(td2);
 909                 }
 910         }
 911         PROC_SUNLOCK(p);
 912         return (0);
 913 }
 914
 915 bool
 916 thread_suspend_check_needed(void)
 917 {
 918         struct proc *p;
 919         struct thread *td;
 920
 921         td = curthread;
 922         p = td->td_proc;
 923         PROC_LOCK_ASSERT(p, MA_OWNED);
 924         return (P_SHOULDSTOP(p) || ((p->p_flag & P_TRACED) != 0 &&
 925             (td->td_dbgflags & TDB_SUSPEND) != 0));
 926 }
 927
 928 /*
 929  * Called in from locations that can safely check to see
 930  * whether we have to suspend or at least throttle for a
 931  * single-thread event (e.g. fork).
 932  *
 933  * Such locations include userret().
 934  * If the "return_instead" argument is non zero, the thread must be able to
 935  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
 936  *
 937  * The 'return_instead' argument tells the function if it may do a
 938  * thread_exit() or suspend, or whether the caller must abort and back
 939  * out instead.
 940  *
 941  * If the thread that set the single_threading request has set the
 942  * P_SINGLE_EXIT bit in the process flags then this call will never return
 943  * if 'return_instead' is false, but will exit.
 944  *
 945  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
 946  *---------------+--------------------+---------------------
 947  *       0       | returns 0          |   returns 0 or 1
 948  *               | when ST ends       |   immediately
 949  *---------------+--------------------+---------------------
 950  *       1       | thread exits       |   returns 1
 951  *               |                    |  immediately
 952  * 0 = thread_exit() or suspension ok,
 953  * other = return error instead of stopping the thread.
 954  *
 955  * While a full suspension is under effect, even a single threading
 956  * thread would be suspended if it made this call (but it shouldn't).
 957  * This call should only be made from places where
 958  * thread_exit() would be safe as that may be the outcome unless
 959  * return_instead is set.
 960  */
 961 int
 962 thread_suspend_check(int return_instead)
 963 {
 964         struct thread *td;
 965         struct proc *p;
 966         int wakeup_swapper;
 967
 968         td = curthread;
 969         p = td->td_proc;
 970         mtx_assert(&Giant, MA_NOTOWNED);
 971         PROC_LOCK_ASSERT(p, MA_OWNED);
 972         while (thread_suspend_check_needed()) {
 973                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 974                         KASSERT(p->p_singlethread != NULL,
 975                             ("singlethread not set"));
 976                         /*
 977                          * The only suspension in action is a
 978                          * single-threading. Single threader need not stop.
 979                          * It is safe to access p->p_singlethread unlocked
 980                          * because it can only be set to our address by us.
 981                          */
 982                         if (p->p_singlethread == td)
 983                                 return (0);     /* Exempt from stopping. */
 984                 }
 985                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
 986                         return (EINTR);
 987
 988                 /* Should we goto user boundary if we didn't come from there? */
 989                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
 990                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
 991                         return (ERESTART);
 992
 993                 /*
 994                  * Ignore suspend requests if they are deferred.
 995                  */
 996                 if ((td->td_flags & TDF_SBDRY) != 0) {
 997                         KASSERT(return_instead,
 998                             ("TDF_SBDRY set for unsafe thread_suspend_check"));
 999                         KASSERT((td->td_flags & (TDF_SEINTR | TDF_SERESTART)) !=
1000                             (TDF_SEINTR | TDF_SERESTART),
1001                             ("both TDF_SEINTR and TDF_SERESTART"));
1002                         return (TD_SBDRY_INTR(td) ? TD_SBDRY_ERRNO(td) : 0);
1003                 }
1004
1005                 /*
1006                  * If the process is waiting for us to exit,
1007                  * this thread should just suicide.
1008                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
1009                  */
1010                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td)) {
1011                         PROC_UNLOCK(p);
1012
1013                         /*
1014                          * Allow Linux emulation layer to do some work
1015                          * before thread suicide.
1016                          */
1017                         if (__predict_false(p->p_sysent->sv_thread_detach != NULL))
1018                                 (p->p_sysent->sv_thread_detach)(td);
1019                         umtx_thread_exit(td);
1020                         kern_thr_exit(td);
1021                         panic("stopped thread did not exit");
1022                 }
1023
1024                 PROC_SLOCK(p);
1025                 thread_stopped(p);
1026                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
1027                         if (p->p_numthreads == p->p_suspcount + 1) {
1028                                 thread_lock(p->p_singlethread);
1029                                 wakeup_swapper = thread_unsuspend_one(
1030                                     p->p_singlethread, p, false);
1031                                 thread_unlock(p->p_singlethread);
1032                                 if (wakeup_swapper)
1033                                         kick_proc0();
1034                         }
1035                 }
1036                 PROC_UNLOCK(p);
1037                 thread_lock(td);
1038                 /*
1039                  * When a thread suspends, it just
1040                  * gets taken off all queues.
1041                  */
1042                 thread_suspend_one(td);
1043                 if (return_instead == 0) {
1044                         p->p_boundary_count++;
1045                         td->td_flags |= TDF_BOUNDARY;
1046                 }
1047                 PROC_SUNLOCK(p);
1048                 mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
1049                 thread_unlock(td);
1050                 PROC_LOCK(p);
1051         }
1052         return (0);
1053 }
1054
1055 void
1056 thread_suspend_switch(struct thread *td, struct proc *p)
1057 {
1058
1059         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
1060         PROC_LOCK_ASSERT(p, MA_OWNED);
1061         PROC_SLOCK_ASSERT(p, MA_OWNED);
1062         /*
1063          * We implement thread_suspend_one in stages here to avoid
1064          * dropping the proc lock while the thread lock is owned.
1065          */
1066         if (p == td->td_proc) {
1067                 thread_stopped(p);
1068                 p->p_suspcount++;
1069         }
1070         PROC_UNLOCK(p);
1071         thread_lock(td);
1072         td->td_flags &= ~TDF_NEEDSUSPCHK;
1073         TD_SET_SUSPENDED(td);
1074         sched_sleep(td, 0);
1075         PROC_SUNLOCK(p);
1076         DROP_GIANT();
1077         mi_switch(SW_VOL | SWT_SUSPEND, NULL);
1078         thread_unlock(td);
1079         PICKUP_GIANT();
1080         PROC_LOCK(p);
1081         PROC_SLOCK(p);
1082 }
1083
1084 void
1085 thread_suspend_one(struct thread *td)
1086 {
1087         struct proc *p;
1088
1089         p = td->td_proc;
1090         PROC_SLOCK_ASSERT(p, MA_OWNED);
1091         THREAD_LOCK_ASSERT(td, MA_OWNED);
1092         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
1093         p->p_suspcount++;
1094         td->td_flags &= ~TDF_NEEDSUSPCHK;
1095         TD_SET_SUSPENDED(td);
1096         sched_sleep(td, 0);
1097 }
1098
1099 static int
1100 thread_unsuspend_one(struct thread *td, struct proc *p, bool boundary)
1101 {
1102
1103         THREAD_LOCK_ASSERT(td, MA_OWNED);
1104         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
1105         TD_CLR_SUSPENDED(td);
1106         td->td_flags &= ~TDF_ALLPROCSUSP;
1107         if (td->td_proc == p) {
1108                 PROC_SLOCK_ASSERT(p, MA_OWNED);
1109                 p->p_suspcount--;
1110                 if (boundary && (td->td_flags & TDF_BOUNDARY) != 0) {
1111                         td->td_flags &= ~TDF_BOUNDARY;
1112                         p->p_boundary_count--;
1113                 }
1114         }
1115         return (setrunnable(td));
1116 }
1117
1118 /*
1119  * Allow all threads blocked by single threading to continue running.
1120  */
1121 void
1122 thread_unsuspend(struct proc *p)
1123 {
1124         struct thread *td;
1125         int wakeup_swapper;
1126
1127         PROC_LOCK_ASSERT(p, MA_OWNED);
1128         PROC_SLOCK_ASSERT(p, MA_OWNED);
1129         wakeup_swapper = 0;
1130         if (!P_SHOULDSTOP(p)) {
1131                 FOREACH_THREAD_IN_PROC(p, td) {
1132                         thread_lock(td);
1133                         if (TD_IS_SUSPENDED(td)) {
1134                                 wakeup_swapper |= thread_unsuspend_one(td, p,
1135                                     true);
1136                         }
1137                         thread_unlock(td);
1138                 }
1139         } else if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
1140             p->p_numthreads == p->p_suspcount) {
1141                 /*
1142                  * Stopping everything also did the job for the single
1143                  * threading request. Now we've downgraded to single-threaded,
1144                  * let it continue.
1145                  */
1146                 if (p->p_singlethread->td_proc == p) {
1147                         thread_lock(p->p_singlethread);
1148                         wakeup_swapper = thread_unsuspend_one(
1149                             p->p_singlethread, p, false);
1150                         thread_unlock(p->p_singlethread);
1151                 }
1152         }
1153         if (wakeup_swapper)
1154                 kick_proc0();
1155 }
1156
1157 /*
1158  * End the single threading mode..
1159  */
1160 void
1161 thread_single_end(struct proc *p, int mode)
1162 {
1163         struct thread *td;
1164         int wakeup_swapper;
1165
1166         KASSERT(mode == SINGLE_EXIT || mode == SINGLE_BOUNDARY ||
1167             mode == SINGLE_ALLPROC || mode == SINGLE_NO_EXIT,
1168             ("invalid mode %d", mode));
1169         PROC_LOCK_ASSERT(p, MA_OWNED);
1170         KASSERT((mode == SINGLE_ALLPROC && (p->p_flag & P_TOTAL_STOP) != 0) ||
1171             (mode != SINGLE_ALLPROC && (p->p_flag & P_TOTAL_STOP) == 0),
1172             ("mode %d does not match P_TOTAL_STOP", mode));
1173         KASSERT(mode == SINGLE_ALLPROC || p->p_singlethread == curthread,
1174             ("thread_single_end from other thread %p %p",
1175             curthread, p->p_singlethread));
1176         KASSERT(mode != SINGLE_BOUNDARY ||
1177             (p->p_flag & P_SINGLE_BOUNDARY) != 0,
1178             ("mis-matched SINGLE_BOUNDARY flags %x", p->p_flag));
1179         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY |
1180             P_TOTAL_STOP);
1181         PROC_SLOCK(p);
1182         p->p_singlethread = NULL;
1183         wakeup_swapper = 0;
1184         /*
1185          * If there are other threads they may now run,
1186          * unless of course there is a blanket 'stop order'
1187          * on the process. The single threader must be allowed
1188          * to continue however as this is a bad place to stop.
1189          */
1190         if (p->p_numthreads != remain_for_mode(mode) && !P_SHOULDSTOP(p)) {
1191                 FOREACH_THREAD_IN_PROC(p, td) {
1192                         thread_lock(td);
1193                         if (TD_IS_SUSPENDED(td)) {
1194                                 wakeup_swapper |= thread_unsuspend_one(td, p,
1195                                     mode == SINGLE_BOUNDARY);
1196                         }
1197                         thread_unlock(td);
1198                 }
1199         }
1200         KASSERT(mode != SINGLE_BOUNDARY || p->p_boundary_count == 0,
1201             ("inconsistent boundary count %d", p->p_boundary_count));
1202         PROC_SUNLOCK(p);
1203         if (wakeup_swapper)
1204                 kick_proc0();
1205 }
1206
1207 struct thread *
1208 thread_find(struct proc *p, lwpid_t tid)
1209 {
1210         struct thread *td;
1211
1212         PROC_LOCK_ASSERT(p, MA_OWNED);
1213         FOREACH_THREAD_IN_PROC(p, td) {
1214                 if (td->td_tid == tid)
1215                         break;
1216         }
1217         return (td);
1218 }
1219
1220 /* Locate a thread by number; return with proc lock held. */
1221 struct thread *
1222 tdfind(lwpid_t tid, pid_t pid)
1223 {
1224 #define RUN_THRESH      16
1225         struct thread *td;
1226         int run = 0;
1227
1228         rw_rlock(&tidhash_lock);
1229         LIST_FOREACH(td, TIDHASH(tid), td_hash) {
1230                 if (td->td_tid == tid) {
1231                         if (pid != -1 && td->td_proc->p_pid != pid) {
1232                                 td = NULL;
1233                                 break;
1234                         }
1235                         PROC_LOCK(td->td_proc);
1236                         if (td->td_proc->p_state == PRS_NEW) {
1237                                 PROC_UNLOCK(td->td_proc);
1238                                 td = NULL;
1239                                 break;
1240                         }
1241                         if (run > RUN_THRESH) {
1242                                 if (rw_try_upgrade(&tidhash_lock)) {
1243                                         LIST_REMOVE(td, td_hash);
1244                                         LIST_INSERT_HEAD(TIDHASH(td->td_tid),
1245                                                 td, td_hash);
1246                                         rw_wunlock(&tidhash_lock);
1247                                         return (td);
1248                                 }
1249                         }
1250                         break;
1251                 }
1252                 run++;
1253         }
1254         rw_runlock(&tidhash_lock);
1255         return (td);
1256 }
1257
1258 void
1259 tidhash_add(struct thread *td)
1260 {
1261         rw_wlock(&tidhash_lock);
1262         LIST_INSERT_HEAD(TIDHASH(td->td_tid), td, td_hash);
1263         rw_wunlock(&tidhash_lock);
1264 }
1265
1266 void
1267 tidhash_remove(struct thread *td)
1268 {
1269         rw_wlock(&tidhash_lock);
1270         LIST_REMOVE(td, td_hash);
1271         rw_wunlock(&tidhash_lock);
1272 }