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) == 0x540,
  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         epoch_thread_init(td);
 277         td->td_kstack = 0;
 278         td->td_sel = NULL;
 279         return (0);
 280 }
 281
 282 /*
 283  * Tear down type-stable parts of a thread (just before being discarded).
 284  */
 285 static void
 286 thread_fini(void *mem, int size)
 287 {
 288         struct thread *td;
 289
 290         td = (struct thread *)mem;
 291         EVENTHANDLER_DIRECT_INVOKE(thread_fini, td);
 292         rlqentry_free(td->td_rlqe);
 293         turnstile_free(td->td_turnstile);
 294         sleepq_free(td->td_sleepqueue);
 295         umtx_thread_fini(td);
 296         epoch_thread_fini(td);
 297         seltdfini(td);
 298 }
 299
 300 /*
 301  * For a newly created process,
 302  * link up all the structures and its initial threads etc.
 303  * called from:
 304  * {arch}/{arch}/machdep.c   {arch}_init(), init386() etc.
 305  * proc_dtor() (should go away)
 306  * proc_init()
 307  */
 308 void
 309 proc_linkup0(struct proc *p, struct thread *td)
 310 {
 311         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
 312         proc_linkup(p, td);
 313 }
 314
 315 void
 316 proc_linkup(struct proc *p, struct thread *td)
 317 {
 318
 319         sigqueue_init(&p->p_sigqueue, p);
 320         p->p_ksi = ksiginfo_alloc(1);
 321         if (p->p_ksi != NULL) {
 322                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
 323                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
 324         }
 325         LIST_INIT(&p->p_mqnotifier);
 326         p->p_numthreads = 0;
 327         thread_link(td, p);
 328 }
 329
 330 /*
 331  * Initialize global thread allocation resources.
 332  */
 333 void
 334 threadinit(void)
 335 {
 336
 337         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
 338
 339         /*
 340          * pid_max cannot be greater than PID_MAX.
 341          * leave one number for thread0.
 342          */
 343         tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
 344
 345         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
 346             thread_ctor, thread_dtor, thread_init, thread_fini,
 347             32 - 1, UMA_ZONE_NOFREE);
 348         tidhashtbl = hashinit(maxproc / 2, M_TIDHASH, &tidhash);
 349         rw_init(&tidhash_lock, "tidhash");
 350 }
 351
 352 /*
 353  * Place an unused thread on the zombie list.
 354  * Use the slpq as that must be unused by now.
 355  */
 356 void
 357 thread_zombie(struct thread *td)
 358 {
 359         mtx_lock_spin(&zombie_lock);
 360         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
 361         mtx_unlock_spin(&zombie_lock);
 362 }
 363
 364 /*
 365  * Release a thread that has exited after cpu_throw().
 366  */
 367 void
 368 thread_stash(struct thread *td)
 369 {
 370         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
 371         thread_zombie(td);
 372 }
 373
 374 /*
 375  * Reap zombie resources.
 376  */
 377 void
 378 thread_reap(void)
 379 {
 380         struct thread *td_first, *td_next;
 381
 382         /*
 383          * Don't even bother to lock if none at this instant,
 384          * we really don't care about the next instant.
 385          */
 386         if (!TAILQ_EMPTY(&zombie_threads)) {
 387                 mtx_lock_spin(&zombie_lock);
 388                 td_first = TAILQ_FIRST(&zombie_threads);
 389                 if (td_first)
 390                         TAILQ_INIT(&zombie_threads);
 391                 mtx_unlock_spin(&zombie_lock);
 392                 while (td_first) {
 393                         td_next = TAILQ_NEXT(td_first, td_slpq);
 394                         thread_cow_free(td_first);
 395                         thread_free(td_first);
 396                         td_first = td_next;
 397                 }
 398         }
 399 }
 400
 401 /*
 402  * Allocate a thread.
 403  */
 404 struct thread *
 405 thread_alloc(int pages)
 406 {
 407         struct thread *td;
 408
 409         thread_reap(); /* check if any zombies to get */
 410
 411         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
 412         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
 413         if (!vm_thread_new(td, pages)) {
 414                 uma_zfree(thread_zone, td);
 415                 return (NULL);
 416         }
 417         cpu_thread_alloc(td);
 418         return (td);
 419 }
 420
 421 int
 422 thread_alloc_stack(struct thread *td, int pages)
 423 {
 424
 425         KASSERT(td->td_kstack == 0,
 426             ("thread_alloc_stack called on a thread with kstack"));
 427         if (!vm_thread_new(td, pages))
 428                 return (0);
 429         cpu_thread_alloc(td);
 430         return (1);
 431 }
 432
 433 /*
 434  * Deallocate a thread.
 435  */
 436 void
 437 thread_free(struct thread *td)
 438 {
 439
 440         lock_profile_thread_exit(td);
 441         if (td->td_cpuset)
 442                 cpuset_rel(td->td_cpuset);
 443         td->td_cpuset = NULL;
 444         cpu_thread_free(td);
 445         if (td->td_kstack != 0)
 446                 vm_thread_dispose(td);
 447         callout_drain(&td->td_slpcallout);
 448         uma_zfree(thread_zone, td);
 449 }
 450
 451 void
 452 thread_cow_get_proc(struct thread *newtd, struct proc *p)
 453 {
 454
 455         PROC_LOCK_ASSERT(p, MA_OWNED);
 456         newtd->td_ucred = crhold(p->p_ucred);
 457         newtd->td_limit = lim_hold(p->p_limit);
 458         newtd->td_cowgen = p->p_cowgen;
 459 }
 460
 461 void
 462 thread_cow_get(struct thread *newtd, struct thread *td)
 463 {
 464
 465         newtd->td_ucred = crhold(td->td_ucred);
 466         newtd->td_limit = lim_hold(td->td_limit);
 467         newtd->td_cowgen = td->td_cowgen;
 468 }
 469
 470 void
 471 thread_cow_free(struct thread *td)
 472 {
 473
 474         if (td->td_ucred != NULL)
 475                 crfree(td->td_ucred);
 476         if (td->td_limit != NULL)
 477                 lim_free(td->td_limit);
 478 }
 479
 480 void
 481 thread_cow_update(struct thread *td)
 482 {
 483         struct proc *p;
 484         struct ucred *oldcred;
 485         struct plimit *oldlimit;
 486
 487         p = td->td_proc;
 488         oldcred = NULL;
 489         oldlimit = NULL;
 490         PROC_LOCK(p);
 491         if (td->td_ucred != p->p_ucred) {
 492                 oldcred = td->td_ucred;
 493                 td->td_ucred = crhold(p->p_ucred);
 494         }
 495         if (td->td_limit != p->p_limit) {
 496                 oldlimit = td->td_limit;
 497                 td->td_limit = lim_hold(p->p_limit);
 498         }
 499         td->td_cowgen = p->p_cowgen;
 500         PROC_UNLOCK(p);
 501         if (oldcred != NULL)
 502                 crfree(oldcred);
 503         if (oldlimit != NULL)
 504                 lim_free(oldlimit);
 505 }
 506
 507 /*
 508  * Discard the current thread and exit from its context.
 509  * Always called with scheduler locked.
 510  *
 511  * Because we can't free a thread while we're operating under its context,
 512  * push the current thread into our CPU's deadthread holder. This means
 513  * we needn't worry about someone else grabbing our context before we
 514  * do a cpu_throw().
 515  */
 516 void
 517 thread_exit(void)
 518 {
 519         uint64_t runtime, new_switchtime;
 520         struct thread *td;
 521         struct thread *td2;
 522         struct proc *p;
 523         int wakeup_swapper;
 524
 525         td = curthread;
 526         p = td->td_proc;
 527
 528         PROC_SLOCK_ASSERT(p, MA_OWNED);
 529         mtx_assert(&Giant, MA_NOTOWNED);
 530
 531         PROC_LOCK_ASSERT(p, MA_OWNED);
 532         KASSERT(p != NULL, ("thread exiting without a process"));
 533         CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
 534             (long)p->p_pid, td->td_name);
 535         SDT_PROBE0(proc, , , lwp__exit);
 536         KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
 537
 538         /*
 539          * drop FPU & debug register state storage, or any other
 540          * architecture specific resources that
 541          * would not be on a new untouched process.
 542          */
 543         cpu_thread_exit(td);
 544
 545         /*
 546          * The last thread is left attached to the process
 547          * So that the whole bundle gets recycled. Skip
 548          * all this stuff if we never had threads.
 549          * EXIT clears all sign of other threads when
 550          * it goes to single threading, so the last thread always
 551          * takes the short path.
 552          */
 553         if (p->p_flag & P_HADTHREADS) {
 554                 if (p->p_numthreads > 1) {
 555                         atomic_add_int(&td->td_proc->p_exitthreads, 1);
 556                         thread_unlink(td);
 557                         td2 = FIRST_THREAD_IN_PROC(p);
 558                         sched_exit_thread(td2, td);
 559
 560                         /*
 561                          * The test below is NOT true if we are the
 562                          * sole exiting thread. P_STOPPED_SINGLE is unset
 563                          * in exit1() after it is the only survivor.
 564                          */
 565                         if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 566                                 if (p->p_numthreads == p->p_suspcount) {
 567                                         thread_lock(p->p_singlethread);
 568                                         wakeup_swapper = thread_unsuspend_one(
 569                                                 p->p_singlethread, p, false);
 570                                         thread_unlock(p->p_singlethread);
 571                                         if (wakeup_swapper)
 572                                                 kick_proc0();
 573                                 }
 574                         }
 575
 576                         PCPU_SET(deadthread, td);
 577                 } else {
 578                         /*
 579                          * The last thread is exiting.. but not through exit()
 580                          */
 581                         panic ("thread_exit: Last thread exiting on its own");
 582                 }
 583         }
 584 #ifdef  HWPMC_HOOKS
 585         /*
 586          * If this thread is part of a process that is being tracked by hwpmc(4),
 587          * inform the module of the thread's impending exit.
 588          */
 589         if (PMC_PROC_IS_USING_PMCS(td->td_proc)) {
 590                 PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
 591                 PMC_CALL_HOOK_UNLOCKED(td, PMC_FN_THR_EXIT, NULL);
 592         } else if (PMC_SYSTEM_SAMPLING_ACTIVE())
 593                 PMC_CALL_HOOK_UNLOCKED(td, PMC_FN_THR_EXIT_LOG, NULL);
 594 #endif
 595         PROC_UNLOCK(p);
 596         PROC_STATLOCK(p);
 597         thread_lock(td);
 598         PROC_SUNLOCK(p);
 599
 600         /* Do the same timestamp bookkeeping that mi_switch() would do. */
 601         new_switchtime = cpu_ticks();
 602         runtime = new_switchtime - PCPU_GET(switchtime);
 603         td->td_runtime += runtime;
 604         td->td_incruntime += runtime;
 605         PCPU_SET(switchtime, new_switchtime);
 606         PCPU_SET(switchticks, ticks);
 607         VM_CNT_INC(v_swtch);
 608
 609         /* Save our resource usage in our process. */
 610         td->td_ru.ru_nvcsw++;
 611         ruxagg(p, td);
 612         rucollect(&p->p_ru, &td->td_ru);
 613         PROC_STATUNLOCK(p);
 614
 615         td->td_state = TDS_INACTIVE;
 616 #ifdef WITNESS
 617         witness_thread_exit(td);
 618 #endif
 619         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
 620         sched_throw(td);
 621         panic("I'm a teapot!");
 622         /* NOTREACHED */
 623 }
 624
 625 /*
 626  * Do any thread specific cleanups that may be needed in wait()
 627  * called with Giant, proc and schedlock not held.
 628  */
 629 void
 630 thread_wait(struct proc *p)
 631 {
 632         struct thread *td;
 633
 634         mtx_assert(&Giant, MA_NOTOWNED);
 635         KASSERT(p->p_numthreads == 1, ("multiple threads in thread_wait()"));
 636         KASSERT(p->p_exitthreads == 0, ("p_exitthreads leaking"));
 637         td = FIRST_THREAD_IN_PROC(p);
 638         /* Lock the last thread so we spin until it exits cpu_throw(). */
 639         thread_lock(td);
 640         thread_unlock(td);
 641         lock_profile_thread_exit(td);
 642         cpuset_rel(td->td_cpuset);
 643         td->td_cpuset = NULL;
 644         cpu_thread_clean(td);
 645         thread_cow_free(td);
 646         callout_drain(&td->td_slpcallout);
 647         thread_reap();  /* check for zombie threads etc. */
 648 }
 649
 650 /*
 651  * Link a thread to a process.
 652  * set up anything that needs to be initialized for it to
 653  * be used by the process.
 654  */
 655 void
 656 thread_link(struct thread *td, struct proc *p)
 657 {
 658
 659         /*
 660          * XXX This can't be enabled because it's called for proc0 before
 661          * its lock has been created.
 662          * PROC_LOCK_ASSERT(p, MA_OWNED);
 663          */
 664         td->td_state    = TDS_INACTIVE;
 665         td->td_proc     = p;
 666         td->td_flags    = TDF_INMEM;
 667
 668         LIST_INIT(&td->td_contested);
 669         LIST_INIT(&td->td_lprof[0]);
 670         LIST_INIT(&td->td_lprof[1]);
 671         SLIST_INIT(&td->td_epochs);
 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         MPASS(SLIST_EMPTY(&td->td_epochs));
 689
 690         TAILQ_REMOVE(&p->p_threads, td, td_plist);
 691         p->p_numthreads--;
 692         /* could clear a few other things here */
 693         /* Must  NOT clear links to proc! */
 694 }
 695
 696 static int
 697 calc_remaining(struct proc *p, int mode)
 698 {
 699         int remaining;
 700
 701         PROC_LOCK_ASSERT(p, MA_OWNED);
 702         PROC_SLOCK_ASSERT(p, MA_OWNED);
 703         if (mode == SINGLE_EXIT)
 704                 remaining = p->p_numthreads;
 705         else if (mode == SINGLE_BOUNDARY)
 706                 remaining = p->p_numthreads - p->p_boundary_count;
 707         else if (mode == SINGLE_NO_EXIT || mode == SINGLE_ALLPROC)
 708                 remaining = p->p_numthreads - p->p_suspcount;
 709         else
 710                 panic("calc_remaining: wrong mode %d", mode);
 711         return (remaining);
 712 }
 713
 714 static int
 715 remain_for_mode(int mode)
 716 {
 717
 718         return (mode == SINGLE_ALLPROC ? 0 : 1);
 719 }
 720
 721 static int
 722 weed_inhib(int mode, struct thread *td2, struct proc *p)
 723 {
 724         int wakeup_swapper;
 725
 726         PROC_LOCK_ASSERT(p, MA_OWNED);
 727         PROC_SLOCK_ASSERT(p, MA_OWNED);
 728         THREAD_LOCK_ASSERT(td2, MA_OWNED);
 729
 730         wakeup_swapper = 0;
 731         switch (mode) {
 732         case SINGLE_EXIT:
 733                 if (TD_IS_SUSPENDED(td2))
 734                         wakeup_swapper |= thread_unsuspend_one(td2, p, true);
 735                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0)
 736                         wakeup_swapper |= sleepq_abort(td2, EINTR);
 737                 break;
 738         case SINGLE_BOUNDARY:
 739         case SINGLE_NO_EXIT:
 740                 if (TD_IS_SUSPENDED(td2) && (td2->td_flags & TDF_BOUNDARY) == 0)
 741                         wakeup_swapper |= thread_unsuspend_one(td2, p, false);
 742                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0)
 743                         wakeup_swapper |= sleepq_abort(td2, ERESTART);
 744                 break;
 745         case SINGLE_ALLPROC:
 746                 /*
 747                  * ALLPROC suspend tries to avoid spurious EINTR for
 748                  * threads sleeping interruptable, by suspending the
 749                  * thread directly, similarly to sig_suspend_threads().
 750                  * Since such sleep is not performed at the user
 751                  * boundary, TDF_BOUNDARY flag is not set, and TDF_ALLPROCSUSP
 752                  * is used to avoid immediate un-suspend.
 753                  */
 754                 if (TD_IS_SUSPENDED(td2) && (td2->td_flags & (TDF_BOUNDARY |
 755                     TDF_ALLPROCSUSP)) == 0)
 756                         wakeup_swapper |= thread_unsuspend_one(td2, p, false);
 757                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0) {
 758                         if ((td2->td_flags & TDF_SBDRY) == 0) {
 759                                 thread_suspend_one(td2);
 760                                 td2->td_flags |= TDF_ALLPROCSUSP;
 761                         } else {
 762                                 wakeup_swapper |= sleepq_abort(td2, ERESTART);
 763                         }
 764                 }
 765                 break;
 766         }
 767         return (wakeup_swapper);
 768 }
 769
 770 /*
 771  * Enforce single-threading.
 772  *
 773  * Returns 1 if the caller must abort (another thread is waiting to
 774  * exit the process or similar). Process is locked!
 775  * Returns 0 when you are successfully the only thread running.
 776  * A process has successfully single threaded in the suspend mode when
 777  * There are no threads in user mode. Threads in the kernel must be
 778  * allowed to continue until they get to the user boundary. They may even
 779  * copy out their return values and data before suspending. They may however be
 780  * accelerated in reaching the user boundary as we will wake up
 781  * any sleeping threads that are interruptable. (PCATCH).
 782  */
 783 int
 784 thread_single(struct proc *p, int mode)
 785 {
 786         struct thread *td;
 787         struct thread *td2;
 788         int remaining, wakeup_swapper;
 789
 790         td = curthread;
 791         KASSERT(mode == SINGLE_EXIT || mode == SINGLE_BOUNDARY ||
 792             mode == SINGLE_ALLPROC || mode == SINGLE_NO_EXIT,
 793             ("invalid mode %d", mode));
 794         /*
 795          * If allowing non-ALLPROC singlethreading for non-curproc
 796          * callers, calc_remaining() and remain_for_mode() should be
 797          * adjusted to also account for td->td_proc != p.  For now
 798          * this is not implemented because it is not used.
 799          */
 800         KASSERT((mode == SINGLE_ALLPROC && td->td_proc != p) ||
 801             (mode != SINGLE_ALLPROC && td->td_proc == p),
 802             ("mode %d proc %p curproc %p", mode, p, td->td_proc));
 803         mtx_assert(&Giant, MA_NOTOWNED);
 804         PROC_LOCK_ASSERT(p, MA_OWNED);
 805
 806         if ((p->p_flag & P_HADTHREADS) == 0 && mode != SINGLE_ALLPROC)
 807                 return (0);
 808
 809         /* Is someone already single threading? */
 810         if (p->p_singlethread != NULL && p->p_singlethread != td)
 811                 return (1);
 812
 813         if (mode == SINGLE_EXIT) {
 814                 p->p_flag |= P_SINGLE_EXIT;
 815                 p->p_flag &= ~P_SINGLE_BOUNDARY;
 816         } else {
 817                 p->p_flag &= ~P_SINGLE_EXIT;
 818                 if (mode == SINGLE_BOUNDARY)
 819                         p->p_flag |= P_SINGLE_BOUNDARY;
 820                 else
 821                         p->p_flag &= ~P_SINGLE_BOUNDARY;
 822         }
 823         if (mode == SINGLE_ALLPROC)
 824                 p->p_flag |= P_TOTAL_STOP;
 825         p->p_flag |= P_STOPPED_SINGLE;
 826         PROC_SLOCK(p);
 827         p->p_singlethread = td;
 828         remaining = calc_remaining(p, mode);
 829         while (remaining != remain_for_mode(mode)) {
 830                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
 831                         goto stopme;
 832                 wakeup_swapper = 0;
 833                 FOREACH_THREAD_IN_PROC(p, td2) {
 834                         if (td2 == td)
 835                                 continue;
 836                         thread_lock(td2);
 837                         td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
 838                         if (TD_IS_INHIBITED(td2)) {
 839                                 wakeup_swapper |= weed_inhib(mode, td2, p);
 840 #ifdef SMP
 841                         } else if (TD_IS_RUNNING(td2) && td != td2) {
 842                                 forward_signal(td2);
 843 #endif
 844                         }
 845                         thread_unlock(td2);
 846                 }
 847                 if (wakeup_swapper)
 848                         kick_proc0();
 849                 remaining = calc_remaining(p, mode);
 850
 851                 /*
 852                  * Maybe we suspended some threads.. was it enough?
 853                  */
 854                 if (remaining == remain_for_mode(mode))
 855                         break;
 856
 857 stopme:
 858                 /*
 859                  * Wake us up when everyone else has suspended.
 860                  * In the mean time we suspend as well.
 861                  */
 862                 thread_suspend_switch(td, p);
 863                 remaining = calc_remaining(p, mode);
 864         }
 865         if (mode == SINGLE_EXIT) {
 866                 /*
 867                  * Convert the process to an unthreaded process.  The
 868                  * SINGLE_EXIT is called by exit1() or execve(), in
 869                  * both cases other threads must be retired.
 870                  */
 871                 KASSERT(p->p_numthreads == 1, ("Unthreading with >1 threads"));
 872                 p->p_singlethread = NULL;
 873                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_HADTHREADS);
 874
 875                 /*
 876                  * Wait for any remaining threads to exit cpu_throw().
 877                  */
 878                 while (p->p_exitthreads != 0) {
 879                         PROC_SUNLOCK(p);
 880                         PROC_UNLOCK(p);
 881                         sched_relinquish(td);
 882                         PROC_LOCK(p);
 883                         PROC_SLOCK(p);
 884                 }
 885         } else if (mode == SINGLE_BOUNDARY) {
 886                 /*
 887                  * Wait until all suspended threads are removed from
 888                  * the processors.  The thread_suspend_check()
 889                  * increments p_boundary_count while it is still
 890                  * running, which makes it possible for the execve()
 891                  * to destroy vmspace while our other threads are
 892                  * still using the address space.
 893                  *
 894                  * We lock the thread, which is only allowed to
 895                  * succeed after context switch code finished using
 896                  * the address space.
 897                  */
 898                 FOREACH_THREAD_IN_PROC(p, td2) {
 899                         if (td2 == td)
 900                                 continue;
 901                         thread_lock(td2);
 902                         KASSERT((td2->td_flags & TDF_BOUNDARY) != 0,
 903                             ("td %p not on boundary", td2));
 904                         KASSERT(TD_IS_SUSPENDED(td2),
 905                             ("td %p is not suspended", td2));
 906                         thread_unlock(td2);
 907                 }
 908         }
 909         PROC_SUNLOCK(p);
 910         return (0);
 911 }
 912
 913 bool
 914 thread_suspend_check_needed(void)
 915 {
 916         struct proc *p;
 917         struct thread *td;
 918
 919         td = curthread;
 920         p = td->td_proc;
 921         PROC_LOCK_ASSERT(p, MA_OWNED);
 922         return (P_SHOULDSTOP(p) || ((p->p_flag & P_TRACED) != 0 &&
 923             (td->td_dbgflags & TDB_SUSPEND) != 0));
 924 }
 925
 926 /*
 927  * Called in from locations that can safely check to see
 928  * whether we have to suspend or at least throttle for a
 929  * single-thread event (e.g. fork).
 930  *
 931  * Such locations include userret().
 932  * If the "return_instead" argument is non zero, the thread must be able to
 933  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
 934  *
 935  * The 'return_instead' argument tells the function if it may do a
 936  * thread_exit() or suspend, or whether the caller must abort and back
 937  * out instead.
 938  *
 939  * If the thread that set the single_threading request has set the
 940  * P_SINGLE_EXIT bit in the process flags then this call will never return
 941  * if 'return_instead' is false, but will exit.
 942  *
 943  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
 944  *---------------+--------------------+---------------------
 945  *       0       | returns 0          |   returns 0 or 1
 946  *               | when ST ends       |   immediately
 947  *---------------+--------------------+---------------------
 948  *       1       | thread exits       |   returns 1
 949  *               |                    |  immediately
 950  * 0 = thread_exit() or suspension ok,
 951  * other = return error instead of stopping the thread.
 952  *
 953  * While a full suspension is under effect, even a single threading
 954  * thread would be suspended if it made this call (but it shouldn't).
 955  * This call should only be made from places where
 956  * thread_exit() would be safe as that may be the outcome unless
 957  * return_instead is set.
 958  */
 959 int
 960 thread_suspend_check(int return_instead)
 961 {
 962         struct thread *td;
 963         struct proc *p;
 964         int wakeup_swapper;
 965
 966         td = curthread;
 967         p = td->td_proc;
 968         mtx_assert(&Giant, MA_NOTOWNED);
 969         PROC_LOCK_ASSERT(p, MA_OWNED);
 970         while (thread_suspend_check_needed()) {
 971                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 972                         KASSERT(p->p_singlethread != NULL,
 973                             ("singlethread not set"));
 974                         /*
 975                          * The only suspension in action is a
 976                          * single-threading. Single threader need not stop.
 977                          * It is safe to access p->p_singlethread unlocked
 978                          * because it can only be set to our address by us.
 979                          */
 980                         if (p->p_singlethread == td)
 981                                 return (0);     /* Exempt from stopping. */
 982                 }
 983                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
 984                         return (EINTR);
 985
 986                 /* Should we goto user boundary if we didn't come from there? */
 987                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
 988                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
 989                         return (ERESTART);
 990
 991                 /*
 992                  * Ignore suspend requests if they are deferred.
 993                  */
 994                 if ((td->td_flags & TDF_SBDRY) != 0) {
 995                         KASSERT(return_instead,
 996                             ("TDF_SBDRY set for unsafe thread_suspend_check"));
 997                         KASSERT((td->td_flags & (TDF_SEINTR | TDF_SERESTART)) !=
 998                             (TDF_SEINTR | TDF_SERESTART),
 999                             ("both TDF_SEINTR and TDF_SERESTART"));
1000                         return (TD_SBDRY_INTR(td) ? TD_SBDRY_ERRNO(td) : 0);
1001                 }
1002
1003                 /*
1004                  * If the process is waiting for us to exit,
1005                  * this thread should just suicide.
1006                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
1007                  */
1008                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td)) {
1009                         PROC_UNLOCK(p);
1010
1011                         /*
1012                          * Allow Linux emulation layer to do some work
1013                          * before thread suicide.
1014                          */
1015                         if (__predict_false(p->p_sysent->sv_thread_detach != NULL))
1016                                 (p->p_sysent->sv_thread_detach)(td);
1017                         umtx_thread_exit(td);
1018                         kern_thr_exit(td);
1019                         panic("stopped thread did not exit");
1020                 }
1021
1022                 PROC_SLOCK(p);
1023                 thread_stopped(p);
1024                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
1025                         if (p->p_numthreads == p->p_suspcount + 1) {
1026                                 thread_lock(p->p_singlethread);
1027                                 wakeup_swapper = thread_unsuspend_one(
1028                                     p->p_singlethread, p, false);
1029                                 thread_unlock(p->p_singlethread);
1030                                 if (wakeup_swapper)
1031                                         kick_proc0();
1032                         }
1033                 }
1034                 PROC_UNLOCK(p);
1035                 thread_lock(td);
1036                 /*
1037                  * When a thread suspends, it just
1038                  * gets taken off all queues.
1039                  */
1040                 thread_suspend_one(td);
1041                 if (return_instead == 0) {
1042                         p->p_boundary_count++;
1043                         td->td_flags |= TDF_BOUNDARY;
1044                 }
1045                 PROC_SUNLOCK(p);
1046                 mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
1047                 thread_unlock(td);
1048                 PROC_LOCK(p);
1049         }
1050         return (0);
1051 }
1052
1053 void
1054 thread_suspend_switch(struct thread *td, struct proc *p)
1055 {
1056
1057         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
1058         PROC_LOCK_ASSERT(p, MA_OWNED);
1059         PROC_SLOCK_ASSERT(p, MA_OWNED);
1060         /*
1061          * We implement thread_suspend_one in stages here to avoid
1062          * dropping the proc lock while the thread lock is owned.
1063          */
1064         if (p == td->td_proc) {
1065                 thread_stopped(p);
1066                 p->p_suspcount++;
1067         }
1068         PROC_UNLOCK(p);
1069         thread_lock(td);
1070         td->td_flags &= ~TDF_NEEDSUSPCHK;
1071         TD_SET_SUSPENDED(td);
1072         sched_sleep(td, 0);
1073         PROC_SUNLOCK(p);
1074         DROP_GIANT();
1075         mi_switch(SW_VOL | SWT_SUSPEND, NULL);
1076         thread_unlock(td);
1077         PICKUP_GIANT();
1078         PROC_LOCK(p);
1079         PROC_SLOCK(p);
1080 }
1081
1082 void
1083 thread_suspend_one(struct thread *td)
1084 {
1085         struct proc *p;
1086
1087         p = td->td_proc;
1088         PROC_SLOCK_ASSERT(p, MA_OWNED);
1089         THREAD_LOCK_ASSERT(td, MA_OWNED);
1090         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
1091         p->p_suspcount++;
1092         td->td_flags &= ~TDF_NEEDSUSPCHK;
1093         TD_SET_SUSPENDED(td);
1094         sched_sleep(td, 0);
1095 }
1096
1097 static int
1098 thread_unsuspend_one(struct thread *td, struct proc *p, bool boundary)
1099 {
1100
1101         THREAD_LOCK_ASSERT(td, MA_OWNED);
1102         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
1103         TD_CLR_SUSPENDED(td);
1104         td->td_flags &= ~TDF_ALLPROCSUSP;
1105         if (td->td_proc == p) {
1106                 PROC_SLOCK_ASSERT(p, MA_OWNED);
1107                 p->p_suspcount--;
1108                 if (boundary && (td->td_flags & TDF_BOUNDARY) != 0) {
1109                         td->td_flags &= ~TDF_BOUNDARY;
1110                         p->p_boundary_count--;
1111                 }
1112         }
1113         return (setrunnable(td));
1114 }
1115
1116 /*
1117  * Allow all threads blocked by single threading to continue running.
1118  */
1119 void
1120 thread_unsuspend(struct proc *p)
1121 {
1122         struct thread *td;
1123         int wakeup_swapper;
1124
1125         PROC_LOCK_ASSERT(p, MA_OWNED);
1126         PROC_SLOCK_ASSERT(p, MA_OWNED);
1127         wakeup_swapper = 0;
1128         if (!P_SHOULDSTOP(p)) {
1129                 FOREACH_THREAD_IN_PROC(p, td) {
1130                         thread_lock(td);
1131                         if (TD_IS_SUSPENDED(td)) {
1132                                 wakeup_swapper |= thread_unsuspend_one(td, p,
1133                                     true);
1134                         }
1135                         thread_unlock(td);
1136                 }
1137         } else if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
1138             p->p_numthreads == p->p_suspcount) {
1139                 /*
1140                  * Stopping everything also did the job for the single
1141                  * threading request. Now we've downgraded to single-threaded,
1142                  * let it continue.
1143                  */
1144                 if (p->p_singlethread->td_proc == p) {
1145                         thread_lock(p->p_singlethread);
1146                         wakeup_swapper = thread_unsuspend_one(
1147                             p->p_singlethread, p, false);
1148                         thread_unlock(p->p_singlethread);
1149                 }
1150         }
1151         if (wakeup_swapper)
1152                 kick_proc0();
1153 }
1154
1155 /*
1156  * End the single threading mode..
1157  */
1158 void
1159 thread_single_end(struct proc *p, int mode)
1160 {
1161         struct thread *td;
1162         int wakeup_swapper;
1163
1164         KASSERT(mode == SINGLE_EXIT || mode == SINGLE_BOUNDARY ||
1165             mode == SINGLE_ALLPROC || mode == SINGLE_NO_EXIT,
1166             ("invalid mode %d", mode));
1167         PROC_LOCK_ASSERT(p, MA_OWNED);
1168         KASSERT((mode == SINGLE_ALLPROC && (p->p_flag & P_TOTAL_STOP) != 0) ||
1169             (mode != SINGLE_ALLPROC && (p->p_flag & P_TOTAL_STOP) == 0),
1170             ("mode %d does not match P_TOTAL_STOP", mode));
1171         KASSERT(mode == SINGLE_ALLPROC || p->p_singlethread == curthread,
1172             ("thread_single_end from other thread %p %p",
1173             curthread, p->p_singlethread));
1174         KASSERT(mode != SINGLE_BOUNDARY ||
1175             (p->p_flag & P_SINGLE_BOUNDARY) != 0,
1176             ("mis-matched SINGLE_BOUNDARY flags %x", p->p_flag));
1177         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY |
1178             P_TOTAL_STOP);
1179         PROC_SLOCK(p);
1180         p->p_singlethread = NULL;
1181         wakeup_swapper = 0;
1182         /*
1183          * If there are other threads they may now run,
1184          * unless of course there is a blanket 'stop order'
1185          * on the process. The single threader must be allowed
1186          * to continue however as this is a bad place to stop.
1187          */
1188         if (p->p_numthreads != remain_for_mode(mode) && !P_SHOULDSTOP(p)) {
1189                 FOREACH_THREAD_IN_PROC(p, td) {
1190                         thread_lock(td);
1191                         if (TD_IS_SUSPENDED(td)) {
1192                                 wakeup_swapper |= thread_unsuspend_one(td, p,
1193                                     mode == SINGLE_BOUNDARY);
1194                         }
1195                         thread_unlock(td);
1196                 }
1197         }
1198         KASSERT(mode != SINGLE_BOUNDARY || p->p_boundary_count == 0,
1199             ("inconsistent boundary count %d", p->p_boundary_count));
1200         PROC_SUNLOCK(p);
1201         if (wakeup_swapper)
1202                 kick_proc0();
1203 }
1204
1205 struct thread *
1206 thread_find(struct proc *p, lwpid_t tid)
1207 {
1208         struct thread *td;
1209
1210         PROC_LOCK_ASSERT(p, MA_OWNED);
1211         FOREACH_THREAD_IN_PROC(p, td) {
1212                 if (td->td_tid == tid)
1213                         break;
1214         }
1215         return (td);
1216 }
1217
1218 /* Locate a thread by number; return with proc lock held. */
1219 struct thread *
1220 tdfind(lwpid_t tid, pid_t pid)
1221 {
1222 #define RUN_THRESH      16
1223         struct thread *td;
1224         int run = 0;
1225
1226         rw_rlock(&tidhash_lock);
1227         LIST_FOREACH(td, TIDHASH(tid), td_hash) {
1228                 if (td->td_tid == tid) {
1229                         if (pid != -1 && td->td_proc->p_pid != pid) {
1230                                 td = NULL;
1231                                 break;
1232                         }
1233                         PROC_LOCK(td->td_proc);
1234                         if (td->td_proc->p_state == PRS_NEW) {
1235                                 PROC_UNLOCK(td->td_proc);
1236                                 td = NULL;
1237                                 break;
1238                         }
1239                         if (run > RUN_THRESH) {
1240                                 if (rw_try_upgrade(&tidhash_lock)) {
1241                                         LIST_REMOVE(td, td_hash);
1242                                         LIST_INSERT_HEAD(TIDHASH(td->td_tid),
1243                                                 td, td_hash);
1244                                         rw_wunlock(&tidhash_lock);
1245                                         return (td);
1246                                 }
1247                         }
1248                         break;
1249                 }
1250                 run++;
1251         }
1252         rw_runlock(&tidhash_lock);
1253         return (td);
1254 }
1255
1256 void
1257 tidhash_add(struct thread *td)
1258 {
1259         rw_wlock(&tidhash_lock);
1260         LIST_INSERT_HEAD(TIDHASH(td->td_tid), td, td_hash);
1261         rw_wunlock(&tidhash_lock);
1262 }
1263
1264 void
1265 tidhash_remove(struct thread *td)
1266 {
1267         rw_wlock(&tidhash_lock);
1268         LIST_REMOVE(td, td_hash);
1269         rw_wunlock(&tidhash_lock);
1270 }