sys/kern/kern_thread.c

   1 /*-
   2  * Copyright (C) 2001 Julian Elischer <julian@freebsd.org>.
   3  *  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice(s), this list of conditions and the following disclaimer as
  10  *    the first lines of this file unmodified other than the possible
  11  *    addition of one or more copyright notices.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice(s), this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
  17  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  18  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  19  * DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
  20  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  21  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  22  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  23  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
  26  * DAMAGE.
  27  */
  28
  29 #include "opt_witness.h"
  30 #include "opt_hwpmc_hooks.h"
  31
  32 #include <sys/cdefs.h>
  33 __FBSDID("$FreeBSD$");
  34
  35 #include <sys/param.h>
  36 #include <sys/systm.h>
  37 #include <sys/kernel.h>
  38 #include <sys/lock.h>
  39 #include <sys/mutex.h>
  40 #include <sys/proc.h>
  41 #include <sys/rangelock.h>
  42 #include <sys/resourcevar.h>
  43 #include <sys/sdt.h>
  44 #include <sys/smp.h>
  45 #include <sys/sched.h>
  46 #include <sys/sleepqueue.h>
  47 #include <sys/selinfo.h>
  48 #include <sys/syscallsubr.h>
  49 #include <sys/sysent.h>
  50 #include <sys/turnstile.h>
  51 #include <sys/ktr.h>
  52 #include <sys/rwlock.h>
  53 #include <sys/umtx.h>
  54 #include <sys/vmmeter.h>
  55 #include <sys/cpuset.h>
  56 #ifdef  HWPMC_HOOKS
  57 #include <sys/pmckern.h>
  58 #endif
  59
  60 #include <security/audit/audit.h>
  61
  62 #include <vm/vm.h>
  63 #include <vm/vm_extern.h>
  64 #include <vm/uma.h>
  65 #include <vm/vm_domain.h>
  66 #include <sys/eventhandler.h>
  67
  68 /*
  69  * Asserts below verify the stability of struct thread and struct proc
  70  * layout, as exposed by KBI to modules.  On head, the KBI is allowed
  71  * to drift, change to the structures must be accompanied by the
  72  * assert update.
  73  *
  74  * On the stable branches after KBI freeze, conditions must not be
  75  * violated.  Typically new fields are moved to the end of the
  76  * structures.
  77  */
  78 #ifdef __amd64__
  79 _Static_assert(offsetof(struct thread, td_flags) == 0xe4,
  80     "struct thread KBI td_flags");
  81 _Static_assert(offsetof(struct thread, td_pflags) == 0xec,
  82     "struct thread KBI td_pflags");
  83 _Static_assert(offsetof(struct thread, td_frame) == 0x418,
  84     "struct thread KBI td_frame");
  85 _Static_assert(offsetof(struct thread, td_emuldata) == 0x4c0,
  86     "struct thread KBI td_emuldata");
  87 _Static_assert(offsetof(struct proc, p_flag) == 0xb0,
  88     "struct proc KBI p_flag");
  89 _Static_assert(offsetof(struct proc, p_pid) == 0xbc,
  90     "struct proc KBI p_pid");
  91 _Static_assert(offsetof(struct proc, p_filemon) == 0x3c0,
  92     "struct proc KBI p_filemon");
  93 _Static_assert(offsetof(struct proc, p_comm) == 0x3d0,
  94     "struct proc KBI p_comm");
  95 _Static_assert(offsetof(struct proc, p_emuldata) == 0x4a0,
  96     "struct proc KBI p_emuldata");
  97 #endif
  98 #ifdef __i386__
  99 _Static_assert(offsetof(struct thread, td_flags) == 0x8c,
 100     "struct thread KBI td_flags");
 101 _Static_assert(offsetof(struct thread, td_pflags) == 0x94,
 102     "struct thread KBI td_pflags");
 103 _Static_assert(offsetof(struct thread, td_frame) == 0x2c0,
 104     "struct thread KBI td_frame");
 105 _Static_assert(offsetof(struct thread, td_emuldata) == 0x30c,
 106     "struct thread KBI td_emuldata");
 107 _Static_assert(offsetof(struct proc, p_flag) == 0x68,
 108     "struct proc KBI p_flag");
 109 _Static_assert(offsetof(struct proc, p_pid) == 0x74,
 110     "struct proc KBI p_pid");
 111 _Static_assert(offsetof(struct proc, p_filemon) == 0x268,
 112     "struct proc KBI p_filemon");
 113 _Static_assert(offsetof(struct proc, p_comm) == 0x274,
 114     "struct proc KBI p_comm");
 115 _Static_assert(offsetof(struct proc, p_emuldata) == 0x2f4,
 116     "struct proc KBI p_emuldata");
 117 #endif
 118
 119 SDT_PROVIDER_DECLARE(proc);
 120 SDT_PROBE_DEFINE(proc, , , lwp__exit);
 121
 122 /*
 123  * thread related storage.
 124  */
 125 static uma_zone_t thread_zone;
 126
 127 TAILQ_HEAD(, thread) zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
 128 static struct mtx zombie_lock;
 129 MTX_SYSINIT(zombie_lock, &zombie_lock, "zombie lock", MTX_SPIN);
 130
 131 static void thread_zombie(struct thread *);
 132 static int thread_unsuspend_one(struct thread *td, struct proc *p,
 133     bool boundary);
 134
 135 #define TID_BUFFER_SIZE 1024
 136
 137 struct mtx tid_lock;
 138 static struct unrhdr *tid_unrhdr;
 139 static lwpid_t tid_buffer[TID_BUFFER_SIZE];
 140 static int tid_head, tid_tail;
 141 static MALLOC_DEFINE(M_TIDHASH, "tidhash", "thread hash");
 142
 143 struct  tidhashhead *tidhashtbl;
 144 u_long  tidhash;
 145 struct  rwlock tidhash_lock;
 146
 147 EVENTHANDLER_LIST_DEFINE(thread_ctor);
 148 EVENTHANDLER_LIST_DEFINE(thread_dtor);
 149 EVENTHANDLER_LIST_DEFINE(thread_init);
 150 EVENTHANDLER_LIST_DEFINE(thread_fini);
 151
 152 static lwpid_t
 153 tid_alloc(void)
 154 {
 155         lwpid_t tid;
 156
 157         tid = alloc_unr(tid_unrhdr);
 158         if (tid != -1)
 159                 return (tid);
 160         mtx_lock(&tid_lock);
 161         if (tid_head == tid_tail) {
 162                 mtx_unlock(&tid_lock);
 163                 return (-1);
 164         }
 165         tid = tid_buffer[tid_head];
 166         tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
 167         mtx_unlock(&tid_lock);
 168         return (tid);
 169 }
 170
 171 static void
 172 tid_free(lwpid_t tid)
 173 {
 174         lwpid_t tmp_tid = -1;
 175
 176         mtx_lock(&tid_lock);
 177         if ((tid_tail + 1) % TID_BUFFER_SIZE == tid_head) {
 178                 tmp_tid = tid_buffer[tid_head];
 179                 tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
 180         }
 181         tid_buffer[tid_tail] = tid;
 182         tid_tail = (tid_tail + 1) % TID_BUFFER_SIZE;
 183         mtx_unlock(&tid_lock);
 184         if (tmp_tid != -1)
 185                 free_unr(tid_unrhdr, tmp_tid);
 186 }
 187
 188 /*
 189  * Prepare a thread for use.
 190  */
 191 static int
 192 thread_ctor(void *mem, int size, void *arg, int flags)
 193 {
 194         struct thread   *td;
 195
 196         td = (struct thread *)mem;
 197         td->td_state = TDS_INACTIVE;
 198         td->td_oncpu = NOCPU;
 199
 200         td->td_tid = tid_alloc();
 201
 202         /*
 203          * Note that td_critnest begins life as 1 because the thread is not
 204          * running and is thereby implicitly waiting to be on the receiving
 205          * end of a context switch.
 206          */
 207         td->td_critnest = 1;
 208         td->td_lend_user_pri = PRI_MAX;
 209         EVENTHANDLER_DIRECT_INVOKE(thread_ctor, td);
 210 #ifdef AUDIT
 211         audit_thread_alloc(td);
 212 #endif
 213         umtx_thread_alloc(td);
 214         return (0);
 215 }
 216
 217 /*
 218  * Reclaim a thread after use.
 219  */
 220 static void
 221 thread_dtor(void *mem, int size, void *arg)
 222 {
 223         struct thread *td;
 224
 225         td = (struct thread *)mem;
 226
 227 #ifdef INVARIANTS
 228         /* Verify that this thread is in a safe state to free. */
 229         switch (td->td_state) {
 230         case TDS_INHIBITED:
 231         case TDS_RUNNING:
 232         case TDS_CAN_RUN:
 233         case TDS_RUNQ:
 234                 /*
 235                  * We must never unlink a thread that is in one of
 236                  * these states, because it is currently active.
 237                  */
 238                 panic("bad state for thread unlinking");
 239                 /* NOTREACHED */
 240         case TDS_INACTIVE:
 241                 break;
 242         default:
 243                 panic("bad thread state");
 244                 /* NOTREACHED */
 245         }
 246 #endif
 247 #ifdef AUDIT
 248         audit_thread_free(td);
 249 #endif
 250         /* Free all OSD associated to this thread. */
 251         osd_thread_exit(td);
 252         td_softdep_cleanup(td);
 253         MPASS(td->td_su == NULL);
 254
 255         EVENTHANDLER_DIRECT_INVOKE(thread_dtor, td);
 256         tid_free(td->td_tid);
 257 }
 258
 259 /*
 260  * Initialize type-stable parts of a thread (when newly created).
 261  */
 262 static int
 263 thread_init(void *mem, int size, int flags)
 264 {
 265         struct thread *td;
 266
 267         td = (struct thread *)mem;
 268
 269         td->td_sleepqueue = sleepq_alloc();
 270         td->td_turnstile = turnstile_alloc();
 271         td->td_rlqe = NULL;
 272         EVENTHANDLER_DIRECT_INVOKE(thread_init, td);
 273         umtx_thread_init(td);
 274         td->td_kstack = 0;
 275         td->td_sel = NULL;
 276         return (0);
 277 }
 278
 279 /*
 280  * Tear down type-stable parts of a thread (just before being discarded).
 281  */
 282 static void
 283 thread_fini(void *mem, int size)
 284 {
 285         struct thread *td;
 286
 287         td = (struct thread *)mem;
 288         EVENTHANDLER_DIRECT_INVOKE(thread_fini, td);
 289         rlqentry_free(td->td_rlqe);
 290         turnstile_free(td->td_turnstile);
 291         sleepq_free(td->td_sleepqueue);
 292         umtx_thread_fini(td);
 293         seltdfini(td);
 294 }
 295
 296 /*
 297  * For a newly created process,
 298  * link up all the structures and its initial threads etc.
 299  * called from:
 300  * {arch}/{arch}/machdep.c   {arch}_init(), init386() etc.
 301  * proc_dtor() (should go away)
 302  * proc_init()
 303  */
 304 void
 305 proc_linkup0(struct proc *p, struct thread *td)
 306 {
 307         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
 308         proc_linkup(p, td);
 309 }
 310
 311 void
 312 proc_linkup(struct proc *p, struct thread *td)
 313 {
 314
 315         sigqueue_init(&p->p_sigqueue, p);
 316         p->p_ksi = ksiginfo_alloc(1);
 317         if (p->p_ksi != NULL) {
 318                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
 319                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
 320         }
 321         LIST_INIT(&p->p_mqnotifier);
 322         p->p_numthreads = 0;
 323         thread_link(td, p);
 324 }
 325
 326 /*
 327  * Initialize global thread allocation resources.
 328  */
 329 void
 330 threadinit(void)
 331 {
 332
 333         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
 334
 335         /*
 336          * pid_max cannot be greater than PID_MAX.
 337          * leave one number for thread0.
 338          */
 339         tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
 340
 341         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
 342             thread_ctor, thread_dtor, thread_init, thread_fini,
 343             32 - 1, UMA_ZONE_NOFREE);
 344         tidhashtbl = hashinit(maxproc / 2, M_TIDHASH, &tidhash);
 345         rw_init(&tidhash_lock, "tidhash");
 346 }
 347
 348 /*
 349  * Place an unused thread on the zombie list.
 350  * Use the slpq as that must be unused by now.
 351  */
 352 void
 353 thread_zombie(struct thread *td)
 354 {
 355         mtx_lock_spin(&zombie_lock);
 356         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
 357         mtx_unlock_spin(&zombie_lock);
 358 }
 359
 360 /*
 361  * Release a thread that has exited after cpu_throw().
 362  */
 363 void
 364 thread_stash(struct thread *td)
 365 {
 366         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
 367         thread_zombie(td);
 368 }
 369
 370 /*
 371  * Reap zombie resources.
 372  */
 373 void
 374 thread_reap(void)
 375 {
 376         struct thread *td_first, *td_next;
 377
 378         /*
 379          * Don't even bother to lock if none at this instant,
 380          * we really don't care about the next instant.
 381          */
 382         if (!TAILQ_EMPTY(&zombie_threads)) {
 383                 mtx_lock_spin(&zombie_lock);
 384                 td_first = TAILQ_FIRST(&zombie_threads);
 385                 if (td_first)
 386                         TAILQ_INIT(&zombie_threads);
 387                 mtx_unlock_spin(&zombie_lock);
 388                 while (td_first) {
 389                         td_next = TAILQ_NEXT(td_first, td_slpq);
 390                         thread_cow_free(td_first);
 391                         thread_free(td_first);
 392                         td_first = td_next;
 393                 }
 394         }
 395 }
 396
 397 /*
 398  * Allocate a thread.
 399  */
 400 struct thread *
 401 thread_alloc(int pages)
 402 {
 403         struct thread *td;
 404
 405         thread_reap(); /* check if any zombies to get */
 406
 407         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
 408         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
 409         if (!vm_thread_new(td, pages)) {
 410                 uma_zfree(thread_zone, td);
 411                 return (NULL);
 412         }
 413         cpu_thread_alloc(td);
 414         vm_domain_policy_init(&td->td_vm_dom_policy);
 415         return (td);
 416 }
 417
 418 int
 419 thread_alloc_stack(struct thread *td, int pages)
 420 {
 421
 422         KASSERT(td->td_kstack == 0,
 423             ("thread_alloc_stack called on a thread with kstack"));
 424         if (!vm_thread_new(td, pages))
 425                 return (0);
 426         cpu_thread_alloc(td);
 427         return (1);
 428 }
 429
 430 /*
 431  * Deallocate a thread.
 432  */
 433 void
 434 thread_free(struct thread *td)
 435 {
 436
 437         lock_profile_thread_exit(td);
 438         if (td->td_cpuset)
 439                 cpuset_rel(td->td_cpuset);
 440         td->td_cpuset = NULL;
 441         cpu_thread_free(td);
 442         if (td->td_kstack != 0)
 443                 vm_thread_dispose(td);
 444         vm_domain_policy_cleanup(&td->td_vm_dom_policy);
 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 #endif
 590         PROC_UNLOCK(p);
 591         PROC_STATLOCK(p);
 592         thread_lock(td);
 593         PROC_SUNLOCK(p);
 594
 595         /* Do the same timestamp bookkeeping that mi_switch() would do. */
 596         new_switchtime = cpu_ticks();
 597         runtime = new_switchtime - PCPU_GET(switchtime);
 598         td->td_runtime += runtime;
 599         td->td_incruntime += runtime;
 600         PCPU_SET(switchtime, new_switchtime);
 601         PCPU_SET(switchticks, ticks);
 602         PCPU_INC(cnt.v_swtch);
 603
 604         /* Save our resource usage in our process. */
 605         td->td_ru.ru_nvcsw++;
 606         ruxagg(p, td);
 607         rucollect(&p->p_ru, &td->td_ru);
 608         PROC_STATUNLOCK(p);
 609
 610         td->td_state = TDS_INACTIVE;
 611 #ifdef WITNESS
 612         witness_thread_exit(td);
 613 #endif
 614         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
 615         sched_throw(td);
 616         panic("I'm a teapot!");
 617         /* NOTREACHED */
 618 }
 619
 620 /*
 621  * Do any thread specific cleanups that may be needed in wait()
 622  * called with Giant, proc and schedlock not held.
 623  */
 624 void
 625 thread_wait(struct proc *p)
 626 {
 627         struct thread *td;
 628
 629         mtx_assert(&Giant, MA_NOTOWNED);
 630         KASSERT(p->p_numthreads == 1, ("multiple threads in thread_wait()"));
 631         KASSERT(p->p_exitthreads == 0, ("p_exitthreads leaking"));
 632         td = FIRST_THREAD_IN_PROC(p);
 633         /* Lock the last thread so we spin until it exits cpu_throw(). */
 634         thread_lock(td);
 635         thread_unlock(td);
 636         lock_profile_thread_exit(td);
 637         cpuset_rel(td->td_cpuset);
 638         td->td_cpuset = NULL;
 639         cpu_thread_clean(td);
 640         thread_cow_free(td);
 641         callout_drain(&td->td_slpcallout);
 642         thread_reap();  /* check for zombie threads etc. */
 643 }
 644
 645 /*
 646  * Link a thread to a process.
 647  * set up anything that needs to be initialized for it to
 648  * be used by the process.
 649  */
 650 void
 651 thread_link(struct thread *td, struct proc *p)
 652 {
 653
 654         /*
 655          * XXX This can't be enabled because it's called for proc0 before
 656          * its lock has been created.
 657          * PROC_LOCK_ASSERT(p, MA_OWNED);
 658          */
 659         td->td_state    = TDS_INACTIVE;
 660         td->td_proc     = p;
 661         td->td_flags    = TDF_INMEM;
 662
 663         LIST_INIT(&td->td_contested);
 664         LIST_INIT(&td->td_lprof[0]);
 665         LIST_INIT(&td->td_lprof[1]);
 666         sigqueue_init(&td->td_sigqueue, p);
 667         callout_init(&td->td_slpcallout, 1);
 668         TAILQ_INSERT_TAIL(&p->p_threads, td, td_plist);
 669         p->p_numthreads++;
 670 }
 671
 672 /*
 673  * Called from:
 674  *  thread_exit()
 675  */
 676 void
 677 thread_unlink(struct thread *td)
 678 {
 679         struct proc *p = td->td_proc;
 680
 681         PROC_LOCK_ASSERT(p, MA_OWNED);
 682         TAILQ_REMOVE(&p->p_threads, td, td_plist);
 683         p->p_numthreads--;
 684         /* could clear a few other things here */
 685         /* Must  NOT clear links to proc! */
 686 }
 687
 688 static int
 689 calc_remaining(struct proc *p, int mode)
 690 {
 691         int remaining;
 692
 693         PROC_LOCK_ASSERT(p, MA_OWNED);
 694         PROC_SLOCK_ASSERT(p, MA_OWNED);
 695         if (mode == SINGLE_EXIT)
 696                 remaining = p->p_numthreads;
 697         else if (mode == SINGLE_BOUNDARY)
 698                 remaining = p->p_numthreads - p->p_boundary_count;
 699         else if (mode == SINGLE_NO_EXIT || mode == SINGLE_ALLPROC)
 700                 remaining = p->p_numthreads - p->p_suspcount;
 701         else
 702                 panic("calc_remaining: wrong mode %d", mode);
 703         return (remaining);
 704 }
 705
 706 static int
 707 remain_for_mode(int mode)
 708 {
 709
 710         return (mode == SINGLE_ALLPROC ? 0 : 1);
 711 }
 712
 713 static int
 714 weed_inhib(int mode, struct thread *td2, struct proc *p)
 715 {
 716         int wakeup_swapper;
 717
 718         PROC_LOCK_ASSERT(p, MA_OWNED);
 719         PROC_SLOCK_ASSERT(p, MA_OWNED);
 720         THREAD_LOCK_ASSERT(td2, MA_OWNED);
 721
 722         wakeup_swapper = 0;
 723         switch (mode) {
 724         case SINGLE_EXIT:
 725                 if (TD_IS_SUSPENDED(td2))
 726                         wakeup_swapper |= thread_unsuspend_one(td2, p, true);
 727                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0)
 728                         wakeup_swapper |= sleepq_abort(td2, EINTR);
 729                 break;
 730         case SINGLE_BOUNDARY:
 731         case SINGLE_NO_EXIT:
 732                 if (TD_IS_SUSPENDED(td2) && (td2->td_flags & TDF_BOUNDARY) == 0)
 733                         wakeup_swapper |= thread_unsuspend_one(td2, p, false);
 734                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0)
 735                         wakeup_swapper |= sleepq_abort(td2, ERESTART);
 736                 break;
 737         case SINGLE_ALLPROC:
 738                 /*
 739                  * ALLPROC suspend tries to avoid spurious EINTR for
 740                  * threads sleeping interruptable, by suspending the
 741                  * thread directly, similarly to sig_suspend_threads().
 742                  * Since such sleep is not performed at the user
 743                  * boundary, TDF_BOUNDARY flag is not set, and TDF_ALLPROCSUSP
 744                  * is used to avoid immediate un-suspend.
 745                  */
 746                 if (TD_IS_SUSPENDED(td2) && (td2->td_flags & (TDF_BOUNDARY |
 747                     TDF_ALLPROCSUSP)) == 0)
 748                         wakeup_swapper |= thread_unsuspend_one(td2, p, false);
 749                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0) {
 750                         if ((td2->td_flags & TDF_SBDRY) == 0) {
 751                                 thread_suspend_one(td2);
 752                                 td2->td_flags |= TDF_ALLPROCSUSP;
 753                         } else {
 754                                 wakeup_swapper |= sleepq_abort(td2, ERESTART);
 755                         }
 756                 }
 757                 break;
 758         }
 759         return (wakeup_swapper);
 760 }
 761
 762 /*
 763  * Enforce single-threading.
 764  *
 765  * Returns 1 if the caller must abort (another thread is waiting to
 766  * exit the process or similar). Process is locked!
 767  * Returns 0 when you are successfully the only thread running.
 768  * A process has successfully single threaded in the suspend mode when
 769  * There are no threads in user mode. Threads in the kernel must be
 770  * allowed to continue until they get to the user boundary. They may even
 771  * copy out their return values and data before suspending. They may however be
 772  * accelerated in reaching the user boundary as we will wake up
 773  * any sleeping threads that are interruptable. (PCATCH).
 774  */
 775 int
 776 thread_single(struct proc *p, int mode)
 777 {
 778         struct thread *td;
 779         struct thread *td2;
 780         int remaining, wakeup_swapper;
 781
 782         td = curthread;
 783         KASSERT(mode == SINGLE_EXIT || mode == SINGLE_BOUNDARY ||
 784             mode == SINGLE_ALLPROC || mode == SINGLE_NO_EXIT,
 785             ("invalid mode %d", mode));
 786         /*
 787          * If allowing non-ALLPROC singlethreading for non-curproc
 788          * callers, calc_remaining() and remain_for_mode() should be
 789          * adjusted to also account for td->td_proc != p.  For now
 790          * this is not implemented because it is not used.
 791          */
 792         KASSERT((mode == SINGLE_ALLPROC && td->td_proc != p) ||
 793             (mode != SINGLE_ALLPROC && td->td_proc == p),
 794             ("mode %d proc %p curproc %p", mode, p, td->td_proc));
 795         mtx_assert(&Giant, MA_NOTOWNED);
 796         PROC_LOCK_ASSERT(p, MA_OWNED);
 797
 798         if ((p->p_flag & P_HADTHREADS) == 0 && mode != SINGLE_ALLPROC)
 799                 return (0);
 800
 801         /* Is someone already single threading? */
 802         if (p->p_singlethread != NULL && p->p_singlethread != td)
 803                 return (1);
 804
 805         if (mode == SINGLE_EXIT) {
 806                 p->p_flag |= P_SINGLE_EXIT;
 807                 p->p_flag &= ~P_SINGLE_BOUNDARY;
 808         } else {
 809                 p->p_flag &= ~P_SINGLE_EXIT;
 810                 if (mode == SINGLE_BOUNDARY)
 811                         p->p_flag |= P_SINGLE_BOUNDARY;
 812                 else
 813                         p->p_flag &= ~P_SINGLE_BOUNDARY;
 814         }
 815         if (mode == SINGLE_ALLPROC)
 816                 p->p_flag |= P_TOTAL_STOP;
 817         p->p_flag |= P_STOPPED_SINGLE;
 818         PROC_SLOCK(p);
 819         p->p_singlethread = td;
 820         remaining = calc_remaining(p, mode);
 821         while (remaining != remain_for_mode(mode)) {
 822                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
 823                         goto stopme;
 824                 wakeup_swapper = 0;
 825                 FOREACH_THREAD_IN_PROC(p, td2) {
 826                         if (td2 == td)
 827                                 continue;
 828                         thread_lock(td2);
 829                         td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
 830                         if (TD_IS_INHIBITED(td2)) {
 831                                 wakeup_swapper |= weed_inhib(mode, td2, p);
 832 #ifdef SMP
 833                         } else if (TD_IS_RUNNING(td2) && td != td2) {
 834                                 forward_signal(td2);
 835 #endif
 836                         }
 837                         thread_unlock(td2);
 838                 }
 839                 if (wakeup_swapper)
 840                         kick_proc0();
 841                 remaining = calc_remaining(p, mode);
 842
 843                 /*
 844                  * Maybe we suspended some threads.. was it enough?
 845                  */
 846                 if (remaining == remain_for_mode(mode))
 847                         break;
 848
 849 stopme:
 850                 /*
 851                  * Wake us up when everyone else has suspended.
 852                  * In the mean time we suspend as well.
 853                  */
 854                 thread_suspend_switch(td, p);
 855                 remaining = calc_remaining(p, mode);
 856         }
 857         if (mode == SINGLE_EXIT) {
 858                 /*
 859                  * Convert the process to an unthreaded process.  The
 860                  * SINGLE_EXIT is called by exit1() or execve(), in
 861                  * both cases other threads must be retired.
 862                  */
 863                 KASSERT(p->p_numthreads == 1, ("Unthreading with >1 threads"));
 864                 p->p_singlethread = NULL;
 865                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_HADTHREADS);
 866
 867                 /*
 868                  * Wait for any remaining threads to exit cpu_throw().
 869                  */
 870                 while (p->p_exitthreads != 0) {
 871                         PROC_SUNLOCK(p);
 872                         PROC_UNLOCK(p);
 873                         sched_relinquish(td);
 874                         PROC_LOCK(p);
 875                         PROC_SLOCK(p);
 876                 }
 877         } else if (mode == SINGLE_BOUNDARY) {
 878                 /*
 879                  * Wait until all suspended threads are removed from
 880                  * the processors.  The thread_suspend_check()
 881                  * increments p_boundary_count while it is still
 882                  * running, which makes it possible for the execve()
 883                  * to destroy vmspace while our other threads are
 884                  * still using the address space.
 885                  *
 886                  * We lock the thread, which is only allowed to
 887                  * succeed after context switch code finished using
 888                  * the address space.
 889                  */
 890                 FOREACH_THREAD_IN_PROC(p, td2) {
 891                         if (td2 == td)
 892                                 continue;
 893                         thread_lock(td2);
 894                         KASSERT((td2->td_flags & TDF_BOUNDARY) != 0,
 895                             ("td %p not on boundary", td2));
 896                         KASSERT(TD_IS_SUSPENDED(td2),
 897                             ("td %p is not suspended", td2));
 898                         thread_unlock(td2);
 899                 }
 900         }
 901         PROC_SUNLOCK(p);
 902         return (0);
 903 }
 904
 905 bool
 906 thread_suspend_check_needed(void)
 907 {
 908         struct proc *p;
 909         struct thread *td;
 910
 911         td = curthread;
 912         p = td->td_proc;
 913         PROC_LOCK_ASSERT(p, MA_OWNED);
 914         return (P_SHOULDSTOP(p) || ((p->p_flag & P_TRACED) != 0 &&
 915             (td->td_dbgflags & TDB_SUSPEND) != 0));
 916 }
 917
 918 /*
 919  * Called in from locations that can safely check to see
 920  * whether we have to suspend or at least throttle for a
 921  * single-thread event (e.g. fork).
 922  *
 923  * Such locations include userret().
 924  * If the "return_instead" argument is non zero, the thread must be able to
 925  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
 926  *
 927  * The 'return_instead' argument tells the function if it may do a
 928  * thread_exit() or suspend, or whether the caller must abort and back
 929  * out instead.
 930  *
 931  * If the thread that set the single_threading request has set the
 932  * P_SINGLE_EXIT bit in the process flags then this call will never return
 933  * if 'return_instead' is false, but will exit.
 934  *
 935  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
 936  *---------------+--------------------+---------------------
 937  *       0       | returns 0          |   returns 0 or 1
 938  *               | when ST ends       |   immediately
 939  *---------------+--------------------+---------------------
 940  *       1       | thread exits       |   returns 1
 941  *               |                    |  immediately
 942  * 0 = thread_exit() or suspension ok,
 943  * other = return error instead of stopping the thread.
 944  *
 945  * While a full suspension is under effect, even a single threading
 946  * thread would be suspended if it made this call (but it shouldn't).
 947  * This call should only be made from places where
 948  * thread_exit() would be safe as that may be the outcome unless
 949  * return_instead is set.
 950  */
 951 int
 952 thread_suspend_check(int return_instead)
 953 {
 954         struct thread *td;
 955         struct proc *p;
 956         int wakeup_swapper;
 957
 958         td = curthread;
 959         p = td->td_proc;
 960         mtx_assert(&Giant, MA_NOTOWNED);
 961         PROC_LOCK_ASSERT(p, MA_OWNED);
 962         while (thread_suspend_check_needed()) {
 963                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 964                         KASSERT(p->p_singlethread != NULL,
 965                             ("singlethread not set"));
 966                         /*
 967                          * The only suspension in action is a
 968                          * single-threading. Single threader need not stop.
 969                          * It is safe to access p->p_singlethread unlocked
 970                          * because it can only be set to our address by us.
 971                          */
 972                         if (p->p_singlethread == td)
 973                                 return (0);     /* Exempt from stopping. */
 974                 }
 975                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
 976                         return (EINTR);
 977
 978                 /* Should we goto user boundary if we didn't come from there? */
 979                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
 980                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
 981                         return (ERESTART);
 982
 983                 /*
 984                  * Ignore suspend requests if they are deferred.
 985                  */
 986                 if ((td->td_flags & TDF_SBDRY) != 0) {
 987                         KASSERT(return_instead,
 988                             ("TDF_SBDRY set for unsafe thread_suspend_check"));
 989                         KASSERT((td->td_flags & (TDF_SEINTR | TDF_SERESTART)) !=
 990                             (TDF_SEINTR | TDF_SERESTART),
 991                             ("both TDF_SEINTR and TDF_SERESTART"));
 992                         return (TD_SBDRY_INTR(td) ? TD_SBDRY_ERRNO(td) : 0);
 993                 }
 994
 995                 /*
 996                  * If the process is waiting for us to exit,
 997                  * this thread should just suicide.
 998                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
 999                  */
1000                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td)) {
1001                         PROC_UNLOCK(p);
1002
1003                         /*
1004                          * Allow Linux emulation layer to do some work
1005                          * before thread suicide.
1006                          */
1007                         if (__predict_false(p->p_sysent->sv_thread_detach != NULL))
1008                                 (p->p_sysent->sv_thread_detach)(td);
1009                         umtx_thread_exit(td);
1010                         kern_thr_exit(td);
1011                         panic("stopped thread did not exit");
1012                 }
1013
1014                 PROC_SLOCK(p);
1015                 thread_stopped(p);
1016                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
1017                         if (p->p_numthreads == p->p_suspcount + 1) {
1018                                 thread_lock(p->p_singlethread);
1019                                 wakeup_swapper = thread_unsuspend_one(
1020                                     p->p_singlethread, p, false);
1021                                 thread_unlock(p->p_singlethread);
1022                                 if (wakeup_swapper)
1023                                         kick_proc0();
1024                         }
1025                 }
1026                 PROC_UNLOCK(p);
1027                 thread_lock(td);
1028                 /*
1029                  * When a thread suspends, it just
1030                  * gets taken off all queues.
1031                  */
1032                 thread_suspend_one(td);
1033                 if (return_instead == 0) {
1034                         p->p_boundary_count++;
1035                         td->td_flags |= TDF_BOUNDARY;
1036                 }
1037                 PROC_SUNLOCK(p);
1038                 mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
1039                 thread_unlock(td);
1040                 PROC_LOCK(p);
1041         }
1042         return (0);
1043 }
1044
1045 void
1046 thread_suspend_switch(struct thread *td, struct proc *p)
1047 {
1048
1049         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
1050         PROC_LOCK_ASSERT(p, MA_OWNED);
1051         PROC_SLOCK_ASSERT(p, MA_OWNED);
1052         /*
1053          * We implement thread_suspend_one in stages here to avoid
1054          * dropping the proc lock while the thread lock is owned.
1055          */
1056         if (p == td->td_proc) {
1057                 thread_stopped(p);
1058                 p->p_suspcount++;
1059         }
1060         PROC_UNLOCK(p);
1061         thread_lock(td);
1062         td->td_flags &= ~TDF_NEEDSUSPCHK;
1063         TD_SET_SUSPENDED(td);
1064         sched_sleep(td, 0);
1065         PROC_SUNLOCK(p);
1066         DROP_GIANT();
1067         mi_switch(SW_VOL | SWT_SUSPEND, NULL);
1068         thread_unlock(td);
1069         PICKUP_GIANT();
1070         PROC_LOCK(p);
1071         PROC_SLOCK(p);
1072 }
1073
1074 void
1075 thread_suspend_one(struct thread *td)
1076 {
1077         struct proc *p;
1078
1079         p = td->td_proc;
1080         PROC_SLOCK_ASSERT(p, MA_OWNED);
1081         THREAD_LOCK_ASSERT(td, MA_OWNED);
1082         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
1083         p->p_suspcount++;
1084         td->td_flags &= ~TDF_NEEDSUSPCHK;
1085         TD_SET_SUSPENDED(td);
1086         sched_sleep(td, 0);
1087 }
1088
1089 static int
1090 thread_unsuspend_one(struct thread *td, struct proc *p, bool boundary)
1091 {
1092
1093         THREAD_LOCK_ASSERT(td, MA_OWNED);
1094         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
1095         TD_CLR_SUSPENDED(td);
1096         td->td_flags &= ~TDF_ALLPROCSUSP;
1097         if (td->td_proc == p) {
1098                 PROC_SLOCK_ASSERT(p, MA_OWNED);
1099                 p->p_suspcount--;
1100                 if (boundary && (td->td_flags & TDF_BOUNDARY) != 0) {
1101                         td->td_flags &= ~TDF_BOUNDARY;
1102                         p->p_boundary_count--;
1103                 }
1104         }
1105         return (setrunnable(td));
1106 }
1107
1108 /*
1109  * Allow all threads blocked by single threading to continue running.
1110  */
1111 void
1112 thread_unsuspend(struct proc *p)
1113 {
1114         struct thread *td;
1115         int wakeup_swapper;
1116
1117         PROC_LOCK_ASSERT(p, MA_OWNED);
1118         PROC_SLOCK_ASSERT(p, MA_OWNED);
1119         wakeup_swapper = 0;
1120         if (!P_SHOULDSTOP(p)) {
1121                 FOREACH_THREAD_IN_PROC(p, td) {
1122                         thread_lock(td);
1123                         if (TD_IS_SUSPENDED(td)) {
1124                                 wakeup_swapper |= thread_unsuspend_one(td, p,
1125                                     true);
1126                         }
1127                         thread_unlock(td);
1128                 }
1129         } else if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
1130             p->p_numthreads == p->p_suspcount) {
1131                 /*
1132                  * Stopping everything also did the job for the single
1133                  * threading request. Now we've downgraded to single-threaded,
1134                  * let it continue.
1135                  */
1136                 if (p->p_singlethread->td_proc == p) {
1137                         thread_lock(p->p_singlethread);
1138                         wakeup_swapper = thread_unsuspend_one(
1139                             p->p_singlethread, p, false);
1140                         thread_unlock(p->p_singlethread);
1141                 }
1142         }
1143         if (wakeup_swapper)
1144                 kick_proc0();
1145 }
1146
1147 /*
1148  * End the single threading mode..
1149  */
1150 void
1151 thread_single_end(struct proc *p, int mode)
1152 {
1153         struct thread *td;
1154         int wakeup_swapper;
1155
1156         KASSERT(mode == SINGLE_EXIT || mode == SINGLE_BOUNDARY ||
1157             mode == SINGLE_ALLPROC || mode == SINGLE_NO_EXIT,
1158             ("invalid mode %d", mode));
1159         PROC_LOCK_ASSERT(p, MA_OWNED);
1160         KASSERT((mode == SINGLE_ALLPROC && (p->p_flag & P_TOTAL_STOP) != 0) ||
1161             (mode != SINGLE_ALLPROC && (p->p_flag & P_TOTAL_STOP) == 0),
1162             ("mode %d does not match P_TOTAL_STOP", mode));
1163         KASSERT(mode == SINGLE_ALLPROC || p->p_singlethread == curthread,
1164             ("thread_single_end from other thread %p %p",
1165             curthread, p->p_singlethread));
1166         KASSERT(mode != SINGLE_BOUNDARY ||
1167             (p->p_flag & P_SINGLE_BOUNDARY) != 0,
1168             ("mis-matched SINGLE_BOUNDARY flags %x", p->p_flag));
1169         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY |
1170             P_TOTAL_STOP);
1171         PROC_SLOCK(p);
1172         p->p_singlethread = NULL;
1173         wakeup_swapper = 0;
1174         /*
1175          * If there are other threads they may now run,
1176          * unless of course there is a blanket 'stop order'
1177          * on the process. The single threader must be allowed
1178          * to continue however as this is a bad place to stop.
1179          */
1180         if (p->p_numthreads != remain_for_mode(mode) && !P_SHOULDSTOP(p)) {
1181                 FOREACH_THREAD_IN_PROC(p, td) {
1182                         thread_lock(td);
1183                         if (TD_IS_SUSPENDED(td)) {
1184                                 wakeup_swapper |= thread_unsuspend_one(td, p,
1185                                     mode == SINGLE_BOUNDARY);
1186                         }
1187                         thread_unlock(td);
1188                 }
1189         }
1190         KASSERT(mode != SINGLE_BOUNDARY || p->p_boundary_count == 0,
1191             ("inconsistent boundary count %d", p->p_boundary_count));
1192         PROC_SUNLOCK(p);
1193         if (wakeup_swapper)
1194                 kick_proc0();
1195 }
1196
1197 struct thread *
1198 thread_find(struct proc *p, lwpid_t tid)
1199 {
1200         struct thread *td;
1201
1202         PROC_LOCK_ASSERT(p, MA_OWNED);
1203         FOREACH_THREAD_IN_PROC(p, td) {
1204                 if (td->td_tid == tid)
1205                         break;
1206         }
1207         return (td);
1208 }
1209
1210 /* Locate a thread by number; return with proc lock held. */
1211 struct thread *
1212 tdfind(lwpid_t tid, pid_t pid)
1213 {
1214 #define RUN_THRESH      16
1215         struct thread *td;
1216         int run = 0;
1217
1218         rw_rlock(&tidhash_lock);
1219         LIST_FOREACH(td, TIDHASH(tid), td_hash) {
1220                 if (td->td_tid == tid) {
1221                         if (pid != -1 && td->td_proc->p_pid != pid) {
1222                                 td = NULL;
1223                                 break;
1224                         }
1225                         PROC_LOCK(td->td_proc);
1226                         if (td->td_proc->p_state == PRS_NEW) {
1227                                 PROC_UNLOCK(td->td_proc);
1228                                 td = NULL;
1229                                 break;
1230                         }
1231                         if (run > RUN_THRESH) {
1232                                 if (rw_try_upgrade(&tidhash_lock)) {
1233                                         LIST_REMOVE(td, td_hash);
1234                                         LIST_INSERT_HEAD(TIDHASH(td->td_tid),
1235                                                 td, td_hash);
1236                                         rw_wunlock(&tidhash_lock);
1237                                         return (td);
1238                                 }
1239                         }
1240                         break;
1241                 }
1242                 run++;
1243         }
1244         rw_runlock(&tidhash_lock);
1245         return (td);
1246 }
1247
1248 void
1249 tidhash_add(struct thread *td)
1250 {
1251         rw_wlock(&tidhash_lock);
1252         LIST_INSERT_HEAD(TIDHASH(td->td_tid), td, td_hash);
1253         rw_wunlock(&tidhash_lock);
1254 }
1255
1256 void
1257 tidhash_remove(struct thread *td)
1258 {
1259         rw_wlock(&tidhash_lock);
1260         LIST_REMOVE(td, td_hash);
1261         rw_wunlock(&tidhash_lock);
1262 }