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) == 0xf4,
  80     "struct thread KBI td_flags");
  81 _Static_assert(offsetof(struct thread, td_pflags) == 0xfc,
  82     "struct thread KBI td_pflags");
  83 _Static_assert(offsetof(struct thread, td_frame) == 0x460,
  84     "struct thread KBI td_frame");
  85 _Static_assert(offsetof(struct thread, td_emuldata) == 0x508,
  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) == 0x3d0,
  92     "struct proc KBI p_filemon");
  93 _Static_assert(offsetof(struct proc, p_comm) == 0x3e0,
  94     "struct proc KBI p_comm");
  95 _Static_assert(offsetof(struct proc, p_emuldata) == 0x4b8,
  96     "struct proc KBI p_emuldata");
  97 #endif
  98 #ifdef __i386__
  99 _Static_assert(offsetof(struct thread, td_flags) == 0x9c,
 100     "struct thread KBI td_flags");
 101 _Static_assert(offsetof(struct thread, td_pflags) == 0xa4,
 102     "struct thread KBI td_pflags");
 103 _Static_assert(offsetof(struct thread, td_frame) == 0x2ec,
 104     "struct thread KBI td_frame");
 105 _Static_assert(offsetof(struct thread, td_emuldata) == 0x338,
 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) == 0x27c,
 112     "struct proc KBI p_filemon");
 113 _Static_assert(offsetof(struct proc, p_comm) == 0x288,
 114     "struct proc KBI p_comm");
 115 _Static_assert(offsetof(struct proc, p_emuldata) == 0x314,
 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 static lwpid_t
 148 tid_alloc(void)
 149 {
 150         lwpid_t tid;
 151
 152         tid = alloc_unr(tid_unrhdr);
 153         if (tid != -1)
 154                 return (tid);
 155         mtx_lock(&tid_lock);
 156         if (tid_head == tid_tail) {
 157                 mtx_unlock(&tid_lock);
 158                 return (-1);
 159         }
 160         tid = tid_buffer[tid_head];
 161         tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
 162         mtx_unlock(&tid_lock);
 163         return (tid);
 164 }
 165
 166 static void
 167 tid_free(lwpid_t tid)
 168 {
 169         lwpid_t tmp_tid = -1;
 170
 171         mtx_lock(&tid_lock);
 172         if ((tid_tail + 1) % TID_BUFFER_SIZE == tid_head) {
 173                 tmp_tid = tid_buffer[tid_head];
 174                 tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
 175         }
 176         tid_buffer[tid_tail] = tid;
 177         tid_tail = (tid_tail + 1) % TID_BUFFER_SIZE;
 178         mtx_unlock(&tid_lock);
 179         if (tmp_tid != -1)
 180                 free_unr(tid_unrhdr, tmp_tid);
 181 }
 182
 183 /*
 184  * Prepare a thread for use.
 185  */
 186 static int
 187 thread_ctor(void *mem, int size, void *arg, int flags)
 188 {
 189         struct thread   *td;
 190
 191         td = (struct thread *)mem;
 192         td->td_state = TDS_INACTIVE;
 193         td->td_oncpu = NOCPU;
 194
 195         td->td_tid = tid_alloc();
 196
 197         /*
 198          * Note that td_critnest begins life as 1 because the thread is not
 199          * running and is thereby implicitly waiting to be on the receiving
 200          * end of a context switch.
 201          */
 202         td->td_critnest = 1;
 203         td->td_lend_user_pri = PRI_MAX;
 204         EVENTHANDLER_INVOKE(thread_ctor, td);
 205 #ifdef AUDIT
 206         audit_thread_alloc(td);
 207 #endif
 208         umtx_thread_alloc(td);
 209         return (0);
 210 }
 211
 212 /*
 213  * Reclaim a thread after use.
 214  */
 215 static void
 216 thread_dtor(void *mem, int size, void *arg)
 217 {
 218         struct thread *td;
 219
 220         td = (struct thread *)mem;
 221
 222 #ifdef INVARIANTS
 223         /* Verify that this thread is in a safe state to free. */
 224         switch (td->td_state) {
 225         case TDS_INHIBITED:
 226         case TDS_RUNNING:
 227         case TDS_CAN_RUN:
 228         case TDS_RUNQ:
 229                 /*
 230                  * We must never unlink a thread that is in one of
 231                  * these states, because it is currently active.
 232                  */
 233                 panic("bad state for thread unlinking");
 234                 /* NOTREACHED */
 235         case TDS_INACTIVE:
 236                 break;
 237         default:
 238                 panic("bad thread state");
 239                 /* NOTREACHED */
 240         }
 241 #endif
 242 #ifdef AUDIT
 243         audit_thread_free(td);
 244 #endif
 245         /* Free all OSD associated to this thread. */
 246         osd_thread_exit(td);
 247         td_softdep_cleanup(td);
 248         MPASS(td->td_su == NULL);
 249
 250         EVENTHANDLER_INVOKE(thread_dtor, td);
 251         tid_free(td->td_tid);
 252 }
 253
 254 /*
 255  * Initialize type-stable parts of a thread (when newly created).
 256  */
 257 static int
 258 thread_init(void *mem, int size, int flags)
 259 {
 260         struct thread *td;
 261
 262         td = (struct thread *)mem;
 263
 264         td->td_sleepqueue = sleepq_alloc();
 265         td->td_turnstile = turnstile_alloc();
 266         td->td_rlqe = NULL;
 267         EVENTHANDLER_INVOKE(thread_init, td);
 268         umtx_thread_init(td);
 269         td->td_kstack = 0;
 270         td->td_sel = NULL;
 271         return (0);
 272 }
 273
 274 /*
 275  * Tear down type-stable parts of a thread (just before being discarded).
 276  */
 277 static void
 278 thread_fini(void *mem, int size)
 279 {
 280         struct thread *td;
 281
 282         td = (struct thread *)mem;
 283         EVENTHANDLER_INVOKE(thread_fini, td);
 284         rlqentry_free(td->td_rlqe);
 285         turnstile_free(td->td_turnstile);
 286         sleepq_free(td->td_sleepqueue);
 287         umtx_thread_fini(td);
 288         seltdfini(td);
 289 }
 290
 291 /*
 292  * For a newly created process,
 293  * link up all the structures and its initial threads etc.
 294  * called from:
 295  * {arch}/{arch}/machdep.c   {arch}_init(), init386() etc.
 296  * proc_dtor() (should go away)
 297  * proc_init()
 298  */
 299 void
 300 proc_linkup0(struct proc *p, struct thread *td)
 301 {
 302         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
 303         proc_linkup(p, td);
 304 }
 305
 306 void
 307 proc_linkup(struct proc *p, struct thread *td)
 308 {
 309
 310         sigqueue_init(&p->p_sigqueue, p);
 311         p->p_ksi = ksiginfo_alloc(1);
 312         if (p->p_ksi != NULL) {
 313                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
 314                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
 315         }
 316         LIST_INIT(&p->p_mqnotifier);
 317         p->p_numthreads = 0;
 318         thread_link(td, p);
 319 }
 320
 321 /*
 322  * Initialize global thread allocation resources.
 323  */
 324 void
 325 threadinit(void)
 326 {
 327
 328         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
 329
 330         /*
 331          * pid_max cannot be greater than PID_MAX.
 332          * leave one number for thread0.
 333          */
 334         tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
 335
 336         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
 337             thread_ctor, thread_dtor, thread_init, thread_fini,
 338             32 - 1, UMA_ZONE_NOFREE);
 339         tidhashtbl = hashinit(maxproc / 2, M_TIDHASH, &tidhash);
 340         rw_init(&tidhash_lock, "tidhash");
 341 }
 342
 343 /*
 344  * Place an unused thread on the zombie list.
 345  * Use the slpq as that must be unused by now.
 346  */
 347 void
 348 thread_zombie(struct thread *td)
 349 {
 350         mtx_lock_spin(&zombie_lock);
 351         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
 352         mtx_unlock_spin(&zombie_lock);
 353 }
 354
 355 /*
 356  * Release a thread that has exited after cpu_throw().
 357  */
 358 void
 359 thread_stash(struct thread *td)
 360 {
 361         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
 362         thread_zombie(td);
 363 }
 364
 365 /*
 366  * Reap zombie resources.
 367  */
 368 void
 369 thread_reap(void)
 370 {
 371         struct thread *td_first, *td_next;
 372
 373         /*
 374          * Don't even bother to lock if none at this instant,
 375          * we really don't care about the next instant.
 376          */
 377         if (!TAILQ_EMPTY(&zombie_threads)) {
 378                 mtx_lock_spin(&zombie_lock);
 379                 td_first = TAILQ_FIRST(&zombie_threads);
 380                 if (td_first)
 381                         TAILQ_INIT(&zombie_threads);
 382                 mtx_unlock_spin(&zombie_lock);
 383                 while (td_first) {
 384                         td_next = TAILQ_NEXT(td_first, td_slpq);
 385                         thread_cow_free(td_first);
 386                         thread_free(td_first);
 387                         td_first = td_next;
 388                 }
 389         }
 390 }
 391
 392 /*
 393  * Allocate a thread.
 394  */
 395 struct thread *
 396 thread_alloc(int pages)
 397 {
 398         struct thread *td;
 399
 400         thread_reap(); /* check if any zombies to get */
 401
 402         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
 403         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
 404         if (!vm_thread_new(td, pages)) {
 405                 uma_zfree(thread_zone, td);
 406                 return (NULL);
 407         }
 408         cpu_thread_alloc(td);
 409         vm_domain_policy_init(&td->td_vm_dom_policy);
 410         return (td);
 411 }
 412
 413 int
 414 thread_alloc_stack(struct thread *td, int pages)
 415 {
 416
 417         KASSERT(td->td_kstack == 0,
 418             ("thread_alloc_stack called on a thread with kstack"));
 419         if (!vm_thread_new(td, pages))
 420                 return (0);
 421         cpu_thread_alloc(td);
 422         return (1);
 423 }
 424
 425 /*
 426  * Deallocate a thread.
 427  */
 428 void
 429 thread_free(struct thread *td)
 430 {
 431
 432         lock_profile_thread_exit(td);
 433         if (td->td_cpuset)
 434                 cpuset_rel(td->td_cpuset);
 435         td->td_cpuset = NULL;
 436         cpu_thread_free(td);
 437         if (td->td_kstack != 0)
 438                 vm_thread_dispose(td);
 439         vm_domain_policy_cleanup(&td->td_vm_dom_policy);
 440         callout_drain(&td->td_slpcallout);
 441         uma_zfree(thread_zone, td);
 442 }
 443
 444 void
 445 thread_cow_get_proc(struct thread *newtd, struct proc *p)
 446 {
 447
 448         PROC_LOCK_ASSERT(p, MA_OWNED);
 449         newtd->td_ucred = crhold(p->p_ucred);
 450         newtd->td_limit = lim_hold(p->p_limit);
 451         newtd->td_cowgen = p->p_cowgen;
 452 }
 453
 454 void
 455 thread_cow_get(struct thread *newtd, struct thread *td)
 456 {
 457
 458         newtd->td_ucred = crhold(td->td_ucred);
 459         newtd->td_limit = lim_hold(td->td_limit);
 460         newtd->td_cowgen = td->td_cowgen;
 461 }
 462
 463 void
 464 thread_cow_free(struct thread *td)
 465 {
 466
 467         if (td->td_ucred != NULL)
 468                 crfree(td->td_ucred);
 469         if (td->td_limit != NULL)
 470                 lim_free(td->td_limit);
 471 }
 472
 473 void
 474 thread_cow_update(struct thread *td)
 475 {
 476         struct proc *p;
 477         struct ucred *oldcred;
 478         struct plimit *oldlimit;
 479
 480         p = td->td_proc;
 481         oldcred = NULL;
 482         oldlimit = NULL;
 483         PROC_LOCK(p);
 484         if (td->td_ucred != p->p_ucred) {
 485                 oldcred = td->td_ucred;
 486                 td->td_ucred = crhold(p->p_ucred);
 487         }
 488         if (td->td_limit != p->p_limit) {
 489                 oldlimit = td->td_limit;
 490                 td->td_limit = lim_hold(p->p_limit);
 491         }
 492         td->td_cowgen = p->p_cowgen;
 493         PROC_UNLOCK(p);
 494         if (oldcred != NULL)
 495                 crfree(oldcred);
 496         if (oldlimit != NULL)
 497                 lim_free(oldlimit);
 498 }
 499
 500 /*
 501  * Discard the current thread and exit from its context.
 502  * Always called with scheduler locked.
 503  *
 504  * Because we can't free a thread while we're operating under its context,
 505  * push the current thread into our CPU's deadthread holder. This means
 506  * we needn't worry about someone else grabbing our context before we
 507  * do a cpu_throw().
 508  */
 509 void
 510 thread_exit(void)
 511 {
 512         uint64_t runtime, new_switchtime;
 513         struct thread *td;
 514         struct thread *td2;
 515         struct proc *p;
 516         int wakeup_swapper;
 517
 518         td = curthread;
 519         p = td->td_proc;
 520
 521         PROC_SLOCK_ASSERT(p, MA_OWNED);
 522         mtx_assert(&Giant, MA_NOTOWNED);
 523
 524         PROC_LOCK_ASSERT(p, MA_OWNED);
 525         KASSERT(p != NULL, ("thread exiting without a process"));
 526         CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
 527             (long)p->p_pid, td->td_name);
 528         SDT_PROBE0(proc, , , lwp__exit);
 529         KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
 530
 531 #ifdef AUDIT
 532         AUDIT_SYSCALL_EXIT(0, td);
 533 #endif
 534         /*
 535          * drop FPU & debug register state storage, or any other
 536          * architecture specific resources that
 537          * would not be on a new untouched process.
 538          */
 539         cpu_thread_exit(td);
 540
 541         /*
 542          * The last thread is left attached to the process
 543          * So that the whole bundle gets recycled. Skip
 544          * all this stuff if we never had threads.
 545          * EXIT clears all sign of other threads when
 546          * it goes to single threading, so the last thread always
 547          * takes the short path.
 548          */
 549         if (p->p_flag & P_HADTHREADS) {
 550                 if (p->p_numthreads > 1) {
 551                         atomic_add_int(&td->td_proc->p_exitthreads, 1);
 552                         thread_unlink(td);
 553                         td2 = FIRST_THREAD_IN_PROC(p);
 554                         sched_exit_thread(td2, td);
 555
 556                         /*
 557                          * The test below is NOT true if we are the
 558                          * sole exiting thread. P_STOPPED_SINGLE is unset
 559                          * in exit1() after it is the only survivor.
 560                          */
 561                         if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 562                                 if (p->p_numthreads == p->p_suspcount) {
 563                                         thread_lock(p->p_singlethread);
 564                                         wakeup_swapper = thread_unsuspend_one(
 565                                                 p->p_singlethread, p, false);
 566                                         thread_unlock(p->p_singlethread);
 567                                         if (wakeup_swapper)
 568                                                 kick_proc0();
 569                                 }
 570                         }
 571
 572                         PCPU_SET(deadthread, td);
 573                 } else {
 574                         /*
 575                          * The last thread is exiting.. but not through exit()
 576                          */
 577                         panic ("thread_exit: Last thread exiting on its own");
 578                 }
 579         }
 580 #ifdef  HWPMC_HOOKS
 581         /*
 582          * If this thread is part of a process that is being tracked by hwpmc(4),
 583          * inform the module of the thread's impending exit.
 584          */
 585         if (PMC_PROC_IS_USING_PMCS(td->td_proc))
 586                 PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
 587 #endif
 588         PROC_UNLOCK(p);
 589         PROC_STATLOCK(p);
 590         thread_lock(td);
 591         PROC_SUNLOCK(p);
 592
 593         /* Do the same timestamp bookkeeping that mi_switch() would do. */
 594         new_switchtime = cpu_ticks();
 595         runtime = new_switchtime - PCPU_GET(switchtime);
 596         td->td_runtime += runtime;
 597         td->td_incruntime += runtime;
 598         PCPU_SET(switchtime, new_switchtime);
 599         PCPU_SET(switchticks, ticks);
 600         VM_CNT_INC(v_swtch);
 601
 602         /* Save our resource usage in our process. */
 603         td->td_ru.ru_nvcsw++;
 604         ruxagg(p, td);
 605         rucollect(&p->p_ru, &td->td_ru);
 606         PROC_STATUNLOCK(p);
 607
 608         td->td_state = TDS_INACTIVE;
 609 #ifdef WITNESS
 610         witness_thread_exit(td);
 611 #endif
 612         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
 613         sched_throw(td);
 614         panic("I'm a teapot!");
 615         /* NOTREACHED */
 616 }
 617
 618 /*
 619  * Do any thread specific cleanups that may be needed in wait()
 620  * called with Giant, proc and schedlock not held.
 621  */
 622 void
 623 thread_wait(struct proc *p)
 624 {
 625         struct thread *td;
 626
 627         mtx_assert(&Giant, MA_NOTOWNED);
 628         KASSERT(p->p_numthreads == 1, ("multiple threads in thread_wait()"));
 629         KASSERT(p->p_exitthreads == 0, ("p_exitthreads leaking"));
 630         td = FIRST_THREAD_IN_PROC(p);
 631         /* Lock the last thread so we spin until it exits cpu_throw(). */
 632         thread_lock(td);
 633         thread_unlock(td);
 634         lock_profile_thread_exit(td);
 635         cpuset_rel(td->td_cpuset);
 636         td->td_cpuset = NULL;
 637         cpu_thread_clean(td);
 638         thread_cow_free(td);
 639         callout_drain(&td->td_slpcallout);
 640         thread_reap();  /* check for zombie threads etc. */
 641 }
 642
 643 /*
 644  * Link a thread to a process.
 645  * set up anything that needs to be initialized for it to
 646  * be used by the process.
 647  */
 648 void
 649 thread_link(struct thread *td, struct proc *p)
 650 {
 651
 652         /*
 653          * XXX This can't be enabled because it's called for proc0 before
 654          * its lock has been created.
 655          * PROC_LOCK_ASSERT(p, MA_OWNED);
 656          */
 657         td->td_state    = TDS_INACTIVE;
 658         td->td_proc     = p;
 659         td->td_flags    = TDF_INMEM;
 660
 661         LIST_INIT(&td->td_contested);
 662         LIST_INIT(&td->td_lprof[0]);
 663         LIST_INIT(&td->td_lprof[1]);
 664         sigqueue_init(&td->td_sigqueue, p);
 665         callout_init(&td->td_slpcallout, 1);
 666         TAILQ_INSERT_TAIL(&p->p_threads, td, td_plist);
 667         p->p_numthreads++;
 668 }
 669
 670 /*
 671  * Called from:
 672  *  thread_exit()
 673  */
 674 void
 675 thread_unlink(struct thread *td)
 676 {
 677         struct proc *p = td->td_proc;
 678
 679         PROC_LOCK_ASSERT(p, MA_OWNED);
 680         TAILQ_REMOVE(&p->p_threads, td, td_plist);
 681         p->p_numthreads--;
 682         /* could clear a few other things here */
 683         /* Must  NOT clear links to proc! */
 684 }
 685
 686 static int
 687 calc_remaining(struct proc *p, int mode)
 688 {
 689         int remaining;
 690
 691         PROC_LOCK_ASSERT(p, MA_OWNED);
 692         PROC_SLOCK_ASSERT(p, MA_OWNED);
 693         if (mode == SINGLE_EXIT)
 694                 remaining = p->p_numthreads;
 695         else if (mode == SINGLE_BOUNDARY)
 696                 remaining = p->p_numthreads - p->p_boundary_count;
 697         else if (mode == SINGLE_NO_EXIT || mode == SINGLE_ALLPROC)
 698                 remaining = p->p_numthreads - p->p_suspcount;
 699         else
 700                 panic("calc_remaining: wrong mode %d", mode);
 701         return (remaining);
 702 }
 703
 704 static int
 705 remain_for_mode(int mode)
 706 {
 707
 708         return (mode == SINGLE_ALLPROC ? 0 : 1);
 709 }
 710
 711 static int
 712 weed_inhib(int mode, struct thread *td2, struct proc *p)
 713 {
 714         int wakeup_swapper;
 715
 716         PROC_LOCK_ASSERT(p, MA_OWNED);
 717         PROC_SLOCK_ASSERT(p, MA_OWNED);
 718         THREAD_LOCK_ASSERT(td2, MA_OWNED);
 719
 720         wakeup_swapper = 0;
 721         switch (mode) {
 722         case SINGLE_EXIT:
 723                 if (TD_IS_SUSPENDED(td2))
 724                         wakeup_swapper |= thread_unsuspend_one(td2, p, true);
 725                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0)
 726                         wakeup_swapper |= sleepq_abort(td2, EINTR);
 727                 break;
 728         case SINGLE_BOUNDARY:
 729         case SINGLE_NO_EXIT:
 730                 if (TD_IS_SUSPENDED(td2) && (td2->td_flags & TDF_BOUNDARY) == 0)
 731                         wakeup_swapper |= thread_unsuspend_one(td2, p, false);
 732                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0)
 733                         wakeup_swapper |= sleepq_abort(td2, ERESTART);
 734                 break;
 735         case SINGLE_ALLPROC:
 736                 /*
 737                  * ALLPROC suspend tries to avoid spurious EINTR for
 738                  * threads sleeping interruptable, by suspending the
 739                  * thread directly, similarly to sig_suspend_threads().
 740                  * Since such sleep is not performed at the user
 741                  * boundary, TDF_BOUNDARY flag is not set, and TDF_ALLPROCSUSP
 742                  * is used to avoid immediate un-suspend.
 743                  */
 744                 if (TD_IS_SUSPENDED(td2) && (td2->td_flags & (TDF_BOUNDARY |
 745                     TDF_ALLPROCSUSP)) == 0)
 746                         wakeup_swapper |= thread_unsuspend_one(td2, p, false);
 747                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0) {
 748                         if ((td2->td_flags & TDF_SBDRY) == 0) {
 749                                 thread_suspend_one(td2);
 750                                 td2->td_flags |= TDF_ALLPROCSUSP;
 751                         } else {
 752                                 wakeup_swapper |= sleepq_abort(td2, ERESTART);
 753                         }
 754                 }
 755                 break;
 756         }
 757         return (wakeup_swapper);
 758 }
 759
 760 /*
 761  * Enforce single-threading.
 762  *
 763  * Returns 1 if the caller must abort (another thread is waiting to
 764  * exit the process or similar). Process is locked!
 765  * Returns 0 when you are successfully the only thread running.
 766  * A process has successfully single threaded in the suspend mode when
 767  * There are no threads in user mode. Threads in the kernel must be
 768  * allowed to continue until they get to the user boundary. They may even
 769  * copy out their return values and data before suspending. They may however be
 770  * accelerated in reaching the user boundary as we will wake up
 771  * any sleeping threads that are interruptable. (PCATCH).
 772  */
 773 int
 774 thread_single(struct proc *p, int mode)
 775 {
 776         struct thread *td;
 777         struct thread *td2;
 778         int remaining, wakeup_swapper;
 779
 780         td = curthread;
 781         KASSERT(mode == SINGLE_EXIT || mode == SINGLE_BOUNDARY ||
 782             mode == SINGLE_ALLPROC || mode == SINGLE_NO_EXIT,
 783             ("invalid mode %d", mode));
 784         /*
 785          * If allowing non-ALLPROC singlethreading for non-curproc
 786          * callers, calc_remaining() and remain_for_mode() should be
 787          * adjusted to also account for td->td_proc != p.  For now
 788          * this is not implemented because it is not used.
 789          */
 790         KASSERT((mode == SINGLE_ALLPROC && td->td_proc != p) ||
 791             (mode != SINGLE_ALLPROC && td->td_proc == p),
 792             ("mode %d proc %p curproc %p", mode, p, td->td_proc));
 793         mtx_assert(&Giant, MA_NOTOWNED);
 794         PROC_LOCK_ASSERT(p, MA_OWNED);
 795
 796         if ((p->p_flag & P_HADTHREADS) == 0 && mode != SINGLE_ALLPROC)
 797                 return (0);
 798
 799         /* Is someone already single threading? */
 800         if (p->p_singlethread != NULL && p->p_singlethread != td)
 801                 return (1);
 802
 803         if (mode == SINGLE_EXIT) {
 804                 p->p_flag |= P_SINGLE_EXIT;
 805                 p->p_flag &= ~P_SINGLE_BOUNDARY;
 806         } else {
 807                 p->p_flag &= ~P_SINGLE_EXIT;
 808                 if (mode == SINGLE_BOUNDARY)
 809                         p->p_flag |= P_SINGLE_BOUNDARY;
 810                 else
 811                         p->p_flag &= ~P_SINGLE_BOUNDARY;
 812         }
 813         if (mode == SINGLE_ALLPROC)
 814                 p->p_flag |= P_TOTAL_STOP;
 815         p->p_flag |= P_STOPPED_SINGLE;
 816         PROC_SLOCK(p);
 817         p->p_singlethread = td;
 818         remaining = calc_remaining(p, mode);
 819         while (remaining != remain_for_mode(mode)) {
 820                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
 821                         goto stopme;
 822                 wakeup_swapper = 0;
 823                 FOREACH_THREAD_IN_PROC(p, td2) {
 824                         if (td2 == td)
 825                                 continue;
 826                         thread_lock(td2);
 827                         td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
 828                         if (TD_IS_INHIBITED(td2)) {
 829                                 wakeup_swapper |= weed_inhib(mode, td2, p);
 830 #ifdef SMP
 831                         } else if (TD_IS_RUNNING(td2) && td != td2) {
 832                                 forward_signal(td2);
 833 #endif
 834                         }
 835                         thread_unlock(td2);
 836                 }
 837                 if (wakeup_swapper)
 838                         kick_proc0();
 839                 remaining = calc_remaining(p, mode);
 840
 841                 /*
 842                  * Maybe we suspended some threads.. was it enough?
 843                  */
 844                 if (remaining == remain_for_mode(mode))
 845                         break;
 846
 847 stopme:
 848                 /*
 849                  * Wake us up when everyone else has suspended.
 850                  * In the mean time we suspend as well.
 851                  */
 852                 thread_suspend_switch(td, p);
 853                 remaining = calc_remaining(p, mode);
 854         }
 855         if (mode == SINGLE_EXIT) {
 856                 /*
 857                  * Convert the process to an unthreaded process.  The
 858                  * SINGLE_EXIT is called by exit1() or execve(), in
 859                  * both cases other threads must be retired.
 860                  */
 861                 KASSERT(p->p_numthreads == 1, ("Unthreading with >1 threads"));
 862                 p->p_singlethread = NULL;
 863                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_HADTHREADS);
 864
 865                 /*
 866                  * Wait for any remaining threads to exit cpu_throw().
 867                  */
 868                 while (p->p_exitthreads != 0) {
 869                         PROC_SUNLOCK(p);
 870                         PROC_UNLOCK(p);
 871                         sched_relinquish(td);
 872                         PROC_LOCK(p);
 873                         PROC_SLOCK(p);
 874                 }
 875         } else if (mode == SINGLE_BOUNDARY) {
 876                 /*
 877                  * Wait until all suspended threads are removed from
 878                  * the processors.  The thread_suspend_check()
 879                  * increments p_boundary_count while it is still
 880                  * running, which makes it possible for the execve()
 881                  * to destroy vmspace while our other threads are
 882                  * still using the address space.
 883                  *
 884                  * We lock the thread, which is only allowed to
 885                  * succeed after context switch code finished using
 886                  * the address space.
 887                  */
 888                 FOREACH_THREAD_IN_PROC(p, td2) {
 889                         if (td2 == td)
 890                                 continue;
 891                         thread_lock(td2);
 892                         KASSERT((td2->td_flags & TDF_BOUNDARY) != 0,
 893                             ("td %p not on boundary", td2));
 894                         KASSERT(TD_IS_SUSPENDED(td2),
 895                             ("td %p is not suspended", td2));
 896                         thread_unlock(td2);
 897                 }
 898         }
 899         PROC_SUNLOCK(p);
 900         return (0);
 901 }
 902
 903 bool
 904 thread_suspend_check_needed(void)
 905 {
 906         struct proc *p;
 907         struct thread *td;
 908
 909         td = curthread;
 910         p = td->td_proc;
 911         PROC_LOCK_ASSERT(p, MA_OWNED);
 912         return (P_SHOULDSTOP(p) || ((p->p_flag & P_TRACED) != 0 &&
 913             (td->td_dbgflags & TDB_SUSPEND) != 0));
 914 }
 915
 916 /*
 917  * Called in from locations that can safely check to see
 918  * whether we have to suspend or at least throttle for a
 919  * single-thread event (e.g. fork).
 920  *
 921  * Such locations include userret().
 922  * If the "return_instead" argument is non zero, the thread must be able to
 923  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
 924  *
 925  * The 'return_instead' argument tells the function if it may do a
 926  * thread_exit() or suspend, or whether the caller must abort and back
 927  * out instead.
 928  *
 929  * If the thread that set the single_threading request has set the
 930  * P_SINGLE_EXIT bit in the process flags then this call will never return
 931  * if 'return_instead' is false, but will exit.
 932  *
 933  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
 934  *---------------+--------------------+---------------------
 935  *       0       | returns 0          |   returns 0 or 1
 936  *               | when ST ends       |   immediately
 937  *---------------+--------------------+---------------------
 938  *       1       | thread exits       |   returns 1
 939  *               |                    |  immediately
 940  * 0 = thread_exit() or suspension ok,
 941  * other = return error instead of stopping the thread.
 942  *
 943  * While a full suspension is under effect, even a single threading
 944  * thread would be suspended if it made this call (but it shouldn't).
 945  * This call should only be made from places where
 946  * thread_exit() would be safe as that may be the outcome unless
 947  * return_instead is set.
 948  */
 949 int
 950 thread_suspend_check(int return_instead)
 951 {
 952         struct thread *td;
 953         struct proc *p;
 954         int wakeup_swapper;
 955
 956         td = curthread;
 957         p = td->td_proc;
 958         mtx_assert(&Giant, MA_NOTOWNED);
 959         PROC_LOCK_ASSERT(p, MA_OWNED);
 960         while (thread_suspend_check_needed()) {
 961                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 962                         KASSERT(p->p_singlethread != NULL,
 963                             ("singlethread not set"));
 964                         /*
 965                          * The only suspension in action is a
 966                          * single-threading. Single threader need not stop.
 967                          * It is safe to access p->p_singlethread unlocked
 968                          * because it can only be set to our address by us.
 969                          */
 970                         if (p->p_singlethread == td)
 971                                 return (0);     /* Exempt from stopping. */
 972                 }
 973                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
 974                         return (EINTR);
 975
 976                 /* Should we goto user boundary if we didn't come from there? */
 977                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
 978                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
 979                         return (ERESTART);
 980
 981                 /*
 982                  * Ignore suspend requests if they are deferred.
 983                  */
 984                 if ((td->td_flags & TDF_SBDRY) != 0) {
 985                         KASSERT(return_instead,
 986                             ("TDF_SBDRY set for unsafe thread_suspend_check"));
 987                         KASSERT((td->td_flags & (TDF_SEINTR | TDF_SERESTART)) !=
 988                             (TDF_SEINTR | TDF_SERESTART),
 989                             ("both TDF_SEINTR and TDF_SERESTART"));
 990                         return (TD_SBDRY_INTR(td) ? TD_SBDRY_ERRNO(td) : 0);
 991                 }
 992
 993                 /*
 994                  * If the process is waiting for us to exit,
 995                  * this thread should just suicide.
 996                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
 997                  */
 998                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td)) {
 999                         PROC_UNLOCK(p);
1000
1001                         /*
1002                          * Allow Linux emulation layer to do some work
1003                          * before thread suicide.
1004                          */
1005                         if (__predict_false(p->p_sysent->sv_thread_detach != NULL))
1006                                 (p->p_sysent->sv_thread_detach)(td);
1007                         umtx_thread_exit(td);
1008                         kern_thr_exit(td);
1009                         panic("stopped thread did not exit");
1010                 }
1011
1012                 PROC_SLOCK(p);
1013                 thread_stopped(p);
1014                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
1015                         if (p->p_numthreads == p->p_suspcount + 1) {
1016                                 thread_lock(p->p_singlethread);
1017                                 wakeup_swapper = thread_unsuspend_one(
1018                                     p->p_singlethread, p, false);
1019                                 thread_unlock(p->p_singlethread);
1020                                 if (wakeup_swapper)
1021                                         kick_proc0();
1022                         }
1023                 }
1024                 PROC_UNLOCK(p);
1025                 thread_lock(td);
1026                 /*
1027                  * When a thread suspends, it just
1028                  * gets taken off all queues.
1029                  */
1030                 thread_suspend_one(td);
1031                 if (return_instead == 0) {
1032                         p->p_boundary_count++;
1033                         td->td_flags |= TDF_BOUNDARY;
1034                 }
1035                 PROC_SUNLOCK(p);
1036                 mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
1037                 thread_unlock(td);
1038                 PROC_LOCK(p);
1039         }
1040         return (0);
1041 }
1042
1043 void
1044 thread_suspend_switch(struct thread *td, struct proc *p)
1045 {
1046
1047         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
1048         PROC_LOCK_ASSERT(p, MA_OWNED);
1049         PROC_SLOCK_ASSERT(p, MA_OWNED);
1050         /*
1051          * We implement thread_suspend_one in stages here to avoid
1052          * dropping the proc lock while the thread lock is owned.
1053          */
1054         if (p == td->td_proc) {
1055                 thread_stopped(p);
1056                 p->p_suspcount++;
1057         }
1058         PROC_UNLOCK(p);
1059         thread_lock(td);
1060         td->td_flags &= ~TDF_NEEDSUSPCHK;
1061         TD_SET_SUSPENDED(td);
1062         sched_sleep(td, 0);
1063         PROC_SUNLOCK(p);
1064         DROP_GIANT();
1065         mi_switch(SW_VOL | SWT_SUSPEND, NULL);
1066         thread_unlock(td);
1067         PICKUP_GIANT();
1068         PROC_LOCK(p);
1069         PROC_SLOCK(p);
1070 }
1071
1072 void
1073 thread_suspend_one(struct thread *td)
1074 {
1075         struct proc *p;
1076
1077         p = td->td_proc;
1078         PROC_SLOCK_ASSERT(p, MA_OWNED);
1079         THREAD_LOCK_ASSERT(td, MA_OWNED);
1080         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
1081         p->p_suspcount++;
1082         td->td_flags &= ~TDF_NEEDSUSPCHK;
1083         TD_SET_SUSPENDED(td);
1084         sched_sleep(td, 0);
1085 }
1086
1087 static int
1088 thread_unsuspend_one(struct thread *td, struct proc *p, bool boundary)
1089 {
1090
1091         THREAD_LOCK_ASSERT(td, MA_OWNED);
1092         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
1093         TD_CLR_SUSPENDED(td);
1094         td->td_flags &= ~TDF_ALLPROCSUSP;
1095         if (td->td_proc == p) {
1096                 PROC_SLOCK_ASSERT(p, MA_OWNED);
1097                 p->p_suspcount--;
1098                 if (boundary && (td->td_flags & TDF_BOUNDARY) != 0) {
1099                         td->td_flags &= ~TDF_BOUNDARY;
1100                         p->p_boundary_count--;
1101                 }
1102         }
1103         return (setrunnable(td));
1104 }
1105
1106 /*
1107  * Allow all threads blocked by single threading to continue running.
1108  */
1109 void
1110 thread_unsuspend(struct proc *p)
1111 {
1112         struct thread *td;
1113         int wakeup_swapper;
1114
1115         PROC_LOCK_ASSERT(p, MA_OWNED);
1116         PROC_SLOCK_ASSERT(p, MA_OWNED);
1117         wakeup_swapper = 0;
1118         if (!P_SHOULDSTOP(p)) {
1119                 FOREACH_THREAD_IN_PROC(p, td) {
1120                         thread_lock(td);
1121                         if (TD_IS_SUSPENDED(td)) {
1122                                 wakeup_swapper |= thread_unsuspend_one(td, p,
1123                                     true);
1124                         }
1125                         thread_unlock(td);
1126                 }
1127         } else if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
1128             p->p_numthreads == p->p_suspcount) {
1129                 /*
1130                  * Stopping everything also did the job for the single
1131                  * threading request. Now we've downgraded to single-threaded,
1132                  * let it continue.
1133                  */
1134                 if (p->p_singlethread->td_proc == p) {
1135                         thread_lock(p->p_singlethread);
1136                         wakeup_swapper = thread_unsuspend_one(
1137                             p->p_singlethread, p, false);
1138                         thread_unlock(p->p_singlethread);
1139                 }
1140         }
1141         if (wakeup_swapper)
1142                 kick_proc0();
1143 }
1144
1145 /*
1146  * End the single threading mode..
1147  */
1148 void
1149 thread_single_end(struct proc *p, int mode)
1150 {
1151         struct thread *td;
1152         int wakeup_swapper;
1153
1154         KASSERT(mode == SINGLE_EXIT || mode == SINGLE_BOUNDARY ||
1155             mode == SINGLE_ALLPROC || mode == SINGLE_NO_EXIT,
1156             ("invalid mode %d", mode));
1157         PROC_LOCK_ASSERT(p, MA_OWNED);
1158         KASSERT((mode == SINGLE_ALLPROC && (p->p_flag & P_TOTAL_STOP) != 0) ||
1159             (mode != SINGLE_ALLPROC && (p->p_flag & P_TOTAL_STOP) == 0),
1160             ("mode %d does not match P_TOTAL_STOP", mode));
1161         KASSERT(mode == SINGLE_ALLPROC || p->p_singlethread == curthread,
1162             ("thread_single_end from other thread %p %p",
1163             curthread, p->p_singlethread));
1164         KASSERT(mode != SINGLE_BOUNDARY ||
1165             (p->p_flag & P_SINGLE_BOUNDARY) != 0,
1166             ("mis-matched SINGLE_BOUNDARY flags %x", p->p_flag));
1167         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY |
1168             P_TOTAL_STOP);
1169         PROC_SLOCK(p);
1170         p->p_singlethread = NULL;
1171         wakeup_swapper = 0;
1172         /*
1173          * If there are other threads they may now run,
1174          * unless of course there is a blanket 'stop order'
1175          * on the process. The single threader must be allowed
1176          * to continue however as this is a bad place to stop.
1177          */
1178         if (p->p_numthreads != remain_for_mode(mode) && !P_SHOULDSTOP(p)) {
1179                 FOREACH_THREAD_IN_PROC(p, td) {
1180                         thread_lock(td);
1181                         if (TD_IS_SUSPENDED(td)) {
1182                                 wakeup_swapper |= thread_unsuspend_one(td, p,
1183                                     mode == SINGLE_BOUNDARY);
1184                         }
1185                         thread_unlock(td);
1186                 }
1187         }
1188         KASSERT(mode != SINGLE_BOUNDARY || p->p_boundary_count == 0,
1189             ("inconsistent boundary count %d", p->p_boundary_count));
1190         PROC_SUNLOCK(p);
1191         if (wakeup_swapper)
1192                 kick_proc0();
1193 }
1194
1195 struct thread *
1196 thread_find(struct proc *p, lwpid_t tid)
1197 {
1198         struct thread *td;
1199
1200         PROC_LOCK_ASSERT(p, MA_OWNED);
1201         FOREACH_THREAD_IN_PROC(p, td) {
1202                 if (td->td_tid == tid)
1203                         break;
1204         }
1205         return (td);
1206 }
1207
1208 /* Locate a thread by number; return with proc lock held. */
1209 struct thread *
1210 tdfind(lwpid_t tid, pid_t pid)
1211 {
1212 #define RUN_THRESH      16
1213         struct thread *td;
1214         int run = 0;
1215
1216         rw_rlock(&tidhash_lock);
1217         LIST_FOREACH(td, TIDHASH(tid), td_hash) {
1218                 if (td->td_tid == tid) {
1219                         if (pid != -1 && td->td_proc->p_pid != pid) {
1220                                 td = NULL;
1221                                 break;
1222                         }
1223                         PROC_LOCK(td->td_proc);
1224                         if (td->td_proc->p_state == PRS_NEW) {
1225                                 PROC_UNLOCK(td->td_proc);
1226                                 td = NULL;
1227                                 break;
1228                         }
1229                         if (run > RUN_THRESH) {
1230                                 if (rw_try_upgrade(&tidhash_lock)) {
1231                                         LIST_REMOVE(td, td_hash);
1232                                         LIST_INSERT_HEAD(TIDHASH(td->td_tid),
1233                                                 td, td_hash);
1234                                         rw_wunlock(&tidhash_lock);
1235                                         return (td);
1236                                 }
1237                         }
1238                         break;
1239                 }
1240                 run++;
1241         }
1242         rw_runlock(&tidhash_lock);
1243         return (td);
1244 }
1245
1246 void
1247 tidhash_add(struct thread *td)
1248 {
1249         rw_wlock(&tidhash_lock);
1250         LIST_INSERT_HEAD(TIDHASH(td->td_tid), td, td_hash);
1251         rw_wunlock(&tidhash_lock);
1252 }
1253
1254 void
1255 tidhash_remove(struct thread *td)
1256 {
1257         rw_wlock(&tidhash_lock);
1258         LIST_REMOVE(td, td_hash);
1259         rw_wunlock(&tidhash_lock);
1260 }