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/resourcevar.h>
  42 #include <sys/smp.h>
  43 #include <sys/sched.h>
  44 #include <sys/sleepqueue.h>
  45 #include <sys/selinfo.h>
  46 #include <sys/turnstile.h>
  47 #include <sys/ktr.h>
  48 #include <sys/umtx.h>
  49 #include <sys/cpuset.h>
  50 #ifdef  HWPMC_HOOKS
  51 #include <sys/pmckern.h>
  52 #endif
  53
  54 #include <security/audit/audit.h>
  55
  56 #include <vm/vm.h>
  57 #include <vm/vm_extern.h>
  58 #include <vm/uma.h>
  59 #include <sys/eventhandler.h>
  60
  61 /*
  62  * thread related storage.
  63  */
  64 static uma_zone_t thread_zone;
  65
  66 TAILQ_HEAD(, thread) zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
  67 static struct mtx zombie_lock;
  68 MTX_SYSINIT(zombie_lock, &zombie_lock, "zombie lock", MTX_SPIN);
  69
  70 static void thread_zombie(struct thread *);
  71
  72 struct mtx tid_lock;
  73 static struct unrhdr *tid_unrhdr;
  74
  75 /*
  76  * Prepare a thread for use.
  77  */
  78 static int
  79 thread_ctor(void *mem, int size, void *arg, int flags)
  80 {
  81         struct thread   *td;
  82
  83         td = (struct thread *)mem;
  84         td->td_state = TDS_INACTIVE;
  85         td->td_oncpu = NOCPU;
  86
  87         td->td_tid = alloc_unr(tid_unrhdr);
  88         td->td_syscalls = 0;
  89
  90         /*
  91          * Note that td_critnest begins life as 1 because the thread is not
  92          * running and is thereby implicitly waiting to be on the receiving
  93          * end of a context switch.
  94          */
  95         td->td_critnest = 1;
  96         EVENTHANDLER_INVOKE(thread_ctor, td);
  97 #ifdef AUDIT
  98         audit_thread_alloc(td);
  99 #endif
 100         umtx_thread_alloc(td);
 101         return (0);
 102 }
 103
 104 /*
 105  * Reclaim a thread after use.
 106  */
 107 static void
 108 thread_dtor(void *mem, int size, void *arg)
 109 {
 110         struct thread *td;
 111
 112         td = (struct thread *)mem;
 113
 114 #ifdef INVARIANTS
 115         /* Verify that this thread is in a safe state to free. */
 116         switch (td->td_state) {
 117         case TDS_INHIBITED:
 118         case TDS_RUNNING:
 119         case TDS_CAN_RUN:
 120         case TDS_RUNQ:
 121                 /*
 122                  * We must never unlink a thread that is in one of
 123                  * these states, because it is currently active.
 124                  */
 125                 panic("bad state for thread unlinking");
 126                 /* NOTREACHED */
 127         case TDS_INACTIVE:
 128                 break;
 129         default:
 130                 panic("bad thread state");
 131                 /* NOTREACHED */
 132         }
 133 #endif
 134 #ifdef AUDIT
 135         audit_thread_free(td);
 136 #endif
 137         /* Free all OSD associated to this thread. */
 138         osd_thread_exit(td);
 139
 140         EVENTHANDLER_INVOKE(thread_dtor, td);
 141         free_unr(tid_unrhdr, td->td_tid);
 142 }
 143
 144 /*
 145  * Initialize type-stable parts of a thread (when newly created).
 146  */
 147 static int
 148 thread_init(void *mem, int size, int flags)
 149 {
 150         struct thread *td;
 151
 152         td = (struct thread *)mem;
 153
 154         td->td_sleepqueue = sleepq_alloc();
 155         td->td_turnstile = turnstile_alloc();
 156         EVENTHANDLER_INVOKE(thread_init, td);
 157         td->td_sched = (struct td_sched *)&td[1];
 158         umtx_thread_init(td);
 159         td->td_kstack = 0;
 160         return (0);
 161 }
 162
 163 /*
 164  * Tear down type-stable parts of a thread (just before being discarded).
 165  */
 166 static void
 167 thread_fini(void *mem, int size)
 168 {
 169         struct thread *td;
 170
 171         td = (struct thread *)mem;
 172         EVENTHANDLER_INVOKE(thread_fini, td);
 173         turnstile_free(td->td_turnstile);
 174         sleepq_free(td->td_sleepqueue);
 175         umtx_thread_fini(td);
 176         seltdfini(td);
 177 }
 178
 179 /*
 180  * For a newly created process,
 181  * link up all the structures and its initial threads etc.
 182  * called from:
 183  * {arch}/{arch}/machdep.c   ia64_init(), init386() etc.
 184  * proc_dtor() (should go away)
 185  * proc_init()
 186  */
 187 void
 188 proc_linkup0(struct proc *p, struct thread *td)
 189 {
 190         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
 191         proc_linkup(p, td);
 192 }
 193
 194 void
 195 proc_linkup(struct proc *p, struct thread *td)
 196 {
 197
 198         sigqueue_init(&p->p_sigqueue, p);
 199         p->p_ksi = ksiginfo_alloc(1);
 200         if (p->p_ksi != NULL) {
 201                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
 202                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
 203         }
 204         LIST_INIT(&p->p_mqnotifier);
 205         p->p_numthreads = 0;
 206         thread_link(td, p);
 207 }
 208
 209 /*
 210  * Initialize global thread allocation resources.
 211  */
 212 void
 213 threadinit(void)
 214 {
 215
 216         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
 217         /* leave one number for thread0 */
 218         tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
 219
 220         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
 221             thread_ctor, thread_dtor, thread_init, thread_fini,
 222             16 - 1, 0);
 223 }
 224
 225 /*
 226  * Place an unused thread on the zombie list.
 227  * Use the slpq as that must be unused by now.
 228  */
 229 void
 230 thread_zombie(struct thread *td)
 231 {
 232         mtx_lock_spin(&zombie_lock);
 233         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
 234         mtx_unlock_spin(&zombie_lock);
 235 }
 236
 237 /*
 238  * Release a thread that has exited after cpu_throw().
 239  */
 240 void
 241 thread_stash(struct thread *td)
 242 {
 243         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
 244         thread_zombie(td);
 245 }
 246
 247 /*
 248  * Reap zombie resources.
 249  */
 250 void
 251 thread_reap(void)
 252 {
 253         struct thread *td_first, *td_next;
 254
 255         /*
 256          * Don't even bother to lock if none at this instant,
 257          * we really don't care about the next instant..
 258          */
 259         if (!TAILQ_EMPTY(&zombie_threads)) {
 260                 mtx_lock_spin(&zombie_lock);
 261                 td_first = TAILQ_FIRST(&zombie_threads);
 262                 if (td_first)
 263                         TAILQ_INIT(&zombie_threads);
 264                 mtx_unlock_spin(&zombie_lock);
 265                 while (td_first) {
 266                         td_next = TAILQ_NEXT(td_first, td_slpq);
 267                         if (td_first->td_ucred)
 268                                 crfree(td_first->td_ucred);
 269                         thread_free(td_first);
 270                         td_first = td_next;
 271                 }
 272         }
 273 }
 274
 275 /*
 276  * Allocate a thread.
 277  */
 278 struct thread *
 279 thread_alloc(int pages)
 280 {
 281         struct thread *td;
 282
 283         thread_reap(); /* check if any zombies to get */
 284
 285         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
 286         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
 287         if (!vm_thread_new(td, pages)) {
 288                 uma_zfree(thread_zone, td);
 289                 return (NULL);
 290         }
 291         cpu_thread_alloc(td);
 292         return (td);
 293 }
 294
 295 int
 296 thread_alloc_stack(struct thread *td, int pages)
 297 {
 298
 299         KASSERT(td->td_kstack == 0,
 300             ("thread_alloc_stack called on a thread with kstack"));
 301         if (!vm_thread_new(td, pages))
 302                 return (0);
 303         cpu_thread_alloc(td);
 304         return (1);
 305 }
 306
 307 /*
 308  * Deallocate a thread.
 309  */
 310 void
 311 thread_free(struct thread *td)
 312 {
 313
 314         lock_profile_thread_exit(td);
 315         if (td->td_cpuset)
 316                 cpuset_rel(td->td_cpuset);
 317         td->td_cpuset = NULL;
 318         cpu_thread_free(td);
 319         if (td->td_kstack != 0)
 320                 vm_thread_dispose(td);
 321         uma_zfree(thread_zone, td);
 322 }
 323
 324 /*
 325  * Discard the current thread and exit from its context.
 326  * Always called with scheduler locked.
 327  *
 328  * Because we can't free a thread while we're operating under its context,
 329  * push the current thread into our CPU's deadthread holder. This means
 330  * we needn't worry about someone else grabbing our context before we
 331  * do a cpu_throw().
 332  */
 333 void
 334 thread_exit(void)
 335 {
 336         uint64_t runtime, new_switchtime;
 337         struct thread *td;
 338         struct thread *td2;
 339         struct proc *p;
 340         int wakeup_swapper;
 341
 342         td = curthread;
 343         p = td->td_proc;
 344
 345         PROC_SLOCK_ASSERT(p, MA_OWNED);
 346         mtx_assert(&Giant, MA_NOTOWNED);
 347
 348         PROC_LOCK_ASSERT(p, MA_OWNED);
 349         KASSERT(p != NULL, ("thread exiting without a process"));
 350         CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
 351             (long)p->p_pid, td->td_name);
 352         KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
 353
 354 #ifdef AUDIT
 355         AUDIT_SYSCALL_EXIT(0, td);
 356 #endif
 357         umtx_thread_exit(td);
 358         /*
 359          * drop FPU & debug register state storage, or any other
 360          * architecture specific resources that
 361          * would not be on a new untouched process.
 362          */
 363         cpu_thread_exit(td);    /* XXXSMP */
 364
 365         /*
 366          * The last thread is left attached to the process
 367          * So that the whole bundle gets recycled. Skip
 368          * all this stuff if we never had threads.
 369          * EXIT clears all sign of other threads when
 370          * it goes to single threading, so the last thread always
 371          * takes the short path.
 372          */
 373         if (p->p_flag & P_HADTHREADS) {
 374                 if (p->p_numthreads > 1) {
 375                         thread_unlink(td);
 376                         td2 = FIRST_THREAD_IN_PROC(p);
 377                         sched_exit_thread(td2, td);
 378
 379                         /*
 380                          * The test below is NOT true if we are the
 381                          * sole exiting thread. P_STOPPED_SINGLE is unset
 382                          * in exit1() after it is the only survivor.
 383                          */
 384                         if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 385                                 if (p->p_numthreads == p->p_suspcount) {
 386                                         thread_lock(p->p_singlethread);
 387                                         wakeup_swapper = thread_unsuspend_one(
 388                                                 p->p_singlethread);
 389                                         thread_unlock(p->p_singlethread);
 390                                         if (wakeup_swapper)
 391                                                 kick_proc0();
 392                                 }
 393                         }
 394
 395                         atomic_add_int(&td->td_proc->p_exitthreads, 1);
 396                         PCPU_SET(deadthread, td);
 397                 } else {
 398                         /*
 399                          * The last thread is exiting.. but not through exit()
 400                          */
 401                         panic ("thread_exit: Last thread exiting on its own");
 402                 }
 403         }
 404 #ifdef  HWPMC_HOOKS
 405         /*
 406          * If this thread is part of a process that is being tracked by hwpmc(4),
 407          * inform the module of the thread's impending exit.
 408          */
 409         if (PMC_PROC_IS_USING_PMCS(td->td_proc))
 410                 PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
 411 #endif
 412         PROC_UNLOCK(p);
 413
 414         /* Do the same timestamp bookkeeping that mi_switch() would do. */
 415         new_switchtime = cpu_ticks();
 416         runtime = new_switchtime - PCPU_GET(switchtime);
 417         td->td_runtime += runtime;
 418         td->td_incruntime += runtime;
 419         PCPU_SET(switchtime, new_switchtime);
 420         PCPU_SET(switchticks, ticks);
 421         PCPU_INC(cnt.v_swtch);
 422
 423         /* Save our resource usage in our process. */
 424         td->td_ru.ru_nvcsw++;
 425         ruxagg(p, td);
 426         rucollect(&p->p_ru, &td->td_ru);
 427
 428         thread_lock(td);
 429         PROC_SUNLOCK(p);
 430         td->td_state = TDS_INACTIVE;
 431 #ifdef WITNESS
 432         witness_thread_exit(td);
 433 #endif
 434         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
 435         sched_throw(td);
 436         panic("I'm a teapot!");
 437         /* NOTREACHED */
 438 }
 439
 440 /*
 441  * Do any thread specific cleanups that may be needed in wait()
 442  * called with Giant, proc and schedlock not held.
 443  */
 444 void
 445 thread_wait(struct proc *p)
 446 {
 447         struct thread *td;
 448
 449         mtx_assert(&Giant, MA_NOTOWNED);
 450         KASSERT((p->p_numthreads == 1), ("Multiple threads in wait1()"));
 451         td = FIRST_THREAD_IN_PROC(p);
 452         /* Lock the last thread so we spin until it exits cpu_throw(). */
 453         thread_lock(td);
 454         thread_unlock(td);
 455         /* Wait for any remaining threads to exit cpu_throw(). */
 456         while (p->p_exitthreads)
 457                 sched_relinquish(curthread);
 458         lock_profile_thread_exit(td);
 459         cpuset_rel(td->td_cpuset);
 460         td->td_cpuset = NULL;
 461         cpu_thread_clean(td);
 462         crfree(td->td_ucred);
 463         thread_reap();  /* check for zombie threads etc. */
 464 }
 465
 466 /*
 467  * Link a thread to a process.
 468  * set up anything that needs to be initialized for it to
 469  * be used by the process.
 470  */
 471 void
 472 thread_link(struct thread *td, struct proc *p)
 473 {
 474
 475         /*
 476          * XXX This can't be enabled because it's called for proc0 before
 477          * its lock has been created.
 478          * PROC_LOCK_ASSERT(p, MA_OWNED);
 479          */
 480         td->td_state    = TDS_INACTIVE;
 481         td->td_proc     = p;
 482         td->td_flags    = TDF_INMEM;
 483
 484         LIST_INIT(&td->td_contested);
 485         LIST_INIT(&td->td_lprof[0]);
 486         LIST_INIT(&td->td_lprof[1]);
 487         sigqueue_init(&td->td_sigqueue, p);
 488         callout_init(&td->td_slpcallout, CALLOUT_MPSAFE);
 489         TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
 490         p->p_numthreads++;
 491 }
 492
 493 /*
 494  * Convert a process with one thread to an unthreaded process.
 495  */
 496 void
 497 thread_unthread(struct thread *td)
 498 {
 499         struct proc *p = td->td_proc;
 500
 501         KASSERT((p->p_numthreads == 1), ("Unthreading with >1 threads"));
 502         p->p_flag &= ~P_HADTHREADS;
 503 }
 504
 505 /*
 506  * Called from:
 507  *  thread_exit()
 508  */
 509 void
 510 thread_unlink(struct thread *td)
 511 {
 512         struct proc *p = td->td_proc;
 513
 514         PROC_LOCK_ASSERT(p, MA_OWNED);
 515         TAILQ_REMOVE(&p->p_threads, td, td_plist);
 516         p->p_numthreads--;
 517         /* could clear a few other things here */
 518         /* Must  NOT clear links to proc! */
 519 }
 520
 521 static int
 522 calc_remaining(struct proc *p, int mode)
 523 {
 524         int remaining;
 525
 526         PROC_LOCK_ASSERT(p, MA_OWNED);
 527         PROC_SLOCK_ASSERT(p, MA_OWNED);
 528         if (mode == SINGLE_EXIT)
 529                 remaining = p->p_numthreads;
 530         else if (mode == SINGLE_BOUNDARY)
 531                 remaining = p->p_numthreads - p->p_boundary_count;
 532         else if (mode == SINGLE_NO_EXIT)
 533                 remaining = p->p_numthreads - p->p_suspcount;
 534         else
 535                 panic("calc_remaining: wrong mode %d", mode);
 536         return (remaining);
 537 }
 538
 539 /*
 540  * Enforce single-threading.
 541  *
 542  * Returns 1 if the caller must abort (another thread is waiting to
 543  * exit the process or similar). Process is locked!
 544  * Returns 0 when you are successfully the only thread running.
 545  * A process has successfully single threaded in the suspend mode when
 546  * There are no threads in user mode. Threads in the kernel must be
 547  * allowed to continue until they get to the user boundary. They may even
 548  * copy out their return values and data before suspending. They may however be
 549  * accelerated in reaching the user boundary as we will wake up
 550  * any sleeping threads that are interruptable. (PCATCH).
 551  */
 552 int
 553 thread_single(int mode)
 554 {
 555         struct thread *td;
 556         struct thread *td2;
 557         struct proc *p;
 558         int remaining, wakeup_swapper;
 559
 560         td = curthread;
 561         p = td->td_proc;
 562         mtx_assert(&Giant, MA_NOTOWNED);
 563         PROC_LOCK_ASSERT(p, MA_OWNED);
 564         KASSERT((td != NULL), ("curthread is NULL"));
 565
 566         if ((p->p_flag & P_HADTHREADS) == 0)
 567                 return (0);
 568
 569         /* Is someone already single threading? */
 570         if (p->p_singlethread != NULL && p->p_singlethread != td)
 571                 return (1);
 572
 573         if (mode == SINGLE_EXIT) {
 574                 p->p_flag |= P_SINGLE_EXIT;
 575                 p->p_flag &= ~P_SINGLE_BOUNDARY;
 576         } else {
 577                 p->p_flag &= ~P_SINGLE_EXIT;
 578                 if (mode == SINGLE_BOUNDARY)
 579                         p->p_flag |= P_SINGLE_BOUNDARY;
 580                 else
 581                         p->p_flag &= ~P_SINGLE_BOUNDARY;
 582         }
 583         p->p_flag |= P_STOPPED_SINGLE;
 584         PROC_SLOCK(p);
 585         p->p_singlethread = td;
 586         remaining = calc_remaining(p, mode);
 587         while (remaining != 1) {
 588                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
 589                         goto stopme;
 590                 wakeup_swapper = 0;
 591                 FOREACH_THREAD_IN_PROC(p, td2) {
 592                         if (td2 == td)
 593                                 continue;
 594                         thread_lock(td2);
 595                         td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
 596                         if (TD_IS_INHIBITED(td2)) {
 597                                 switch (mode) {
 598                                 case SINGLE_EXIT:
 599                                         if (TD_IS_SUSPENDED(td2))
 600                                                 wakeup_swapper |=
 601                                                     thread_unsuspend_one(td2);
 602                                         if (TD_ON_SLEEPQ(td2) &&
 603                                             (td2->td_flags & TDF_SINTR))
 604                                                 wakeup_swapper |=
 605                                                     sleepq_abort(td2, EINTR);
 606                                         break;
 607                                 case SINGLE_BOUNDARY:
 608                                         if (TD_IS_SUSPENDED(td2) &&
 609                                             !(td2->td_flags & TDF_BOUNDARY))
 610                                                 wakeup_swapper |=
 611                                                     thread_unsuspend_one(td2);
 612                                         if (TD_ON_SLEEPQ(td2) &&
 613                                             (td2->td_flags & TDF_SINTR))
 614                                                 wakeup_swapper |=
 615                                                     sleepq_abort(td2, ERESTART);
 616                                         break;
 617                                 case SINGLE_NO_EXIT:
 618                                         if (TD_IS_SUSPENDED(td2) &&
 619                                             !(td2->td_flags & TDF_BOUNDARY))
 620                                                 wakeup_swapper |=
 621                                                     thread_unsuspend_one(td2);
 622                                         if (TD_ON_SLEEPQ(td2) &&
 623                                             (td2->td_flags & TDF_SINTR))
 624                                                 wakeup_swapper |=
 625                                                     sleepq_abort(td2, ERESTART);
 626                                         break;
 627                                 default:
 628                                         break;
 629                                 }
 630                         }
 631 #ifdef SMP
 632                         else if (TD_IS_RUNNING(td2) && td != td2) {
 633                                 forward_signal(td2);
 634                         }
 635 #endif
 636                         thread_unlock(td2);
 637                 }
 638                 if (wakeup_swapper)
 639                         kick_proc0();
 640                 remaining = calc_remaining(p, mode);
 641
 642                 /*
 643                  * Maybe we suspended some threads.. was it enough?
 644                  */
 645                 if (remaining == 1)
 646                         break;
 647
 648 stopme:
 649                 /*
 650                  * Wake us up when everyone else has suspended.
 651                  * In the mean time we suspend as well.
 652                  */
 653                 thread_suspend_switch(td);
 654                 remaining = calc_remaining(p, mode);
 655         }
 656         if (mode == SINGLE_EXIT) {
 657                 /*
 658                  * We have gotten rid of all the other threads and we
 659                  * are about to either exit or exec. In either case,
 660                  * we try our utmost  to revert to being a non-threaded
 661                  * process.
 662                  */
 663                 p->p_singlethread = NULL;
 664                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT);
 665                 thread_unthread(td);
 666         }
 667         PROC_SUNLOCK(p);
 668         return (0);
 669 }
 670
 671 /*
 672  * Called in from locations that can safely check to see
 673  * whether we have to suspend or at least throttle for a
 674  * single-thread event (e.g. fork).
 675  *
 676  * Such locations include userret().
 677  * If the "return_instead" argument is non zero, the thread must be able to
 678  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
 679  *
 680  * The 'return_instead' argument tells the function if it may do a
 681  * thread_exit() or suspend, or whether the caller must abort and back
 682  * out instead.
 683  *
 684  * If the thread that set the single_threading request has set the
 685  * P_SINGLE_EXIT bit in the process flags then this call will never return
 686  * if 'return_instead' is false, but will exit.
 687  *
 688  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
 689  *---------------+--------------------+---------------------
 690  *       0       | returns 0          |   returns 0 or 1
 691  *               | when ST ends       |   immediatly
 692  *---------------+--------------------+---------------------
 693  *       1       | thread exits       |   returns 1
 694  *               |                    |  immediatly
 695  * 0 = thread_exit() or suspension ok,
 696  * other = return error instead of stopping the thread.
 697  *
 698  * While a full suspension is under effect, even a single threading
 699  * thread would be suspended if it made this call (but it shouldn't).
 700  * This call should only be made from places where
 701  * thread_exit() would be safe as that may be the outcome unless
 702  * return_instead is set.
 703  */
 704 int
 705 thread_suspend_check(int return_instead)
 706 {
 707         struct thread *td;
 708         struct proc *p;
 709         int wakeup_swapper;
 710
 711         td = curthread;
 712         p = td->td_proc;
 713         mtx_assert(&Giant, MA_NOTOWNED);
 714         PROC_LOCK_ASSERT(p, MA_OWNED);
 715         while (P_SHOULDSTOP(p) ||
 716               ((p->p_flag & P_TRACED) && (td->td_dbgflags & TDB_SUSPEND))) {
 717                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 718                         KASSERT(p->p_singlethread != NULL,
 719                             ("singlethread not set"));
 720                         /*
 721                          * The only suspension in action is a
 722                          * single-threading. Single threader need not stop.
 723                          * XXX Should be safe to access unlocked
 724                          * as it can only be set to be true by us.
 725                          */
 726                         if (p->p_singlethread == td)
 727                                 return (0);     /* Exempt from stopping. */
 728                 }
 729                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
 730                         return (EINTR);
 731
 732                 /* Should we goto user boundary if we didn't come from there? */
 733                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
 734                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
 735                         return (ERESTART);
 736
 737                 /* If thread will exit, flush its pending signals */
 738                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td))
 739                         sigqueue_flush(&td->td_sigqueue);
 740
 741                 PROC_SLOCK(p);
 742                 thread_stopped(p);
 743                 /*
 744                  * If the process is waiting for us to exit,
 745                  * this thread should just suicide.
 746                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
 747                  */
 748                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td))
 749                         thread_exit();
 750                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 751                         if (p->p_numthreads == p->p_suspcount + 1) {
 752                                 thread_lock(p->p_singlethread);
 753                                 wakeup_swapper =
 754                                     thread_unsuspend_one(p->p_singlethread);
 755                                 thread_unlock(p->p_singlethread);
 756                                 if (wakeup_swapper)
 757                                         kick_proc0();
 758                         }
 759                 }
 760                 PROC_UNLOCK(p);
 761                 thread_lock(td);
 762                 /*
 763                  * When a thread suspends, it just
 764                  * gets taken off all queues.
 765                  */
 766                 thread_suspend_one(td);
 767                 if (return_instead == 0) {
 768                         p->p_boundary_count++;
 769                         td->td_flags |= TDF_BOUNDARY;
 770                 }
 771                 PROC_SUNLOCK(p);
 772                 mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
 773                 if (return_instead == 0)
 774                         td->td_flags &= ~TDF_BOUNDARY;
 775                 thread_unlock(td);
 776                 PROC_LOCK(p);
 777                 if (return_instead == 0) {
 778                         PROC_SLOCK(p);
 779                         p->p_boundary_count--;
 780                         PROC_SUNLOCK(p);
 781                 }
 782         }
 783         return (0);
 784 }
 785
 786 void
 787 thread_suspend_switch(struct thread *td)
 788 {
 789         struct proc *p;
 790
 791         p = td->td_proc;
 792         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
 793         PROC_LOCK_ASSERT(p, MA_OWNED);
 794         PROC_SLOCK_ASSERT(p, MA_OWNED);
 795         /*
 796          * We implement thread_suspend_one in stages here to avoid
 797          * dropping the proc lock while the thread lock is owned.
 798          */
 799         thread_stopped(p);
 800         p->p_suspcount++;
 801         PROC_UNLOCK(p);
 802         thread_lock(td);
 803         td->td_flags &= ~TDF_NEEDSUSPCHK;
 804         TD_SET_SUSPENDED(td);
 805         sched_sleep(td, 0);
 806         PROC_SUNLOCK(p);
 807         DROP_GIANT();
 808         mi_switch(SW_VOL | SWT_SUSPEND, NULL);
 809         thread_unlock(td);
 810         PICKUP_GIANT();
 811         PROC_LOCK(p);
 812         PROC_SLOCK(p);
 813 }
 814
 815 void
 816 thread_suspend_one(struct thread *td)
 817 {
 818         struct proc *p = td->td_proc;
 819
 820         PROC_SLOCK_ASSERT(p, MA_OWNED);
 821         THREAD_LOCK_ASSERT(td, MA_OWNED);
 822         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
 823         p->p_suspcount++;
 824         td->td_flags &= ~TDF_NEEDSUSPCHK;
 825         TD_SET_SUSPENDED(td);
 826         sched_sleep(td, 0);
 827 }
 828
 829 int
 830 thread_unsuspend_one(struct thread *td)
 831 {
 832         struct proc *p = td->td_proc;
 833
 834         PROC_SLOCK_ASSERT(p, MA_OWNED);
 835         THREAD_LOCK_ASSERT(td, MA_OWNED);
 836         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
 837         TD_CLR_SUSPENDED(td);
 838         p->p_suspcount--;
 839         return (setrunnable(td));
 840 }
 841
 842 /*
 843  * Allow all threads blocked by single threading to continue running.
 844  */
 845 void
 846 thread_unsuspend(struct proc *p)
 847 {
 848         struct thread *td;
 849         int wakeup_swapper;
 850
 851         PROC_LOCK_ASSERT(p, MA_OWNED);
 852         PROC_SLOCK_ASSERT(p, MA_OWNED);
 853         wakeup_swapper = 0;
 854         if (!P_SHOULDSTOP(p)) {
 855                 FOREACH_THREAD_IN_PROC(p, td) {
 856                         thread_lock(td);
 857                         if (TD_IS_SUSPENDED(td)) {
 858                                 wakeup_swapper |= thread_unsuspend_one(td);
 859                         }
 860                         thread_unlock(td);
 861                 }
 862         } else if ((P_SHOULDSTOP(p) == P_STOPPED_SINGLE) &&
 863             (p->p_numthreads == p->p_suspcount)) {
 864                 /*
 865                  * Stopping everything also did the job for the single
 866                  * threading request. Now we've downgraded to single-threaded,
 867                  * let it continue.
 868                  */
 869                 thread_lock(p->p_singlethread);
 870                 wakeup_swapper = thread_unsuspend_one(p->p_singlethread);
 871                 thread_unlock(p->p_singlethread);
 872         }
 873         if (wakeup_swapper)
 874                 kick_proc0();
 875 }
 876
 877 /*
 878  * End the single threading mode..
 879  */
 880 void
 881 thread_single_end(void)
 882 {
 883         struct thread *td;
 884         struct proc *p;
 885         int wakeup_swapper;
 886
 887         td = curthread;
 888         p = td->td_proc;
 889         PROC_LOCK_ASSERT(p, MA_OWNED);
 890         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY);
 891         PROC_SLOCK(p);
 892         p->p_singlethread = NULL;
 893         wakeup_swapper = 0;
 894         /*
 895          * If there are other threads they may now run,
 896          * unless of course there is a blanket 'stop order'
 897          * on the process. The single threader must be allowed
 898          * to continue however as this is a bad place to stop.
 899          */
 900         if ((p->p_numthreads != 1) && (!P_SHOULDSTOP(p))) {
 901                 FOREACH_THREAD_IN_PROC(p, td) {
 902                         thread_lock(td);
 903                         if (TD_IS_SUSPENDED(td)) {
 904                                 wakeup_swapper |= thread_unsuspend_one(td);
 905                         }
 906                         thread_unlock(td);
 907                 }
 908         }
 909         PROC_SUNLOCK(p);
 910         if (wakeup_swapper)
 911                 kick_proc0();
 912 }
 913
 914 struct thread *
 915 thread_find(struct proc *p, lwpid_t tid)
 916 {
 917         struct thread *td;
 918
 919         PROC_LOCK_ASSERT(p, MA_OWNED);
 920         FOREACH_THREAD_IN_PROC(p, td) {
 921                 if (td->td_tid == tid)
 922                         break;
 923         }
 924         return (td);
 925 }