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_kdtrace.h"
  31 #include "opt_hwpmc_hooks.h"
  32
  33 #include <sys/cdefs.h>
  34 __FBSDID("$FreeBSD$");
  35
  36 #include <sys/param.h>
  37 #include <sys/systm.h>
  38 #include <sys/kernel.h>
  39 #include <sys/lock.h>
  40 #include <sys/mutex.h>
  41 #include <sys/proc.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/turnstile.h>
  49 #include <sys/ktr.h>
  50 #include <sys/umtx.h>
  51 #include <sys/cpuset.h>
  52 #ifdef  HWPMC_HOOKS
  53 #include <sys/pmckern.h>
  54 #endif
  55
  56 #include <security/audit/audit.h>
  57
  58 #include <vm/vm.h>
  59 #include <vm/vm_extern.h>
  60 #include <vm/uma.h>
  61 #include <sys/eventhandler.h>
  62
  63 SDT_PROVIDER_DECLARE(proc);
  64 SDT_PROBE_DEFINE(proc, , , lwp_exit, lwp-exit);
  65
  66
  67 /*
  68  * thread related storage.
  69  */
  70 static uma_zone_t thread_zone;
  71
  72 TAILQ_HEAD(, thread) zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
  73 static struct mtx zombie_lock;
  74 MTX_SYSINIT(zombie_lock, &zombie_lock, "zombie lock", MTX_SPIN);
  75
  76 static void thread_zombie(struct thread *);
  77
  78 struct mtx tid_lock;
  79 static struct unrhdr *tid_unrhdr;
  80
  81 /*
  82  * Prepare a thread for use.
  83  */
  84 static int
  85 thread_ctor(void *mem, int size, void *arg, int flags)
  86 {
  87         struct thread   *td;
  88
  89         td = (struct thread *)mem;
  90         td->td_state = TDS_INACTIVE;
  91         td->td_oncpu = NOCPU;
  92
  93         td->td_tid = alloc_unr(tid_unrhdr);
  94         td->td_syscalls = 0;
  95
  96         /*
  97          * Note that td_critnest begins life as 1 because the thread is not
  98          * running and is thereby implicitly waiting to be on the receiving
  99          * end of a context switch.
 100          */
 101         td->td_critnest = 1;
 102         EVENTHANDLER_INVOKE(thread_ctor, td);
 103 #ifdef AUDIT
 104         audit_thread_alloc(td);
 105 #endif
 106         umtx_thread_alloc(td);
 107         return (0);
 108 }
 109
 110 /*
 111  * Reclaim a thread after use.
 112  */
 113 static void
 114 thread_dtor(void *mem, int size, void *arg)
 115 {
 116         struct thread *td;
 117
 118         td = (struct thread *)mem;
 119
 120 #ifdef INVARIANTS
 121         /* Verify that this thread is in a safe state to free. */
 122         switch (td->td_state) {
 123         case TDS_INHIBITED:
 124         case TDS_RUNNING:
 125         case TDS_CAN_RUN:
 126         case TDS_RUNQ:
 127                 /*
 128                  * We must never unlink a thread that is in one of
 129                  * these states, because it is currently active.
 130                  */
 131                 panic("bad state for thread unlinking");
 132                 /* NOTREACHED */
 133         case TDS_INACTIVE:
 134                 break;
 135         default:
 136                 panic("bad thread state");
 137                 /* NOTREACHED */
 138         }
 139 #endif
 140 #ifdef AUDIT
 141         audit_thread_free(td);
 142 #endif
 143         /* Free all OSD associated to this thread. */
 144         osd_thread_exit(td);
 145
 146         EVENTHANDLER_INVOKE(thread_dtor, td);
 147         free_unr(tid_unrhdr, td->td_tid);
 148 }
 149
 150 /*
 151  * Initialize type-stable parts of a thread (when newly created).
 152  */
 153 static int
 154 thread_init(void *mem, int size, int flags)
 155 {
 156         struct thread *td;
 157
 158         td = (struct thread *)mem;
 159
 160         td->td_sleepqueue = sleepq_alloc();
 161         td->td_turnstile = turnstile_alloc();
 162         td->td_vp_reserv = 0;
 163         EVENTHANDLER_INVOKE(thread_init, td);
 164         td->td_sched = (struct td_sched *)&td[1];
 165         umtx_thread_init(td);
 166         td->td_kstack = 0;
 167         return (0);
 168 }
 169
 170 /*
 171  * Tear down type-stable parts of a thread (just before being discarded).
 172  */
 173 static void
 174 thread_fini(void *mem, int size)
 175 {
 176         struct thread *td;
 177
 178         td = (struct thread *)mem;
 179         EVENTHANDLER_INVOKE(thread_fini, td);
 180         turnstile_free(td->td_turnstile);
 181         sleepq_free(td->td_sleepqueue);
 182         umtx_thread_fini(td);
 183         seltdfini(td);
 184 }
 185
 186 /*
 187  * For a newly created process,
 188  * link up all the structures and its initial threads etc.
 189  * called from:
 190  * {arch}/{arch}/machdep.c   ia64_init(), init386() etc.
 191  * proc_dtor() (should go away)
 192  * proc_init()
 193  */
 194 void
 195 proc_linkup0(struct proc *p, struct thread *td)
 196 {
 197         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
 198         proc_linkup(p, td);
 199 }
 200
 201 void
 202 proc_linkup(struct proc *p, struct thread *td)
 203 {
 204
 205         sigqueue_init(&p->p_sigqueue, p);
 206         p->p_ksi = ksiginfo_alloc(1);
 207         if (p->p_ksi != NULL) {
 208                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
 209                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
 210         }
 211         LIST_INIT(&p->p_mqnotifier);
 212         p->p_numthreads = 0;
 213         thread_link(td, p);
 214 }
 215
 216 /*
 217  * Initialize global thread allocation resources.
 218  */
 219 void
 220 threadinit(void)
 221 {
 222
 223         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
 224         /* leave one number for thread0 */
 225         tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
 226
 227         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
 228             thread_ctor, thread_dtor, thread_init, thread_fini,
 229             16 - 1, 0);
 230 }
 231
 232 /*
 233  * Place an unused thread on the zombie list.
 234  * Use the slpq as that must be unused by now.
 235  */
 236 void
 237 thread_zombie(struct thread *td)
 238 {
 239         mtx_lock_spin(&zombie_lock);
 240         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
 241         mtx_unlock_spin(&zombie_lock);
 242 }
 243
 244 /*
 245  * Release a thread that has exited after cpu_throw().
 246  */
 247 void
 248 thread_stash(struct thread *td)
 249 {
 250         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
 251         thread_zombie(td);
 252 }
 253
 254 /*
 255  * Reap zombie resources.
 256  */
 257 void
 258 thread_reap(void)
 259 {
 260         struct thread *td_first, *td_next;
 261
 262         /*
 263          * Don't even bother to lock if none at this instant,
 264          * we really don't care about the next instant..
 265          */
 266         if (!TAILQ_EMPTY(&zombie_threads)) {
 267                 mtx_lock_spin(&zombie_lock);
 268                 td_first = TAILQ_FIRST(&zombie_threads);
 269                 if (td_first)
 270                         TAILQ_INIT(&zombie_threads);
 271                 mtx_unlock_spin(&zombie_lock);
 272                 while (td_first) {
 273                         td_next = TAILQ_NEXT(td_first, td_slpq);
 274                         if (td_first->td_ucred)
 275                                 crfree(td_first->td_ucred);
 276                         thread_free(td_first);
 277                         td_first = td_next;
 278                 }
 279         }
 280 }
 281
 282 /*
 283  * Allocate a thread.
 284  */
 285 struct thread *
 286 thread_alloc(int pages)
 287 {
 288         struct thread *td;
 289
 290         thread_reap(); /* check if any zombies to get */
 291
 292         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
 293         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
 294         if (!vm_thread_new(td, pages)) {
 295                 uma_zfree(thread_zone, td);
 296                 return (NULL);
 297         }
 298         cpu_thread_alloc(td);
 299         return (td);
 300 }
 301
 302 int
 303 thread_alloc_stack(struct thread *td, int pages)
 304 {
 305
 306         KASSERT(td->td_kstack == 0,
 307             ("thread_alloc_stack called on a thread with kstack"));
 308         if (!vm_thread_new(td, pages))
 309                 return (0);
 310         cpu_thread_alloc(td);
 311         return (1);
 312 }
 313
 314 /*
 315  * Deallocate a thread.
 316  */
 317 void
 318 thread_free(struct thread *td)
 319 {
 320
 321         lock_profile_thread_exit(td);
 322         if (td->td_cpuset)
 323                 cpuset_rel(td->td_cpuset);
 324         td->td_cpuset = NULL;
 325         cpu_thread_free(td);
 326         if (td->td_kstack != 0)
 327                 vm_thread_dispose(td);
 328         uma_zfree(thread_zone, td);
 329 }
 330
 331 /*
 332  * Discard the current thread and exit from its context.
 333  * Always called with scheduler locked.
 334  *
 335  * Because we can't free a thread while we're operating under its context,
 336  * push the current thread into our CPU's deadthread holder. This means
 337  * we needn't worry about someone else grabbing our context before we
 338  * do a cpu_throw().
 339  */
 340 void
 341 thread_exit(void)
 342 {
 343         uint64_t runtime, new_switchtime;
 344         struct thread *td;
 345         struct thread *td2;
 346         struct proc *p;
 347         int wakeup_swapper;
 348
 349         td = curthread;
 350         p = td->td_proc;
 351
 352         PROC_SLOCK_ASSERT(p, MA_OWNED);
 353         mtx_assert(&Giant, MA_NOTOWNED);
 354
 355         PROC_LOCK_ASSERT(p, MA_OWNED);
 356         KASSERT(p != NULL, ("thread exiting without a process"));
 357         CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
 358             (long)p->p_pid, td->td_name);
 359         KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
 360
 361 #ifdef AUDIT
 362         AUDIT_SYSCALL_EXIT(0, td);
 363 #endif
 364         umtx_thread_exit(td);
 365         /*
 366          * drop FPU & debug register state storage, or any other
 367          * architecture specific resources that
 368          * would not be on a new untouched process.
 369          */
 370         cpu_thread_exit(td);    /* XXXSMP */
 371
 372         /*
 373          * The last thread is left attached to the process
 374          * So that the whole bundle gets recycled. Skip
 375          * all this stuff if we never had threads.
 376          * EXIT clears all sign of other threads when
 377          * it goes to single threading, so the last thread always
 378          * takes the short path.
 379          */
 380         if (p->p_flag & P_HADTHREADS) {
 381                 if (p->p_numthreads > 1) {
 382                         thread_unlink(td);
 383                         td2 = FIRST_THREAD_IN_PROC(p);
 384                         sched_exit_thread(td2, td);
 385
 386                         /*
 387                          * The test below is NOT true if we are the
 388                          * sole exiting thread. P_STOPPED_SINGLE is unset
 389                          * in exit1() after it is the only survivor.
 390                          */
 391                         if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 392                                 if (p->p_numthreads == p->p_suspcount) {
 393                                         thread_lock(p->p_singlethread);
 394                                         wakeup_swapper = thread_unsuspend_one(
 395                                                 p->p_singlethread);
 396                                         thread_unlock(p->p_singlethread);
 397                                         if (wakeup_swapper)
 398                                                 kick_proc0();
 399                                 }
 400                         }
 401
 402                         atomic_add_int(&td->td_proc->p_exitthreads, 1);
 403                         PCPU_SET(deadthread, td);
 404                 } else {
 405                         /*
 406                          * The last thread is exiting.. but not through exit()
 407                          */
 408                         panic ("thread_exit: Last thread exiting on its own");
 409                 }
 410         }
 411 #ifdef  HWPMC_HOOKS
 412         /*
 413          * If this thread is part of a process that is being tracked by hwpmc(4),
 414          * inform the module of the thread's impending exit.
 415          */
 416         if (PMC_PROC_IS_USING_PMCS(td->td_proc))
 417                 PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
 418 #endif
 419         PROC_UNLOCK(p);
 420
 421         /* Do the same timestamp bookkeeping that mi_switch() would do. */
 422         new_switchtime = cpu_ticks();
 423         runtime = new_switchtime - PCPU_GET(switchtime);
 424         td->td_runtime += runtime;
 425         td->td_incruntime += runtime;
 426         PCPU_SET(switchtime, new_switchtime);
 427         PCPU_SET(switchticks, ticks);
 428         PCPU_INC(cnt.v_swtch);
 429
 430         /* Save our resource usage in our process. */
 431         td->td_ru.ru_nvcsw++;
 432         ruxagg(p, td);
 433         rucollect(&p->p_ru, &td->td_ru);
 434
 435         thread_lock(td);
 436         PROC_SUNLOCK(p);
 437         td->td_state = TDS_INACTIVE;
 438 #ifdef WITNESS
 439         witness_thread_exit(td);
 440 #endif
 441         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
 442         sched_throw(td);
 443         panic("I'm a teapot!");
 444         /* NOTREACHED */
 445 }
 446
 447 /*
 448  * Do any thread specific cleanups that may be needed in wait()
 449  * called with Giant, proc and schedlock not held.
 450  */
 451 void
 452 thread_wait(struct proc *p)
 453 {
 454         struct thread *td;
 455
 456         mtx_assert(&Giant, MA_NOTOWNED);
 457         KASSERT((p->p_numthreads == 1), ("Multiple threads in wait1()"));
 458         td = FIRST_THREAD_IN_PROC(p);
 459         /* Lock the last thread so we spin until it exits cpu_throw(). */
 460         thread_lock(td);
 461         thread_unlock(td);
 462         /* Wait for any remaining threads to exit cpu_throw(). */
 463         while (p->p_exitthreads)
 464                 sched_relinquish(curthread);
 465         lock_profile_thread_exit(td);
 466         cpuset_rel(td->td_cpuset);
 467         td->td_cpuset = NULL;
 468         cpu_thread_clean(td);
 469         crfree(td->td_ucred);
 470         thread_reap();  /* check for zombie threads etc. */
 471 }
 472
 473 /*
 474  * Link a thread to a process.
 475  * set up anything that needs to be initialized for it to
 476  * be used by the process.
 477  */
 478 void
 479 thread_link(struct thread *td, struct proc *p)
 480 {
 481
 482         /*
 483          * XXX This can't be enabled because it's called for proc0 before
 484          * its lock has been created.
 485          * PROC_LOCK_ASSERT(p, MA_OWNED);
 486          */
 487         td->td_state    = TDS_INACTIVE;
 488         td->td_proc     = p;
 489         td->td_flags    = TDF_INMEM;
 490
 491         LIST_INIT(&td->td_contested);
 492         LIST_INIT(&td->td_lprof[0]);
 493         LIST_INIT(&td->td_lprof[1]);
 494         sigqueue_init(&td->td_sigqueue, p);
 495         callout_init(&td->td_slpcallout, CALLOUT_MPSAFE);
 496         TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
 497         p->p_numthreads++;
 498 }
 499
 500 /*
 501  * Convert a process with one thread to an unthreaded process.
 502  */
 503 void
 504 thread_unthread(struct thread *td)
 505 {
 506         struct proc *p = td->td_proc;
 507
 508         KASSERT((p->p_numthreads == 1), ("Unthreading with >1 threads"));
 509         p->p_flag &= ~P_HADTHREADS;
 510 }
 511
 512 /*
 513  * Called from:
 514  *  thread_exit()
 515  */
 516 void
 517 thread_unlink(struct thread *td)
 518 {
 519         struct proc *p = td->td_proc;
 520
 521         PROC_LOCK_ASSERT(p, MA_OWNED);
 522         TAILQ_REMOVE(&p->p_threads, td, td_plist);
 523         p->p_numthreads--;
 524         /* could clear a few other things here */
 525         /* Must  NOT clear links to proc! */
 526 }
 527
 528 static int
 529 calc_remaining(struct proc *p, int mode)
 530 {
 531         int remaining;
 532
 533         PROC_LOCK_ASSERT(p, MA_OWNED);
 534         PROC_SLOCK_ASSERT(p, MA_OWNED);
 535         if (mode == SINGLE_EXIT)
 536                 remaining = p->p_numthreads;
 537         else if (mode == SINGLE_BOUNDARY)
 538                 remaining = p->p_numthreads - p->p_boundary_count;
 539         else if (mode == SINGLE_NO_EXIT)
 540                 remaining = p->p_numthreads - p->p_suspcount;
 541         else
 542                 panic("calc_remaining: wrong mode %d", mode);
 543         return (remaining);
 544 }
 545
 546 /*
 547  * Enforce single-threading.
 548  *
 549  * Returns 1 if the caller must abort (another thread is waiting to
 550  * exit the process or similar). Process is locked!
 551  * Returns 0 when you are successfully the only thread running.
 552  * A process has successfully single threaded in the suspend mode when
 553  * There are no threads in user mode. Threads in the kernel must be
 554  * allowed to continue until they get to the user boundary. They may even
 555  * copy out their return values and data before suspending. They may however be
 556  * accelerated in reaching the user boundary as we will wake up
 557  * any sleeping threads that are interruptable. (PCATCH).
 558  */
 559 int
 560 thread_single(int mode)
 561 {
 562         struct thread *td;
 563         struct thread *td2;
 564         struct proc *p;
 565         int remaining, wakeup_swapper;
 566
 567         td = curthread;
 568         p = td->td_proc;
 569         mtx_assert(&Giant, MA_NOTOWNED);
 570         PROC_LOCK_ASSERT(p, MA_OWNED);
 571         KASSERT((td != NULL), ("curthread is NULL"));
 572
 573         if ((p->p_flag & P_HADTHREADS) == 0)
 574                 return (0);
 575
 576         /* Is someone already single threading? */
 577         if (p->p_singlethread != NULL && p->p_singlethread != td)
 578                 return (1);
 579
 580         if (mode == SINGLE_EXIT) {
 581                 p->p_flag |= P_SINGLE_EXIT;
 582                 p->p_flag &= ~P_SINGLE_BOUNDARY;
 583         } else {
 584                 p->p_flag &= ~P_SINGLE_EXIT;
 585                 if (mode == SINGLE_BOUNDARY)
 586                         p->p_flag |= P_SINGLE_BOUNDARY;
 587                 else
 588                         p->p_flag &= ~P_SINGLE_BOUNDARY;
 589         }
 590         p->p_flag |= P_STOPPED_SINGLE;
 591         PROC_SLOCK(p);
 592         p->p_singlethread = td;
 593         remaining = calc_remaining(p, mode);
 594         while (remaining != 1) {
 595                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
 596                         goto stopme;
 597                 wakeup_swapper = 0;
 598                 FOREACH_THREAD_IN_PROC(p, td2) {
 599                         if (td2 == td)
 600                                 continue;
 601                         thread_lock(td2);
 602                         td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
 603                         if (TD_IS_INHIBITED(td2)) {
 604                                 switch (mode) {
 605                                 case SINGLE_EXIT:
 606                                         if (TD_IS_SUSPENDED(td2))
 607                                                 wakeup_swapper |=
 608                                                     thread_unsuspend_one(td2);
 609                                         if (TD_ON_SLEEPQ(td2) &&
 610                                             (td2->td_flags & TDF_SINTR))
 611                                                 wakeup_swapper |=
 612                                                     sleepq_abort(td2, EINTR);
 613                                         break;
 614                                 case SINGLE_BOUNDARY:
 615                                         if (TD_IS_SUSPENDED(td2) &&
 616                                             !(td2->td_flags & TDF_BOUNDARY))
 617                                                 wakeup_swapper |=
 618                                                     thread_unsuspend_one(td2);
 619                                         if (TD_ON_SLEEPQ(td2) &&
 620                                             (td2->td_flags & TDF_SINTR))
 621                                                 wakeup_swapper |=
 622                                                     sleepq_abort(td2, ERESTART);
 623                                         break;
 624                                 case SINGLE_NO_EXIT:
 625                                         if (TD_IS_SUSPENDED(td2) &&
 626                                             !(td2->td_flags & TDF_BOUNDARY))
 627                                                 wakeup_swapper |=
 628                                                     thread_unsuspend_one(td2);
 629                                         if (TD_ON_SLEEPQ(td2) &&
 630                                             (td2->td_flags & TDF_SINTR))
 631                                                 wakeup_swapper |=
 632                                                     sleepq_abort(td2, ERESTART);
 633                                         break;
 634                                 default:
 635                                         break;
 636                                 }
 637                         }
 638 #ifdef SMP
 639                         else if (TD_IS_RUNNING(td2) && td != td2) {
 640                                 forward_signal(td2);
 641                         }
 642 #endif
 643                         thread_unlock(td2);
 644                 }
 645                 if (wakeup_swapper)
 646                         kick_proc0();
 647                 remaining = calc_remaining(p, mode);
 648
 649                 /*
 650                  * Maybe we suspended some threads.. was it enough?
 651                  */
 652                 if (remaining == 1)
 653                         break;
 654
 655 stopme:
 656                 /*
 657                  * Wake us up when everyone else has suspended.
 658                  * In the mean time we suspend as well.
 659                  */
 660                 thread_suspend_switch(td);
 661                 remaining = calc_remaining(p, mode);
 662         }
 663         if (mode == SINGLE_EXIT) {
 664                 /*
 665                  * We have gotten rid of all the other threads and we
 666                  * are about to either exit or exec. In either case,
 667                  * we try our utmost  to revert to being a non-threaded
 668                  * process.
 669                  */
 670                 p->p_singlethread = NULL;
 671                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT);
 672                 thread_unthread(td);
 673         }
 674         PROC_SUNLOCK(p);
 675         return (0);
 676 }
 677
 678 /*
 679  * Called in from locations that can safely check to see
 680  * whether we have to suspend or at least throttle for a
 681  * single-thread event (e.g. fork).
 682  *
 683  * Such locations include userret().
 684  * If the "return_instead" argument is non zero, the thread must be able to
 685  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
 686  *
 687  * The 'return_instead' argument tells the function if it may do a
 688  * thread_exit() or suspend, or whether the caller must abort and back
 689  * out instead.
 690  *
 691  * If the thread that set the single_threading request has set the
 692  * P_SINGLE_EXIT bit in the process flags then this call will never return
 693  * if 'return_instead' is false, but will exit.
 694  *
 695  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
 696  *---------------+--------------------+---------------------
 697  *       0       | returns 0          |   returns 0 or 1
 698  *               | when ST ends       |   immediatly
 699  *---------------+--------------------+---------------------
 700  *       1       | thread exits       |   returns 1
 701  *               |                    |  immediatly
 702  * 0 = thread_exit() or suspension ok,
 703  * other = return error instead of stopping the thread.
 704  *
 705  * While a full suspension is under effect, even a single threading
 706  * thread would be suspended if it made this call (but it shouldn't).
 707  * This call should only be made from places where
 708  * thread_exit() would be safe as that may be the outcome unless
 709  * return_instead is set.
 710  */
 711 int
 712 thread_suspend_check(int return_instead)
 713 {
 714         struct thread *td;
 715         struct proc *p;
 716         int wakeup_swapper;
 717
 718         td = curthread;
 719         p = td->td_proc;
 720         mtx_assert(&Giant, MA_NOTOWNED);
 721         PROC_LOCK_ASSERT(p, MA_OWNED);
 722         while (P_SHOULDSTOP(p) ||
 723               ((p->p_flag & P_TRACED) && (td->td_dbgflags & TDB_SUSPEND))) {
 724                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 725                         KASSERT(p->p_singlethread != NULL,
 726                             ("singlethread not set"));
 727                         /*
 728                          * The only suspension in action is a
 729                          * single-threading. Single threader need not stop.
 730                          * XXX Should be safe to access unlocked
 731                          * as it can only be set to be true by us.
 732                          */
 733                         if (p->p_singlethread == td)
 734                                 return (0);     /* Exempt from stopping. */
 735                 }
 736                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
 737                         return (EINTR);
 738
 739                 /* Should we goto user boundary if we didn't come from there? */
 740                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
 741                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
 742                         return (ERESTART);
 743
 744                 /*
 745                  * Ignore suspend requests for stop signals if they
 746                  * are deferred.
 747                  */
 748                 if (P_SHOULDSTOP(p) == P_STOPPED_SIG &&
 749                     td->td_flags & TDF_SBDRY) {
 750                         KASSERT(return_instead,
 751                             ("TDF_SBDRY set for unsafe thread_suspend_check"));
 752                         return (0);
 753                 }
 754
 755                 /* If thread will exit, flush its pending signals */
 756                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td))
 757                         sigqueue_flush(&td->td_sigqueue);
 758
 759                 PROC_SLOCK(p);
 760                 thread_stopped(p);
 761                 /*
 762                  * If the process is waiting for us to exit,
 763                  * this thread should just suicide.
 764                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
 765                  */
 766                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td))
 767                         thread_exit();
 768                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 769                         if (p->p_numthreads == p->p_suspcount + 1) {
 770                                 thread_lock(p->p_singlethread);
 771                                 wakeup_swapper =
 772                                     thread_unsuspend_one(p->p_singlethread);
 773                                 thread_unlock(p->p_singlethread);
 774                                 if (wakeup_swapper)
 775                                         kick_proc0();
 776                         }
 777                 }
 778                 PROC_UNLOCK(p);
 779                 thread_lock(td);
 780                 /*
 781                  * When a thread suspends, it just
 782                  * gets taken off all queues.
 783                  */
 784                 thread_suspend_one(td);
 785                 if (return_instead == 0) {
 786                         p->p_boundary_count++;
 787                         td->td_flags |= TDF_BOUNDARY;
 788                 }
 789                 PROC_SUNLOCK(p);
 790                 mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
 791                 if (return_instead == 0)
 792                         td->td_flags &= ~TDF_BOUNDARY;
 793                 thread_unlock(td);
 794                 PROC_LOCK(p);
 795                 if (return_instead == 0) {
 796                         PROC_SLOCK(p);
 797                         p->p_boundary_count--;
 798                         PROC_SUNLOCK(p);
 799                 }
 800         }
 801         return (0);
 802 }
 803
 804 void
 805 thread_suspend_switch(struct thread *td)
 806 {
 807         struct proc *p;
 808
 809         p = td->td_proc;
 810         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
 811         PROC_LOCK_ASSERT(p, MA_OWNED);
 812         PROC_SLOCK_ASSERT(p, MA_OWNED);
 813         /*
 814          * We implement thread_suspend_one in stages here to avoid
 815          * dropping the proc lock while the thread lock is owned.
 816          */
 817         thread_stopped(p);
 818         p->p_suspcount++;
 819         PROC_UNLOCK(p);
 820         thread_lock(td);
 821         td->td_flags &= ~TDF_NEEDSUSPCHK;
 822         TD_SET_SUSPENDED(td);
 823         sched_sleep(td, 0);
 824         PROC_SUNLOCK(p);
 825         DROP_GIANT();
 826         mi_switch(SW_VOL | SWT_SUSPEND, NULL);
 827         thread_unlock(td);
 828         PICKUP_GIANT();
 829         PROC_LOCK(p);
 830         PROC_SLOCK(p);
 831 }
 832
 833 void
 834 thread_suspend_one(struct thread *td)
 835 {
 836         struct proc *p = td->td_proc;
 837
 838         PROC_SLOCK_ASSERT(p, MA_OWNED);
 839         THREAD_LOCK_ASSERT(td, MA_OWNED);
 840         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
 841         p->p_suspcount++;
 842         td->td_flags &= ~TDF_NEEDSUSPCHK;
 843         TD_SET_SUSPENDED(td);
 844         sched_sleep(td, 0);
 845 }
 846
 847 int
 848 thread_unsuspend_one(struct thread *td)
 849 {
 850         struct proc *p = td->td_proc;
 851
 852         PROC_SLOCK_ASSERT(p, MA_OWNED);
 853         THREAD_LOCK_ASSERT(td, MA_OWNED);
 854         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
 855         TD_CLR_SUSPENDED(td);
 856         p->p_suspcount--;
 857         return (setrunnable(td));
 858 }
 859
 860 /*
 861  * Allow all threads blocked by single threading to continue running.
 862  */
 863 void
 864 thread_unsuspend(struct proc *p)
 865 {
 866         struct thread *td;
 867         int wakeup_swapper;
 868
 869         PROC_LOCK_ASSERT(p, MA_OWNED);
 870         PROC_SLOCK_ASSERT(p, MA_OWNED);
 871         wakeup_swapper = 0;
 872         if (!P_SHOULDSTOP(p)) {
 873                 FOREACH_THREAD_IN_PROC(p, td) {
 874                         thread_lock(td);
 875                         if (TD_IS_SUSPENDED(td)) {
 876                                 wakeup_swapper |= thread_unsuspend_one(td);
 877                         }
 878                         thread_unlock(td);
 879                 }
 880         } else if ((P_SHOULDSTOP(p) == P_STOPPED_SINGLE) &&
 881             (p->p_numthreads == p->p_suspcount)) {
 882                 /*
 883                  * Stopping everything also did the job for the single
 884                  * threading request. Now we've downgraded to single-threaded,
 885                  * let it continue.
 886                  */
 887                 thread_lock(p->p_singlethread);
 888                 wakeup_swapper = thread_unsuspend_one(p->p_singlethread);
 889                 thread_unlock(p->p_singlethread);
 890         }
 891         if (wakeup_swapper)
 892                 kick_proc0();
 893 }
 894
 895 /*
 896  * End the single threading mode..
 897  */
 898 void
 899 thread_single_end(void)
 900 {
 901         struct thread *td;
 902         struct proc *p;
 903         int wakeup_swapper;
 904
 905         td = curthread;
 906         p = td->td_proc;
 907         PROC_LOCK_ASSERT(p, MA_OWNED);
 908         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY);
 909         PROC_SLOCK(p);
 910         p->p_singlethread = NULL;
 911         wakeup_swapper = 0;
 912         /*
 913          * If there are other threads they may now run,
 914          * unless of course there is a blanket 'stop order'
 915          * on the process. The single threader must be allowed
 916          * to continue however as this is a bad place to stop.
 917          */
 918         if ((p->p_numthreads != 1) && (!P_SHOULDSTOP(p))) {
 919                 FOREACH_THREAD_IN_PROC(p, td) {
 920                         thread_lock(td);
 921                         if (TD_IS_SUSPENDED(td)) {
 922                                 wakeup_swapper |= thread_unsuspend_one(td);
 923                         }
 924                         thread_unlock(td);
 925                 }
 926         }
 927         PROC_SUNLOCK(p);
 928         if (wakeup_swapper)
 929                 kick_proc0();
 930 }
 931
 932 struct thread *
 933 thread_find(struct proc *p, lwpid_t tid)
 934 {
 935         struct thread *td;
 936
 937         PROC_LOCK_ASSERT(p, MA_OWNED);
 938         FOREACH_THREAD_IN_PROC(p, td) {
 939                 if (td->td_tid == tid)
 940                         break;
 941         }
 942         return (td);
 943 }