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
  31 #include <sys/cdefs.h>
  32 __FBSDID("$FreeBSD$");
  33
  34 #include <sys/param.h>
  35 #include <sys/systm.h>
  36 #include <sys/kernel.h>
  37 #include <sys/lock.h>
  38 #include <sys/mutex.h>
  39 #include <sys/proc.h>
  40 #include <sys/resourcevar.h>
  41 #include <sys/smp.h>
  42 #include <sys/sysctl.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
  51 #include <security/audit/audit.h>
  52
  53 #include <vm/vm.h>
  54 #include <vm/vm_extern.h>
  55 #include <vm/uma.h>
  56 #include <sys/eventhandler.h>
  57
  58 /*
  59  * thread related storage.
  60  */
  61 static uma_zone_t thread_zone;
  62
  63 SYSCTL_NODE(_kern, OID_AUTO, threads, CTLFLAG_RW, 0, "thread allocation");
  64
  65 int max_threads_per_proc = 1500;
  66 SYSCTL_INT(_kern_threads, OID_AUTO, max_threads_per_proc, CTLFLAG_RW,
  67         &max_threads_per_proc, 0, "Limit on threads per proc");
  68
  69 int max_threads_hits;
  70 SYSCTL_INT(_kern_threads, OID_AUTO, max_threads_hits, CTLFLAG_RD,
  71         &max_threads_hits, 0, "");
  72
  73 TAILQ_HEAD(, thread) zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
  74 static struct mtx zombie_lock;
  75 MTX_SYSINIT(zombie_lock, &zombie_lock, "zombie lock", MTX_SPIN);
  76
  77 static void thread_zombie(struct thread *);
  78
  79 struct mtx tid_lock;
  80 static struct unrhdr *tid_unrhdr;
  81
  82 /*
  83  * Prepare a thread for use.
  84  */
  85 static int
  86 thread_ctor(void *mem, int size, void *arg, int flags)
  87 {
  88         struct thread   *td;
  89
  90         td = (struct thread *)mem;
  91         td->td_state = TDS_INACTIVE;
  92         td->td_oncpu = NOCPU;
  93
  94         td->td_tid = alloc_unr(tid_unrhdr);
  95         td->td_syscalls = 0;
  96
  97         /*
  98          * Note that td_critnest begins life as 1 because the thread is not
  99          * running and is thereby implicitly waiting to be on the receiving
 100          * end of a context switch.
 101          */
 102         td->td_critnest = 1;
 103         EVENTHANDLER_INVOKE(thread_ctor, td);
 104 #ifdef AUDIT
 105         audit_thread_alloc(td);
 106 #endif
 107         umtx_thread_alloc(td);
 108         return (0);
 109 }
 110
 111 /*
 112  * Reclaim a thread after use.
 113  */
 114 static void
 115 thread_dtor(void *mem, int size, void *arg)
 116 {
 117         struct thread *td;
 118
 119         td = (struct thread *)mem;
 120
 121 #ifdef INVARIANTS
 122         /* Verify that this thread is in a safe state to free. */
 123         switch (td->td_state) {
 124         case TDS_INHIBITED:
 125         case TDS_RUNNING:
 126         case TDS_CAN_RUN:
 127         case TDS_RUNQ:
 128                 /*
 129                  * We must never unlink a thread that is in one of
 130                  * these states, because it is currently active.
 131                  */
 132                 panic("bad state for thread unlinking");
 133                 /* NOTREACHED */
 134         case TDS_INACTIVE:
 135                 break;
 136         default:
 137                 panic("bad thread state");
 138                 /* NOTREACHED */
 139         }
 140 #endif
 141 #ifdef AUDIT
 142         audit_thread_free(td);
 143 #endif
 144         EVENTHANDLER_INVOKE(thread_dtor, td);
 145         free_unr(tid_unrhdr, td->td_tid);
 146 }
 147
 148 /*
 149  * Initialize type-stable parts of a thread (when newly created).
 150  */
 151 static int
 152 thread_init(void *mem, int size, int flags)
 153 {
 154         struct thread *td;
 155
 156         td = (struct thread *)mem;
 157
 158         td->td_sleepqueue = sleepq_alloc();
 159         td->td_turnstile = turnstile_alloc();
 160         EVENTHANDLER_INVOKE(thread_init, td);
 161         td->td_sched = (struct td_sched *)&td[1];
 162         umtx_thread_init(td);
 163         td->td_kstack = 0;
 164         return (0);
 165 }
 166
 167 /*
 168  * Tear down type-stable parts of a thread (just before being discarded).
 169  */
 170 static void
 171 thread_fini(void *mem, int size)
 172 {
 173         struct thread *td;
 174
 175         td = (struct thread *)mem;
 176         EVENTHANDLER_INVOKE(thread_fini, td);
 177         turnstile_free(td->td_turnstile);
 178         sleepq_free(td->td_sleepqueue);
 179         umtx_thread_fini(td);
 180         seltdfini(td);
 181 }
 182
 183 /*
 184  * For a newly created process,
 185  * link up all the structures and its initial threads etc.
 186  * called from:
 187  * {arch}/{arch}/machdep.c   ia64_init(), init386() etc.
 188  * proc_dtor() (should go away)
 189  * proc_init()
 190  */
 191 void
 192 proc_linkup0(struct proc *p, struct thread *td)
 193 {
 194         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
 195         proc_linkup(p, td);
 196 }
 197
 198 void
 199 proc_linkup(struct proc *p, struct thread *td)
 200 {
 201
 202         sigqueue_init(&p->p_sigqueue, p);
 203         p->p_ksi = ksiginfo_alloc(1);
 204         if (p->p_ksi != NULL) {
 205                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
 206                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
 207         }
 208         LIST_INIT(&p->p_mqnotifier);
 209         p->p_numthreads = 0;
 210         thread_link(td, p);
 211 }
 212
 213 /*
 214  * Initialize global thread allocation resources.
 215  */
 216 void
 217 threadinit(void)
 218 {
 219
 220         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
 221         /* leave one number for thread0 */
 222         tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
 223
 224         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
 225             thread_ctor, thread_dtor, thread_init, thread_fini,
 226             16 - 1, 0);
 227 }
 228
 229 /*
 230  * Place an unused thread on the zombie list.
 231  * Use the slpq as that must be unused by now.
 232  */
 233 void
 234 thread_zombie(struct thread *td)
 235 {
 236         mtx_lock_spin(&zombie_lock);
 237         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
 238         mtx_unlock_spin(&zombie_lock);
 239 }
 240
 241 /*
 242  * Release a thread that has exited after cpu_throw().
 243  */
 244 void
 245 thread_stash(struct thread *td)
 246 {
 247         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
 248         thread_zombie(td);
 249 }
 250
 251 /*
 252  * Reap zombie resources.
 253  */
 254 void
 255 thread_reap(void)
 256 {
 257         struct thread *td_first, *td_next;
 258
 259         /*
 260          * Don't even bother to lock if none at this instant,
 261          * we really don't care about the next instant..
 262          */
 263         if (!TAILQ_EMPTY(&zombie_threads)) {
 264                 mtx_lock_spin(&zombie_lock);
 265                 td_first = TAILQ_FIRST(&zombie_threads);
 266                 if (td_first)
 267                         TAILQ_INIT(&zombie_threads);
 268                 mtx_unlock_spin(&zombie_lock);
 269                 while (td_first) {
 270                         td_next = TAILQ_NEXT(td_first, td_slpq);
 271                         if (td_first->td_ucred)
 272                                 crfree(td_first->td_ucred);
 273                         thread_free(td_first);
 274                         td_first = td_next;
 275                 }
 276         }
 277 }
 278
 279 /*
 280  * Allocate a thread.
 281  */
 282 struct thread *
 283 thread_alloc(void)
 284 {
 285         struct thread *td;
 286
 287         thread_reap(); /* check if any zombies to get */
 288
 289         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
 290         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
 291         if (!vm_thread_new(td, 0)) {
 292                 uma_zfree(thread_zone, td);
 293                 return (NULL);
 294         }
 295         cpu_thread_alloc(td);
 296         return (td);
 297 }
 298
 299
 300 /*
 301  * Deallocate a thread.
 302  */
 303 void
 304 thread_free(struct thread *td)
 305 {
 306         if (td->td_cpuset)
 307                 cpuset_rel(td->td_cpuset);
 308         td->td_cpuset = NULL;
 309         cpu_thread_free(td);
 310         if (td->td_altkstack != 0)
 311                 vm_thread_dispose_altkstack(td);
 312         if (td->td_kstack != 0)
 313                 vm_thread_dispose(td);
 314         uma_zfree(thread_zone, td);
 315 }
 316
 317 /*
 318  * Discard the current thread and exit from its context.
 319  * Always called with scheduler locked.
 320  *
 321  * Because we can't free a thread while we're operating under its context,
 322  * push the current thread into our CPU's deadthread holder. This means
 323  * we needn't worry about someone else grabbing our context before we
 324  * do a cpu_throw().
 325  */
 326 void
 327 thread_exit(void)
 328 {
 329         uint64_t new_switchtime;
 330         struct thread *td;
 331         struct thread *td2;
 332         struct proc *p;
 333         int wakeup_swapper;
 334
 335         td = curthread;
 336         p = td->td_proc;
 337
 338         PROC_SLOCK_ASSERT(p, MA_OWNED);
 339         mtx_assert(&Giant, MA_NOTOWNED);
 340
 341         PROC_LOCK_ASSERT(p, MA_OWNED);
 342         KASSERT(p != NULL, ("thread exiting without a process"));
 343         CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
 344             (long)p->p_pid, td->td_name);
 345         KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
 346
 347 #ifdef AUDIT
 348         AUDIT_SYSCALL_EXIT(0, td);
 349 #endif
 350         umtx_thread_exit(td);
 351         /*
 352          * drop FPU & debug register state storage, or any other
 353          * architecture specific resources that
 354          * would not be on a new untouched process.
 355          */
 356         cpu_thread_exit(td);    /* XXXSMP */
 357
 358         /* Do the same timestamp bookkeeping that mi_switch() would do. */
 359         new_switchtime = cpu_ticks();
 360         p->p_rux.rux_runtime += (new_switchtime - PCPU_GET(switchtime));
 361         PCPU_SET(switchtime, new_switchtime);
 362         PCPU_SET(switchticks, ticks);
 363         PCPU_INC(cnt.v_swtch);
 364         /* Save our resource usage in our process. */
 365         td->td_ru.ru_nvcsw++;
 366         rucollect(&p->p_ru, &td->td_ru);
 367         /*
 368          * The last thread is left attached to the process
 369          * So that the whole bundle gets recycled. Skip
 370          * all this stuff if we never had threads.
 371          * EXIT clears all sign of other threads when
 372          * it goes to single threading, so the last thread always
 373          * takes the short path.
 374          */
 375         if (p->p_flag & P_HADTHREADS) {
 376                 if (p->p_numthreads > 1) {
 377                         thread_unlink(td);
 378                         td2 = FIRST_THREAD_IN_PROC(p);
 379                         sched_exit_thread(td2, td);
 380
 381                         /*
 382                          * The test below is NOT true if we are the
 383                          * sole exiting thread. P_STOPPED_SNGL is unset
 384                          * in exit1() after it is the only survivor.
 385                          */
 386                         if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 387                                 if (p->p_numthreads == p->p_suspcount) {
 388                                         thread_lock(p->p_singlethread);
 389                                         wakeup_swapper = thread_unsuspend_one(
 390                                                 p->p_singlethread);
 391                                         thread_unlock(p->p_singlethread);
 392                                         if (wakeup_swapper)
 393                                                 kick_proc0();
 394                                 }
 395                         }
 396
 397                         atomic_add_int(&td->td_proc->p_exitthreads, 1);
 398                         PCPU_SET(deadthread, td);
 399                 } else {
 400                         /*
 401                          * The last thread is exiting.. but not through exit()
 402                          */
 403                         panic ("thread_exit: Last thread exiting on its own");
 404                 }
 405         }
 406         PROC_UNLOCK(p);
 407         thread_lock(td);
 408         /* Save our tick information with both the thread and proc locked */
 409         ruxagg(&p->p_rux, td);
 410         PROC_SUNLOCK(p);
 411         td->td_state = TDS_INACTIVE;
 412 #ifdef WITNESS
 413         witness_thread_exit(td);
 414 #endif
 415         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
 416         sched_throw(td);
 417         panic("I'm a teapot!");
 418         /* NOTREACHED */
 419 }
 420
 421 /*
 422  * Do any thread specific cleanups that may be needed in wait()
 423  * called with Giant, proc and schedlock not held.
 424  */
 425 void
 426 thread_wait(struct proc *p)
 427 {
 428         struct thread *td;
 429
 430         mtx_assert(&Giant, MA_NOTOWNED);
 431         KASSERT((p->p_numthreads == 1), ("Multiple threads in wait1()"));
 432         td = FIRST_THREAD_IN_PROC(p);
 433         /* Lock the last thread so we spin until it exits cpu_throw(). */
 434         thread_lock(td);
 435         thread_unlock(td);
 436         /* Wait for any remaining threads to exit cpu_throw(). */
 437         while (p->p_exitthreads)
 438                 sched_relinquish(curthread);
 439         cpuset_rel(td->td_cpuset);
 440         td->td_cpuset = NULL;
 441         cpu_thread_clean(td);
 442         crfree(td->td_ucred);
 443         thread_reap();  /* check for zombie threads etc. */
 444 }
 445
 446 /*
 447  * Link a thread to a process.
 448  * set up anything that needs to be initialized for it to
 449  * be used by the process.
 450  */
 451 void
 452 thread_link(struct thread *td, struct proc *p)
 453 {
 454
 455         /*
 456          * XXX This can't be enabled because it's called for proc0 before
 457          * its lock has been created.
 458          * PROC_LOCK_ASSERT(p, MA_OWNED);
 459          */
 460         td->td_state    = TDS_INACTIVE;
 461         td->td_proc     = p;
 462         td->td_flags    = TDF_INMEM;
 463
 464         LIST_INIT(&td->td_contested);
 465         LIST_INIT(&td->td_lprof[0]);
 466         LIST_INIT(&td->td_lprof[1]);
 467         sigqueue_init(&td->td_sigqueue, p);
 468         callout_init(&td->td_slpcallout, CALLOUT_MPSAFE);
 469         TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
 470         p->p_numthreads++;
 471 }
 472
 473 /*
 474  * Convert a process with one thread to an unthreaded process.
 475  */
 476 void
 477 thread_unthread(struct thread *td)
 478 {
 479         struct proc *p = td->td_proc;
 480
 481         KASSERT((p->p_numthreads == 1), ("Unthreading with >1 threads"));
 482         p->p_flag &= ~P_HADTHREADS;
 483 }
 484
 485 /*
 486  * Called from:
 487  *  thread_exit()
 488  */
 489 void
 490 thread_unlink(struct thread *td)
 491 {
 492         struct proc *p = td->td_proc;
 493
 494         PROC_LOCK_ASSERT(p, MA_OWNED);
 495         TAILQ_REMOVE(&p->p_threads, td, td_plist);
 496         p->p_numthreads--;
 497         /* could clear a few other things here */
 498         /* Must  NOT clear links to proc! */
 499 }
 500
 501 /*
 502  * Enforce single-threading.
 503  *
 504  * Returns 1 if the caller must abort (another thread is waiting to
 505  * exit the process or similar). Process is locked!
 506  * Returns 0 when you are successfully the only thread running.
 507  * A process has successfully single threaded in the suspend mode when
 508  * There are no threads in user mode. Threads in the kernel must be
 509  * allowed to continue until they get to the user boundary. They may even
 510  * copy out their return values and data before suspending. They may however be
 511  * accelerated in reaching the user boundary as we will wake up
 512  * any sleeping threads that are interruptable. (PCATCH).
 513  */
 514 int
 515 thread_single(int mode)
 516 {
 517         struct thread *td;
 518         struct thread *td2;
 519         struct proc *p;
 520         int remaining, wakeup_swapper;
 521
 522         td = curthread;
 523         p = td->td_proc;
 524         mtx_assert(&Giant, MA_NOTOWNED);
 525         PROC_LOCK_ASSERT(p, MA_OWNED);
 526         KASSERT((td != NULL), ("curthread is NULL"));
 527
 528         if ((p->p_flag & P_HADTHREADS) == 0)
 529                 return (0);
 530
 531         /* Is someone already single threading? */
 532         if (p->p_singlethread != NULL && p->p_singlethread != td)
 533                 return (1);
 534
 535         if (mode == SINGLE_EXIT) {
 536                 p->p_flag |= P_SINGLE_EXIT;
 537                 p->p_flag &= ~P_SINGLE_BOUNDARY;
 538         } else {
 539                 p->p_flag &= ~P_SINGLE_EXIT;
 540                 if (mode == SINGLE_BOUNDARY)
 541                         p->p_flag |= P_SINGLE_BOUNDARY;
 542                 else
 543                         p->p_flag &= ~P_SINGLE_BOUNDARY;
 544         }
 545         p->p_flag |= P_STOPPED_SINGLE;
 546         PROC_SLOCK(p);
 547         p->p_singlethread = td;
 548         if (mode == SINGLE_EXIT)
 549                 remaining = p->p_numthreads;
 550         else if (mode == SINGLE_BOUNDARY)
 551                 remaining = p->p_numthreads - p->p_boundary_count;
 552         else
 553                 remaining = p->p_numthreads - p->p_suspcount;
 554         while (remaining != 1) {
 555                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
 556                         goto stopme;
 557                 wakeup_swapper = 0;
 558                 FOREACH_THREAD_IN_PROC(p, td2) {
 559                         if (td2 == td)
 560                                 continue;
 561                         thread_lock(td2);
 562                         td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
 563                         if (TD_IS_INHIBITED(td2)) {
 564                                 switch (mode) {
 565                                 case SINGLE_EXIT:
 566                                         if (TD_IS_SUSPENDED(td2))
 567                                                 wakeup_swapper |=
 568                                                     thread_unsuspend_one(td2);
 569                                         if (TD_ON_SLEEPQ(td2) &&
 570                                             (td2->td_flags & TDF_SINTR))
 571                                                 wakeup_swapper |=
 572                                                     sleepq_abort(td2, EINTR);
 573                                         break;
 574                                 case SINGLE_BOUNDARY:
 575                                         if (TD_IS_SUSPENDED(td2) &&
 576                                             !(td2->td_flags & TDF_BOUNDARY))
 577                                                 wakeup_swapper |=
 578                                                     thread_unsuspend_one(td2);
 579                                         if (TD_ON_SLEEPQ(td2) &&
 580                                             (td2->td_flags & TDF_SINTR))
 581                                                 wakeup_swapper |=
 582                                                     sleepq_abort(td2, ERESTART);
 583                                         break;
 584                                 default:
 585                                         if (TD_IS_SUSPENDED(td2)) {
 586                                                 thread_unlock(td2);
 587                                                 continue;
 588                                         }
 589                                         /*
 590                                          * maybe other inhibited states too?
 591                                          */
 592                                         if ((td2->td_flags & TDF_SINTR) &&
 593                                             (td2->td_inhibitors &
 594                                             (TDI_SLEEPING | TDI_SWAPPED)))
 595                                                 thread_suspend_one(td2);
 596                                         break;
 597                                 }
 598                         }
 599 #ifdef SMP
 600                         else if (TD_IS_RUNNING(td2) && td != td2) {
 601                                 forward_signal(td2);
 602                         }
 603 #endif
 604                         thread_unlock(td2);
 605                 }
 606                 if (wakeup_swapper)
 607                         kick_proc0();
 608                 if (mode == SINGLE_EXIT)
 609                         remaining = p->p_numthreads;
 610                 else if (mode == SINGLE_BOUNDARY)
 611                         remaining = p->p_numthreads - p->p_boundary_count;
 612                 else
 613                         remaining = p->p_numthreads - p->p_suspcount;
 614
 615                 /*
 616                  * Maybe we suspended some threads.. was it enough?
 617                  */
 618                 if (remaining == 1)
 619                         break;
 620
 621 stopme:
 622                 /*
 623                  * Wake us up when everyone else has suspended.
 624                  * In the mean time we suspend as well.
 625                  */
 626                 thread_suspend_switch(td);
 627                 if (mode == SINGLE_EXIT)
 628                         remaining = p->p_numthreads;
 629                 else if (mode == SINGLE_BOUNDARY)
 630                         remaining = p->p_numthreads - p->p_boundary_count;
 631                 else
 632                         remaining = p->p_numthreads - p->p_suspcount;
 633         }
 634         if (mode == SINGLE_EXIT) {
 635                 /*
 636                  * We have gotten rid of all the other threads and we
 637                  * are about to either exit or exec. In either case,
 638                  * we try our utmost  to revert to being a non-threaded
 639                  * process.
 640                  */
 641                 p->p_singlethread = NULL;
 642                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT);
 643                 thread_unthread(td);
 644         }
 645         PROC_SUNLOCK(p);
 646         return (0);
 647 }
 648
 649 /*
 650  * Called in from locations that can safely check to see
 651  * whether we have to suspend or at least throttle for a
 652  * single-thread event (e.g. fork).
 653  *
 654  * Such locations include userret().
 655  * If the "return_instead" argument is non zero, the thread must be able to
 656  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
 657  *
 658  * The 'return_instead' argument tells the function if it may do a
 659  * thread_exit() or suspend, or whether the caller must abort and back
 660  * out instead.
 661  *
 662  * If the thread that set the single_threading request has set the
 663  * P_SINGLE_EXIT bit in the process flags then this call will never return
 664  * if 'return_instead' is false, but will exit.
 665  *
 666  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
 667  *---------------+--------------------+---------------------
 668  *       0       | returns 0          |   returns 0 or 1
 669  *               | when ST ends       |   immediatly
 670  *---------------+--------------------+---------------------
 671  *       1       | thread exits       |   returns 1
 672  *               |                    |  immediatly
 673  * 0 = thread_exit() or suspension ok,
 674  * other = return error instead of stopping the thread.
 675  *
 676  * While a full suspension is under effect, even a single threading
 677  * thread would be suspended if it made this call (but it shouldn't).
 678  * This call should only be made from places where
 679  * thread_exit() would be safe as that may be the outcome unless
 680  * return_instead is set.
 681  */
 682 int
 683 thread_suspend_check(int return_instead)
 684 {
 685         struct thread *td;
 686         struct proc *p;
 687         int wakeup_swapper;
 688
 689         td = curthread;
 690         p = td->td_proc;
 691         mtx_assert(&Giant, MA_NOTOWNED);
 692         PROC_LOCK_ASSERT(p, MA_OWNED);
 693         while (P_SHOULDSTOP(p) ||
 694               ((p->p_flag & P_TRACED) && (td->td_dbgflags & TDB_SUSPEND))) {
 695                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 696                         KASSERT(p->p_singlethread != NULL,
 697                             ("singlethread not set"));
 698                         /*
 699                          * The only suspension in action is a
 700                          * single-threading. Single threader need not stop.
 701                          * XXX Should be safe to access unlocked
 702                          * as it can only be set to be true by us.
 703                          */
 704                         if (p->p_singlethread == td)
 705                                 return (0);     /* Exempt from stopping. */
 706                 }
 707                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
 708                         return (EINTR);
 709
 710                 /* Should we goto user boundary if we didn't come from there? */
 711                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
 712                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
 713                         return (ERESTART);
 714
 715                 /* If thread will exit, flush its pending signals */
 716                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td))
 717                         sigqueue_flush(&td->td_sigqueue);
 718
 719                 PROC_SLOCK(p);
 720                 thread_stopped(p);
 721                 /*
 722                  * If the process is waiting for us to exit,
 723                  * this thread should just suicide.
 724                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
 725                  */
 726                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td))
 727                         thread_exit();
 728                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
 729                         if (p->p_numthreads == p->p_suspcount + 1) {
 730                                 thread_lock(p->p_singlethread);
 731                                 wakeup_swapper =
 732                                     thread_unsuspend_one(p->p_singlethread);
 733                                 thread_unlock(p->p_singlethread);
 734                                 if (wakeup_swapper)
 735                                         kick_proc0();
 736                         }
 737                 }
 738                 PROC_UNLOCK(p);
 739                 thread_lock(td);
 740                 /*
 741                  * When a thread suspends, it just
 742                  * gets taken off all queues.
 743                  */
 744                 thread_suspend_one(td);
 745                 if (return_instead == 0) {
 746                         p->p_boundary_count++;
 747                         td->td_flags |= TDF_BOUNDARY;
 748                 }
 749                 PROC_SUNLOCK(p);
 750                 mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
 751                 if (return_instead == 0)
 752                         td->td_flags &= ~TDF_BOUNDARY;
 753                 thread_unlock(td);
 754                 PROC_LOCK(p);
 755                 if (return_instead == 0)
 756                         p->p_boundary_count--;
 757         }
 758         return (0);
 759 }
 760
 761 void
 762 thread_suspend_switch(struct thread *td)
 763 {
 764         struct proc *p;
 765
 766         p = td->td_proc;
 767         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
 768         PROC_LOCK_ASSERT(p, MA_OWNED);
 769         PROC_SLOCK_ASSERT(p, MA_OWNED);
 770         /*
 771          * We implement thread_suspend_one in stages here to avoid
 772          * dropping the proc lock while the thread lock is owned.
 773          */
 774         thread_stopped(p);
 775         p->p_suspcount++;
 776         PROC_UNLOCK(p);
 777         thread_lock(td);
 778         td->td_flags &= ~TDF_NEEDSUSPCHK;
 779         TD_SET_SUSPENDED(td);
 780         sched_sleep(td, 0);
 781         PROC_SUNLOCK(p);
 782         DROP_GIANT();
 783         mi_switch(SW_VOL | SWT_SUSPEND, NULL);
 784         thread_unlock(td);
 785         PICKUP_GIANT();
 786         PROC_LOCK(p);
 787         PROC_SLOCK(p);
 788 }
 789
 790 void
 791 thread_suspend_one(struct thread *td)
 792 {
 793         struct proc *p = td->td_proc;
 794
 795         PROC_SLOCK_ASSERT(p, MA_OWNED);
 796         THREAD_LOCK_ASSERT(td, MA_OWNED);
 797         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
 798         p->p_suspcount++;
 799         td->td_flags &= ~TDF_NEEDSUSPCHK;
 800         TD_SET_SUSPENDED(td);
 801         sched_sleep(td, 0);
 802 }
 803
 804 int
 805 thread_unsuspend_one(struct thread *td)
 806 {
 807         struct proc *p = td->td_proc;
 808
 809         PROC_SLOCK_ASSERT(p, MA_OWNED);
 810         THREAD_LOCK_ASSERT(td, MA_OWNED);
 811         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
 812         TD_CLR_SUSPENDED(td);
 813         p->p_suspcount--;
 814         return (setrunnable(td));
 815 }
 816
 817 /*
 818  * Allow all threads blocked by single threading to continue running.
 819  */
 820 void
 821 thread_unsuspend(struct proc *p)
 822 {
 823         struct thread *td;
 824         int wakeup_swapper;
 825
 826         PROC_LOCK_ASSERT(p, MA_OWNED);
 827         PROC_SLOCK_ASSERT(p, MA_OWNED);
 828         wakeup_swapper = 0;
 829         if (!P_SHOULDSTOP(p)) {
 830                 FOREACH_THREAD_IN_PROC(p, td) {
 831                         thread_lock(td);
 832                         if (TD_IS_SUSPENDED(td)) {
 833                                 wakeup_swapper |= thread_unsuspend_one(td);
 834                         }
 835                         thread_unlock(td);
 836                 }
 837         } else if ((P_SHOULDSTOP(p) == P_STOPPED_SINGLE) &&
 838             (p->p_numthreads == p->p_suspcount)) {
 839                 /*
 840                  * Stopping everything also did the job for the single
 841                  * threading request. Now we've downgraded to single-threaded,
 842                  * let it continue.
 843                  */
 844                 thread_lock(p->p_singlethread);
 845                 wakeup_swapper = thread_unsuspend_one(p->p_singlethread);
 846                 thread_unlock(p->p_singlethread);
 847         }
 848         if (wakeup_swapper)
 849                 kick_proc0();
 850 }
 851
 852 /*
 853  * End the single threading mode..
 854  */
 855 void
 856 thread_single_end(void)
 857 {
 858         struct thread *td;
 859         struct proc *p;
 860         int wakeup_swapper;
 861
 862         td = curthread;
 863         p = td->td_proc;
 864         PROC_LOCK_ASSERT(p, MA_OWNED);
 865         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY);
 866         PROC_SLOCK(p);
 867         p->p_singlethread = NULL;
 868         wakeup_swapper = 0;
 869         /*
 870          * If there are other threads they may now run,
 871          * unless of course there is a blanket 'stop order'
 872          * on the process. The single threader must be allowed
 873          * to continue however as this is a bad place to stop.
 874          */
 875         if ((p->p_numthreads != 1) && (!P_SHOULDSTOP(p))) {
 876                 FOREACH_THREAD_IN_PROC(p, td) {
 877                         thread_lock(td);
 878                         if (TD_IS_SUSPENDED(td)) {
 879                                 wakeup_swapper |= thread_unsuspend_one(td);
 880                         }
 881                         thread_unlock(td);
 882                 }
 883         }
 884         PROC_SUNLOCK(p);
 885         if (wakeup_swapper)
 886                 kick_proc0();
 887 }
 888
 889 struct thread *
 890 thread_find(struct proc *p, lwpid_t tid)
 891 {
 892         struct thread *td;
 893
 894         PROC_LOCK_ASSERT(p, MA_OWNED);
 895         FOREACH_THREAD_IN_PROC(p, td) {
 896                 if (td->td_tid == tid)
 897                         break;
 898         }
 899         return (td);
 900 }