The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_thread.c

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    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: releng/8.3/sys/kern/kern_thread.c 230080 2012-01-13 20:15:49Z jhb $");
   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 }

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