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/8.2/sys/kern/kern_thread.c 208580 2010-05-26 19:26:28Z kib $");
   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/sysctl.h>
   44 #include <sys/sched.h>
   45 #include <sys/sleepqueue.h>
   46 #include <sys/selinfo.h>
   47 #include <sys/turnstile.h>
   48 #include <sys/ktr.h>
   49 #include <sys/umtx.h>
   50 #include <sys/cpuset.h>
   51 #ifdef  HWPMC_HOOKS
   52 #include <sys/pmckern.h>
   53 #endif
   54 
   55 #include <security/audit/audit.h>
   56 
   57 #include <vm/vm.h>
   58 #include <vm/vm_extern.h>
   59 #include <vm/uma.h>
   60 #include <sys/eventhandler.h>
   61 
   62 /*
   63  * thread related storage.
   64  */
   65 static uma_zone_t thread_zone;
   66 
   67 SYSCTL_NODE(_kern, OID_AUTO, threads, CTLFLAG_RW, 0, "thread allocation");
   68 
   69 int max_threads_per_proc = 1500;
   70 SYSCTL_INT(_kern_threads, OID_AUTO, max_threads_per_proc, CTLFLAG_RW,
   71         &max_threads_per_proc, 0, "Limit on threads per proc");
   72 
   73 int max_threads_hits;
   74 SYSCTL_INT(_kern_threads, OID_AUTO, max_threads_hits, CTLFLAG_RD,
   75         &max_threads_hits, 0, "");
   76 
   77 TAILQ_HEAD(, thread) zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
   78 static struct mtx zombie_lock;
   79 MTX_SYSINIT(zombie_lock, &zombie_lock, "zombie lock", MTX_SPIN);
   80 
   81 static void thread_zombie(struct thread *);
   82 
   83 struct mtx tid_lock;
   84 static struct unrhdr *tid_unrhdr;
   85 
   86 /*
   87  * Prepare a thread for use.
   88  */
   89 static int
   90 thread_ctor(void *mem, int size, void *arg, int flags)
   91 {
   92         struct thread   *td;
   93 
   94         td = (struct thread *)mem;
   95         td->td_state = TDS_INACTIVE;
   96         td->td_oncpu = NOCPU;
   97 
   98         td->td_tid = alloc_unr(tid_unrhdr);
   99         td->td_syscalls = 0;
  100 
  101         /*
  102          * Note that td_critnest begins life as 1 because the thread is not
  103          * running and is thereby implicitly waiting to be on the receiving
  104          * end of a context switch.
  105          */
  106         td->td_critnest = 1;
  107         EVENTHANDLER_INVOKE(thread_ctor, td);
  108 #ifdef AUDIT
  109         audit_thread_alloc(td);
  110 #endif
  111         umtx_thread_alloc(td);
  112         return (0);
  113 }
  114 
  115 /*
  116  * Reclaim a thread after use.
  117  */
  118 static void
  119 thread_dtor(void *mem, int size, void *arg)
  120 {
  121         struct thread *td;
  122 
  123         td = (struct thread *)mem;
  124 
  125 #ifdef INVARIANTS
  126         /* Verify that this thread is in a safe state to free. */
  127         switch (td->td_state) {
  128         case TDS_INHIBITED:
  129         case TDS_RUNNING:
  130         case TDS_CAN_RUN:
  131         case TDS_RUNQ:
  132                 /*
  133                  * We must never unlink a thread that is in one of
  134                  * these states, because it is currently active.
  135                  */
  136                 panic("bad state for thread unlinking");
  137                 /* NOTREACHED */
  138         case TDS_INACTIVE:
  139                 break;
  140         default:
  141                 panic("bad thread state");
  142                 /* NOTREACHED */
  143         }
  144 #endif
  145 #ifdef AUDIT
  146         audit_thread_free(td);
  147 #endif
  148         /* Free all OSD associated to this thread. */
  149         osd_thread_exit(td);
  150 
  151         EVENTHANDLER_INVOKE(thread_dtor, td);
  152         free_unr(tid_unrhdr, td->td_tid);
  153 }
  154 
  155 /*
  156  * Initialize type-stable parts of a thread (when newly created).
  157  */
  158 static int
  159 thread_init(void *mem, int size, int flags)
  160 {
  161         struct thread *td;
  162 
  163         td = (struct thread *)mem;
  164 
  165         td->td_sleepqueue = sleepq_alloc();
  166         td->td_turnstile = turnstile_alloc();
  167         EVENTHANDLER_INVOKE(thread_init, td);
  168         td->td_sched = (struct td_sched *)&td[1];
  169         umtx_thread_init(td);
  170         td->td_kstack = 0;
  171         return (0);
  172 }
  173 
  174 /*
  175  * Tear down type-stable parts of a thread (just before being discarded).
  176  */
  177 static void
  178 thread_fini(void *mem, int size)
  179 {
  180         struct thread *td;
  181 
  182         td = (struct thread *)mem;
  183         EVENTHANDLER_INVOKE(thread_fini, td);
  184         turnstile_free(td->td_turnstile);
  185         sleepq_free(td->td_sleepqueue);
  186         umtx_thread_fini(td);
  187         seltdfini(td);
  188 }
  189 
  190 /*
  191  * For a newly created process,
  192  * link up all the structures and its initial threads etc.
  193  * called from:
  194  * {arch}/{arch}/machdep.c   ia64_init(), init386() etc.
  195  * proc_dtor() (should go away)
  196  * proc_init()
  197  */
  198 void
  199 proc_linkup0(struct proc *p, struct thread *td)
  200 {
  201         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
  202         proc_linkup(p, td);
  203 }
  204 
  205 void
  206 proc_linkup(struct proc *p, struct thread *td)
  207 {
  208 
  209         sigqueue_init(&p->p_sigqueue, p);
  210         p->p_ksi = ksiginfo_alloc(1);
  211         if (p->p_ksi != NULL) {
  212                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
  213                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
  214         }
  215         LIST_INIT(&p->p_mqnotifier);
  216         p->p_numthreads = 0;
  217         thread_link(td, p);
  218 }
  219 
  220 /*
  221  * Initialize global thread allocation resources.
  222  */
  223 void
  224 threadinit(void)
  225 {
  226 
  227         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
  228         /* leave one number for thread0 */
  229         tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
  230 
  231         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
  232             thread_ctor, thread_dtor, thread_init, thread_fini,
  233             16 - 1, 0);
  234 }
  235 
  236 /*
  237  * Place an unused thread on the zombie list.
  238  * Use the slpq as that must be unused by now.
  239  */
  240 void
  241 thread_zombie(struct thread *td)
  242 {
  243         mtx_lock_spin(&zombie_lock);
  244         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
  245         mtx_unlock_spin(&zombie_lock);
  246 }
  247 
  248 /*
  249  * Release a thread that has exited after cpu_throw().
  250  */
  251 void
  252 thread_stash(struct thread *td)
  253 {
  254         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
  255         thread_zombie(td);
  256 }
  257 
  258 /*
  259  * Reap zombie resources.
  260  */
  261 void
  262 thread_reap(void)
  263 {
  264         struct thread *td_first, *td_next;
  265 
  266         /*
  267          * Don't even bother to lock if none at this instant,
  268          * we really don't care about the next instant..
  269          */
  270         if (!TAILQ_EMPTY(&zombie_threads)) {
  271                 mtx_lock_spin(&zombie_lock);
  272                 td_first = TAILQ_FIRST(&zombie_threads);
  273                 if (td_first)
  274                         TAILQ_INIT(&zombie_threads);
  275                 mtx_unlock_spin(&zombie_lock);
  276                 while (td_first) {
  277                         td_next = TAILQ_NEXT(td_first, td_slpq);
  278                         if (td_first->td_ucred)
  279                                 crfree(td_first->td_ucred);
  280                         thread_free(td_first);
  281                         td_first = td_next;
  282                 }
  283         }
  284 }
  285 
  286 /*
  287  * Allocate a thread.
  288  */
  289 struct thread *
  290 thread_alloc(int pages)
  291 {
  292         struct thread *td;
  293 
  294         thread_reap(); /* check if any zombies to get */
  295 
  296         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
  297         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
  298         if (!vm_thread_new(td, pages)) {
  299                 uma_zfree(thread_zone, td);
  300                 return (NULL);
  301         }
  302         cpu_thread_alloc(td);
  303         return (td);
  304 }
  305 
  306 int
  307 thread_alloc_stack(struct thread *td, int pages)
  308 {
  309 
  310         KASSERT(td->td_kstack == 0,
  311             ("thread_alloc_stack called on a thread with kstack"));
  312         if (!vm_thread_new(td, pages))
  313                 return (0);
  314         cpu_thread_alloc(td);
  315         return (1);
  316 }
  317 
  318 /*
  319  * Deallocate a thread.
  320  */
  321 void
  322 thread_free(struct thread *td)
  323 {
  324 
  325         lock_profile_thread_exit(td);
  326         if (td->td_cpuset)
  327                 cpuset_rel(td->td_cpuset);
  328         td->td_cpuset = NULL;
  329         cpu_thread_free(td);
  330         if (td->td_kstack != 0)
  331                 vm_thread_dispose(td);
  332         uma_zfree(thread_zone, td);
  333 }
  334 
  335 /*
  336  * Discard the current thread and exit from its context.
  337  * Always called with scheduler locked.
  338  *
  339  * Because we can't free a thread while we're operating under its context,
  340  * push the current thread into our CPU's deadthread holder. This means
  341  * we needn't worry about someone else grabbing our context before we
  342  * do a cpu_throw().
  343  */
  344 void
  345 thread_exit(void)
  346 {
  347         uint64_t new_switchtime;
  348         struct thread *td;
  349         struct thread *td2;
  350         struct proc *p;
  351         int wakeup_swapper;
  352 
  353         td = curthread;
  354         p = td->td_proc;
  355 
  356         PROC_SLOCK_ASSERT(p, MA_OWNED);
  357         mtx_assert(&Giant, MA_NOTOWNED);
  358 
  359         PROC_LOCK_ASSERT(p, MA_OWNED);
  360         KASSERT(p != NULL, ("thread exiting without a process"));
  361         CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
  362             (long)p->p_pid, td->td_name);
  363         KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
  364 
  365 #ifdef AUDIT
  366         AUDIT_SYSCALL_EXIT(0, td);
  367 #endif
  368         umtx_thread_exit(td);
  369         /*
  370          * drop FPU & debug register state storage, or any other
  371          * architecture specific resources that
  372          * would not be on a new untouched process.
  373          */
  374         cpu_thread_exit(td);    /* XXXSMP */
  375 
  376         /* Do the same timestamp bookkeeping that mi_switch() would do. */
  377         new_switchtime = cpu_ticks();
  378         p->p_rux.rux_runtime += (new_switchtime - PCPU_GET(switchtime));
  379         PCPU_SET(switchtime, new_switchtime);
  380         PCPU_SET(switchticks, ticks);
  381         PCPU_INC(cnt.v_swtch);
  382         /* Save our resource usage in our process. */
  383         td->td_ru.ru_nvcsw++;
  384         rucollect(&p->p_ru, &td->td_ru);
  385         /*
  386          * The last thread is left attached to the process
  387          * So that the whole bundle gets recycled. Skip
  388          * all this stuff if we never had threads.
  389          * EXIT clears all sign of other threads when
  390          * it goes to single threading, so the last thread always
  391          * takes the short path.
  392          */
  393         if (p->p_flag & P_HADTHREADS) {
  394                 if (p->p_numthreads > 1) {
  395                         thread_unlink(td);
  396                         td2 = FIRST_THREAD_IN_PROC(p);
  397                         sched_exit_thread(td2, td);
  398 
  399                         /*
  400                          * The test below is NOT true if we are the
  401                          * sole exiting thread. P_STOPPED_SINGLE is unset
  402                          * in exit1() after it is the only survivor.
  403                          */
  404                         if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  405                                 if (p->p_numthreads == p->p_suspcount) {
  406                                         thread_lock(p->p_singlethread);
  407                                         wakeup_swapper = thread_unsuspend_one(
  408                                                 p->p_singlethread);
  409                                         thread_unlock(p->p_singlethread);
  410                                         if (wakeup_swapper)
  411                                                 kick_proc0();
  412                                 }
  413                         }
  414 
  415                         atomic_add_int(&td->td_proc->p_exitthreads, 1);
  416                         PCPU_SET(deadthread, td);
  417                 } else {
  418                         /*
  419                          * The last thread is exiting.. but not through exit()
  420                          */
  421                         panic ("thread_exit: Last thread exiting on its own");
  422                 }
  423         } 
  424 #ifdef  HWPMC_HOOKS
  425         /*
  426          * If this thread is part of a process that is being tracked by hwpmc(4),
  427          * inform the module of the thread's impending exit.
  428          */
  429         if (PMC_PROC_IS_USING_PMCS(td->td_proc))
  430                 PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
  431 #endif
  432         PROC_UNLOCK(p);
  433         ruxagg(p, td);
  434         thread_lock(td);
  435         PROC_SUNLOCK(p);
  436         td->td_state = TDS_INACTIVE;
  437 #ifdef WITNESS
  438         witness_thread_exit(td);
  439 #endif
  440         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
  441         sched_throw(td);
  442         panic("I'm a teapot!");
  443         /* NOTREACHED */
  444 }
  445 
  446 /*
  447  * Do any thread specific cleanups that may be needed in wait()
  448  * called with Giant, proc and schedlock not held.
  449  */
  450 void
  451 thread_wait(struct proc *p)
  452 {
  453         struct thread *td;
  454 
  455         mtx_assert(&Giant, MA_NOTOWNED);
  456         KASSERT((p->p_numthreads == 1), ("Multiple threads in wait1()"));
  457         td = FIRST_THREAD_IN_PROC(p);
  458         /* Lock the last thread so we spin until it exits cpu_throw(). */
  459         thread_lock(td);
  460         thread_unlock(td);
  461         /* Wait for any remaining threads to exit cpu_throw(). */
  462         while (p->p_exitthreads)
  463                 sched_relinquish(curthread);
  464         lock_profile_thread_exit(td);
  465         cpuset_rel(td->td_cpuset);
  466         td->td_cpuset = NULL;
  467         cpu_thread_clean(td);
  468         crfree(td->td_ucred);
  469         thread_reap();  /* check for zombie threads etc. */
  470 }
  471 
  472 /*
  473  * Link a thread to a process.
  474  * set up anything that needs to be initialized for it to
  475  * be used by the process.
  476  */
  477 void
  478 thread_link(struct thread *td, struct proc *p)
  479 {
  480 
  481         /*
  482          * XXX This can't be enabled because it's called for proc0 before
  483          * its lock has been created.
  484          * PROC_LOCK_ASSERT(p, MA_OWNED);
  485          */
  486         td->td_state    = TDS_INACTIVE;
  487         td->td_proc     = p;
  488         td->td_flags    = TDF_INMEM;
  489 
  490         LIST_INIT(&td->td_contested);
  491         LIST_INIT(&td->td_lprof[0]);
  492         LIST_INIT(&td->td_lprof[1]);
  493         sigqueue_init(&td->td_sigqueue, p);
  494         callout_init(&td->td_slpcallout, CALLOUT_MPSAFE);
  495         TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
  496         p->p_numthreads++;
  497 }
  498 
  499 /*
  500  * Convert a process with one thread to an unthreaded process.
  501  */
  502 void
  503 thread_unthread(struct thread *td)
  504 {
  505         struct proc *p = td->td_proc;
  506 
  507         KASSERT((p->p_numthreads == 1), ("Unthreading with >1 threads"));
  508         p->p_flag &= ~P_HADTHREADS;
  509 }
  510 
  511 /*
  512  * Called from:
  513  *  thread_exit()
  514  */
  515 void
  516 thread_unlink(struct thread *td)
  517 {
  518         struct proc *p = td->td_proc;
  519 
  520         PROC_LOCK_ASSERT(p, MA_OWNED);
  521         TAILQ_REMOVE(&p->p_threads, td, td_plist);
  522         p->p_numthreads--;
  523         /* could clear a few other things here */
  524         /* Must  NOT clear links to proc! */
  525 }
  526 
  527 static int
  528 calc_remaining(struct proc *p, int mode)
  529 {
  530         int remaining;
  531 
  532         if (mode == SINGLE_EXIT)
  533                 remaining = p->p_numthreads;
  534         else if (mode == SINGLE_BOUNDARY)
  535                 remaining = p->p_numthreads - p->p_boundary_count;
  536         else if (mode == SINGLE_NO_EXIT)
  537                 remaining = p->p_numthreads - p->p_suspcount;
  538         else
  539                 panic("calc_remaining: wrong mode %d", mode);
  540         return (remaining);
  541 }
  542 
  543 /*
  544  * Enforce single-threading.
  545  *
  546  * Returns 1 if the caller must abort (another thread is waiting to
  547  * exit the process or similar). Process is locked!
  548  * Returns 0 when you are successfully the only thread running.
  549  * A process has successfully single threaded in the suspend mode when
  550  * There are no threads in user mode. Threads in the kernel must be
  551  * allowed to continue until they get to the user boundary. They may even
  552  * copy out their return values and data before suspending. They may however be
  553  * accelerated in reaching the user boundary as we will wake up
  554  * any sleeping threads that are interruptable. (PCATCH).
  555  */
  556 int
  557 thread_single(int mode)
  558 {
  559         struct thread *td;
  560         struct thread *td2;
  561         struct proc *p;
  562         int remaining, wakeup_swapper;
  563 
  564         td = curthread;
  565         p = td->td_proc;
  566         mtx_assert(&Giant, MA_NOTOWNED);
  567         PROC_LOCK_ASSERT(p, MA_OWNED);
  568         KASSERT((td != NULL), ("curthread is NULL"));
  569 
  570         if ((p->p_flag & P_HADTHREADS) == 0)
  571                 return (0);
  572 
  573         /* Is someone already single threading? */
  574         if (p->p_singlethread != NULL && p->p_singlethread != td)
  575                 return (1);
  576 
  577         if (mode == SINGLE_EXIT) {
  578                 p->p_flag |= P_SINGLE_EXIT;
  579                 p->p_flag &= ~P_SINGLE_BOUNDARY;
  580         } else {
  581                 p->p_flag &= ~P_SINGLE_EXIT;
  582                 if (mode == SINGLE_BOUNDARY)
  583                         p->p_flag |= P_SINGLE_BOUNDARY;
  584                 else
  585                         p->p_flag &= ~P_SINGLE_BOUNDARY;
  586         }
  587         p->p_flag |= P_STOPPED_SINGLE;
  588         PROC_SLOCK(p);
  589         p->p_singlethread = td;
  590         remaining = calc_remaining(p, mode);
  591         while (remaining != 1) {
  592                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
  593                         goto stopme;
  594                 wakeup_swapper = 0;
  595                 FOREACH_THREAD_IN_PROC(p, td2) {
  596                         if (td2 == td)
  597                                 continue;
  598                         thread_lock(td2);
  599                         td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
  600                         if (TD_IS_INHIBITED(td2)) {
  601                                 switch (mode) {
  602                                 case SINGLE_EXIT:
  603                                         if (TD_IS_SUSPENDED(td2))
  604                                                 wakeup_swapper |=
  605                                                     thread_unsuspend_one(td2);
  606                                         if (TD_ON_SLEEPQ(td2) &&
  607                                             (td2->td_flags & TDF_SINTR))
  608                                                 wakeup_swapper |=
  609                                                     sleepq_abort(td2, EINTR);
  610                                         break;
  611                                 case SINGLE_BOUNDARY:
  612                                         if (TD_IS_SUSPENDED(td2) &&
  613                                             !(td2->td_flags & TDF_BOUNDARY))
  614                                                 wakeup_swapper |=
  615                                                     thread_unsuspend_one(td2);
  616                                         if (TD_ON_SLEEPQ(td2) &&
  617                                             (td2->td_flags & TDF_SINTR))
  618                                                 wakeup_swapper |=
  619                                                     sleepq_abort(td2, ERESTART);
  620                                         break;
  621                                 case SINGLE_NO_EXIT:
  622                                         if (TD_IS_SUSPENDED(td2) &&
  623                                             !(td2->td_flags & TDF_BOUNDARY))
  624                                                 wakeup_swapper |=
  625                                                     thread_unsuspend_one(td2);
  626                                         if (TD_ON_SLEEPQ(td2) &&
  627                                             (td2->td_flags & TDF_SINTR))
  628                                                 wakeup_swapper |=
  629                                                     sleepq_abort(td2, ERESTART);
  630                                         break;
  631                                 default:
  632                                         break;
  633                                 }
  634                         }
  635 #ifdef SMP
  636                         else if (TD_IS_RUNNING(td2) && td != td2) {
  637                                 forward_signal(td2);
  638                         }
  639 #endif
  640                         thread_unlock(td2);
  641                 }
  642                 if (wakeup_swapper)
  643                         kick_proc0();
  644                 remaining = calc_remaining(p, mode);
  645 
  646                 /*
  647                  * Maybe we suspended some threads.. was it enough?
  648                  */
  649                 if (remaining == 1)
  650                         break;
  651 
  652 stopme:
  653                 /*
  654                  * Wake us up when everyone else has suspended.
  655                  * In the mean time we suspend as well.
  656                  */
  657                 thread_suspend_switch(td);
  658                 remaining = calc_remaining(p, mode);
  659         }
  660         if (mode == SINGLE_EXIT) {
  661                 /*
  662                  * We have gotten rid of all the other threads and we
  663                  * are about to either exit or exec. In either case,
  664                  * we try our utmost  to revert to being a non-threaded
  665                  * process.
  666                  */
  667                 p->p_singlethread = NULL;
  668                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT);
  669                 thread_unthread(td);
  670         }
  671         PROC_SUNLOCK(p);
  672         return (0);
  673 }
  674 
  675 /*
  676  * Called in from locations that can safely check to see
  677  * whether we have to suspend or at least throttle for a
  678  * single-thread event (e.g. fork).
  679  *
  680  * Such locations include userret().
  681  * If the "return_instead" argument is non zero, the thread must be able to
  682  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
  683  *
  684  * The 'return_instead' argument tells the function if it may do a
  685  * thread_exit() or suspend, or whether the caller must abort and back
  686  * out instead.
  687  *
  688  * If the thread that set the single_threading request has set the
  689  * P_SINGLE_EXIT bit in the process flags then this call will never return
  690  * if 'return_instead' is false, but will exit.
  691  *
  692  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
  693  *---------------+--------------------+---------------------
  694  *       0       | returns 0          |   returns 0 or 1
  695  *               | when ST ends       |   immediatly
  696  *---------------+--------------------+---------------------
  697  *       1       | thread exits       |   returns 1
  698  *               |                    |  immediatly
  699  * 0 = thread_exit() or suspension ok,
  700  * other = return error instead of stopping the thread.
  701  *
  702  * While a full suspension is under effect, even a single threading
  703  * thread would be suspended if it made this call (but it shouldn't).
  704  * This call should only be made from places where
  705  * thread_exit() would be safe as that may be the outcome unless
  706  * return_instead is set.
  707  */
  708 int
  709 thread_suspend_check(int return_instead)
  710 {
  711         struct thread *td;
  712         struct proc *p;
  713         int wakeup_swapper;
  714 
  715         td = curthread;
  716         p = td->td_proc;
  717         mtx_assert(&Giant, MA_NOTOWNED);
  718         PROC_LOCK_ASSERT(p, MA_OWNED);
  719         while (P_SHOULDSTOP(p) ||
  720               ((p->p_flag & P_TRACED) && (td->td_dbgflags & TDB_SUSPEND))) {
  721                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  722                         KASSERT(p->p_singlethread != NULL,
  723                             ("singlethread not set"));
  724                         /*
  725                          * The only suspension in action is a
  726                          * single-threading. Single threader need not stop.
  727                          * XXX Should be safe to access unlocked
  728                          * as it can only be set to be true by us.
  729                          */
  730                         if (p->p_singlethread == td)
  731                                 return (0);     /* Exempt from stopping. */
  732                 }
  733                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
  734                         return (EINTR);
  735 
  736                 /* Should we goto user boundary if we didn't come from there? */
  737                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
  738                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
  739                         return (ERESTART);
  740 
  741                 /* If thread will exit, flush its pending signals */
  742                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td))
  743                         sigqueue_flush(&td->td_sigqueue);
  744 
  745                 PROC_SLOCK(p);
  746                 thread_stopped(p);
  747                 /*
  748                  * If the process is waiting for us to exit,
  749                  * this thread should just suicide.
  750                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
  751                  */
  752                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td))
  753                         thread_exit();
  754                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  755                         if (p->p_numthreads == p->p_suspcount + 1) {
  756                                 thread_lock(p->p_singlethread);
  757                                 wakeup_swapper =
  758                                     thread_unsuspend_one(p->p_singlethread);
  759                                 thread_unlock(p->p_singlethread);
  760                                 if (wakeup_swapper)
  761                                         kick_proc0();
  762                         }
  763                 }
  764                 PROC_UNLOCK(p);
  765                 thread_lock(td);
  766                 /*
  767                  * When a thread suspends, it just
  768                  * gets taken off all queues.
  769                  */
  770                 thread_suspend_one(td);
  771                 if (return_instead == 0) {
  772                         p->p_boundary_count++;
  773                         td->td_flags |= TDF_BOUNDARY;
  774                 }
  775                 PROC_SUNLOCK(p);
  776                 mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
  777                 if (return_instead == 0)
  778                         td->td_flags &= ~TDF_BOUNDARY;
  779                 thread_unlock(td);
  780                 PROC_LOCK(p);
  781                 if (return_instead == 0)
  782                         p->p_boundary_count--;
  783         }
  784         return (0);
  785 }
  786 
  787 void
  788 thread_suspend_switch(struct thread *td)
  789 {
  790         struct proc *p;
  791 
  792         p = td->td_proc;
  793         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  794         PROC_LOCK_ASSERT(p, MA_OWNED);
  795         PROC_SLOCK_ASSERT(p, MA_OWNED);
  796         /*
  797          * We implement thread_suspend_one in stages here to avoid
  798          * dropping the proc lock while the thread lock is owned.
  799          */
  800         thread_stopped(p);
  801         p->p_suspcount++;
  802         PROC_UNLOCK(p);
  803         thread_lock(td);
  804         td->td_flags &= ~TDF_NEEDSUSPCHK;
  805         TD_SET_SUSPENDED(td);
  806         sched_sleep(td, 0);
  807         PROC_SUNLOCK(p);
  808         DROP_GIANT();
  809         mi_switch(SW_VOL | SWT_SUSPEND, NULL);
  810         thread_unlock(td);
  811         PICKUP_GIANT();
  812         PROC_LOCK(p);
  813         PROC_SLOCK(p);
  814 }
  815 
  816 void
  817 thread_suspend_one(struct thread *td)
  818 {
  819         struct proc *p = td->td_proc;
  820 
  821         PROC_SLOCK_ASSERT(p, MA_OWNED);
  822         THREAD_LOCK_ASSERT(td, MA_OWNED);
  823         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  824         p->p_suspcount++;
  825         td->td_flags &= ~TDF_NEEDSUSPCHK;
  826         TD_SET_SUSPENDED(td);
  827         sched_sleep(td, 0);
  828 }
  829 
  830 int
  831 thread_unsuspend_one(struct thread *td)
  832 {
  833         struct proc *p = td->td_proc;
  834 
  835         PROC_SLOCK_ASSERT(p, MA_OWNED);
  836         THREAD_LOCK_ASSERT(td, MA_OWNED);
  837         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
  838         TD_CLR_SUSPENDED(td);
  839         p->p_suspcount--;
  840         return (setrunnable(td));
  841 }
  842 
  843 /*
  844  * Allow all threads blocked by single threading to continue running.
  845  */
  846 void
  847 thread_unsuspend(struct proc *p)
  848 {
  849         struct thread *td;
  850         int wakeup_swapper;
  851 
  852         PROC_LOCK_ASSERT(p, MA_OWNED);
  853         PROC_SLOCK_ASSERT(p, MA_OWNED);
  854         wakeup_swapper = 0;
  855         if (!P_SHOULDSTOP(p)) {
  856                 FOREACH_THREAD_IN_PROC(p, td) {
  857                         thread_lock(td);
  858                         if (TD_IS_SUSPENDED(td)) {
  859                                 wakeup_swapper |= thread_unsuspend_one(td);
  860                         }
  861                         thread_unlock(td);
  862                 }
  863         } else if ((P_SHOULDSTOP(p) == P_STOPPED_SINGLE) &&
  864             (p->p_numthreads == p->p_suspcount)) {
  865                 /*
  866                  * Stopping everything also did the job for the single
  867                  * threading request. Now we've downgraded to single-threaded,
  868                  * let it continue.
  869                  */
  870                 thread_lock(p->p_singlethread);
  871                 wakeup_swapper = thread_unsuspend_one(p->p_singlethread);
  872                 thread_unlock(p->p_singlethread);
  873         }
  874         if (wakeup_swapper)
  875                 kick_proc0();
  876 }
  877 
  878 /*
  879  * End the single threading mode..
  880  */
  881 void
  882 thread_single_end(void)
  883 {
  884         struct thread *td;
  885         struct proc *p;
  886         int wakeup_swapper;
  887 
  888         td = curthread;
  889         p = td->td_proc;
  890         PROC_LOCK_ASSERT(p, MA_OWNED);
  891         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY);
  892         PROC_SLOCK(p);
  893         p->p_singlethread = NULL;
  894         wakeup_swapper = 0;
  895         /*
  896          * If there are other threads they may now run,
  897          * unless of course there is a blanket 'stop order'
  898          * on the process. The single threader must be allowed
  899          * to continue however as this is a bad place to stop.
  900          */
  901         if ((p->p_numthreads != 1) && (!P_SHOULDSTOP(p))) {
  902                 FOREACH_THREAD_IN_PROC(p, td) {
  903                         thread_lock(td);
  904                         if (TD_IS_SUSPENDED(td)) {
  905                                 wakeup_swapper |= thread_unsuspend_one(td);
  906                         }
  907                         thread_unlock(td);
  908                 }
  909         }
  910         PROC_SUNLOCK(p);
  911         if (wakeup_swapper)
  912                 kick_proc0();
  913 }
  914 
  915 struct thread *
  916 thread_find(struct proc *p, lwpid_t tid)
  917 {
  918         struct thread *td;
  919 
  920         PROC_LOCK_ASSERT(p, MA_OWNED);
  921         FOREACH_THREAD_IN_PROC(p, td) {
  922                 if (td->td_tid == tid)
  923                         break;
  924         }
  925         return (td);
  926 }

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