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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_kdtrace.h"
   31 #include "opt_hwpmc_hooks.h"
   32 
   33 #include <sys/cdefs.h>
   34 __FBSDID("$FreeBSD: stable/9/sys/kern/kern_thread.c 251147 2013-05-30 19:14:34Z jhb $");
   35 
   36 #include <sys/param.h>
   37 #include <sys/systm.h>
   38 #include <sys/kernel.h>
   39 #include <sys/lock.h>
   40 #include <sys/mutex.h>
   41 #include <sys/proc.h>
   42 #include <sys/rangelock.h>
   43 #include <sys/resourcevar.h>
   44 #include <sys/sdt.h>
   45 #include <sys/smp.h>
   46 #include <sys/sched.h>
   47 #include <sys/sleepqueue.h>
   48 #include <sys/selinfo.h>
   49 #include <sys/turnstile.h>
   50 #include <sys/ktr.h>
   51 #include <sys/rwlock.h>
   52 #include <sys/umtx.h>
   53 #include <sys/cpuset.h>
   54 #ifdef  HWPMC_HOOKS
   55 #include <sys/pmckern.h>
   56 #endif
   57 
   58 #include <security/audit/audit.h>
   59 
   60 #include <vm/vm.h>
   61 #include <vm/vm_extern.h>
   62 #include <vm/uma.h>
   63 #include <sys/eventhandler.h>
   64 
   65 SDT_PROVIDER_DECLARE(proc);
   66 SDT_PROBE_DEFINE(proc, , , lwp_exit, lwp-exit);
   67 
   68 
   69 /*
   70  * thread related storage.
   71  */
   72 static uma_zone_t thread_zone;
   73 
   74 TAILQ_HEAD(, thread) zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
   75 static struct mtx zombie_lock;
   76 MTX_SYSINIT(zombie_lock, &zombie_lock, "zombie lock", MTX_SPIN);
   77 
   78 static void thread_zombie(struct thread *);
   79 
   80 #define TID_BUFFER_SIZE 1024
   81 
   82 struct mtx tid_lock;
   83 static struct unrhdr *tid_unrhdr;
   84 static lwpid_t tid_buffer[TID_BUFFER_SIZE];
   85 static int tid_head, tid_tail;
   86 static MALLOC_DEFINE(M_TIDHASH, "tidhash", "thread hash");
   87 
   88 struct  tidhashhead *tidhashtbl;
   89 u_long  tidhash;
   90 struct  rwlock tidhash_lock;
   91 
   92 static lwpid_t
   93 tid_alloc(void)
   94 {
   95         lwpid_t tid;
   96 
   97         tid = alloc_unr(tid_unrhdr);
   98         if (tid != -1)
   99                 return (tid);
  100         mtx_lock(&tid_lock);
  101         if (tid_head == tid_tail) {
  102                 mtx_unlock(&tid_lock);
  103                 return (-1);
  104         }
  105         tid = tid_buffer[tid_head];
  106         tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
  107         mtx_unlock(&tid_lock);
  108         return (tid);
  109 }
  110 
  111 static void
  112 tid_free(lwpid_t tid)
  113 {
  114         lwpid_t tmp_tid = -1;
  115 
  116         mtx_lock(&tid_lock);
  117         if ((tid_tail + 1) % TID_BUFFER_SIZE == tid_head) {
  118                 tmp_tid = tid_buffer[tid_head];
  119                 tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
  120         }
  121         tid_buffer[tid_tail] = tid;
  122         tid_tail = (tid_tail + 1) % TID_BUFFER_SIZE;
  123         mtx_unlock(&tid_lock);
  124         if (tmp_tid != -1)
  125                 free_unr(tid_unrhdr, tmp_tid);
  126 }
  127 
  128 /*
  129  * Prepare a thread for use.
  130  */
  131 static int
  132 thread_ctor(void *mem, int size, void *arg, int flags)
  133 {
  134         struct thread   *td;
  135 
  136         td = (struct thread *)mem;
  137         td->td_state = TDS_INACTIVE;
  138         td->td_oncpu = NOCPU;
  139 
  140         td->td_tid = tid_alloc();
  141 
  142         /*
  143          * Note that td_critnest begins life as 1 because the thread is not
  144          * running and is thereby implicitly waiting to be on the receiving
  145          * end of a context switch.
  146          */
  147         td->td_critnest = 1;
  148         td->td_lend_user_pri = PRI_MAX;
  149         EVENTHANDLER_INVOKE(thread_ctor, td);
  150 #ifdef AUDIT
  151         audit_thread_alloc(td);
  152 #endif
  153         umtx_thread_alloc(td);
  154         return (0);
  155 }
  156 
  157 /*
  158  * Reclaim a thread after use.
  159  */
  160 static void
  161 thread_dtor(void *mem, int size, void *arg)
  162 {
  163         struct thread *td;
  164 
  165         td = (struct thread *)mem;
  166 
  167 #ifdef INVARIANTS
  168         /* Verify that this thread is in a safe state to free. */
  169         switch (td->td_state) {
  170         case TDS_INHIBITED:
  171         case TDS_RUNNING:
  172         case TDS_CAN_RUN:
  173         case TDS_RUNQ:
  174                 /*
  175                  * We must never unlink a thread that is in one of
  176                  * these states, because it is currently active.
  177                  */
  178                 panic("bad state for thread unlinking");
  179                 /* NOTREACHED */
  180         case TDS_INACTIVE:
  181                 break;
  182         default:
  183                 panic("bad thread state");
  184                 /* NOTREACHED */
  185         }
  186 #endif
  187 #ifdef AUDIT
  188         audit_thread_free(td);
  189 #endif
  190         /* Free all OSD associated to this thread. */
  191         osd_thread_exit(td);
  192 
  193         EVENTHANDLER_INVOKE(thread_dtor, td);
  194         tid_free(td->td_tid);
  195 }
  196 
  197 /*
  198  * Initialize type-stable parts of a thread (when newly created).
  199  */
  200 static int
  201 thread_init(void *mem, int size, int flags)
  202 {
  203         struct thread *td;
  204 
  205         td = (struct thread *)mem;
  206 
  207         td->td_sleepqueue = sleepq_alloc();
  208         td->td_turnstile = turnstile_alloc();
  209         td->td_rlqe = NULL;
  210         td->td_vp_reserv = 0;
  211         EVENTHANDLER_INVOKE(thread_init, td);
  212         td->td_sched = (struct td_sched *)&td[1];
  213         umtx_thread_init(td);
  214         td->td_kstack = 0;
  215         return (0);
  216 }
  217 
  218 /*
  219  * Tear down type-stable parts of a thread (just before being discarded).
  220  */
  221 static void
  222 thread_fini(void *mem, int size)
  223 {
  224         struct thread *td;
  225 
  226         td = (struct thread *)mem;
  227         EVENTHANDLER_INVOKE(thread_fini, td);
  228         rlqentry_free(td->td_rlqe);
  229         turnstile_free(td->td_turnstile);
  230         sleepq_free(td->td_sleepqueue);
  231         umtx_thread_fini(td);
  232         seltdfini(td);
  233 }
  234 
  235 /*
  236  * For a newly created process,
  237  * link up all the structures and its initial threads etc.
  238  * called from:
  239  * {arch}/{arch}/machdep.c   ia64_init(), init386() etc.
  240  * proc_dtor() (should go away)
  241  * proc_init()
  242  */
  243 void
  244 proc_linkup0(struct proc *p, struct thread *td)
  245 {
  246         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
  247         proc_linkup(p, td);
  248 }
  249 
  250 void
  251 proc_linkup(struct proc *p, struct thread *td)
  252 {
  253 
  254         sigqueue_init(&p->p_sigqueue, p);
  255         p->p_ksi = ksiginfo_alloc(1);
  256         if (p->p_ksi != NULL) {
  257                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
  258                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
  259         }
  260         LIST_INIT(&p->p_mqnotifier);
  261         p->p_numthreads = 0;
  262         thread_link(td, p);
  263 }
  264 
  265 /*
  266  * Initialize global thread allocation resources.
  267  */
  268 void
  269 threadinit(void)
  270 {
  271 
  272         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
  273 
  274         /*
  275          * pid_max cannot be greater than PID_MAX.
  276          * leave one number for thread0.
  277          */
  278         tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
  279 
  280         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
  281             thread_ctor, thread_dtor, thread_init, thread_fini,
  282             16 - 1, 0);
  283         tidhashtbl = hashinit(maxproc / 2, M_TIDHASH, &tidhash);
  284         rw_init(&tidhash_lock, "tidhash");
  285 }
  286 
  287 /*
  288  * Place an unused thread on the zombie list.
  289  * Use the slpq as that must be unused by now.
  290  */
  291 void
  292 thread_zombie(struct thread *td)
  293 {
  294         mtx_lock_spin(&zombie_lock);
  295         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
  296         mtx_unlock_spin(&zombie_lock);
  297 }
  298 
  299 /*
  300  * Release a thread that has exited after cpu_throw().
  301  */
  302 void
  303 thread_stash(struct thread *td)
  304 {
  305         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
  306         thread_zombie(td);
  307 }
  308 
  309 /*
  310  * Reap zombie resources.
  311  */
  312 void
  313 thread_reap(void)
  314 {
  315         struct thread *td_first, *td_next;
  316 
  317         /*
  318          * Don't even bother to lock if none at this instant,
  319          * we really don't care about the next instant..
  320          */
  321         if (!TAILQ_EMPTY(&zombie_threads)) {
  322                 mtx_lock_spin(&zombie_lock);
  323                 td_first = TAILQ_FIRST(&zombie_threads);
  324                 if (td_first)
  325                         TAILQ_INIT(&zombie_threads);
  326                 mtx_unlock_spin(&zombie_lock);
  327                 while (td_first) {
  328                         td_next = TAILQ_NEXT(td_first, td_slpq);
  329                         if (td_first->td_ucred)
  330                                 crfree(td_first->td_ucred);
  331                         thread_free(td_first);
  332                         td_first = td_next;
  333                 }
  334         }
  335 }
  336 
  337 /*
  338  * Allocate a thread.
  339  */
  340 struct thread *
  341 thread_alloc(int pages)
  342 {
  343         struct thread *td;
  344 
  345         thread_reap(); /* check if any zombies to get */
  346 
  347         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
  348         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
  349         if (!vm_thread_new(td, pages)) {
  350                 uma_zfree(thread_zone, td);
  351                 return (NULL);
  352         }
  353         cpu_thread_alloc(td);
  354         return (td);
  355 }
  356 
  357 int
  358 thread_alloc_stack(struct thread *td, int pages)
  359 {
  360 
  361         KASSERT(td->td_kstack == 0,
  362             ("thread_alloc_stack called on a thread with kstack"));
  363         if (!vm_thread_new(td, pages))
  364                 return (0);
  365         cpu_thread_alloc(td);
  366         return (1);
  367 }
  368 
  369 /*
  370  * Deallocate a thread.
  371  */
  372 void
  373 thread_free(struct thread *td)
  374 {
  375 
  376         lock_profile_thread_exit(td);
  377         if (td->td_cpuset)
  378                 cpuset_rel(td->td_cpuset);
  379         td->td_cpuset = NULL;
  380         cpu_thread_free(td);
  381         if (td->td_kstack != 0)
  382                 vm_thread_dispose(td);
  383         uma_zfree(thread_zone, td);
  384 }
  385 
  386 /*
  387  * Discard the current thread and exit from its context.
  388  * Always called with scheduler locked.
  389  *
  390  * Because we can't free a thread while we're operating under its context,
  391  * push the current thread into our CPU's deadthread holder. This means
  392  * we needn't worry about someone else grabbing our context before we
  393  * do a cpu_throw().
  394  */
  395 void
  396 thread_exit(void)
  397 {
  398         uint64_t runtime, new_switchtime;
  399         struct thread *td;
  400         struct thread *td2;
  401         struct proc *p;
  402         int wakeup_swapper;
  403 
  404         td = curthread;
  405         p = td->td_proc;
  406 
  407         PROC_SLOCK_ASSERT(p, MA_OWNED);
  408         mtx_assert(&Giant, MA_NOTOWNED);
  409 
  410         PROC_LOCK_ASSERT(p, MA_OWNED);
  411         KASSERT(p != NULL, ("thread exiting without a process"));
  412         CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
  413             (long)p->p_pid, td->td_name);
  414         KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
  415 
  416 #ifdef AUDIT
  417         AUDIT_SYSCALL_EXIT(0, td);
  418 #endif
  419         umtx_thread_exit(td);
  420         /*
  421          * drop FPU & debug register state storage, or any other
  422          * architecture specific resources that
  423          * would not be on a new untouched process.
  424          */
  425         cpu_thread_exit(td);    /* XXXSMP */
  426 
  427         /*
  428          * The last thread is left attached to the process
  429          * So that the whole bundle gets recycled. Skip
  430          * all this stuff if we never had threads.
  431          * EXIT clears all sign of other threads when
  432          * it goes to single threading, so the last thread always
  433          * takes the short path.
  434          */
  435         if (p->p_flag & P_HADTHREADS) {
  436                 if (p->p_numthreads > 1) {
  437                         thread_unlink(td);
  438                         td2 = FIRST_THREAD_IN_PROC(p);
  439                         sched_exit_thread(td2, td);
  440 
  441                         /*
  442                          * The test below is NOT true if we are the
  443                          * sole exiting thread. P_STOPPED_SINGLE is unset
  444                          * in exit1() after it is the only survivor.
  445                          */
  446                         if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  447                                 if (p->p_numthreads == p->p_suspcount) {
  448                                         thread_lock(p->p_singlethread);
  449                                         wakeup_swapper = thread_unsuspend_one(
  450                                                 p->p_singlethread);
  451                                         thread_unlock(p->p_singlethread);
  452                                         if (wakeup_swapper)
  453                                                 kick_proc0();
  454                                 }
  455                         }
  456 
  457                         atomic_add_int(&td->td_proc->p_exitthreads, 1);
  458                         PCPU_SET(deadthread, td);
  459                 } else {
  460                         /*
  461                          * The last thread is exiting.. but not through exit()
  462                          */
  463                         panic ("thread_exit: Last thread exiting on its own");
  464                 }
  465         } 
  466 #ifdef  HWPMC_HOOKS
  467         /*
  468          * If this thread is part of a process that is being tracked by hwpmc(4),
  469          * inform the module of the thread's impending exit.
  470          */
  471         if (PMC_PROC_IS_USING_PMCS(td->td_proc))
  472                 PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
  473 #endif
  474         PROC_UNLOCK(p);
  475 
  476         /* Do the same timestamp bookkeeping that mi_switch() would do. */
  477         new_switchtime = cpu_ticks();
  478         runtime = new_switchtime - PCPU_GET(switchtime);
  479         td->td_runtime += runtime;
  480         td->td_incruntime += runtime;
  481         PCPU_SET(switchtime, new_switchtime);
  482         PCPU_SET(switchticks, ticks);
  483         PCPU_INC(cnt.v_swtch);
  484 
  485         /* Save our resource usage in our process. */
  486         td->td_ru.ru_nvcsw++;
  487         ruxagg(p, td);
  488         rucollect(&p->p_ru, &td->td_ru);
  489 
  490         thread_lock(td);
  491         PROC_SUNLOCK(p);
  492         td->td_state = TDS_INACTIVE;
  493 #ifdef WITNESS
  494         witness_thread_exit(td);
  495 #endif
  496         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
  497         sched_throw(td);
  498         panic("I'm a teapot!");
  499         /* NOTREACHED */
  500 }
  501 
  502 /*
  503  * Do any thread specific cleanups that may be needed in wait()
  504  * called with Giant, proc and schedlock not held.
  505  */
  506 void
  507 thread_wait(struct proc *p)
  508 {
  509         struct thread *td;
  510 
  511         mtx_assert(&Giant, MA_NOTOWNED);
  512         KASSERT((p->p_numthreads == 1), ("Multiple threads in wait1()"));
  513         td = FIRST_THREAD_IN_PROC(p);
  514         /* Lock the last thread so we spin until it exits cpu_throw(). */
  515         thread_lock(td);
  516         thread_unlock(td);
  517         /* Wait for any remaining threads to exit cpu_throw(). */
  518         while (p->p_exitthreads)
  519                 sched_relinquish(curthread);
  520         lock_profile_thread_exit(td);
  521         cpuset_rel(td->td_cpuset);
  522         td->td_cpuset = NULL;
  523         cpu_thread_clean(td);
  524         crfree(td->td_ucred);
  525         thread_reap();  /* check for zombie threads etc. */
  526 }
  527 
  528 /*
  529  * Link a thread to a process.
  530  * set up anything that needs to be initialized for it to
  531  * be used by the process.
  532  */
  533 void
  534 thread_link(struct thread *td, struct proc *p)
  535 {
  536 
  537         /*
  538          * XXX This can't be enabled because it's called for proc0 before
  539          * its lock has been created.
  540          * PROC_LOCK_ASSERT(p, MA_OWNED);
  541          */
  542         td->td_state    = TDS_INACTIVE;
  543         td->td_proc     = p;
  544         td->td_flags    = TDF_INMEM;
  545 
  546         LIST_INIT(&td->td_contested);
  547         LIST_INIT(&td->td_lprof[0]);
  548         LIST_INIT(&td->td_lprof[1]);
  549         sigqueue_init(&td->td_sigqueue, p);
  550         callout_init(&td->td_slpcallout, CALLOUT_MPSAFE);
  551         TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
  552         p->p_numthreads++;
  553 }
  554 
  555 /*
  556  * Convert a process with one thread to an unthreaded process.
  557  */
  558 void
  559 thread_unthread(struct thread *td)
  560 {
  561         struct proc *p = td->td_proc;
  562 
  563         KASSERT((p->p_numthreads == 1), ("Unthreading with >1 threads"));
  564         p->p_flag &= ~P_HADTHREADS;
  565 }
  566 
  567 /*
  568  * Called from:
  569  *  thread_exit()
  570  */
  571 void
  572 thread_unlink(struct thread *td)
  573 {
  574         struct proc *p = td->td_proc;
  575 
  576         PROC_LOCK_ASSERT(p, MA_OWNED);
  577         TAILQ_REMOVE(&p->p_threads, td, td_plist);
  578         p->p_numthreads--;
  579         /* could clear a few other things here */
  580         /* Must  NOT clear links to proc! */
  581 }
  582 
  583 static int
  584 calc_remaining(struct proc *p, int mode)
  585 {
  586         int remaining;
  587 
  588         PROC_LOCK_ASSERT(p, MA_OWNED);
  589         PROC_SLOCK_ASSERT(p, MA_OWNED);
  590         if (mode == SINGLE_EXIT)
  591                 remaining = p->p_numthreads;
  592         else if (mode == SINGLE_BOUNDARY)
  593                 remaining = p->p_numthreads - p->p_boundary_count;
  594         else if (mode == SINGLE_NO_EXIT)
  595                 remaining = p->p_numthreads - p->p_suspcount;
  596         else
  597                 panic("calc_remaining: wrong mode %d", mode);
  598         return (remaining);
  599 }
  600 
  601 /*
  602  * Enforce single-threading.
  603  *
  604  * Returns 1 if the caller must abort (another thread is waiting to
  605  * exit the process or similar). Process is locked!
  606  * Returns 0 when you are successfully the only thread running.
  607  * A process has successfully single threaded in the suspend mode when
  608  * There are no threads in user mode. Threads in the kernel must be
  609  * allowed to continue until they get to the user boundary. They may even
  610  * copy out their return values and data before suspending. They may however be
  611  * accelerated in reaching the user boundary as we will wake up
  612  * any sleeping threads that are interruptable. (PCATCH).
  613  */
  614 int
  615 thread_single(int mode)
  616 {
  617         struct thread *td;
  618         struct thread *td2;
  619         struct proc *p;
  620         int remaining, wakeup_swapper;
  621 
  622         td = curthread;
  623         p = td->td_proc;
  624         mtx_assert(&Giant, MA_NOTOWNED);
  625         PROC_LOCK_ASSERT(p, MA_OWNED);
  626 
  627         if ((p->p_flag & P_HADTHREADS) == 0)
  628                 return (0);
  629 
  630         /* Is someone already single threading? */
  631         if (p->p_singlethread != NULL && p->p_singlethread != td)
  632                 return (1);
  633 
  634         if (mode == SINGLE_EXIT) {
  635                 p->p_flag |= P_SINGLE_EXIT;
  636                 p->p_flag &= ~P_SINGLE_BOUNDARY;
  637         } else {
  638                 p->p_flag &= ~P_SINGLE_EXIT;
  639                 if (mode == SINGLE_BOUNDARY)
  640                         p->p_flag |= P_SINGLE_BOUNDARY;
  641                 else
  642                         p->p_flag &= ~P_SINGLE_BOUNDARY;
  643         }
  644         p->p_flag |= P_STOPPED_SINGLE;
  645         PROC_SLOCK(p);
  646         p->p_singlethread = td;
  647         remaining = calc_remaining(p, mode);
  648         while (remaining != 1) {
  649                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
  650                         goto stopme;
  651                 wakeup_swapper = 0;
  652                 FOREACH_THREAD_IN_PROC(p, td2) {
  653                         if (td2 == td)
  654                                 continue;
  655                         thread_lock(td2);
  656                         td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
  657                         if (TD_IS_INHIBITED(td2)) {
  658                                 switch (mode) {
  659                                 case SINGLE_EXIT:
  660                                         if (TD_IS_SUSPENDED(td2))
  661                                                 wakeup_swapper |=
  662                                                     thread_unsuspend_one(td2);
  663                                         if (TD_ON_SLEEPQ(td2) &&
  664                                             (td2->td_flags & TDF_SINTR))
  665                                                 wakeup_swapper |=
  666                                                     sleepq_abort(td2, EINTR);
  667                                         break;
  668                                 case SINGLE_BOUNDARY:
  669                                         if (TD_IS_SUSPENDED(td2) &&
  670                                             !(td2->td_flags & TDF_BOUNDARY))
  671                                                 wakeup_swapper |=
  672                                                     thread_unsuspend_one(td2);
  673                                         if (TD_ON_SLEEPQ(td2) &&
  674                                             (td2->td_flags & TDF_SINTR))
  675                                                 wakeup_swapper |=
  676                                                     sleepq_abort(td2, ERESTART);
  677                                         break;
  678                                 case SINGLE_NO_EXIT:
  679                                         if (TD_IS_SUSPENDED(td2) &&
  680                                             !(td2->td_flags & TDF_BOUNDARY))
  681                                                 wakeup_swapper |=
  682                                                     thread_unsuspend_one(td2);
  683                                         if (TD_ON_SLEEPQ(td2) &&
  684                                             (td2->td_flags & TDF_SINTR))
  685                                                 wakeup_swapper |=
  686                                                     sleepq_abort(td2, ERESTART);
  687                                         break;
  688                                 default:
  689                                         break;
  690                                 }
  691                         }
  692 #ifdef SMP
  693                         else if (TD_IS_RUNNING(td2) && td != td2) {
  694                                 forward_signal(td2);
  695                         }
  696 #endif
  697                         thread_unlock(td2);
  698                 }
  699                 if (wakeup_swapper)
  700                         kick_proc0();
  701                 remaining = calc_remaining(p, mode);
  702 
  703                 /*
  704                  * Maybe we suspended some threads.. was it enough?
  705                  */
  706                 if (remaining == 1)
  707                         break;
  708 
  709 stopme:
  710                 /*
  711                  * Wake us up when everyone else has suspended.
  712                  * In the mean time we suspend as well.
  713                  */
  714                 thread_suspend_switch(td);
  715                 remaining = calc_remaining(p, mode);
  716         }
  717         if (mode == SINGLE_EXIT) {
  718                 /*
  719                  * We have gotten rid of all the other threads and we
  720                  * are about to either exit or exec. In either case,
  721                  * we try our utmost  to revert to being a non-threaded
  722                  * process.
  723                  */
  724                 p->p_singlethread = NULL;
  725                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT);
  726                 thread_unthread(td);
  727         }
  728         PROC_SUNLOCK(p);
  729         return (0);
  730 }
  731 
  732 /*
  733  * Called in from locations that can safely check to see
  734  * whether we have to suspend or at least throttle for a
  735  * single-thread event (e.g. fork).
  736  *
  737  * Such locations include userret().
  738  * If the "return_instead" argument is non zero, the thread must be able to
  739  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
  740  *
  741  * The 'return_instead' argument tells the function if it may do a
  742  * thread_exit() or suspend, or whether the caller must abort and back
  743  * out instead.
  744  *
  745  * If the thread that set the single_threading request has set the
  746  * P_SINGLE_EXIT bit in the process flags then this call will never return
  747  * if 'return_instead' is false, but will exit.
  748  *
  749  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
  750  *---------------+--------------------+---------------------
  751  *       0       | returns 0          |   returns 0 or 1
  752  *               | when ST ends       |   immediatly
  753  *---------------+--------------------+---------------------
  754  *       1       | thread exits       |   returns 1
  755  *               |                    |  immediatly
  756  * 0 = thread_exit() or suspension ok,
  757  * other = return error instead of stopping the thread.
  758  *
  759  * While a full suspension is under effect, even a single threading
  760  * thread would be suspended if it made this call (but it shouldn't).
  761  * This call should only be made from places where
  762  * thread_exit() would be safe as that may be the outcome unless
  763  * return_instead is set.
  764  */
  765 int
  766 thread_suspend_check(int return_instead)
  767 {
  768         struct thread *td;
  769         struct proc *p;
  770         int wakeup_swapper;
  771 
  772         td = curthread;
  773         p = td->td_proc;
  774         mtx_assert(&Giant, MA_NOTOWNED);
  775         PROC_LOCK_ASSERT(p, MA_OWNED);
  776         while (P_SHOULDSTOP(p) ||
  777               ((p->p_flag & P_TRACED) && (td->td_dbgflags & TDB_SUSPEND))) {
  778                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  779                         KASSERT(p->p_singlethread != NULL,
  780                             ("singlethread not set"));
  781                         /*
  782                          * The only suspension in action is a
  783                          * single-threading. Single threader need not stop.
  784                          * XXX Should be safe to access unlocked
  785                          * as it can only be set to be true by us.
  786                          */
  787                         if (p->p_singlethread == td)
  788                                 return (0);     /* Exempt from stopping. */
  789                 }
  790                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
  791                         return (EINTR);
  792 
  793                 /* Should we goto user boundary if we didn't come from there? */
  794                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
  795                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
  796                         return (ERESTART);
  797 
  798                 /*
  799                  * Ignore suspend requests for stop signals if they
  800                  * are deferred.
  801                  */
  802                 if (P_SHOULDSTOP(p) == P_STOPPED_SIG &&
  803                     td->td_flags & TDF_SBDRY) {
  804                         KASSERT(return_instead,
  805                             ("TDF_SBDRY set for unsafe thread_suspend_check"));
  806                         return (0);
  807                 }
  808 
  809                 /*
  810                  * If the process is waiting for us to exit,
  811                  * this thread should just suicide.
  812                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
  813                  */
  814                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td)) {
  815                         PROC_UNLOCK(p);
  816                         tidhash_remove(td);
  817                         PROC_LOCK(p);
  818                         tdsigcleanup(td);
  819                         PROC_SLOCK(p);
  820                         thread_stopped(p);
  821                         thread_exit();
  822                 }
  823 
  824                 PROC_SLOCK(p);
  825                 thread_stopped(p);
  826                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  827                         if (p->p_numthreads == p->p_suspcount + 1) {
  828                                 thread_lock(p->p_singlethread);
  829                                 wakeup_swapper =
  830                                     thread_unsuspend_one(p->p_singlethread);
  831                                 thread_unlock(p->p_singlethread);
  832                                 if (wakeup_swapper)
  833                                         kick_proc0();
  834                         }
  835                 }
  836                 PROC_UNLOCK(p);
  837                 thread_lock(td);
  838                 /*
  839                  * When a thread suspends, it just
  840                  * gets taken off all queues.
  841                  */
  842                 thread_suspend_one(td);
  843                 if (return_instead == 0) {
  844                         p->p_boundary_count++;
  845                         td->td_flags |= TDF_BOUNDARY;
  846                 }
  847                 PROC_SUNLOCK(p);
  848                 mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
  849                 if (return_instead == 0)
  850                         td->td_flags &= ~TDF_BOUNDARY;
  851                 thread_unlock(td);
  852                 PROC_LOCK(p);
  853                 if (return_instead == 0) {
  854                         PROC_SLOCK(p);
  855                         p->p_boundary_count--;
  856                         PROC_SUNLOCK(p);
  857                 }
  858         }
  859         return (0);
  860 }
  861 
  862 void
  863 thread_suspend_switch(struct thread *td)
  864 {
  865         struct proc *p;
  866 
  867         p = td->td_proc;
  868         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  869         PROC_LOCK_ASSERT(p, MA_OWNED);
  870         PROC_SLOCK_ASSERT(p, MA_OWNED);
  871         /*
  872          * We implement thread_suspend_one in stages here to avoid
  873          * dropping the proc lock while the thread lock is owned.
  874          */
  875         thread_stopped(p);
  876         p->p_suspcount++;
  877         PROC_UNLOCK(p);
  878         thread_lock(td);
  879         td->td_flags &= ~TDF_NEEDSUSPCHK;
  880         TD_SET_SUSPENDED(td);
  881         sched_sleep(td, 0);
  882         PROC_SUNLOCK(p);
  883         DROP_GIANT();
  884         mi_switch(SW_VOL | SWT_SUSPEND, NULL);
  885         thread_unlock(td);
  886         PICKUP_GIANT();
  887         PROC_LOCK(p);
  888         PROC_SLOCK(p);
  889 }
  890 
  891 void
  892 thread_suspend_one(struct thread *td)
  893 {
  894         struct proc *p = td->td_proc;
  895 
  896         PROC_SLOCK_ASSERT(p, MA_OWNED);
  897         THREAD_LOCK_ASSERT(td, MA_OWNED);
  898         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  899         p->p_suspcount++;
  900         td->td_flags &= ~TDF_NEEDSUSPCHK;
  901         TD_SET_SUSPENDED(td);
  902         sched_sleep(td, 0);
  903 }
  904 
  905 int
  906 thread_unsuspend_one(struct thread *td)
  907 {
  908         struct proc *p = td->td_proc;
  909 
  910         PROC_SLOCK_ASSERT(p, MA_OWNED);
  911         THREAD_LOCK_ASSERT(td, MA_OWNED);
  912         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
  913         TD_CLR_SUSPENDED(td);
  914         p->p_suspcount--;
  915         return (setrunnable(td));
  916 }
  917 
  918 /*
  919  * Allow all threads blocked by single threading to continue running.
  920  */
  921 void
  922 thread_unsuspend(struct proc *p)
  923 {
  924         struct thread *td;
  925         int wakeup_swapper;
  926 
  927         PROC_LOCK_ASSERT(p, MA_OWNED);
  928         PROC_SLOCK_ASSERT(p, MA_OWNED);
  929         wakeup_swapper = 0;
  930         if (!P_SHOULDSTOP(p)) {
  931                 FOREACH_THREAD_IN_PROC(p, td) {
  932                         thread_lock(td);
  933                         if (TD_IS_SUSPENDED(td)) {
  934                                 wakeup_swapper |= thread_unsuspend_one(td);
  935                         }
  936                         thread_unlock(td);
  937                 }
  938         } else if ((P_SHOULDSTOP(p) == P_STOPPED_SINGLE) &&
  939             (p->p_numthreads == p->p_suspcount)) {
  940                 /*
  941                  * Stopping everything also did the job for the single
  942                  * threading request. Now we've downgraded to single-threaded,
  943                  * let it continue.
  944                  */
  945                 thread_lock(p->p_singlethread);
  946                 wakeup_swapper = thread_unsuspend_one(p->p_singlethread);
  947                 thread_unlock(p->p_singlethread);
  948         }
  949         if (wakeup_swapper)
  950                 kick_proc0();
  951 }
  952 
  953 /*
  954  * End the single threading mode..
  955  */
  956 void
  957 thread_single_end(void)
  958 {
  959         struct thread *td;
  960         struct proc *p;
  961         int wakeup_swapper;
  962 
  963         td = curthread;
  964         p = td->td_proc;
  965         PROC_LOCK_ASSERT(p, MA_OWNED);
  966         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY);
  967         PROC_SLOCK(p);
  968         p->p_singlethread = NULL;
  969         wakeup_swapper = 0;
  970         /*
  971          * If there are other threads they may now run,
  972          * unless of course there is a blanket 'stop order'
  973          * on the process. The single threader must be allowed
  974          * to continue however as this is a bad place to stop.
  975          */
  976         if ((p->p_numthreads != 1) && (!P_SHOULDSTOP(p))) {
  977                 FOREACH_THREAD_IN_PROC(p, td) {
  978                         thread_lock(td);
  979                         if (TD_IS_SUSPENDED(td)) {
  980                                 wakeup_swapper |= thread_unsuspend_one(td);
  981                         }
  982                         thread_unlock(td);
  983                 }
  984         }
  985         PROC_SUNLOCK(p);
  986         if (wakeup_swapper)
  987                 kick_proc0();
  988 }
  989 
  990 struct thread *
  991 thread_find(struct proc *p, lwpid_t tid)
  992 {
  993         struct thread *td;
  994 
  995         PROC_LOCK_ASSERT(p, MA_OWNED);
  996         FOREACH_THREAD_IN_PROC(p, td) {
  997                 if (td->td_tid == tid)
  998                         break;
  999         }
 1000         return (td);
 1001 }
 1002 
 1003 /* Locate a thread by number; return with proc lock held. */
 1004 struct thread *
 1005 tdfind(lwpid_t tid, pid_t pid)
 1006 {
 1007 #define RUN_THRESH      16
 1008         struct thread *td;
 1009         int run = 0;
 1010 
 1011         rw_rlock(&tidhash_lock);
 1012         LIST_FOREACH(td, TIDHASH(tid), td_hash) {
 1013                 if (td->td_tid == tid) {
 1014                         if (pid != -1 && td->td_proc->p_pid != pid) {
 1015                                 td = NULL;
 1016                                 break;
 1017                         }
 1018                         PROC_LOCK(td->td_proc);
 1019                         if (td->td_proc->p_state == PRS_NEW) {
 1020                                 PROC_UNLOCK(td->td_proc);
 1021                                 td = NULL;
 1022                                 break;
 1023                         }
 1024                         if (run > RUN_THRESH) {
 1025                                 if (rw_try_upgrade(&tidhash_lock)) {
 1026                                         LIST_REMOVE(td, td_hash);
 1027                                         LIST_INSERT_HEAD(TIDHASH(td->td_tid),
 1028                                                 td, td_hash);
 1029                                         rw_wunlock(&tidhash_lock);
 1030                                         return (td);
 1031                                 }
 1032                         }
 1033                         break;
 1034                 }
 1035                 run++;
 1036         }
 1037         rw_runlock(&tidhash_lock);
 1038         return (td);
 1039 }
 1040 
 1041 void
 1042 tidhash_add(struct thread *td)
 1043 {
 1044         rw_wlock(&tidhash_lock);
 1045         LIST_INSERT_HEAD(TIDHASH(td->td_tid), td, td_hash);
 1046         rw_wunlock(&tidhash_lock);
 1047 }
 1048 
 1049 void
 1050 tidhash_remove(struct thread *td)
 1051 {
 1052         rw_wlock(&tidhash_lock);
 1053         LIST_REMOVE(td, td_hash);
 1054         rw_wunlock(&tidhash_lock);
 1055 }

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