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_kdtrace.h"
   31 #include "opt_hwpmc_hooks.h"
   32 
   33 #include <sys/cdefs.h>
   34 __FBSDID("$FreeBSD: stable/10/sys/kern/kern_thread.c 337258 2018-08-03 14:45:53Z asomers $");
   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/syscallsubr.h>
   50 #include <sys/sysent.h>
   51 #include <sys/turnstile.h>
   52 #include <sys/ktr.h>
   53 #include <sys/rwlock.h>
   54 #include <sys/umtx.h>
   55 #include <sys/cpuset.h>
   56 #ifdef  HWPMC_HOOKS
   57 #include <sys/pmckern.h>
   58 #endif
   59 
   60 #include <security/audit/audit.h>
   61 
   62 #include <vm/vm.h>
   63 #include <vm/vm_extern.h>
   64 #include <vm/uma.h>
   65 #include <sys/eventhandler.h>
   66 
   67 SDT_PROVIDER_DECLARE(proc);
   68 SDT_PROBE_DEFINE(proc, , , lwp__exit);
   69 
   70 /*
   71  * thread related storage.
   72  */
   73 static uma_zone_t thread_zone;
   74 
   75 TAILQ_HEAD(, thread) zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
   76 static struct mtx zombie_lock;
   77 MTX_SYSINIT(zombie_lock, &zombie_lock, "zombie lock", MTX_SPIN);
   78 
   79 static void thread_zombie(struct thread *);
   80 static int thread_unsuspend_one(struct thread *td, struct proc *p,
   81     bool boundary);
   82 
   83 #define TID_BUFFER_SIZE 1024
   84 
   85 struct mtx tid_lock;
   86 static struct unrhdr *tid_unrhdr;
   87 static lwpid_t tid_buffer[TID_BUFFER_SIZE];
   88 static int tid_head, tid_tail;
   89 static MALLOC_DEFINE(M_TIDHASH, "tidhash", "thread hash");
   90 
   91 struct  tidhashhead *tidhashtbl;
   92 u_long  tidhash;
   93 struct  rwlock tidhash_lock;
   94 
   95 static lwpid_t
   96 tid_alloc(void)
   97 {
   98         lwpid_t tid;
   99 
  100         tid = alloc_unr(tid_unrhdr);
  101         if (tid != -1)
  102                 return (tid);
  103         mtx_lock(&tid_lock);
  104         if (tid_head == tid_tail) {
  105                 mtx_unlock(&tid_lock);
  106                 return (-1);
  107         }
  108         tid = tid_buffer[tid_head];
  109         tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
  110         mtx_unlock(&tid_lock);
  111         return (tid);
  112 }
  113 
  114 static void
  115 tid_free(lwpid_t tid)
  116 {
  117         lwpid_t tmp_tid = -1;
  118 
  119         mtx_lock(&tid_lock);
  120         if ((tid_tail + 1) % TID_BUFFER_SIZE == tid_head) {
  121                 tmp_tid = tid_buffer[tid_head];
  122                 tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
  123         }
  124         tid_buffer[tid_tail] = tid;
  125         tid_tail = (tid_tail + 1) % TID_BUFFER_SIZE;
  126         mtx_unlock(&tid_lock);
  127         if (tmp_tid != -1)
  128                 free_unr(tid_unrhdr, tmp_tid);
  129 }
  130 
  131 /*
  132  * Prepare a thread for use.
  133  */
  134 static int
  135 thread_ctor(void *mem, int size, void *arg, int flags)
  136 {
  137         struct thread   *td;
  138 
  139         td = (struct thread *)mem;
  140         td->td_state = TDS_INACTIVE;
  141         td->td_oncpu = NOCPU;
  142 
  143         td->td_tid = tid_alloc();
  144 
  145         /*
  146          * Note that td_critnest begins life as 1 because the thread is not
  147          * running and is thereby implicitly waiting to be on the receiving
  148          * end of a context switch.
  149          */
  150         td->td_critnest = 1;
  151         td->td_lend_user_pri = PRI_MAX;
  152         EVENTHANDLER_INVOKE(thread_ctor, td);
  153 #ifdef AUDIT
  154         audit_thread_alloc(td);
  155 #endif
  156         umtx_thread_alloc(td);
  157         return (0);
  158 }
  159 
  160 /*
  161  * Reclaim a thread after use.
  162  */
  163 static void
  164 thread_dtor(void *mem, int size, void *arg)
  165 {
  166         struct thread *td;
  167 
  168         td = (struct thread *)mem;
  169 
  170 #ifdef INVARIANTS
  171         /* Verify that this thread is in a safe state to free. */
  172         switch (td->td_state) {
  173         case TDS_INHIBITED:
  174         case TDS_RUNNING:
  175         case TDS_CAN_RUN:
  176         case TDS_RUNQ:
  177                 /*
  178                  * We must never unlink a thread that is in one of
  179                  * these states, because it is currently active.
  180                  */
  181                 panic("bad state for thread unlinking");
  182                 /* NOTREACHED */
  183         case TDS_INACTIVE:
  184                 break;
  185         default:
  186                 panic("bad thread state");
  187                 /* NOTREACHED */
  188         }
  189 #endif
  190 #ifdef AUDIT
  191         audit_thread_free(td);
  192 #endif
  193         /* Free all OSD associated to this thread. */
  194         osd_thread_exit(td);
  195 
  196         EVENTHANDLER_INVOKE(thread_dtor, td);
  197         tid_free(td->td_tid);
  198 }
  199 
  200 /*
  201  * Initialize type-stable parts of a thread (when newly created).
  202  */
  203 static int
  204 thread_init(void *mem, int size, int flags)
  205 {
  206         struct thread *td;
  207 
  208         td = (struct thread *)mem;
  209 
  210         td->td_sleepqueue = sleepq_alloc();
  211         td->td_turnstile = turnstile_alloc();
  212         td->td_rlqe = NULL;
  213         EVENTHANDLER_INVOKE(thread_init, td);
  214         td->td_sched = (struct td_sched *)&td[1];
  215         umtx_thread_init(td);
  216         td->td_kstack = 0;
  217         td->td_sel = NULL;
  218         return (0);
  219 }
  220 
  221 /*
  222  * Tear down type-stable parts of a thread (just before being discarded).
  223  */
  224 static void
  225 thread_fini(void *mem, int size)
  226 {
  227         struct thread *td;
  228 
  229         td = (struct thread *)mem;
  230         EVENTHANDLER_INVOKE(thread_fini, td);
  231         rlqentry_free(td->td_rlqe);
  232         turnstile_free(td->td_turnstile);
  233         sleepq_free(td->td_sleepqueue);
  234         umtx_thread_fini(td);
  235         seltdfini(td);
  236 }
  237 
  238 /*
  239  * For a newly created process,
  240  * link up all the structures and its initial threads etc.
  241  * called from:
  242  * {arch}/{arch}/machdep.c   ia64_init(), init386() etc.
  243  * proc_dtor() (should go away)
  244  * proc_init()
  245  */
  246 void
  247 proc_linkup0(struct proc *p, struct thread *td)
  248 {
  249         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
  250         proc_linkup(p, td);
  251 }
  252 
  253 void
  254 proc_linkup(struct proc *p, struct thread *td)
  255 {
  256 
  257         sigqueue_init(&p->p_sigqueue, p);
  258         p->p_ksi = ksiginfo_alloc(1);
  259         if (p->p_ksi != NULL) {
  260                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
  261                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
  262         }
  263         LIST_INIT(&p->p_mqnotifier);
  264         p->p_numthreads = 0;
  265         thread_link(td, p);
  266 }
  267 
  268 /*
  269  * Initialize global thread allocation resources.
  270  */
  271 void
  272 threadinit(void)
  273 {
  274 
  275         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
  276 
  277         /*
  278          * pid_max cannot be greater than PID_MAX.
  279          * leave one number for thread0.
  280          */
  281         tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
  282 
  283         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
  284             thread_ctor, thread_dtor, thread_init, thread_fini,
  285             16 - 1, UMA_ZONE_NOFREE);
  286         tidhashtbl = hashinit(maxproc / 2, M_TIDHASH, &tidhash);
  287         rw_init(&tidhash_lock, "tidhash");
  288 }
  289 
  290 /*
  291  * Place an unused thread on the zombie list.
  292  * Use the slpq as that must be unused by now.
  293  */
  294 void
  295 thread_zombie(struct thread *td)
  296 {
  297         mtx_lock_spin(&zombie_lock);
  298         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
  299         mtx_unlock_spin(&zombie_lock);
  300 }
  301 
  302 /*
  303  * Release a thread that has exited after cpu_throw().
  304  */
  305 void
  306 thread_stash(struct thread *td)
  307 {
  308         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
  309         thread_zombie(td);
  310 }
  311 
  312 /*
  313  * Reap zombie resources.
  314  */
  315 void
  316 thread_reap(void)
  317 {
  318         struct thread *td_first, *td_next;
  319 
  320         /*
  321          * Don't even bother to lock if none at this instant,
  322          * we really don't care about the next instant.
  323          */
  324         if (!TAILQ_EMPTY(&zombie_threads)) {
  325                 mtx_lock_spin(&zombie_lock);
  326                 td_first = TAILQ_FIRST(&zombie_threads);
  327                 if (td_first)
  328                         TAILQ_INIT(&zombie_threads);
  329                 mtx_unlock_spin(&zombie_lock);
  330                 while (td_first) {
  331                         td_next = TAILQ_NEXT(td_first, td_slpq);
  332                         if (td_first->td_ucred)
  333                                 crfree(td_first->td_ucred);
  334                         thread_free(td_first);
  335                         td_first = td_next;
  336                 }
  337         }
  338 }
  339 
  340 /*
  341  * Allocate a thread.
  342  */
  343 struct thread *
  344 thread_alloc(int pages)
  345 {
  346         struct thread *td;
  347 
  348         thread_reap(); /* check if any zombies to get */
  349 
  350         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
  351         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
  352         if (!vm_thread_new(td, pages)) {
  353                 uma_zfree(thread_zone, td);
  354                 return (NULL);
  355         }
  356         cpu_thread_alloc(td);
  357         return (td);
  358 }
  359 
  360 int
  361 thread_alloc_stack(struct thread *td, int pages)
  362 {
  363 
  364         KASSERT(td->td_kstack == 0,
  365             ("thread_alloc_stack called on a thread with kstack"));
  366         if (!vm_thread_new(td, pages))
  367                 return (0);
  368         cpu_thread_alloc(td);
  369         return (1);
  370 }
  371 
  372 /*
  373  * Deallocate a thread.
  374  */
  375 void
  376 thread_free(struct thread *td)
  377 {
  378 
  379         lock_profile_thread_exit(td);
  380         if (td->td_cpuset)
  381                 cpuset_rel(td->td_cpuset);
  382         td->td_cpuset = NULL;
  383         cpu_thread_free(td);
  384         if (td->td_kstack != 0)
  385                 vm_thread_dispose(td);
  386         callout_drain(&td->td_slpcallout);
  387         uma_zfree(thread_zone, td);
  388 }
  389 
  390 /*
  391  * Discard the current thread and exit from its context.
  392  * Always called with scheduler locked.
  393  *
  394  * Because we can't free a thread while we're operating under its context,
  395  * push the current thread into our CPU's deadthread holder. This means
  396  * we needn't worry about someone else grabbing our context before we
  397  * do a cpu_throw().
  398  */
  399 void
  400 thread_exit(void)
  401 {
  402         uint64_t runtime, new_switchtime;
  403         struct thread *td;
  404         struct thread *td2;
  405         struct proc *p;
  406         int wakeup_swapper;
  407 
  408         td = curthread;
  409         p = td->td_proc;
  410 
  411         PROC_SLOCK_ASSERT(p, MA_OWNED);
  412         mtx_assert(&Giant, MA_NOTOWNED);
  413 
  414         PROC_LOCK_ASSERT(p, MA_OWNED);
  415         KASSERT(p != NULL, ("thread exiting without a process"));
  416         CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
  417             (long)p->p_pid, td->td_name);
  418         SDT_PROBE0(proc, , , lwp__exit);
  419         KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
  420 
  421         /*
  422          * drop FPU & debug register state storage, or any other
  423          * architecture specific resources that
  424          * would not be on a new untouched process.
  425          */
  426         cpu_thread_exit(td);
  427 
  428         /*
  429          * The last thread is left attached to the process
  430          * So that the whole bundle gets recycled. Skip
  431          * all this stuff if we never had threads.
  432          * EXIT clears all sign of other threads when
  433          * it goes to single threading, so the last thread always
  434          * takes the short path.
  435          */
  436         if (p->p_flag & P_HADTHREADS) {
  437                 if (p->p_numthreads > 1) {
  438                         atomic_add_int(&td->td_proc->p_exitthreads, 1);
  439                         thread_unlink(td);
  440                         td2 = FIRST_THREAD_IN_PROC(p);
  441                         sched_exit_thread(td2, td);
  442 
  443                         /*
  444                          * The test below is NOT true if we are the
  445                          * sole exiting thread. P_STOPPED_SINGLE is unset
  446                          * in exit1() after it is the only survivor.
  447                          */
  448                         if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  449                                 if (p->p_numthreads == p->p_suspcount) {
  450                                         thread_lock(p->p_singlethread);
  451                                         wakeup_swapper = thread_unsuspend_one(
  452                                                 p->p_singlethread, p, false);
  453                                         thread_unlock(p->p_singlethread);
  454                                         if (wakeup_swapper)
  455                                                 kick_proc0();
  456                                 }
  457                         }
  458 
  459                         PCPU_SET(deadthread, td);
  460                 } else {
  461                         /*
  462                          * The last thread is exiting.. but not through exit()
  463                          */
  464                         panic ("thread_exit: Last thread exiting on its own");
  465                 }
  466         } 
  467 #ifdef  HWPMC_HOOKS
  468         /*
  469          * If this thread is part of a process that is being tracked by hwpmc(4),
  470          * inform the module of the thread's impending exit.
  471          */
  472         if (PMC_PROC_IS_USING_PMCS(td->td_proc))
  473                 PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
  474 #endif
  475         PROC_UNLOCK(p);
  476         PROC_STATLOCK(p);
  477         thread_lock(td);
  478         PROC_SUNLOCK(p);
  479 
  480         /* Do the same timestamp bookkeeping that mi_switch() would do. */
  481         new_switchtime = cpu_ticks();
  482         runtime = new_switchtime - PCPU_GET(switchtime);
  483         td->td_runtime += runtime;
  484         td->td_incruntime += runtime;
  485         PCPU_SET(switchtime, new_switchtime);
  486         PCPU_SET(switchticks, ticks);
  487         PCPU_INC(cnt.v_swtch);
  488 
  489         /* Save our resource usage in our process. */
  490         td->td_ru.ru_nvcsw++;
  491         ruxagg(p, td);
  492         rucollect(&p->p_ru, &td->td_ru);
  493         PROC_STATUNLOCK(p);
  494 
  495         td->td_state = TDS_INACTIVE;
  496 #ifdef WITNESS
  497         witness_thread_exit(td);
  498 #endif
  499         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
  500         sched_throw(td);
  501         panic("I'm a teapot!");
  502         /* NOTREACHED */
  503 }
  504 
  505 /*
  506  * Do any thread specific cleanups that may be needed in wait()
  507  * called with Giant, proc and schedlock not held.
  508  */
  509 void
  510 thread_wait(struct proc *p)
  511 {
  512         struct thread *td;
  513 
  514         mtx_assert(&Giant, MA_NOTOWNED);
  515         KASSERT(p->p_numthreads == 1, ("multiple threads in thread_wait()"));
  516         KASSERT(p->p_exitthreads == 0, ("p_exitthreads leaking"));
  517         td = FIRST_THREAD_IN_PROC(p);
  518         /* Lock the last thread so we spin until it exits cpu_throw(). */
  519         thread_lock(td);
  520         thread_unlock(td);
  521         lock_profile_thread_exit(td);
  522         cpuset_rel(td->td_cpuset);
  523         td->td_cpuset = NULL;
  524         cpu_thread_clean(td);
  525         crfree(td->td_ucred);
  526         callout_drain(&td->td_slpcallout);
  527         thread_reap();  /* check for zombie threads etc. */
  528 }
  529 
  530 /*
  531  * Link a thread to a process.
  532  * set up anything that needs to be initialized for it to
  533  * be used by the process.
  534  */
  535 void
  536 thread_link(struct thread *td, struct proc *p)
  537 {
  538 
  539         /*
  540          * XXX This can't be enabled because it's called for proc0 before
  541          * its lock has been created.
  542          * PROC_LOCK_ASSERT(p, MA_OWNED);
  543          */
  544         td->td_state    = TDS_INACTIVE;
  545         td->td_proc     = p;
  546         td->td_flags    = TDF_INMEM;
  547 
  548         LIST_INIT(&td->td_contested);
  549         LIST_INIT(&td->td_lprof[0]);
  550         LIST_INIT(&td->td_lprof[1]);
  551         sigqueue_init(&td->td_sigqueue, p);
  552         callout_init(&td->td_slpcallout, 1);
  553         TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
  554         p->p_numthreads++;
  555 }
  556 
  557 /*
  558  * Called from:
  559  *  thread_exit()
  560  */
  561 void
  562 thread_unlink(struct thread *td)
  563 {
  564         struct proc *p = td->td_proc;
  565 
  566         PROC_LOCK_ASSERT(p, MA_OWNED);
  567         TAILQ_REMOVE(&p->p_threads, td, td_plist);
  568         p->p_numthreads--;
  569         /* could clear a few other things here */
  570         /* Must  NOT clear links to proc! */
  571 }
  572 
  573 static int
  574 calc_remaining(struct proc *p, int mode)
  575 {
  576         int remaining;
  577 
  578         PROC_LOCK_ASSERT(p, MA_OWNED);
  579         PROC_SLOCK_ASSERT(p, MA_OWNED);
  580         if (mode == SINGLE_EXIT)
  581                 remaining = p->p_numthreads;
  582         else if (mode == SINGLE_BOUNDARY)
  583                 remaining = p->p_numthreads - p->p_boundary_count;
  584         else if (mode == SINGLE_NO_EXIT || mode == SINGLE_ALLPROC)
  585                 remaining = p->p_numthreads - p->p_suspcount;
  586         else
  587                 panic("calc_remaining: wrong mode %d", mode);
  588         return (remaining);
  589 }
  590 
  591 static int
  592 remain_for_mode(int mode)
  593 {
  594 
  595         return (mode == SINGLE_ALLPROC ? 0 : 1);
  596 }
  597 
  598 static int
  599 weed_inhib(int mode, struct thread *td2, struct proc *p)
  600 {
  601         int wakeup_swapper;
  602 
  603         PROC_LOCK_ASSERT(p, MA_OWNED);
  604         PROC_SLOCK_ASSERT(p, MA_OWNED);
  605         THREAD_LOCK_ASSERT(td2, MA_OWNED);
  606 
  607         wakeup_swapper = 0;
  608         switch (mode) {
  609         case SINGLE_EXIT:
  610                 if (TD_IS_SUSPENDED(td2))
  611                         wakeup_swapper |= thread_unsuspend_one(td2, p, true);
  612                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0)
  613                         wakeup_swapper |= sleepq_abort(td2, EINTR);
  614                 break;
  615         case SINGLE_BOUNDARY:
  616         case SINGLE_NO_EXIT:
  617                 if (TD_IS_SUSPENDED(td2) && (td2->td_flags & TDF_BOUNDARY) == 0)
  618                         wakeup_swapper |= thread_unsuspend_one(td2, p, false);
  619                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0)
  620                         wakeup_swapper |= sleepq_abort(td2, ERESTART);
  621                 break;
  622         case SINGLE_ALLPROC:
  623                 /*
  624                  * ALLPROC suspend tries to avoid spurious EINTR for
  625                  * threads sleeping interruptable, by suspending the
  626                  * thread directly, similarly to sig_suspend_threads().
  627                  * Since such sleep is not performed at the user
  628                  * boundary, TDF_BOUNDARY flag is not set, and TDF_ALLPROCSUSP
  629                  * is used to avoid immediate un-suspend.
  630                  */
  631                 if (TD_IS_SUSPENDED(td2) && (td2->td_flags & (TDF_BOUNDARY |
  632                     TDF_ALLPROCSUSP)) == 0)
  633                         wakeup_swapper |= thread_unsuspend_one(td2, p, false);
  634                 if (TD_ON_SLEEPQ(td2) && (td2->td_flags & TDF_SINTR) != 0) {
  635                         if ((td2->td_flags & TDF_SBDRY) == 0) {
  636                                 thread_suspend_one(td2);
  637                                 td2->td_flags |= TDF_ALLPROCSUSP;
  638                         } else {
  639                                 wakeup_swapper |= sleepq_abort(td2, ERESTART);
  640                         }
  641                 }
  642                 break;
  643         }
  644         return (wakeup_swapper);
  645 }
  646 
  647 /*
  648  * Enforce single-threading.
  649  *
  650  * Returns 1 if the caller must abort (another thread is waiting to
  651  * exit the process or similar). Process is locked!
  652  * Returns 0 when you are successfully the only thread running.
  653  * A process has successfully single threaded in the suspend mode when
  654  * There are no threads in user mode. Threads in the kernel must be
  655  * allowed to continue until they get to the user boundary. They may even
  656  * copy out their return values and data before suspending. They may however be
  657  * accelerated in reaching the user boundary as we will wake up
  658  * any sleeping threads that are interruptable. (PCATCH).
  659  */
  660 int
  661 thread_single(struct proc *p, int mode)
  662 {
  663         struct thread *td;
  664         struct thread *td2;
  665         int remaining, wakeup_swapper;
  666 
  667         td = curthread;
  668         KASSERT(mode == SINGLE_EXIT || mode == SINGLE_BOUNDARY ||
  669             mode == SINGLE_ALLPROC || mode == SINGLE_NO_EXIT,
  670             ("invalid mode %d", mode));
  671         /*
  672          * If allowing non-ALLPROC singlethreading for non-curproc
  673          * callers, calc_remaining() and remain_for_mode() should be
  674          * adjusted to also account for td->td_proc != p.  For now
  675          * this is not implemented because it is not used.
  676          */
  677         KASSERT((mode == SINGLE_ALLPROC && td->td_proc != p) ||
  678             (mode != SINGLE_ALLPROC && td->td_proc == p),
  679             ("mode %d proc %p curproc %p", mode, p, td->td_proc));
  680         mtx_assert(&Giant, MA_NOTOWNED);
  681         PROC_LOCK_ASSERT(p, MA_OWNED);
  682 
  683         if ((p->p_flag & P_HADTHREADS) == 0 && mode != SINGLE_ALLPROC)
  684                 return (0);
  685 
  686         /* Is someone already single threading? */
  687         if (p->p_singlethread != NULL && p->p_singlethread != td)
  688                 return (1);
  689 
  690         if (mode == SINGLE_EXIT) {
  691                 p->p_flag |= P_SINGLE_EXIT;
  692                 p->p_flag &= ~P_SINGLE_BOUNDARY;
  693         } else {
  694                 p->p_flag &= ~P_SINGLE_EXIT;
  695                 if (mode == SINGLE_BOUNDARY)
  696                         p->p_flag |= P_SINGLE_BOUNDARY;
  697                 else
  698                         p->p_flag &= ~P_SINGLE_BOUNDARY;
  699         }
  700         if (mode == SINGLE_ALLPROC)
  701                 p->p_flag |= P_TOTAL_STOP;
  702         p->p_flag |= P_STOPPED_SINGLE;
  703         PROC_SLOCK(p);
  704         p->p_singlethread = td;
  705         remaining = calc_remaining(p, mode);
  706         while (remaining != remain_for_mode(mode)) {
  707                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
  708                         goto stopme;
  709                 wakeup_swapper = 0;
  710                 FOREACH_THREAD_IN_PROC(p, td2) {
  711                         if (td2 == td)
  712                                 continue;
  713                         thread_lock(td2);
  714                         td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
  715                         if (TD_IS_INHIBITED(td2)) {
  716                                 wakeup_swapper |= weed_inhib(mode, td2, p);
  717 #ifdef SMP
  718                         } else if (TD_IS_RUNNING(td2) && td != td2) {
  719                                 forward_signal(td2);
  720 #endif
  721                         }
  722                         thread_unlock(td2);
  723                 }
  724                 if (wakeup_swapper)
  725                         kick_proc0();
  726                 remaining = calc_remaining(p, mode);
  727 
  728                 /*
  729                  * Maybe we suspended some threads.. was it enough?
  730                  */
  731                 if (remaining == remain_for_mode(mode))
  732                         break;
  733 
  734 stopme:
  735                 /*
  736                  * Wake us up when everyone else has suspended.
  737                  * In the mean time we suspend as well.
  738                  */
  739                 thread_suspend_switch(td, p);
  740                 remaining = calc_remaining(p, mode);
  741         }
  742         if (mode == SINGLE_EXIT) {
  743                 /*
  744                  * Convert the process to an unthreaded process.  The
  745                  * SINGLE_EXIT is called by exit1() or execve(), in
  746                  * both cases other threads must be retired.
  747                  */
  748                 KASSERT(p->p_numthreads == 1, ("Unthreading with >1 threads"));
  749                 p->p_singlethread = NULL;
  750                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_HADTHREADS);
  751 
  752                 /*
  753                  * Wait for any remaining threads to exit cpu_throw().
  754                  */
  755                 while (p->p_exitthreads != 0) {
  756                         PROC_SUNLOCK(p);
  757                         PROC_UNLOCK(p);
  758                         sched_relinquish(td);
  759                         PROC_LOCK(p);
  760                         PROC_SLOCK(p);
  761                 }
  762         } else if (mode == SINGLE_BOUNDARY) {
  763                 /*
  764                  * Wait until all suspended threads are removed from
  765                  * the processors.  The thread_suspend_check()
  766                  * increments p_boundary_count while it is still
  767                  * running, which makes it possible for the execve()
  768                  * to destroy vmspace while our other threads are
  769                  * still using the address space.
  770                  *
  771                  * We lock the thread, which is only allowed to
  772                  * succeed after context switch code finished using
  773                  * the address space.
  774                  */
  775                 FOREACH_THREAD_IN_PROC(p, td2) {
  776                         if (td2 == td)
  777                                 continue;
  778                         thread_lock(td2);
  779                         KASSERT((td2->td_flags & TDF_BOUNDARY) != 0,
  780                             ("td %p not on boundary", td2));
  781                         KASSERT(TD_IS_SUSPENDED(td2),
  782                             ("td %p is not suspended", td2));
  783                         thread_unlock(td2);
  784                 }
  785         }
  786         PROC_SUNLOCK(p);
  787         return (0);
  788 }
  789 
  790 bool
  791 thread_suspend_check_needed(void)
  792 {
  793         struct proc *p;
  794         struct thread *td;
  795 
  796         td = curthread;
  797         p = td->td_proc;
  798         PROC_LOCK_ASSERT(p, MA_OWNED);
  799         return (P_SHOULDSTOP(p) || ((p->p_flag & P_TRACED) != 0 &&
  800             (td->td_dbgflags & TDB_SUSPEND) != 0));
  801 }
  802 
  803 /*
  804  * Called in from locations that can safely check to see
  805  * whether we have to suspend or at least throttle for a
  806  * single-thread event (e.g. fork).
  807  *
  808  * Such locations include userret().
  809  * If the "return_instead" argument is non zero, the thread must be able to
  810  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
  811  *
  812  * The 'return_instead' argument tells the function if it may do a
  813  * thread_exit() or suspend, or whether the caller must abort and back
  814  * out instead.
  815  *
  816  * If the thread that set the single_threading request has set the
  817  * P_SINGLE_EXIT bit in the process flags then this call will never return
  818  * if 'return_instead' is false, but will exit.
  819  *
  820  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
  821  *---------------+--------------------+---------------------
  822  *       0       | returns 0          |   returns 0 or 1
  823  *               | when ST ends       |   immediately
  824  *---------------+--------------------+---------------------
  825  *       1       | thread exits       |   returns 1
  826  *               |                    |  immediately
  827  * 0 = thread_exit() or suspension ok,
  828  * other = return error instead of stopping the thread.
  829  *
  830  * While a full suspension is under effect, even a single threading
  831  * thread would be suspended if it made this call (but it shouldn't).
  832  * This call should only be made from places where
  833  * thread_exit() would be safe as that may be the outcome unless
  834  * return_instead is set.
  835  */
  836 int
  837 thread_suspend_check(int return_instead)
  838 {
  839         struct thread *td;
  840         struct proc *p;
  841         int wakeup_swapper;
  842 
  843         td = curthread;
  844         p = td->td_proc;
  845         mtx_assert(&Giant, MA_NOTOWNED);
  846         PROC_LOCK_ASSERT(p, MA_OWNED);
  847         while (thread_suspend_check_needed()) {
  848                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  849                         KASSERT(p->p_singlethread != NULL,
  850                             ("singlethread not set"));
  851                         /*
  852                          * The only suspension in action is a
  853                          * single-threading. Single threader need not stop.
  854                          * It is safe to access p->p_singlethread unlocked
  855                          * because it can only be set to our address by us.
  856                          */
  857                         if (p->p_singlethread == td)
  858                                 return (0);     /* Exempt from stopping. */
  859                 }
  860                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
  861                         return (EINTR);
  862 
  863                 /* Should we goto user boundary if we didn't come from there? */
  864                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
  865                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
  866                         return (ERESTART);
  867 
  868                 /*
  869                  * Ignore suspend requests if they are deferred.
  870                  */
  871                 if ((td->td_flags & TDF_SBDRY) != 0) {
  872                         KASSERT(return_instead,
  873                             ("TDF_SBDRY set for unsafe thread_suspend_check"));
  874                         return (0);
  875                 }
  876 
  877                 /*
  878                  * If the process is waiting for us to exit,
  879                  * this thread should just suicide.
  880                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
  881                  */
  882                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td)) {
  883                         PROC_UNLOCK(p);
  884 
  885                         /*
  886                          * Allow Linux emulation layer to do some work
  887                          * before thread suicide.
  888                          */
  889                         if (__predict_false(p->p_sysent->sv_thread_detach != NULL))
  890                                 (p->p_sysent->sv_thread_detach)(td);
  891                         kern_thr_exit(td);
  892                         panic("stopped thread did not exit");
  893                 }
  894 
  895                 PROC_SLOCK(p);
  896                 thread_stopped(p);
  897                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  898                         if (p->p_numthreads == p->p_suspcount + 1) {
  899                                 thread_lock(p->p_singlethread);
  900                                 wakeup_swapper = thread_unsuspend_one(
  901                                     p->p_singlethread, p, false);
  902                                 thread_unlock(p->p_singlethread);
  903                                 if (wakeup_swapper)
  904                                         kick_proc0();
  905                         }
  906                 }
  907                 PROC_UNLOCK(p);
  908                 thread_lock(td);
  909                 /*
  910                  * When a thread suspends, it just
  911                  * gets taken off all queues.
  912                  */
  913                 thread_suspend_one(td);
  914                 if (return_instead == 0) {
  915                         p->p_boundary_count++;
  916                         td->td_flags |= TDF_BOUNDARY;
  917                 }
  918                 PROC_SUNLOCK(p);
  919                 mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
  920                 thread_unlock(td);
  921                 PROC_LOCK(p);
  922         }
  923         return (0);
  924 }
  925 
  926 void
  927 thread_suspend_switch(struct thread *td, struct proc *p)
  928 {
  929 
  930         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  931         PROC_LOCK_ASSERT(p, MA_OWNED);
  932         PROC_SLOCK_ASSERT(p, MA_OWNED);
  933         /*
  934          * We implement thread_suspend_one in stages here to avoid
  935          * dropping the proc lock while the thread lock is owned.
  936          */
  937         if (p == td->td_proc) {
  938                 thread_stopped(p);
  939                 p->p_suspcount++;
  940         }
  941         PROC_UNLOCK(p);
  942         thread_lock(td);
  943         td->td_flags &= ~TDF_NEEDSUSPCHK;
  944         TD_SET_SUSPENDED(td);
  945         sched_sleep(td, 0);
  946         PROC_SUNLOCK(p);
  947         DROP_GIANT();
  948         mi_switch(SW_VOL | SWT_SUSPEND, NULL);
  949         thread_unlock(td);
  950         PICKUP_GIANT();
  951         PROC_LOCK(p);
  952         PROC_SLOCK(p);
  953 }
  954 
  955 void
  956 thread_suspend_one(struct thread *td)
  957 {
  958         struct proc *p;
  959 
  960         p = td->td_proc;
  961         PROC_SLOCK_ASSERT(p, MA_OWNED);
  962         THREAD_LOCK_ASSERT(td, MA_OWNED);
  963         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  964         p->p_suspcount++;
  965         td->td_flags &= ~TDF_NEEDSUSPCHK;
  966         TD_SET_SUSPENDED(td);
  967         sched_sleep(td, 0);
  968 }
  969 
  970 static int
  971 thread_unsuspend_one(struct thread *td, struct proc *p, bool boundary)
  972 {
  973 
  974         THREAD_LOCK_ASSERT(td, MA_OWNED);
  975         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
  976         TD_CLR_SUSPENDED(td);
  977         td->td_flags &= ~TDF_ALLPROCSUSP;
  978         if (td->td_proc == p) {
  979                 PROC_SLOCK_ASSERT(p, MA_OWNED);
  980                 p->p_suspcount--;
  981                 if (boundary && (td->td_flags & TDF_BOUNDARY) != 0) {
  982                         td->td_flags &= ~TDF_BOUNDARY;
  983                         p->p_boundary_count--;
  984                 }
  985         }
  986         return (setrunnable(td));
  987 }
  988 
  989 /*
  990  * Allow all threads blocked by single threading to continue running.
  991  */
  992 void
  993 thread_unsuspend(struct proc *p)
  994 {
  995         struct thread *td;
  996         int wakeup_swapper;
  997 
  998         PROC_LOCK_ASSERT(p, MA_OWNED);
  999         PROC_SLOCK_ASSERT(p, MA_OWNED);
 1000         wakeup_swapper = 0;
 1001         if (!P_SHOULDSTOP(p)) {
 1002                 FOREACH_THREAD_IN_PROC(p, td) {
 1003                         thread_lock(td);
 1004                         if (TD_IS_SUSPENDED(td)) {
 1005                                 wakeup_swapper |= thread_unsuspend_one(td, p,
 1006                                     true);
 1007                         }
 1008                         thread_unlock(td);
 1009                 }
 1010         } else if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
 1011             p->p_numthreads == p->p_suspcount) {
 1012                 /*
 1013                  * Stopping everything also did the job for the single
 1014                  * threading request. Now we've downgraded to single-threaded,
 1015                  * let it continue.
 1016                  */
 1017                 if (p->p_singlethread->td_proc == p) {
 1018                         thread_lock(p->p_singlethread);
 1019                         wakeup_swapper = thread_unsuspend_one(
 1020                             p->p_singlethread, p, false);
 1021                         thread_unlock(p->p_singlethread);
 1022                 }
 1023         }
 1024         if (wakeup_swapper)
 1025                 kick_proc0();
 1026 }
 1027 
 1028 /*
 1029  * End the single threading mode..
 1030  */
 1031 void
 1032 thread_single_end(struct proc *p, int mode)
 1033 {
 1034         struct thread *td;
 1035         int wakeup_swapper;
 1036 
 1037         KASSERT(mode == SINGLE_EXIT || mode == SINGLE_BOUNDARY ||
 1038             mode == SINGLE_ALLPROC || mode == SINGLE_NO_EXIT,
 1039             ("invalid mode %d", mode));
 1040         PROC_LOCK_ASSERT(p, MA_OWNED);
 1041         KASSERT((mode == SINGLE_ALLPROC && (p->p_flag & P_TOTAL_STOP) != 0) ||
 1042             (mode != SINGLE_ALLPROC && (p->p_flag & P_TOTAL_STOP) == 0),
 1043             ("mode %d does not match P_TOTAL_STOP", mode));
 1044         KASSERT(mode == SINGLE_ALLPROC || p->p_singlethread == curthread,
 1045             ("thread_single_end from other thread %p %p",
 1046             curthread, p->p_singlethread));
 1047         KASSERT(mode != SINGLE_BOUNDARY ||
 1048             (p->p_flag & P_SINGLE_BOUNDARY) != 0,
 1049             ("mis-matched SINGLE_BOUNDARY flags %x", p->p_flag));
 1050         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY |
 1051             P_TOTAL_STOP);
 1052         PROC_SLOCK(p);
 1053         p->p_singlethread = NULL;
 1054         wakeup_swapper = 0;
 1055         /*
 1056          * If there are other threads they may now run,
 1057          * unless of course there is a blanket 'stop order'
 1058          * on the process. The single threader must be allowed
 1059          * to continue however as this is a bad place to stop.
 1060          */
 1061         if (p->p_numthreads != remain_for_mode(mode) && !P_SHOULDSTOP(p)) {
 1062                 FOREACH_THREAD_IN_PROC(p, td) {
 1063                         thread_lock(td);
 1064                         if (TD_IS_SUSPENDED(td)) {
 1065                                 wakeup_swapper |= thread_unsuspend_one(td, p,
 1066                                     mode == SINGLE_BOUNDARY);
 1067                         }
 1068                         thread_unlock(td);
 1069                 }
 1070         }
 1071         KASSERT(mode != SINGLE_BOUNDARY || p->p_boundary_count == 0,
 1072             ("inconsistent boundary count %d", p->p_boundary_count));
 1073         PROC_SUNLOCK(p);
 1074         if (wakeup_swapper)
 1075                 kick_proc0();
 1076 }
 1077 
 1078 struct thread *
 1079 thread_find(struct proc *p, lwpid_t tid)
 1080 {
 1081         struct thread *td;
 1082 
 1083         PROC_LOCK_ASSERT(p, MA_OWNED);
 1084         FOREACH_THREAD_IN_PROC(p, td) {
 1085                 if (td->td_tid == tid)
 1086                         break;
 1087         }
 1088         return (td);
 1089 }
 1090 
 1091 /* Locate a thread by number; return with proc lock held. */
 1092 struct thread *
 1093 tdfind(lwpid_t tid, pid_t pid)
 1094 {
 1095 #define RUN_THRESH      16
 1096         struct thread *td;
 1097         int run = 0;
 1098 
 1099         rw_rlock(&tidhash_lock);
 1100         LIST_FOREACH(td, TIDHASH(tid), td_hash) {
 1101                 if (td->td_tid == tid) {
 1102                         if (pid != -1 && td->td_proc->p_pid != pid) {
 1103                                 td = NULL;
 1104                                 break;
 1105                         }
 1106                         PROC_LOCK(td->td_proc);
 1107                         if (td->td_proc->p_state == PRS_NEW) {
 1108                                 PROC_UNLOCK(td->td_proc);
 1109                                 td = NULL;
 1110                                 break;
 1111                         }
 1112                         if (run > RUN_THRESH) {
 1113                                 if (rw_try_upgrade(&tidhash_lock)) {
 1114                                         LIST_REMOVE(td, td_hash);
 1115                                         LIST_INSERT_HEAD(TIDHASH(td->td_tid),
 1116                                                 td, td_hash);
 1117                                         rw_wunlock(&tidhash_lock);
 1118                                         return (td);
 1119                                 }
 1120                         }
 1121                         break;
 1122                 }
 1123                 run++;
 1124         }
 1125         rw_runlock(&tidhash_lock);
 1126         return (td);
 1127 }
 1128 
 1129 void
 1130 tidhash_add(struct thread *td)
 1131 {
 1132         rw_wlock(&tidhash_lock);
 1133         LIST_INSERT_HEAD(TIDHASH(td->td_tid), td, td_hash);
 1134         rw_wunlock(&tidhash_lock);
 1135 }
 1136 
 1137 void
 1138 tidhash_remove(struct thread *td)
 1139 {
 1140         rw_wlock(&tidhash_lock);
 1141         LIST_REMOVE(td, td_hash);
 1142         rw_wunlock(&tidhash_lock);
 1143 }

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