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 <sys/cdefs.h>
   30 __FBSDID("$FreeBSD$");
   31 
   32 #include <sys/param.h>
   33 #include <sys/systm.h>
   34 #include <sys/kernel.h>
   35 #include <sys/lock.h>
   36 #include <sys/mutex.h>
   37 #include <sys/proc.h>
   38 #include <sys/resourcevar.h>
   39 #include <sys/smp.h>
   40 #include <sys/sysctl.h>
   41 #include <sys/sched.h>
   42 #include <sys/sleepqueue.h>
   43 #include <sys/turnstile.h>
   44 #include <sys/ktr.h>
   45 #include <sys/umtx.h>
   46 #include <sys/cpuset.h>
   47 
   48 #include <security/audit/audit.h>
   49 
   50 #include <vm/vm.h>
   51 #include <vm/vm_extern.h>
   52 #include <vm/uma.h>
   53 #include <sys/eventhandler.h>
   54 
   55 /*
   56  * thread related storage.
   57  */
   58 static uma_zone_t thread_zone;
   59 
   60 SYSCTL_NODE(_kern, OID_AUTO, threads, CTLFLAG_RW, 0, "thread allocation");
   61 
   62 int max_threads_per_proc = 1500;
   63 SYSCTL_INT(_kern_threads, OID_AUTO, max_threads_per_proc, CTLFLAG_RW,
   64         &max_threads_per_proc, 0, "Limit on threads per proc");
   65 
   66 int max_threads_hits;
   67 SYSCTL_INT(_kern_threads, OID_AUTO, max_threads_hits, CTLFLAG_RD,
   68         &max_threads_hits, 0, "");
   69 
   70 #ifdef KSE
   71 int virtual_cpu;
   72 
   73 #endif
   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 #ifdef KSE
   81 static int
   82 sysctl_kse_virtual_cpu(SYSCTL_HANDLER_ARGS)
   83 {
   84         int error, new_val;
   85         int def_val;
   86 
   87         def_val = mp_ncpus;
   88         if (virtual_cpu == 0)
   89                 new_val = def_val;
   90         else
   91                 new_val = virtual_cpu;
   92         error = sysctl_handle_int(oidp, &new_val, 0, req);
   93         if (error != 0 || req->newptr == NULL)
   94                 return (error);
   95         if (new_val < 0)
   96                 return (EINVAL);
   97         virtual_cpu = new_val;
   98         return (0);
   99 }
  100 
  101 /* DEBUG ONLY */
  102 SYSCTL_PROC(_kern_threads, OID_AUTO, virtual_cpu, CTLTYPE_INT|CTLFLAG_RW,
  103         0, sizeof(virtual_cpu), sysctl_kse_virtual_cpu, "I",
  104         "debug virtual cpus");
  105 #endif
  106 
  107 struct mtx tid_lock;
  108 static struct unrhdr *tid_unrhdr;
  109 
  110 /*
  111  * Prepare a thread for use.
  112  */
  113 static int
  114 thread_ctor(void *mem, int size, void *arg, int flags)
  115 {
  116         struct thread   *td;
  117 
  118         td = (struct thread *)mem;
  119         td->td_state = TDS_INACTIVE;
  120         td->td_oncpu = NOCPU;
  121 
  122         td->td_tid = alloc_unr(tid_unrhdr);
  123         td->td_syscalls = 0;
  124         td->td_incruntime = 0;
  125 
  126         /*
  127          * Note that td_critnest begins life as 1 because the thread is not
  128          * running and is thereby implicitly waiting to be on the receiving
  129          * end of a context switch.
  130          */
  131         td->td_critnest = 1;
  132         EVENTHANDLER_INVOKE(thread_ctor, td);
  133 #ifdef AUDIT
  134         audit_thread_alloc(td);
  135 #endif
  136         umtx_thread_alloc(td);
  137         return (0);
  138 }
  139 
  140 /*
  141  * Reclaim a thread after use.
  142  */
  143 static void
  144 thread_dtor(void *mem, int size, void *arg)
  145 {
  146         struct thread *td;
  147 
  148         td = (struct thread *)mem;
  149 
  150 #ifdef INVARIANTS
  151         /* Verify that this thread is in a safe state to free. */
  152         switch (td->td_state) {
  153         case TDS_INHIBITED:
  154         case TDS_RUNNING:
  155         case TDS_CAN_RUN:
  156         case TDS_RUNQ:
  157                 /*
  158                  * We must never unlink a thread that is in one of
  159                  * these states, because it is currently active.
  160                  */
  161                 panic("bad state for thread unlinking");
  162                 /* NOTREACHED */
  163         case TDS_INACTIVE:
  164                 break;
  165         default:
  166                 panic("bad thread state");
  167                 /* NOTREACHED */
  168         }
  169 #endif
  170 #ifdef AUDIT
  171         audit_thread_free(td);
  172 #endif
  173         EVENTHANDLER_INVOKE(thread_dtor, td);
  174         free_unr(tid_unrhdr, td->td_tid);
  175         sched_newthread(td);
  176 }
  177 
  178 /*
  179  * Initialize type-stable parts of a thread (when newly created).
  180  */
  181 static int
  182 thread_init(void *mem, int size, int flags)
  183 {
  184         struct thread *td;
  185 
  186         td = (struct thread *)mem;
  187 
  188         td->td_sleepqueue = sleepq_alloc();
  189         td->td_turnstile = turnstile_alloc();
  190         EVENTHANDLER_INVOKE(thread_init, td);
  191         td->td_sched = (struct td_sched *)&td[1];
  192         sched_newthread(td);
  193         umtx_thread_init(td);
  194         td->td_kstack = 0;
  195         td->td_fpop = NULL;
  196         return (0);
  197 }
  198 
  199 /*
  200  * Tear down type-stable parts of a thread (just before being discarded).
  201  */
  202 static void
  203 thread_fini(void *mem, int size)
  204 {
  205         struct thread *td;
  206 
  207         td = (struct thread *)mem;
  208         EVENTHANDLER_INVOKE(thread_fini, td);
  209         turnstile_free(td->td_turnstile);
  210         sleepq_free(td->td_sleepqueue);
  211         umtx_thread_fini(td);
  212 }
  213 
  214 /*
  215  * For a newly created process,
  216  * link up all the structures and its initial threads etc.
  217  * called from:
  218  * {arch}/{arch}/machdep.c   ia64_init(), init386() etc.
  219  * proc_dtor() (should go away)
  220  * proc_init()
  221  */
  222 void
  223 proc_linkup0(struct proc *p, struct thread *td)
  224 {
  225         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
  226         proc_linkup(p, td);
  227 }
  228 
  229 void
  230 proc_linkup(struct proc *p, struct thread *td)
  231 {
  232 
  233 #ifdef KSE
  234         TAILQ_INIT(&p->p_upcalls);           /* upcall list */
  235 #endif
  236         sigqueue_init(&p->p_sigqueue, p);
  237         p->p_ksi = ksiginfo_alloc(1);
  238         if (p->p_ksi != NULL) {
  239                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
  240                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
  241         }
  242         LIST_INIT(&p->p_mqnotifier);
  243         p->p_numthreads = 0;
  244         thread_link(td, p);
  245 }
  246 
  247 /*
  248  * Initialize global thread allocation resources.
  249  */
  250 void
  251 threadinit(void)
  252 {
  253 
  254         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
  255         tid_unrhdr = new_unrhdr(PID_MAX + 1, INT_MAX, &tid_lock);
  256 
  257         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
  258             thread_ctor, thread_dtor, thread_init, thread_fini,
  259             16 - 1, 0);
  260 #ifdef KSE
  261         kseinit();      /* set up kse specific stuff  e.g. upcall zone*/
  262 #endif
  263 }
  264 
  265 /*
  266  * Place an unused thread on the zombie list.
  267  * Use the slpq as that must be unused by now.
  268  */
  269 void
  270 thread_zombie(struct thread *td)
  271 {
  272         mtx_lock_spin(&zombie_lock);
  273         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
  274         mtx_unlock_spin(&zombie_lock);
  275 }
  276 
  277 /*
  278  * Release a thread that has exited after cpu_throw().
  279  */
  280 void
  281 thread_stash(struct thread *td)
  282 {
  283         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
  284         thread_zombie(td);
  285 }
  286 
  287 /*
  288  * Reap zombie kse resource.
  289  */
  290 void
  291 thread_reap(void)
  292 {
  293         struct thread *td_first, *td_next;
  294 
  295         /*
  296          * Don't even bother to lock if none at this instant,
  297          * we really don't care about the next instant..
  298          */
  299         if (!TAILQ_EMPTY(&zombie_threads)) {
  300                 mtx_lock_spin(&zombie_lock);
  301                 td_first = TAILQ_FIRST(&zombie_threads);
  302                 if (td_first)
  303                         TAILQ_INIT(&zombie_threads);
  304                 mtx_unlock_spin(&zombie_lock);
  305                 while (td_first) {
  306                         td_next = TAILQ_NEXT(td_first, td_slpq);
  307                         if (td_first->td_ucred)
  308                                 crfree(td_first->td_ucred);
  309                         thread_free(td_first);
  310                         td_first = td_next;
  311                 }
  312         }
  313 #ifdef KSE
  314         upcall_reap();
  315 #endif
  316 }
  317 
  318 /*
  319  * Allocate a thread.
  320  */
  321 struct thread *
  322 thread_alloc(void)
  323 {
  324         struct thread *td;
  325 
  326         thread_reap(); /* check if any zombies to get */
  327 
  328         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
  329         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
  330         if (!vm_thread_new(td, 0)) {
  331                 uma_zfree(thread_zone, td);
  332                 return (NULL);
  333         }
  334         cpu_thread_alloc(td);
  335         return (td);
  336 }
  337 
  338 
  339 /*
  340  * Deallocate a thread.
  341  */
  342 void
  343 thread_free(struct thread *td)
  344 {
  345         if (td->td_cpuset)
  346                 cpuset_rel(td->td_cpuset);
  347         td->td_cpuset = NULL;
  348         cpu_thread_free(td);
  349         if (td->td_altkstack != 0)
  350                 vm_thread_dispose_altkstack(td);
  351         if (td->td_kstack != 0)
  352                 vm_thread_dispose(td);
  353         uma_zfree(thread_zone, td);
  354 }
  355 
  356 /*
  357  * Discard the current thread and exit from its context.
  358  * Always called with scheduler locked.
  359  *
  360  * Because we can't free a thread while we're operating under its context,
  361  * push the current thread into our CPU's deadthread holder. This means
  362  * we needn't worry about someone else grabbing our context before we
  363  * do a cpu_throw().  This may not be needed now as we are under schedlock.
  364  * Maybe we can just do a thread_stash() as thr_exit1 does.
  365  */
  366 /*  XXX
  367  * libthr expects its thread exit to return for the last
  368  * thread, meaning that the program is back to non-threaded
  369  * mode I guess. Because we do this (cpu_throw) unconditionally
  370  * here, they have their own version of it. (thr_exit1()) 
  371  * that doesn't do it all if this was the last thread.
  372  * It is also called from thread_suspend_check().
  373  * Of course in the end, they end up coming here through exit1
  374  * anyhow..  After fixing 'thr' to play by the rules we should be able 
  375  * to merge these two functions together.
  376  *
  377  * called from:
  378  * exit1()
  379  * kse_exit()
  380  * thr_exit()
  381  * ifdef KSE
  382  * thread_user_enter()
  383  * thread_userret()
  384  * endif
  385  * thread_suspend_check()
  386  */
  387 void
  388 thread_exit(void)
  389 {
  390         uint64_t new_switchtime;
  391         struct thread *td;
  392         struct thread *td2;
  393         struct proc *p;
  394         int wakeup_swapper;
  395 
  396         td = curthread;
  397         p = td->td_proc;
  398 
  399         PROC_SLOCK_ASSERT(p, MA_OWNED);
  400         mtx_assert(&Giant, MA_NOTOWNED);
  401 
  402         PROC_LOCK_ASSERT(p, MA_OWNED);
  403         KASSERT(p != NULL, ("thread exiting without a process"));
  404         CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
  405             (long)p->p_pid, p->p_comm);
  406         KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
  407 
  408 #ifdef AUDIT
  409         AUDIT_SYSCALL_EXIT(0, td);
  410 #endif
  411 
  412 #ifdef KSE
  413         if (td->td_standin != NULL) {
  414                 /*
  415                  * Note that we don't need to free the cred here as it
  416                  * is done in thread_reap().
  417                  */
  418                 thread_zombie(td->td_standin);
  419                 td->td_standin = NULL;
  420         }
  421 #endif
  422 
  423         umtx_thread_exit(td);
  424 
  425         /*
  426          * drop FPU & debug register state storage, or any other
  427          * architecture specific resources that
  428          * would not be on a new untouched process.
  429          */
  430         cpu_thread_exit(td);    /* XXXSMP */
  431 
  432         /* Do the same timestamp bookkeeping that mi_switch() would do. */
  433         new_switchtime = cpu_ticks();
  434         p->p_rux.rux_runtime += (new_switchtime - PCPU_GET(switchtime));
  435         PCPU_SET(switchtime, new_switchtime);
  436         PCPU_SET(switchticks, ticks);
  437         PCPU_INC(cnt.v_swtch);
  438         /* Save our resource usage in our process. */
  439         td->td_ru.ru_nvcsw++;
  440         rucollect(&p->p_ru, &td->td_ru);
  441         /*
  442          * The last thread is left attached to the process
  443          * So that the whole bundle gets recycled. Skip
  444          * all this stuff if we never had threads.
  445          * EXIT clears all sign of other threads when
  446          * it goes to single threading, so the last thread always
  447          * takes the short path.
  448          */
  449         if (p->p_flag & P_HADTHREADS) {
  450                 if (p->p_numthreads > 1) {
  451                         thread_lock(td);
  452 #ifdef KSE
  453                         kse_unlink(td);
  454 #else
  455                         thread_unlink(td);
  456 #endif
  457                         thread_unlock(td);
  458                         td2 = FIRST_THREAD_IN_PROC(p);
  459                         sched_exit_thread(td2, td);
  460 
  461                         /*
  462                          * The test below is NOT true if we are the
  463                          * sole exiting thread. P_STOPPED_SNGL is unset
  464                          * in exit1() after it is the only survivor.
  465                          */
  466                         if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  467                                 if (p->p_numthreads == p->p_suspcount) {
  468                                         thread_lock(p->p_singlethread);
  469                                         wakeup_swapper = thread_unsuspend_one(
  470                                                 p->p_singlethread);
  471                                         thread_unlock(p->p_singlethread);
  472                                         if (wakeup_swapper)
  473                                                 kick_proc0();
  474                                 }
  475                         }
  476 
  477                         atomic_add_int(&td->td_proc->p_exitthreads, 1);
  478                         PCPU_SET(deadthread, td);
  479                 } else {
  480                         /*
  481                          * The last thread is exiting.. but not through exit()
  482                          * what should we do?
  483                          * Theoretically this can't happen
  484                          * exit1() - clears threading flags before coming here
  485                          * kse_exit() - treats last thread specially
  486                          * thr_exit() - treats last thread specially
  487                          * ifdef KSE
  488                          * thread_user_enter() - only if more exist
  489                          * thread_userret() - only if more exist
  490                          * endif
  491                          * thread_suspend_check() - only if more exist
  492                          */
  493                         panic ("thread_exit: Last thread exiting on its own");
  494                 }
  495         } 
  496         PROC_UNLOCK(p);
  497         thread_lock(td);
  498         /* Save our tick information with both the thread and proc locked */
  499         ruxagg(&p->p_rux, td);
  500         PROC_SUNLOCK(p);
  501         td->td_state = TDS_INACTIVE;
  502         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
  503         sched_throw(td);
  504         panic("I'm a teapot!");
  505         /* NOTREACHED */
  506 }
  507 
  508 /*
  509  * Do any thread specific cleanups that may be needed in wait()
  510  * called with Giant, proc and schedlock not held.
  511  */
  512 void
  513 thread_wait(struct proc *p)
  514 {
  515         struct thread *td;
  516 
  517         mtx_assert(&Giant, MA_NOTOWNED);
  518         KASSERT((p->p_numthreads == 1), ("Multiple threads in wait1()"));
  519         td = FIRST_THREAD_IN_PROC(p);
  520 #ifdef KSE
  521         if (td->td_standin != NULL) {
  522                 if (td->td_standin->td_ucred != NULL) {
  523                         crfree(td->td_standin->td_ucred);
  524                         td->td_standin->td_ucred = NULL;
  525                 }
  526                 thread_free(td->td_standin);
  527                 td->td_standin = NULL;
  528         }
  529 #endif
  530         /* Lock the last thread so we spin until it exits cpu_throw(). */
  531         thread_lock(td);
  532         thread_unlock(td);
  533         /* Wait for any remaining threads to exit cpu_throw(). */
  534         while (p->p_exitthreads)
  535                 sched_relinquish(curthread);
  536         cpuset_rel(td->td_cpuset);
  537         td->td_cpuset = NULL;
  538         cpu_thread_clean(td);
  539         crfree(td->td_ucred);
  540         thread_reap();  /* check for zombie threads etc. */
  541 }
  542 
  543 /*
  544  * Link a thread to a process.
  545  * set up anything that needs to be initialized for it to
  546  * be used by the process.
  547  *
  548  * Note that we do not link to the proc's ucred here.
  549  * The thread is linked as if running but no KSE assigned.
  550  * Called from:
  551  *  proc_linkup()
  552  *  thread_schedule_upcall()
  553  *  thr_create()
  554  */
  555 void
  556 thread_link(struct thread *td, struct proc *p)
  557 {
  558 
  559         /*
  560          * XXX This can't be enabled because it's called for proc0 before
  561          * it's spinlock has been created.
  562          * PROC_SLOCK_ASSERT(p, MA_OWNED);
  563          */
  564         td->td_state    = TDS_INACTIVE;
  565         td->td_proc     = p;
  566         td->td_flags    = TDF_INMEM;
  567 
  568         LIST_INIT(&td->td_contested);
  569         sigqueue_init(&td->td_sigqueue, p);
  570         callout_init(&td->td_slpcallout, CALLOUT_MPSAFE);
  571         TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
  572         p->p_numthreads++;
  573 }
  574 
  575 /*
  576  * Convert a process with one thread to an unthreaded process.
  577  * Called from:
  578  *  thread_single(exit)  (called from execve and exit)
  579  *  kse_exit()          XXX may need cleaning up wrt KSE stuff
  580  */
  581 void
  582 thread_unthread(struct thread *td)
  583 {
  584         struct proc *p = td->td_proc;
  585 
  586         KASSERT((p->p_numthreads == 1), ("Unthreading with >1 threads"));
  587 #ifdef KSE
  588         thread_lock(td);
  589         upcall_remove(td);
  590         thread_unlock(td);
  591         p->p_flag &= ~(P_SA|P_HADTHREADS);
  592         td->td_mailbox = NULL;
  593         td->td_pflags &= ~(TDP_SA | TDP_CAN_UNBIND);
  594         if (td->td_standin != NULL) {
  595                 thread_zombie(td->td_standin);
  596                 td->td_standin = NULL;
  597         }
  598 #else
  599         p->p_flag &= ~P_HADTHREADS;
  600 #endif
  601 }
  602 
  603 /*
  604  * Called from:
  605  *  thread_exit()
  606  */
  607 void
  608 thread_unlink(struct thread *td)
  609 {
  610         struct proc *p = td->td_proc;
  611 
  612         PROC_SLOCK_ASSERT(p, MA_OWNED);
  613         TAILQ_REMOVE(&p->p_threads, td, td_plist);
  614         p->p_numthreads--;
  615         /* could clear a few other things here */
  616         /* Must  NOT clear links to proc! */
  617 }
  618 
  619 /*
  620  * Enforce single-threading.
  621  *
  622  * Returns 1 if the caller must abort (another thread is waiting to
  623  * exit the process or similar). Process is locked!
  624  * Returns 0 when you are successfully the only thread running.
  625  * A process has successfully single threaded in the suspend mode when
  626  * There are no threads in user mode. Threads in the kernel must be
  627  * allowed to continue until they get to the user boundary. They may even
  628  * copy out their return values and data before suspending. They may however be
  629  * accelerated in reaching the user boundary as we will wake up
  630  * any sleeping threads that are interruptable. (PCATCH).
  631  */
  632 int
  633 thread_single(int mode)
  634 {
  635         struct thread *td;
  636         struct thread *td2;
  637         struct proc *p;
  638         int remaining, wakeup_swapper;
  639 
  640         td = curthread;
  641         p = td->td_proc;
  642         mtx_assert(&Giant, MA_NOTOWNED);
  643         PROC_LOCK_ASSERT(p, MA_OWNED);
  644         KASSERT((td != NULL), ("curthread is NULL"));
  645 
  646         if ((p->p_flag & P_HADTHREADS) == 0)
  647                 return (0);
  648 
  649         /* Is someone already single threading? */
  650         if (p->p_singlethread != NULL && p->p_singlethread != td)
  651                 return (1);
  652 
  653         if (mode == SINGLE_EXIT) {
  654                 p->p_flag |= P_SINGLE_EXIT;
  655                 p->p_flag &= ~P_SINGLE_BOUNDARY;
  656         } else {
  657                 p->p_flag &= ~P_SINGLE_EXIT;
  658                 if (mode == SINGLE_BOUNDARY)
  659                         p->p_flag |= P_SINGLE_BOUNDARY;
  660                 else
  661                         p->p_flag &= ~P_SINGLE_BOUNDARY;
  662         }
  663         p->p_flag |= P_STOPPED_SINGLE;
  664         PROC_SLOCK(p);
  665         p->p_singlethread = td;
  666         if (mode == SINGLE_EXIT)
  667                 remaining = p->p_numthreads;
  668         else if (mode == SINGLE_BOUNDARY)
  669                 remaining = p->p_numthreads - p->p_boundary_count;
  670         else
  671                 remaining = p->p_numthreads - p->p_suspcount;
  672         while (remaining != 1) {
  673                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
  674                         goto stopme;
  675                 wakeup_swapper = 0;
  676                 FOREACH_THREAD_IN_PROC(p, td2) {
  677                         if (td2 == td)
  678                                 continue;
  679                         thread_lock(td2);
  680                         td2->td_flags |= TDF_ASTPENDING;
  681                         if (TD_IS_INHIBITED(td2)) {
  682                                 switch (mode) {
  683                                 case SINGLE_EXIT:
  684                                         if (td->td_flags & TDF_DBSUSPEND)
  685                                                 td->td_flags &= ~TDF_DBSUSPEND;
  686                                         if (TD_IS_SUSPENDED(td2))
  687                                                 wakeup_swapper |=
  688                                                     thread_unsuspend_one(td2);
  689                                         if (TD_ON_SLEEPQ(td2) &&
  690                                             (td2->td_flags & TDF_SINTR))
  691                                                 wakeup_swapper |=
  692                                                     sleepq_abort(td2, EINTR);
  693                                         break;
  694                                 case SINGLE_BOUNDARY:
  695                                         if (TD_IS_SUSPENDED(td2) &&
  696                                             !(td2->td_flags & TDF_BOUNDARY))
  697                                                 wakeup_swapper |=
  698                                                     thread_unsuspend_one(td2);
  699                                         if (TD_ON_SLEEPQ(td2) &&
  700                                             (td2->td_flags & TDF_SINTR))
  701                                                 wakeup_swapper |=
  702                                                     sleepq_abort(td2, ERESTART);
  703                                         break;
  704                                 default:        
  705                                         if (TD_IS_SUSPENDED(td2)) {
  706                                                 thread_unlock(td2);
  707                                                 continue;
  708                                         }
  709                                         /*
  710                                          * maybe other inhibited states too?
  711                                          */
  712                                         if ((td2->td_flags & TDF_SINTR) &&
  713                                             (td2->td_inhibitors &
  714                                             (TDI_SLEEPING | TDI_SWAPPED)))
  715                                                 thread_suspend_one(td2);
  716                                         break;
  717                                 }
  718                         }
  719 #ifdef SMP
  720                         else if (TD_IS_RUNNING(td2) && td != td2) {
  721                                 forward_signal(td2);
  722                         }
  723 #endif
  724                         thread_unlock(td2);
  725                 }
  726                 if (wakeup_swapper)
  727                         kick_proc0();
  728                 if (mode == SINGLE_EXIT)
  729                         remaining = p->p_numthreads;
  730                 else if (mode == SINGLE_BOUNDARY)
  731                         remaining = p->p_numthreads - p->p_boundary_count;
  732                 else
  733                         remaining = p->p_numthreads - p->p_suspcount;
  734 
  735                 /*
  736                  * Maybe we suspended some threads.. was it enough?
  737                  */
  738                 if (remaining == 1)
  739                         break;
  740 
  741 stopme:
  742                 /*
  743                  * Wake us up when everyone else has suspended.
  744                  * In the mean time we suspend as well.
  745                  */
  746                 thread_suspend_switch(td);
  747                 if (mode == SINGLE_EXIT)
  748                         remaining = p->p_numthreads;
  749                 else if (mode == SINGLE_BOUNDARY)
  750                         remaining = p->p_numthreads - p->p_boundary_count;
  751                 else
  752                         remaining = p->p_numthreads - p->p_suspcount;
  753         }
  754         if (mode == SINGLE_EXIT) {
  755                 /*
  756                  * We have gotten rid of all the other threads and we
  757                  * are about to either exit or exec. In either case,
  758                  * we try our utmost  to revert to being a non-threaded
  759                  * process.
  760                  */
  761                 p->p_singlethread = NULL;
  762                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT);
  763                 thread_unthread(td);
  764         }
  765         PROC_SUNLOCK(p);
  766         return (0);
  767 }
  768 
  769 /*
  770  * Called in from locations that can safely check to see
  771  * whether we have to suspend or at least throttle for a
  772  * single-thread event (e.g. fork).
  773  *
  774  * Such locations include userret().
  775  * If the "return_instead" argument is non zero, the thread must be able to
  776  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
  777  *
  778  * The 'return_instead' argument tells the function if it may do a
  779  * thread_exit() or suspend, or whether the caller must abort and back
  780  * out instead.
  781  *
  782  * If the thread that set the single_threading request has set the
  783  * P_SINGLE_EXIT bit in the process flags then this call will never return
  784  * if 'return_instead' is false, but will exit.
  785  *
  786  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
  787  *---------------+--------------------+---------------------
  788  *       0       | returns 0          |   returns 0 or 1
  789  *               | when ST ends       |   immediatly
  790  *---------------+--------------------+---------------------
  791  *       1       | thread exits       |   returns 1
  792  *               |                    |  immediatly
  793  * 0 = thread_exit() or suspension ok,
  794  * other = return error instead of stopping the thread.
  795  *
  796  * While a full suspension is under effect, even a single threading
  797  * thread would be suspended if it made this call (but it shouldn't).
  798  * This call should only be made from places where
  799  * thread_exit() would be safe as that may be the outcome unless
  800  * return_instead is set.
  801  */
  802 int
  803 thread_suspend_check(int return_instead)
  804 {
  805         struct thread *td;
  806         struct proc *p;
  807         int wakeup_swapper;
  808 
  809         td = curthread;
  810         p = td->td_proc;
  811         mtx_assert(&Giant, MA_NOTOWNED);
  812         PROC_LOCK_ASSERT(p, MA_OWNED);
  813         while (P_SHOULDSTOP(p) ||
  814               ((p->p_flag & P_TRACED) && (td->td_flags & TDF_DBSUSPEND))) {
  815                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  816                         KASSERT(p->p_singlethread != NULL,
  817                             ("singlethread not set"));
  818                         /*
  819                          * The only suspension in action is a
  820                          * single-threading. Single threader need not stop.
  821                          * XXX Should be safe to access unlocked
  822                          * as it can only be set to be true by us.
  823                          */
  824                         if (p->p_singlethread == td)
  825                                 return (0);     /* Exempt from stopping. */
  826                 }
  827                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
  828                         return (EINTR);
  829 
  830                 /* Should we goto user boundary if we didn't come from there? */
  831                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
  832                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
  833                         return (ERESTART);
  834 
  835                 /* If thread will exit, flush its pending signals */
  836                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td))
  837                         sigqueue_flush(&td->td_sigqueue);
  838 
  839                 PROC_SLOCK(p);
  840                 thread_stopped(p);
  841                 /*
  842                  * If the process is waiting for us to exit,
  843                  * this thread should just suicide.
  844                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
  845                  */
  846                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td))
  847                         thread_exit();
  848                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  849                         if (p->p_numthreads == p->p_suspcount + 1) {
  850                                 thread_lock(p->p_singlethread);
  851                                 wakeup_swapper =
  852                                     thread_unsuspend_one(p->p_singlethread);
  853                                 thread_unlock(p->p_singlethread);
  854                                 if (wakeup_swapper)
  855                                         kick_proc0();
  856                         }
  857                 }
  858                 PROC_UNLOCK(p);
  859                 thread_lock(td);
  860                 /*
  861                  * When a thread suspends, it just
  862                  * gets taken off all queues.
  863                  */
  864                 thread_suspend_one(td);
  865                 if (return_instead == 0) {
  866                         p->p_boundary_count++;
  867                         td->td_flags |= TDF_BOUNDARY;
  868                 }
  869                 PROC_SUNLOCK(p);
  870                 mi_switch(SW_INVOL, NULL);
  871                 if (return_instead == 0)
  872                         td->td_flags &= ~TDF_BOUNDARY;
  873                 thread_unlock(td);
  874                 PROC_LOCK(p);
  875                 if (return_instead == 0)
  876                         p->p_boundary_count--;
  877         }
  878         return (0);
  879 }
  880 
  881 void
  882 thread_suspend_switch(struct thread *td)
  883 {
  884         struct proc *p;
  885 
  886         p = td->td_proc;
  887         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  888         PROC_LOCK_ASSERT(p, MA_OWNED);
  889         PROC_SLOCK_ASSERT(p, MA_OWNED);
  890         /*
  891          * We implement thread_suspend_one in stages here to avoid
  892          * dropping the proc lock while the thread lock is owned.
  893          */
  894         thread_stopped(p);
  895         p->p_suspcount++;
  896         PROC_UNLOCK(p);
  897         thread_lock(td);
  898         sched_sleep(td);
  899         TD_SET_SUSPENDED(td);
  900         PROC_SUNLOCK(p);
  901         DROP_GIANT();
  902         mi_switch(SW_VOL, NULL);
  903         thread_unlock(td);
  904         PICKUP_GIANT();
  905         PROC_LOCK(p);
  906         PROC_SLOCK(p);
  907 }
  908 
  909 void
  910 thread_suspend_one(struct thread *td)
  911 {
  912         struct proc *p = td->td_proc;
  913 
  914         PROC_SLOCK_ASSERT(p, MA_OWNED);
  915         THREAD_LOCK_ASSERT(td, MA_OWNED);
  916         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  917         p->p_suspcount++;
  918         sched_sleep(td);
  919         TD_SET_SUSPENDED(td);
  920 }
  921 
  922 int
  923 thread_unsuspend_one(struct thread *td)
  924 {
  925         struct proc *p = td->td_proc;
  926 
  927         PROC_SLOCK_ASSERT(p, MA_OWNED);
  928         THREAD_LOCK_ASSERT(td, MA_OWNED);
  929         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
  930         TD_CLR_SUSPENDED(td);
  931         p->p_suspcount--;
  932         return (setrunnable(td));
  933 }
  934 
  935 /*
  936  * Allow all threads blocked by single threading to continue running.
  937  */
  938 void
  939 thread_unsuspend(struct proc *p)
  940 {
  941         struct thread *td;
  942         int wakeup_swapper;
  943 
  944         PROC_LOCK_ASSERT(p, MA_OWNED);
  945         PROC_SLOCK_ASSERT(p, MA_OWNED);
  946         wakeup_swapper = 0;
  947         if (!P_SHOULDSTOP(p)) {
  948                 FOREACH_THREAD_IN_PROC(p, td) {
  949                         thread_lock(td);
  950                         if (TD_IS_SUSPENDED(td)) {
  951                                 wakeup_swapper |= thread_unsuspend_one(td);
  952                         }
  953                         thread_unlock(td);
  954                 }
  955         } else if ((P_SHOULDSTOP(p) == P_STOPPED_SINGLE) &&
  956             (p->p_numthreads == p->p_suspcount)) {
  957                 /*
  958                  * Stopping everything also did the job for the single
  959                  * threading request. Now we've downgraded to single-threaded,
  960                  * let it continue.
  961                  */
  962                 thread_lock(p->p_singlethread);
  963                 wakeup_swapper = thread_unsuspend_one(p->p_singlethread);
  964                 thread_unlock(p->p_singlethread);
  965         }
  966         if (wakeup_swapper)
  967                 kick_proc0();
  968 }
  969 
  970 /*
  971  * End the single threading mode..
  972  */
  973 void
  974 thread_single_end(void)
  975 {
  976         struct thread *td;
  977         struct proc *p;
  978         int wakeup_swapper;
  979 
  980         td = curthread;
  981         p = td->td_proc;
  982         PROC_LOCK_ASSERT(p, MA_OWNED);
  983         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY);
  984         PROC_SLOCK(p);
  985         p->p_singlethread = NULL;
  986         wakeup_swapper = 0;
  987         /*
  988          * If there are other threads they may now run,
  989          * unless of course there is a blanket 'stop order'
  990          * on the process. The single threader must be allowed
  991          * to continue however as this is a bad place to stop.
  992          */
  993         if ((p->p_numthreads != 1) && (!P_SHOULDSTOP(p))) {
  994                 FOREACH_THREAD_IN_PROC(p, td) {
  995                         thread_lock(td);
  996                         if (TD_IS_SUSPENDED(td)) {
  997                                 wakeup_swapper |= thread_unsuspend_one(td);
  998                         }
  999                         thread_unlock(td);
 1000                 }
 1001         }
 1002         PROC_SUNLOCK(p);
 1003         if (wakeup_swapper)
 1004                 kick_proc0();
 1005 }
 1006 
 1007 struct thread *
 1008 thread_find(struct proc *p, lwpid_t tid)
 1009 {
 1010         struct thread *td;
 1011 
 1012         PROC_LOCK_ASSERT(p, MA_OWNED);
 1013         PROC_SLOCK(p);
 1014         FOREACH_THREAD_IN_PROC(p, td) {
 1015                 if (td->td_tid == tid)
 1016                         break;
 1017         }
 1018         PROC_SUNLOCK(p);
 1019         return (td);
 1020 }

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