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: releng/10.0/sys/kern/kern_thread.c 248584 2013-03-21 14:06:27Z 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         EVENTHANDLER_INVOKE(thread_init, td);
  211         td->td_sched = (struct td_sched *)&td[1];
  212         umtx_thread_init(td);
  213         td->td_kstack = 0;
  214         return (0);
  215 }
  216 
  217 /*
  218  * Tear down type-stable parts of a thread (just before being discarded).
  219  */
  220 static void
  221 thread_fini(void *mem, int size)
  222 {
  223         struct thread *td;
  224 
  225         td = (struct thread *)mem;
  226         EVENTHANDLER_INVOKE(thread_fini, td);
  227         rlqentry_free(td->td_rlqe);
  228         turnstile_free(td->td_turnstile);
  229         sleepq_free(td->td_sleepqueue);
  230         umtx_thread_fini(td);
  231         seltdfini(td);
  232 }
  233 
  234 /*
  235  * For a newly created process,
  236  * link up all the structures and its initial threads etc.
  237  * called from:
  238  * {arch}/{arch}/machdep.c   ia64_init(), init386() etc.
  239  * proc_dtor() (should go away)
  240  * proc_init()
  241  */
  242 void
  243 proc_linkup0(struct proc *p, struct thread *td)
  244 {
  245         TAILQ_INIT(&p->p_threads);           /* all threads in proc */
  246         proc_linkup(p, td);
  247 }
  248 
  249 void
  250 proc_linkup(struct proc *p, struct thread *td)
  251 {
  252 
  253         sigqueue_init(&p->p_sigqueue, p);
  254         p->p_ksi = ksiginfo_alloc(1);
  255         if (p->p_ksi != NULL) {
  256                 /* XXX p_ksi may be null if ksiginfo zone is not ready */
  257                 p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
  258         }
  259         LIST_INIT(&p->p_mqnotifier);
  260         p->p_numthreads = 0;
  261         thread_link(td, p);
  262 }
  263 
  264 /*
  265  * Initialize global thread allocation resources.
  266  */
  267 void
  268 threadinit(void)
  269 {
  270 
  271         mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
  272 
  273         /*
  274          * pid_max cannot be greater than PID_MAX.
  275          * leave one number for thread0.
  276          */
  277         tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
  278 
  279         thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
  280             thread_ctor, thread_dtor, thread_init, thread_fini,
  281             16 - 1, 0);
  282         tidhashtbl = hashinit(maxproc / 2, M_TIDHASH, &tidhash);
  283         rw_init(&tidhash_lock, "tidhash");
  284 }
  285 
  286 /*
  287  * Place an unused thread on the zombie list.
  288  * Use the slpq as that must be unused by now.
  289  */
  290 void
  291 thread_zombie(struct thread *td)
  292 {
  293         mtx_lock_spin(&zombie_lock);
  294         TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
  295         mtx_unlock_spin(&zombie_lock);
  296 }
  297 
  298 /*
  299  * Release a thread that has exited after cpu_throw().
  300  */
  301 void
  302 thread_stash(struct thread *td)
  303 {
  304         atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
  305         thread_zombie(td);
  306 }
  307 
  308 /*
  309  * Reap zombie resources.
  310  */
  311 void
  312 thread_reap(void)
  313 {
  314         struct thread *td_first, *td_next;
  315 
  316         /*
  317          * Don't even bother to lock if none at this instant,
  318          * we really don't care about the next instant..
  319          */
  320         if (!TAILQ_EMPTY(&zombie_threads)) {
  321                 mtx_lock_spin(&zombie_lock);
  322                 td_first = TAILQ_FIRST(&zombie_threads);
  323                 if (td_first)
  324                         TAILQ_INIT(&zombie_threads);
  325                 mtx_unlock_spin(&zombie_lock);
  326                 while (td_first) {
  327                         td_next = TAILQ_NEXT(td_first, td_slpq);
  328                         if (td_first->td_ucred)
  329                                 crfree(td_first->td_ucred);
  330                         thread_free(td_first);
  331                         td_first = td_next;
  332                 }
  333         }
  334 }
  335 
  336 /*
  337  * Allocate a thread.
  338  */
  339 struct thread *
  340 thread_alloc(int pages)
  341 {
  342         struct thread *td;
  343 
  344         thread_reap(); /* check if any zombies to get */
  345 
  346         td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
  347         KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
  348         if (!vm_thread_new(td, pages)) {
  349                 uma_zfree(thread_zone, td);
  350                 return (NULL);
  351         }
  352         cpu_thread_alloc(td);
  353         return (td);
  354 }
  355 
  356 int
  357 thread_alloc_stack(struct thread *td, int pages)
  358 {
  359 
  360         KASSERT(td->td_kstack == 0,
  361             ("thread_alloc_stack called on a thread with kstack"));
  362         if (!vm_thread_new(td, pages))
  363                 return (0);
  364         cpu_thread_alloc(td);
  365         return (1);
  366 }
  367 
  368 /*
  369  * Deallocate a thread.
  370  */
  371 void
  372 thread_free(struct thread *td)
  373 {
  374 
  375         lock_profile_thread_exit(td);
  376         if (td->td_cpuset)
  377                 cpuset_rel(td->td_cpuset);
  378         td->td_cpuset = NULL;
  379         cpu_thread_free(td);
  380         if (td->td_kstack != 0)
  381                 vm_thread_dispose(td);
  382         uma_zfree(thread_zone, td);
  383 }
  384 
  385 /*
  386  * Discard the current thread and exit from its context.
  387  * Always called with scheduler locked.
  388  *
  389  * Because we can't free a thread while we're operating under its context,
  390  * push the current thread into our CPU's deadthread holder. This means
  391  * we needn't worry about someone else grabbing our context before we
  392  * do a cpu_throw().
  393  */
  394 void
  395 thread_exit(void)
  396 {
  397         uint64_t runtime, new_switchtime;
  398         struct thread *td;
  399         struct thread *td2;
  400         struct proc *p;
  401         int wakeup_swapper;
  402 
  403         td = curthread;
  404         p = td->td_proc;
  405 
  406         PROC_SLOCK_ASSERT(p, MA_OWNED);
  407         mtx_assert(&Giant, MA_NOTOWNED);
  408 
  409         PROC_LOCK_ASSERT(p, MA_OWNED);
  410         KASSERT(p != NULL, ("thread exiting without a process"));
  411         CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
  412             (long)p->p_pid, td->td_name);
  413         KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
  414 
  415 #ifdef AUDIT
  416         AUDIT_SYSCALL_EXIT(0, td);
  417 #endif
  418         umtx_thread_exit(td);
  419         /*
  420          * drop FPU & debug register state storage, or any other
  421          * architecture specific resources that
  422          * would not be on a new untouched process.
  423          */
  424         cpu_thread_exit(td);    /* XXXSMP */
  425 
  426         /*
  427          * The last thread is left attached to the process
  428          * So that the whole bundle gets recycled. Skip
  429          * all this stuff if we never had threads.
  430          * EXIT clears all sign of other threads when
  431          * it goes to single threading, so the last thread always
  432          * takes the short path.
  433          */
  434         if (p->p_flag & P_HADTHREADS) {
  435                 if (p->p_numthreads > 1) {
  436                         thread_unlink(td);
  437                         td2 = FIRST_THREAD_IN_PROC(p);
  438                         sched_exit_thread(td2, td);
  439 
  440                         /*
  441                          * The test below is NOT true if we are the
  442                          * sole exiting thread. P_STOPPED_SINGLE is unset
  443                          * in exit1() after it is the only survivor.
  444                          */
  445                         if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  446                                 if (p->p_numthreads == p->p_suspcount) {
  447                                         thread_lock(p->p_singlethread);
  448                                         wakeup_swapper = thread_unsuspend_one(
  449                                                 p->p_singlethread);
  450                                         thread_unlock(p->p_singlethread);
  451                                         if (wakeup_swapper)
  452                                                 kick_proc0();
  453                                 }
  454                         }
  455 
  456                         atomic_add_int(&td->td_proc->p_exitthreads, 1);
  457                         PCPU_SET(deadthread, td);
  458                 } else {
  459                         /*
  460                          * The last thread is exiting.. but not through exit()
  461                          */
  462                         panic ("thread_exit: Last thread exiting on its own");
  463                 }
  464         } 
  465 #ifdef  HWPMC_HOOKS
  466         /*
  467          * If this thread is part of a process that is being tracked by hwpmc(4),
  468          * inform the module of the thread's impending exit.
  469          */
  470         if (PMC_PROC_IS_USING_PMCS(td->td_proc))
  471                 PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
  472 #endif
  473         PROC_UNLOCK(p);
  474 
  475         /* Do the same timestamp bookkeeping that mi_switch() would do. */
  476         new_switchtime = cpu_ticks();
  477         runtime = new_switchtime - PCPU_GET(switchtime);
  478         td->td_runtime += runtime;
  479         td->td_incruntime += runtime;
  480         PCPU_SET(switchtime, new_switchtime);
  481         PCPU_SET(switchticks, ticks);
  482         PCPU_INC(cnt.v_swtch);
  483 
  484         /* Save our resource usage in our process. */
  485         td->td_ru.ru_nvcsw++;
  486         ruxagg(p, td);
  487         rucollect(&p->p_ru, &td->td_ru);
  488 
  489         thread_lock(td);
  490         PROC_SUNLOCK(p);
  491         td->td_state = TDS_INACTIVE;
  492 #ifdef WITNESS
  493         witness_thread_exit(td);
  494 #endif
  495         CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
  496         sched_throw(td);
  497         panic("I'm a teapot!");
  498         /* NOTREACHED */
  499 }
  500 
  501 /*
  502  * Do any thread specific cleanups that may be needed in wait()
  503  * called with Giant, proc and schedlock not held.
  504  */
  505 void
  506 thread_wait(struct proc *p)
  507 {
  508         struct thread *td;
  509 
  510         mtx_assert(&Giant, MA_NOTOWNED);
  511         KASSERT((p->p_numthreads == 1), ("Multiple threads in wait1()"));
  512         td = FIRST_THREAD_IN_PROC(p);
  513         /* Lock the last thread so we spin until it exits cpu_throw(). */
  514         thread_lock(td);
  515         thread_unlock(td);
  516         /* Wait for any remaining threads to exit cpu_throw(). */
  517         while (p->p_exitthreads)
  518                 sched_relinquish(curthread);
  519         lock_profile_thread_exit(td);
  520         cpuset_rel(td->td_cpuset);
  521         td->td_cpuset = NULL;
  522         cpu_thread_clean(td);
  523         crfree(td->td_ucred);
  524         thread_reap();  /* check for zombie threads etc. */
  525 }
  526 
  527 /*
  528  * Link a thread to a process.
  529  * set up anything that needs to be initialized for it to
  530  * be used by the process.
  531  */
  532 void
  533 thread_link(struct thread *td, struct proc *p)
  534 {
  535 
  536         /*
  537          * XXX This can't be enabled because it's called for proc0 before
  538          * its lock has been created.
  539          * PROC_LOCK_ASSERT(p, MA_OWNED);
  540          */
  541         td->td_state    = TDS_INACTIVE;
  542         td->td_proc     = p;
  543         td->td_flags    = TDF_INMEM;
  544 
  545         LIST_INIT(&td->td_contested);
  546         LIST_INIT(&td->td_lprof[0]);
  547         LIST_INIT(&td->td_lprof[1]);
  548         sigqueue_init(&td->td_sigqueue, p);
  549         callout_init(&td->td_slpcallout, CALLOUT_MPSAFE);
  550         TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
  551         p->p_numthreads++;
  552 }
  553 
  554 /*
  555  * Convert a process with one thread to an unthreaded process.
  556  */
  557 void
  558 thread_unthread(struct thread *td)
  559 {
  560         struct proc *p = td->td_proc;
  561 
  562         KASSERT((p->p_numthreads == 1), ("Unthreading with >1 threads"));
  563         p->p_flag &= ~P_HADTHREADS;
  564 }
  565 
  566 /*
  567  * Called from:
  568  *  thread_exit()
  569  */
  570 void
  571 thread_unlink(struct thread *td)
  572 {
  573         struct proc *p = td->td_proc;
  574 
  575         PROC_LOCK_ASSERT(p, MA_OWNED);
  576         TAILQ_REMOVE(&p->p_threads, td, td_plist);
  577         p->p_numthreads--;
  578         /* could clear a few other things here */
  579         /* Must  NOT clear links to proc! */
  580 }
  581 
  582 static int
  583 calc_remaining(struct proc *p, int mode)
  584 {
  585         int remaining;
  586 
  587         PROC_LOCK_ASSERT(p, MA_OWNED);
  588         PROC_SLOCK_ASSERT(p, MA_OWNED);
  589         if (mode == SINGLE_EXIT)
  590                 remaining = p->p_numthreads;
  591         else if (mode == SINGLE_BOUNDARY)
  592                 remaining = p->p_numthreads - p->p_boundary_count;
  593         else if (mode == SINGLE_NO_EXIT)
  594                 remaining = p->p_numthreads - p->p_suspcount;
  595         else
  596                 panic("calc_remaining: wrong mode %d", mode);
  597         return (remaining);
  598 }
  599 
  600 /*
  601  * Enforce single-threading.
  602  *
  603  * Returns 1 if the caller must abort (another thread is waiting to
  604  * exit the process or similar). Process is locked!
  605  * Returns 0 when you are successfully the only thread running.
  606  * A process has successfully single threaded in the suspend mode when
  607  * There are no threads in user mode. Threads in the kernel must be
  608  * allowed to continue until they get to the user boundary. They may even
  609  * copy out their return values and data before suspending. They may however be
  610  * accelerated in reaching the user boundary as we will wake up
  611  * any sleeping threads that are interruptable. (PCATCH).
  612  */
  613 int
  614 thread_single(int mode)
  615 {
  616         struct thread *td;
  617         struct thread *td2;
  618         struct proc *p;
  619         int remaining, wakeup_swapper;
  620 
  621         td = curthread;
  622         p = td->td_proc;
  623         mtx_assert(&Giant, MA_NOTOWNED);
  624         PROC_LOCK_ASSERT(p, MA_OWNED);
  625 
  626         if ((p->p_flag & P_HADTHREADS) == 0)
  627                 return (0);
  628 
  629         /* Is someone already single threading? */
  630         if (p->p_singlethread != NULL && p->p_singlethread != td)
  631                 return (1);
  632 
  633         if (mode == SINGLE_EXIT) {
  634                 p->p_flag |= P_SINGLE_EXIT;
  635                 p->p_flag &= ~P_SINGLE_BOUNDARY;
  636         } else {
  637                 p->p_flag &= ~P_SINGLE_EXIT;
  638                 if (mode == SINGLE_BOUNDARY)
  639                         p->p_flag |= P_SINGLE_BOUNDARY;
  640                 else
  641                         p->p_flag &= ~P_SINGLE_BOUNDARY;
  642         }
  643         p->p_flag |= P_STOPPED_SINGLE;
  644         PROC_SLOCK(p);
  645         p->p_singlethread = td;
  646         remaining = calc_remaining(p, mode);
  647         while (remaining != 1) {
  648                 if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
  649                         goto stopme;
  650                 wakeup_swapper = 0;
  651                 FOREACH_THREAD_IN_PROC(p, td2) {
  652                         if (td2 == td)
  653                                 continue;
  654                         thread_lock(td2);
  655                         td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
  656                         if (TD_IS_INHIBITED(td2)) {
  657                                 switch (mode) {
  658                                 case SINGLE_EXIT:
  659                                         if (TD_IS_SUSPENDED(td2))
  660                                                 wakeup_swapper |=
  661                                                     thread_unsuspend_one(td2);
  662                                         if (TD_ON_SLEEPQ(td2) &&
  663                                             (td2->td_flags & TDF_SINTR))
  664                                                 wakeup_swapper |=
  665                                                     sleepq_abort(td2, EINTR);
  666                                         break;
  667                                 case SINGLE_BOUNDARY:
  668                                         if (TD_IS_SUSPENDED(td2) &&
  669                                             !(td2->td_flags & TDF_BOUNDARY))
  670                                                 wakeup_swapper |=
  671                                                     thread_unsuspend_one(td2);
  672                                         if (TD_ON_SLEEPQ(td2) &&
  673                                             (td2->td_flags & TDF_SINTR))
  674                                                 wakeup_swapper |=
  675                                                     sleepq_abort(td2, ERESTART);
  676                                         break;
  677                                 case SINGLE_NO_EXIT:
  678                                         if (TD_IS_SUSPENDED(td2) &&
  679                                             !(td2->td_flags & TDF_BOUNDARY))
  680                                                 wakeup_swapper |=
  681                                                     thread_unsuspend_one(td2);
  682                                         if (TD_ON_SLEEPQ(td2) &&
  683                                             (td2->td_flags & TDF_SINTR))
  684                                                 wakeup_swapper |=
  685                                                     sleepq_abort(td2, ERESTART);
  686                                         break;
  687                                 default:
  688                                         break;
  689                                 }
  690                         }
  691 #ifdef SMP
  692                         else if (TD_IS_RUNNING(td2) && td != td2) {
  693                                 forward_signal(td2);
  694                         }
  695 #endif
  696                         thread_unlock(td2);
  697                 }
  698                 if (wakeup_swapper)
  699                         kick_proc0();
  700                 remaining = calc_remaining(p, mode);
  701 
  702                 /*
  703                  * Maybe we suspended some threads.. was it enough?
  704                  */
  705                 if (remaining == 1)
  706                         break;
  707 
  708 stopme:
  709                 /*
  710                  * Wake us up when everyone else has suspended.
  711                  * In the mean time we suspend as well.
  712                  */
  713                 thread_suspend_switch(td);
  714                 remaining = calc_remaining(p, mode);
  715         }
  716         if (mode == SINGLE_EXIT) {
  717                 /*
  718                  * We have gotten rid of all the other threads and we
  719                  * are about to either exit or exec. In either case,
  720                  * we try our utmost to revert to being a non-threaded
  721                  * process.
  722                  */
  723                 p->p_singlethread = NULL;
  724                 p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT);
  725                 thread_unthread(td);
  726         }
  727         PROC_SUNLOCK(p);
  728         return (0);
  729 }
  730 
  731 /*
  732  * Called in from locations that can safely check to see
  733  * whether we have to suspend or at least throttle for a
  734  * single-thread event (e.g. fork).
  735  *
  736  * Such locations include userret().
  737  * If the "return_instead" argument is non zero, the thread must be able to
  738  * accept 0 (caller may continue), or 1 (caller must abort) as a result.
  739  *
  740  * The 'return_instead' argument tells the function if it may do a
  741  * thread_exit() or suspend, or whether the caller must abort and back
  742  * out instead.
  743  *
  744  * If the thread that set the single_threading request has set the
  745  * P_SINGLE_EXIT bit in the process flags then this call will never return
  746  * if 'return_instead' is false, but will exit.
  747  *
  748  * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
  749  *---------------+--------------------+---------------------
  750  *       0       | returns 0          |   returns 0 or 1
  751  *               | when ST ends       |   immediately
  752  *---------------+--------------------+---------------------
  753  *       1       | thread exits       |   returns 1
  754  *               |                    |  immediately
  755  * 0 = thread_exit() or suspension ok,
  756  * other = return error instead of stopping the thread.
  757  *
  758  * While a full suspension is under effect, even a single threading
  759  * thread would be suspended if it made this call (but it shouldn't).
  760  * This call should only be made from places where
  761  * thread_exit() would be safe as that may be the outcome unless
  762  * return_instead is set.
  763  */
  764 int
  765 thread_suspend_check(int return_instead)
  766 {
  767         struct thread *td;
  768         struct proc *p;
  769         int wakeup_swapper;
  770 
  771         td = curthread;
  772         p = td->td_proc;
  773         mtx_assert(&Giant, MA_NOTOWNED);
  774         PROC_LOCK_ASSERT(p, MA_OWNED);
  775         while (P_SHOULDSTOP(p) ||
  776               ((p->p_flag & P_TRACED) && (td->td_dbgflags & TDB_SUSPEND))) {
  777                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  778                         KASSERT(p->p_singlethread != NULL,
  779                             ("singlethread not set"));
  780                         /*
  781                          * The only suspension in action is a
  782                          * single-threading. Single threader need not stop.
  783                          * XXX Should be safe to access unlocked
  784                          * as it can only be set to be true by us.
  785                          */
  786                         if (p->p_singlethread == td)
  787                                 return (0);     /* Exempt from stopping. */
  788                 }
  789                 if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
  790                         return (EINTR);
  791 
  792                 /* Should we goto user boundary if we didn't come from there? */
  793                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
  794                     (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
  795                         return (ERESTART);
  796 
  797                 /*
  798                  * Ignore suspend requests for stop signals if they
  799                  * are deferred.
  800                  */
  801                 if (P_SHOULDSTOP(p) == P_STOPPED_SIG &&
  802                     td->td_flags & TDF_SBDRY) {
  803                         KASSERT(return_instead,
  804                             ("TDF_SBDRY set for unsafe thread_suspend_check"));
  805                         return (0);
  806                 }
  807 
  808                 /*
  809                  * If the process is waiting for us to exit,
  810                  * this thread should just suicide.
  811                  * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
  812                  */
  813                 if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td)) {
  814                         PROC_UNLOCK(p);
  815                         tidhash_remove(td);
  816                         PROC_LOCK(p);
  817                         tdsigcleanup(td);
  818                         PROC_SLOCK(p);
  819                         thread_stopped(p);
  820                         thread_exit();
  821                 }
  822 
  823                 PROC_SLOCK(p);
  824                 thread_stopped(p);
  825                 if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  826                         if (p->p_numthreads == p->p_suspcount + 1) {
  827                                 thread_lock(p->p_singlethread);
  828                                 wakeup_swapper =
  829                                     thread_unsuspend_one(p->p_singlethread);
  830                                 thread_unlock(p->p_singlethread);
  831                                 if (wakeup_swapper)
  832                                         kick_proc0();
  833                         }
  834                 }
  835                 PROC_UNLOCK(p);
  836                 thread_lock(td);
  837                 /*
  838                  * When a thread suspends, it just
  839                  * gets taken off all queues.
  840                  */
  841                 thread_suspend_one(td);
  842                 if (return_instead == 0) {
  843                         p->p_boundary_count++;
  844                         td->td_flags |= TDF_BOUNDARY;
  845                 }
  846                 PROC_SUNLOCK(p);
  847                 mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
  848                 if (return_instead == 0)
  849                         td->td_flags &= ~TDF_BOUNDARY;
  850                 thread_unlock(td);
  851                 PROC_LOCK(p);
  852                 if (return_instead == 0) {
  853                         PROC_SLOCK(p);
  854                         p->p_boundary_count--;
  855                         PROC_SUNLOCK(p);
  856                 }
  857         }
  858         return (0);
  859 }
  860 
  861 void
  862 thread_suspend_switch(struct thread *td)
  863 {
  864         struct proc *p;
  865 
  866         p = td->td_proc;
  867         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  868         PROC_LOCK_ASSERT(p, MA_OWNED);
  869         PROC_SLOCK_ASSERT(p, MA_OWNED);
  870         /*
  871          * We implement thread_suspend_one in stages here to avoid
  872          * dropping the proc lock while the thread lock is owned.
  873          */
  874         thread_stopped(p);
  875         p->p_suspcount++;
  876         PROC_UNLOCK(p);
  877         thread_lock(td);
  878         td->td_flags &= ~TDF_NEEDSUSPCHK;
  879         TD_SET_SUSPENDED(td);
  880         sched_sleep(td, 0);
  881         PROC_SUNLOCK(p);
  882         DROP_GIANT();
  883         mi_switch(SW_VOL | SWT_SUSPEND, NULL);
  884         thread_unlock(td);
  885         PICKUP_GIANT();
  886         PROC_LOCK(p);
  887         PROC_SLOCK(p);
  888 }
  889 
  890 void
  891 thread_suspend_one(struct thread *td)
  892 {
  893         struct proc *p = td->td_proc;
  894 
  895         PROC_SLOCK_ASSERT(p, MA_OWNED);
  896         THREAD_LOCK_ASSERT(td, MA_OWNED);
  897         KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  898         p->p_suspcount++;
  899         td->td_flags &= ~TDF_NEEDSUSPCHK;
  900         TD_SET_SUSPENDED(td);
  901         sched_sleep(td, 0);
  902 }
  903 
  904 int
  905 thread_unsuspend_one(struct thread *td)
  906 {
  907         struct proc *p = td->td_proc;
  908 
  909         PROC_SLOCK_ASSERT(p, MA_OWNED);
  910         THREAD_LOCK_ASSERT(td, MA_OWNED);
  911         KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
  912         TD_CLR_SUSPENDED(td);
  913         p->p_suspcount--;
  914         return (setrunnable(td));
  915 }
  916 
  917 /*
  918  * Allow all threads blocked by single threading to continue running.
  919  */
  920 void
  921 thread_unsuspend(struct proc *p)
  922 {
  923         struct thread *td;
  924         int wakeup_swapper;
  925 
  926         PROC_LOCK_ASSERT(p, MA_OWNED);
  927         PROC_SLOCK_ASSERT(p, MA_OWNED);
  928         wakeup_swapper = 0;
  929         if (!P_SHOULDSTOP(p)) {
  930                 FOREACH_THREAD_IN_PROC(p, td) {
  931                         thread_lock(td);
  932                         if (TD_IS_SUSPENDED(td)) {
  933                                 wakeup_swapper |= thread_unsuspend_one(td);
  934                         }
  935                         thread_unlock(td);
  936                 }
  937         } else if ((P_SHOULDSTOP(p) == P_STOPPED_SINGLE) &&
  938             (p->p_numthreads == p->p_suspcount)) {
  939                 /*
  940                  * Stopping everything also did the job for the single
  941                  * threading request. Now we've downgraded to single-threaded,
  942                  * let it continue.
  943                  */
  944                 thread_lock(p->p_singlethread);
  945                 wakeup_swapper = thread_unsuspend_one(p->p_singlethread);
  946                 thread_unlock(p->p_singlethread);
  947         }
  948         if (wakeup_swapper)
  949                 kick_proc0();
  950 }
  951 
  952 /*
  953  * End the single threading mode..
  954  */
  955 void
  956 thread_single_end(void)
  957 {
  958         struct thread *td;
  959         struct proc *p;
  960         int wakeup_swapper;
  961 
  962         td = curthread;
  963         p = td->td_proc;
  964         PROC_LOCK_ASSERT(p, MA_OWNED);
  965         p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY);
  966         PROC_SLOCK(p);
  967         p->p_singlethread = NULL;
  968         wakeup_swapper = 0;
  969         /*
  970          * If there are other threads they may now run,
  971          * unless of course there is a blanket 'stop order'
  972          * on the process. The single threader must be allowed
  973          * to continue however as this is a bad place to stop.
  974          */
  975         if ((p->p_numthreads != 1) && (!P_SHOULDSTOP(p))) {
  976                 FOREACH_THREAD_IN_PROC(p, td) {
  977                         thread_lock(td);
  978                         if (TD_IS_SUSPENDED(td)) {
  979                                 wakeup_swapper |= thread_unsuspend_one(td);
  980                         }
  981                         thread_unlock(td);
  982                 }
  983         }
  984         PROC_SUNLOCK(p);
  985         if (wakeup_swapper)
  986                 kick_proc0();
  987 }
  988 
  989 struct thread *
  990 thread_find(struct proc *p, lwpid_t tid)
  991 {
  992         struct thread *td;
  993 
  994         PROC_LOCK_ASSERT(p, MA_OWNED);
  995         FOREACH_THREAD_IN_PROC(p, td) {
  996                 if (td->td_tid == tid)
  997                         break;
  998         }
  999         return (td);
 1000 }
 1001 
 1002 /* Locate a thread by number; return with proc lock held. */
 1003 struct thread *
 1004 tdfind(lwpid_t tid, pid_t pid)
 1005 {
 1006 #define RUN_THRESH      16
 1007         struct thread *td;
 1008         int run = 0;
 1009 
 1010         rw_rlock(&tidhash_lock);
 1011         LIST_FOREACH(td, TIDHASH(tid), td_hash) {
 1012                 if (td->td_tid == tid) {
 1013                         if (pid != -1 && td->td_proc->p_pid != pid) {
 1014                                 td = NULL;
 1015                                 break;
 1016                         }
 1017                         PROC_LOCK(td->td_proc);
 1018                         if (td->td_proc->p_state == PRS_NEW) {
 1019                                 PROC_UNLOCK(td->td_proc);
 1020                                 td = NULL;
 1021                                 break;
 1022                         }
 1023                         if (run > RUN_THRESH) {
 1024                                 if (rw_try_upgrade(&tidhash_lock)) {
 1025                                         LIST_REMOVE(td, td_hash);
 1026                                         LIST_INSERT_HEAD(TIDHASH(td->td_tid),
 1027                                                 td, td_hash);
 1028                                         rw_wunlock(&tidhash_lock);
 1029                                         return (td);
 1030                                 }
 1031                         }
 1032                         break;
 1033                 }
 1034                 run++;
 1035         }
 1036         rw_runlock(&tidhash_lock);
 1037         return (td);
 1038 }
 1039 
 1040 void
 1041 tidhash_add(struct thread *td)
 1042 {
 1043         rw_wlock(&tidhash_lock);
 1044         LIST_INSERT_HEAD(TIDHASH(td->td_tid), td, td_hash);
 1045         rw_wunlock(&tidhash_lock);
 1046 }
 1047 
 1048 void
 1049 tidhash_remove(struct thread *td)
 1050 {
 1051         rw_wlock(&tidhash_lock);
 1052         LIST_REMOVE(td, td_hash);
 1053         rw_wunlock(&tidhash_lock);
 1054 }

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