FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_thread.c

     /*-
      * Copyright (C) 2001 Julian Elischer <julian@freebsd.org>.
      *  All rights reserved.
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
      *    notice(s), this list of conditions and the following disclaimer as
     *    the first lines of this file unmodified other than the possible
     *    addition of one or more copyright notices.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice(s), this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
     * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
     * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
     * DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
     * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
     * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
     * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
     * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
     * DAMAGE.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/6.1/sys/kern/kern_thread.c 158179 2006-04-30 16:44:43Z cvs2svn $");
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/mutex.h>
    #include <sys/proc.h>
    #include <sys/resourcevar.h>
    #include <sys/smp.h>
    #include <sys/sysctl.h>
    #include <sys/sched.h>
    #include <sys/sleepqueue.h>
    #include <sys/turnstile.h>
    #include <sys/ktr.h>
    #include <sys/umtx.h>
    
    #include <vm/vm.h>
    #include <vm/vm_extern.h>
    #include <vm/uma.h>
    
    /*
     * KSEGRP related storage.
     */
    static uma_zone_t ksegrp_zone;
    static uma_zone_t thread_zone;
    
    /* DEBUG ONLY */
    SYSCTL_NODE(_kern, OID_AUTO, threads, CTLFLAG_RW, 0, "thread allocation");
    static int thread_debug = 0;
    SYSCTL_INT(_kern_threads, OID_AUTO, debug, CTLFLAG_RW,
            &thread_debug, 0, "thread debug");
    
    int max_threads_per_proc = 1500;
    SYSCTL_INT(_kern_threads, OID_AUTO, max_threads_per_proc, CTLFLAG_RW,
            &max_threads_per_proc, 0, "Limit on threads per proc");
    
    int max_groups_per_proc = 1500;
    SYSCTL_INT(_kern_threads, OID_AUTO, max_groups_per_proc, CTLFLAG_RW,
            &max_groups_per_proc, 0, "Limit on thread groups per proc");
    
    int max_threads_hits;
    SYSCTL_INT(_kern_threads, OID_AUTO, max_threads_hits, CTLFLAG_RD,
            &max_threads_hits, 0, "");
    
    int virtual_cpu;
    
    TAILQ_HEAD(, thread) zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
    TAILQ_HEAD(, ksegrp) zombie_ksegrps = TAILQ_HEAD_INITIALIZER(zombie_ksegrps);
    struct mtx kse_zombie_lock;
    MTX_SYSINIT(kse_zombie_lock, &kse_zombie_lock, "kse zombie lock", MTX_SPIN);
    
    static int
    sysctl_kse_virtual_cpu(SYSCTL_HANDLER_ARGS)
    {
            int error, new_val;
            int def_val;
    
            def_val = mp_ncpus;
            if (virtual_cpu == 0)
                    new_val = def_val;
            else
                    new_val = virtual_cpu;
            error = sysctl_handle_int(oidp, &new_val, 0, req);
            if (error != 0 || req->newptr == NULL)
                    return (error);
            if (new_val < 0)
                    return (EINVAL);
            virtual_cpu = new_val;
            return (0);
   }
   
   /* DEBUG ONLY */
   SYSCTL_PROC(_kern_threads, OID_AUTO, virtual_cpu, CTLTYPE_INT|CTLFLAG_RW,
           0, sizeof(virtual_cpu), sysctl_kse_virtual_cpu, "I",
           "debug virtual cpus");
   
   struct mtx tid_lock;
   static struct unrhdr *tid_unrhdr;
   
   /*
    * Prepare a thread for use.
    */
   static int
   thread_ctor(void *mem, int size, void *arg, int flags)
   {
           struct thread   *td;
   
           td = (struct thread *)mem;
           td->td_state = TDS_INACTIVE;
           td->td_oncpu = NOCPU;
   
           td->td_tid = alloc_unr(tid_unrhdr);
   
           /*
            * Note that td_critnest begins life as 1 because the thread is not
            * running and is thereby implicitly waiting to be on the receiving
            * end of a context switch.  A context switch must occur inside a
            * critical section, and in fact, includes hand-off of the sched_lock.
            * After a context switch to a newly created thread, it will release
            * sched_lock for the first time, and its td_critnest will hit 0 for
            * the first time.  This happens on the far end of a context switch,
            * and when it context switches away from itself, it will in fact go
            * back into a critical section, and hand off the sched lock to the
            * next thread.
            */
           td->td_critnest = 1;
           return (0);
   }
   
   /*
    * Reclaim a thread after use.
    */
   static void
   thread_dtor(void *mem, int size, void *arg)
   {
           struct thread *td;
   
           td = (struct thread *)mem;
   
   #ifdef INVARIANTS
           /* Verify that this thread is in a safe state to free. */
           switch (td->td_state) {
           case TDS_INHIBITED:
           case TDS_RUNNING:
           case TDS_CAN_RUN:
           case TDS_RUNQ:
                   /*
                    * We must never unlink a thread that is in one of
                    * these states, because it is currently active.
                    */
                   panic("bad state for thread unlinking");
                   /* NOTREACHED */
           case TDS_INACTIVE:
                   break;
           default:
                   panic("bad thread state");
                   /* NOTREACHED */
           }
   #endif
   
           free_unr(tid_unrhdr, td->td_tid);
           sched_newthread(td);
   }
   
   /*
    * Initialize type-stable parts of a thread (when newly created).
    */
   static int
   thread_init(void *mem, int size, int flags)
   {
           struct thread *td;
   
           td = (struct thread *)mem;
   
           vm_thread_new(td, 0);
           cpu_thread_setup(td);
           td->td_sleepqueue = sleepq_alloc();
           td->td_turnstile = turnstile_alloc();
           td->td_umtxq = umtxq_alloc();
           td->td_sched = (struct td_sched *)&td[1];
           sched_newthread(td);
           return (0);
   }
   
   /*
    * Tear down type-stable parts of a thread (just before being discarded).
    */
   static void
   thread_fini(void *mem, int size)
   {
           struct thread *td;
   
           td = (struct thread *)mem;
           turnstile_free(td->td_turnstile);
           sleepq_free(td->td_sleepqueue);
           umtxq_free(td->td_umtxq);
           vm_thread_dispose(td);
   }
   
   /*
    * Initialize type-stable parts of a ksegrp (when newly created).
    */
   static int
   ksegrp_ctor(void *mem, int size, void *arg, int flags)
   {
           struct ksegrp   *kg;
   
           kg = (struct ksegrp *)mem;
           bzero(mem, size);
           kg->kg_sched = (struct kg_sched *)&kg[1];
           return (0);
   }
   
   void
   ksegrp_link(struct ksegrp *kg, struct proc *p)
   {
   
           TAILQ_INIT(&kg->kg_threads);
           TAILQ_INIT(&kg->kg_runq);       /* links with td_runq */
           TAILQ_INIT(&kg->kg_upcalls);    /* all upcall structure in ksegrp */
           kg->kg_proc = p;
           /*
            * the following counters are in the -zero- section
            * and may not need clearing
            */
           kg->kg_numthreads = 0;
           kg->kg_numupcalls = 0;
           /* link it in now that it's consistent */
           p->p_numksegrps++;
           TAILQ_INSERT_HEAD(&p->p_ksegrps, kg, kg_ksegrp);
   }
   
   /*
    * Called from:
    *   thread-exit()
    */
   void
   ksegrp_unlink(struct ksegrp *kg)
   {
           struct proc *p;
   
           mtx_assert(&sched_lock, MA_OWNED);
           KASSERT((kg->kg_numthreads == 0), ("ksegrp_unlink: residual threads"));
           KASSERT((kg->kg_numupcalls == 0), ("ksegrp_unlink: residual upcalls"));
   
           p = kg->kg_proc;
           TAILQ_REMOVE(&p->p_ksegrps, kg, kg_ksegrp);
           p->p_numksegrps--;
           /*
            * Aggregate stats from the KSE
            */
           if (p->p_procscopegrp == kg)
                   p->p_procscopegrp = NULL;
   }
   
   /*
    * For a newly created process,
    * link up all the structures and its initial threads etc.
    * called from:
    * {arch}/{arch}/machdep.c   ia64_init(), init386() etc.
    * proc_dtor() (should go away)
    * proc_init()
    */
   void
   proc_linkup(struct proc *p, struct ksegrp *kg, struct thread *td)
   {
   
           TAILQ_INIT(&p->p_ksegrps);           /* all ksegrps in proc */
           TAILQ_INIT(&p->p_threads);           /* all threads in proc */
           TAILQ_INIT(&p->p_suspended);         /* Threads suspended */
           p->p_numksegrps = 0;
           p->p_numthreads = 0;
   
           ksegrp_link(kg, p);
           thread_link(td, kg);
   }
   
   /*
    * Initialize global thread allocation resources.
    */
   void
   threadinit(void)
   {
   
           mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
           tid_unrhdr = new_unrhdr(PID_MAX + 1, INT_MAX, &tid_lock);
   
           thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
               thread_ctor, thread_dtor, thread_init, thread_fini,
               UMA_ALIGN_CACHE, 0);
           ksegrp_zone = uma_zcreate("KSEGRP", sched_sizeof_ksegrp(),
               ksegrp_ctor, NULL, NULL, NULL,
               UMA_ALIGN_CACHE, 0);
           kseinit();      /* set up kse specific stuff  e.g. upcall zone*/
   }
   
   /*
    * Stash an embarasingly extra thread into the zombie thread queue.
    */
   void
   thread_stash(struct thread *td)
   {
           mtx_lock_spin(&kse_zombie_lock);
           TAILQ_INSERT_HEAD(&zombie_threads, td, td_runq);
           mtx_unlock_spin(&kse_zombie_lock);
   }
   
   /*
    * Stash an embarasingly extra ksegrp into the zombie ksegrp queue.
    */
   void
   ksegrp_stash(struct ksegrp *kg)
   {
           mtx_lock_spin(&kse_zombie_lock);
           TAILQ_INSERT_HEAD(&zombie_ksegrps, kg, kg_ksegrp);
           mtx_unlock_spin(&kse_zombie_lock);
   }
   
   /*
    * Reap zombie kse resource.
    */
   void
   thread_reap(void)
   {
           struct thread *td_first, *td_next;
           struct ksegrp *kg_first, * kg_next;
   
           /*
            * Don't even bother to lock if none at this instant,
            * we really don't care about the next instant..
            */
           if ((!TAILQ_EMPTY(&zombie_threads))
               || (!TAILQ_EMPTY(&zombie_ksegrps))) {
                   mtx_lock_spin(&kse_zombie_lock);
                   td_first = TAILQ_FIRST(&zombie_threads);
                   kg_first = TAILQ_FIRST(&zombie_ksegrps);
                   if (td_first)
                           TAILQ_INIT(&zombie_threads);
                   if (kg_first)
                           TAILQ_INIT(&zombie_ksegrps);
                   mtx_unlock_spin(&kse_zombie_lock);
                   while (td_first) {
                           td_next = TAILQ_NEXT(td_first, td_runq);
                           if (td_first->td_ucred)
                                   crfree(td_first->td_ucred);
                           thread_free(td_first);
                           td_first = td_next;
                   }
                   while (kg_first) {
                           kg_next = TAILQ_NEXT(kg_first, kg_ksegrp);
                           ksegrp_free(kg_first);
                           kg_first = kg_next;
                   }
                   /*
                    * there will always be a thread on the list if one of these
                    * is there.
                    */
                   kse_GC();
           }
   }
   
   /*
    * Allocate a ksegrp.
    */
   struct ksegrp *
   ksegrp_alloc(void)
   {
           return (uma_zalloc(ksegrp_zone, M_WAITOK));
   }
   
   /*
    * Allocate a thread.
    */
   struct thread *
   thread_alloc(void)
   {
           thread_reap(); /* check if any zombies to get */
           return (uma_zalloc(thread_zone, M_WAITOK));
   }
   
   /*
    * Deallocate a ksegrp.
    */
   void
   ksegrp_free(struct ksegrp *td)
   {
           uma_zfree(ksegrp_zone, td);
   }
   
   /*
    * Deallocate a thread.
    */
   void
   thread_free(struct thread *td)
   {
   
           cpu_thread_clean(td);
           uma_zfree(thread_zone, td);
   }
   
   /*
    * Discard the current thread and exit from its context.
    * Always called with scheduler locked.
    *
    * Because we can't free a thread while we're operating under its context,
    * push the current thread into our CPU's deadthread holder. This means
    * we needn't worry about someone else grabbing our context before we
    * do a cpu_throw().  This may not be needed now as we are under schedlock.
    * Maybe we can just do a thread_stash() as thr_exit1 does.
    */
   /*  XXX
    * libthr expects its thread exit to return for the last
    * thread, meaning that the program is back to non-threaded
    * mode I guess. Because we do this (cpu_throw) unconditionally
    * here, they have their own version of it. (thr_exit1()) 
    * that doesn't do it all if this was the last thread.
    * It is also called from thread_suspend_check().
    * Of course in the end, they end up coming here through exit1
    * anyhow..  After fixing 'thr' to play by the rules we should be able 
    * to merge these two functions together.
    *
    * called from:
    * exit1()
    * kse_exit()
    * thr_exit()
    * thread_user_enter()
    * thread_userret()
    * thread_suspend_check()
    */
   void
   thread_exit(void)
   {
           struct bintime new_switchtime;
           struct thread *td;
           struct proc *p;
           struct ksegrp   *kg;
   
           td = curthread;
           kg = td->td_ksegrp;
           p = td->td_proc;
   
           mtx_assert(&sched_lock, MA_OWNED);
           mtx_assert(&Giant, MA_NOTOWNED);
           PROC_LOCK_ASSERT(p, MA_OWNED);
           KASSERT(p != NULL, ("thread exiting without a process"));
           KASSERT(kg != NULL, ("thread exiting without a kse group"));
           CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
               (long)p->p_pid, p->p_comm);
   
           if (td->td_standin != NULL) {
                   /*
                    * Note that we don't need to free the cred here as it
                    * is done in thread_reap().
                    */
                   thread_stash(td->td_standin);
                   td->td_standin = NULL;
           }
   
           /*
            * drop FPU & debug register state storage, or any other
            * architecture specific resources that
            * would not be on a new untouched process.
            */
           cpu_thread_exit(td);    /* XXXSMP */
   
           /*
            * The thread is exiting. scheduler can release its stuff
            * and collect stats etc.
            */
           sched_thread_exit(td);
   
           /* Do the same timestamp bookkeeping that mi_switch() would do. */
           binuptime(&new_switchtime);
           bintime_add(&p->p_rux.rux_runtime, &new_switchtime);
           bintime_sub(&p->p_rux.rux_runtime, PCPU_PTR(switchtime));
           PCPU_SET(switchtime, new_switchtime);
           PCPU_SET(switchticks, ticks);
           cnt.v_swtch++;
   
           /* Add our usage into the usage of all our children. */
           if (p->p_numthreads == 1)
                   ruadd(p->p_ru, &p->p_rux, &p->p_stats->p_cru, &p->p_crux);
   
           /*
            * The last thread is left attached to the process
            * So that the whole bundle gets recycled. Skip
            * all this stuff if we never had threads.
            * EXIT clears all sign of other threads when
            * it goes to single threading, so the last thread always
            * takes the short path.
            */
           if (p->p_flag & P_HADTHREADS) {
                   if (p->p_numthreads > 1) {
                           thread_unlink(td);
   
                           /* XXX first arg not used in 4BSD or ULE */
                           sched_exit_thread(FIRST_THREAD_IN_PROC(p), td);
   
                           /*
                            * The test below is NOT true if we are the
                            * sole exiting thread. P_STOPPED_SNGL is unset
                            * in exit1() after it is the only survivor.
                            */
                           if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
                                   if (p->p_numthreads == p->p_suspcount) {
                                           thread_unsuspend_one(p->p_singlethread);
                                   }
                           }
   
                           /*
                            * Because each upcall structure has an owner thread,
                            * owner thread exits only when process is in exiting
                            * state, so upcall to userland is no longer needed,
                            * deleting upcall structure is safe here.
                            * So when all threads in a group is exited, all upcalls
                            * in the group should be automatically freed.
                            *  XXXKSE This is a KSE thing and should be exported
                            * there somehow.
                            */
                           upcall_remove(td);
   
                           /*
                            * If the thread we unlinked above was the last one,
                            * then this ksegrp should go away too.
                            */
                           if (kg->kg_numthreads == 0) {
                                   /*
                                    * let the scheduler know about this in case
                                    * it needs to recover stats or resources.
                                    * Theoretically we could let
                                    * sched_exit_ksegrp()  do the equivalent of
                                    * setting the concurrency to 0
                                    * but don't do it yet to avoid changing
                                    * the existing scheduler code until we
                                    * are ready.
                                    * We supply a random other ksegrp
                                    * as the recipient of any built up
                                    * cpu usage etc. (If the scheduler wants it).
                                    * XXXKSE
                                    * This is probably not fair so think of
                                    * a better answer.
                                    */
                                   sched_exit_ksegrp(FIRST_KSEGRP_IN_PROC(p), td);
                                   sched_set_concurrency(kg, 0); /* XXX TEMP */
                                   ksegrp_unlink(kg);
                                   ksegrp_stash(kg);
                           }
                           PROC_UNLOCK(p);
                           td->td_ksegrp   = NULL;
                           PCPU_SET(deadthread, td);
                   } else {
                           /*
                            * The last thread is exiting.. but not through exit()
                            * what should we do?
                            * Theoretically this can't happen
                            * exit1() - clears threading flags before coming here
                            * kse_exit() - treats last thread specially
                            * thr_exit() - treats last thread specially
                            * thread_user_enter() - only if more exist
                            * thread_userret() - only if more exist
                            * thread_suspend_check() - only if more exist
                            */
                           panic ("thread_exit: Last thread exiting on its own");
                   }
           } else {
                   /*
                    * non threaded process comes here.
                    * This includes an EX threaded process that is coming
                    * here via exit1(). (exit1 dethreads the proc first).
                    */
                   PROC_UNLOCK(p);
           }
           td->td_state = TDS_INACTIVE;
           CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
           cpu_throw(td, choosethread());
           panic("I'm a teapot!");
           /* NOTREACHED */
   }
   
   /*
    * Do any thread specific cleanups that may be needed in wait()
    * called with Giant, proc and schedlock not held.
    */
   void
   thread_wait(struct proc *p)
   {
           struct thread *td;
   
           mtx_assert(&Giant, MA_NOTOWNED);
           KASSERT((p->p_numthreads == 1), ("Multiple threads in wait1()"));
           KASSERT((p->p_numksegrps == 1), ("Multiple ksegrps in wait1()"));
           FOREACH_THREAD_IN_PROC(p, td) {
                   if (td->td_standin != NULL) {
                           if (td->td_standin->td_ucred != NULL) {
                                   crfree(td->td_standin->td_ucred);
                                   td->td_standin->td_ucred = NULL;
                           }
                           thread_free(td->td_standin);
                           td->td_standin = NULL;
                   }
                   cpu_thread_clean(td);
                   crfree(td->td_ucred);
           }
           thread_reap();  /* check for zombie threads etc. */
   }
   
   /*
    * Link a thread to a process.
    * set up anything that needs to be initialized for it to
    * be used by the process.
    *
    * Note that we do not link to the proc's ucred here.
    * The thread is linked as if running but no KSE assigned.
    * Called from:
    *  proc_linkup()
    *  thread_schedule_upcall()
    *  thr_create()
    */
   void
   thread_link(struct thread *td, struct ksegrp *kg)
   {
           struct proc *p;
   
           p = kg->kg_proc;
           td->td_state    = TDS_INACTIVE;
           td->td_proc     = p;
           td->td_ksegrp   = kg;
           td->td_flags    = 0;
           td->td_kflags   = 0;
   
           LIST_INIT(&td->td_contested);
           callout_init(&td->td_slpcallout, CALLOUT_MPSAFE);
           TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
           TAILQ_INSERT_HEAD(&kg->kg_threads, td, td_kglist);
           p->p_numthreads++;
           kg->kg_numthreads++;
   }
   
   /*
    * Convert a process with one thread to an unthreaded process.
    * Called from:
    *  thread_single(exit)  (called from execve and exit)
    *  kse_exit()          XXX may need cleaning up wrt KSE stuff
    */
   void
   thread_unthread(struct thread *td)
   {
           struct proc *p = td->td_proc;
   
           KASSERT((p->p_numthreads == 1), ("Unthreading with >1 threads"));
           upcall_remove(td);
           p->p_flag &= ~(P_SA|P_HADTHREADS);
           td->td_mailbox = NULL;
           td->td_pflags &= ~(TDP_SA | TDP_CAN_UNBIND);
           if (td->td_standin != NULL) {
                   thread_stash(td->td_standin);
                   td->td_standin = NULL;
           }
           sched_set_concurrency(td->td_ksegrp, 1);
   }
   
   /*
    * Called from:
    *  thread_exit()
    */
   void
   thread_unlink(struct thread *td)
   {
           struct proc *p = td->td_proc;
           struct ksegrp *kg = td->td_ksegrp;
   
           mtx_assert(&sched_lock, MA_OWNED);
           TAILQ_REMOVE(&p->p_threads, td, td_plist);
           p->p_numthreads--;
           TAILQ_REMOVE(&kg->kg_threads, td, td_kglist);
           kg->kg_numthreads--;
           /* could clear a few other things here */
           /* Must  NOT clear links to proc and ksegrp! */
   }
   
   /*
    * Enforce single-threading.
    *
    * Returns 1 if the caller must abort (another thread is waiting to
    * exit the process or similar). Process is locked!
    * Returns 0 when you are successfully the only thread running.
    * A process has successfully single threaded in the suspend mode when
    * There are no threads in user mode. Threads in the kernel must be
    * allowed to continue until they get to the user boundary. They may even
    * copy out their return values and data before suspending. They may however be
    * accellerated in reaching the user boundary as we will wake up
    * any sleeping threads that are interruptable. (PCATCH).
    */
   int
   thread_single(int mode)
   {
           struct thread *td;
           struct thread *td2;
           struct proc *p;
           int remaining;
   
           td = curthread;
           p = td->td_proc;
           mtx_assert(&Giant, MA_NOTOWNED);
           PROC_LOCK_ASSERT(p, MA_OWNED);
           KASSERT((td != NULL), ("curthread is NULL"));
   
           if ((p->p_flag & P_HADTHREADS) == 0)
                   return (0);
   
           /* Is someone already single threading? */
           if (p->p_singlethread != NULL && p->p_singlethread != td)
                   return (1);
   
           if (mode == SINGLE_EXIT) {
                   p->p_flag |= P_SINGLE_EXIT;
                   p->p_flag &= ~P_SINGLE_BOUNDARY;
           } else {
                   p->p_flag &= ~P_SINGLE_EXIT;
                   if (mode == SINGLE_BOUNDARY)
                           p->p_flag |= P_SINGLE_BOUNDARY;
                   else
                           p->p_flag &= ~P_SINGLE_BOUNDARY;
           }
           p->p_flag |= P_STOPPED_SINGLE;
           mtx_lock_spin(&sched_lock);
           p->p_singlethread = td;
           if (mode == SINGLE_EXIT)
                   remaining = p->p_numthreads;
           else if (mode == SINGLE_BOUNDARY)
                   remaining = p->p_numthreads - p->p_boundary_count;
           else
                   remaining = p->p_numthreads - p->p_suspcount;
           while (remaining != 1) {
                   if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
                           goto stopme;
                   FOREACH_THREAD_IN_PROC(p, td2) {
                           if (td2 == td)
                                   continue;
                           td2->td_flags |= TDF_ASTPENDING;
                           if (TD_IS_INHIBITED(td2)) {
                                   switch (mode) {
                                   case SINGLE_EXIT:
                                           if (td->td_flags & TDF_DBSUSPEND)
                                                   td->td_flags &= ~TDF_DBSUSPEND;
                                           if (TD_IS_SUSPENDED(td2))
                                                   thread_unsuspend_one(td2);
                                           if (TD_ON_SLEEPQ(td2) &&
                                               (td2->td_flags & TDF_SINTR))
                                                   sleepq_abort(td2, EINTR);
                                           break;
                                   case SINGLE_BOUNDARY:
                                           if (TD_IS_SUSPENDED(td2) &&
                                               !(td2->td_flags & TDF_BOUNDARY))
                                                   thread_unsuspend_one(td2);
                                           if (TD_ON_SLEEPQ(td2) &&
                                               (td2->td_flags & TDF_SINTR))
                                                   sleepq_abort(td2, ERESTART);
                                           break;
                                   default:        
                                           if (TD_IS_SUSPENDED(td2))
                                                   continue;
                                           /*
                                            * maybe other inhibitted states too?
                                            */
                                           if ((td2->td_flags & TDF_SINTR) &&
                                               (td2->td_inhibitors &
                                               (TDI_SLEEPING | TDI_SWAPPED)))
                                                   thread_suspend_one(td2);
                                           break;
                                   }
                           }
   #ifdef SMP
                           else if (TD_IS_RUNNING(td2) && td != td2) {
                                   forward_signal(td2);
                           }
   #endif
                   }
                   if (mode == SINGLE_EXIT)
                           remaining = p->p_numthreads;
                   else if (mode == SINGLE_BOUNDARY)
                           remaining = p->p_numthreads - p->p_boundary_count;
                   else
                           remaining = p->p_numthreads - p->p_suspcount;
   
                   /*
                    * Maybe we suspended some threads.. was it enough?
                    */
                   if (remaining == 1)
                           break;
   
   stopme:
                   /*
                    * Wake us up when everyone else has suspended.
                    * In the mean time we suspend as well.
                    */
                   thread_stopped(p);
                   thread_suspend_one(td);
                   PROC_UNLOCK(p);
                   mi_switch(SW_VOL, NULL);
                   mtx_unlock_spin(&sched_lock);
                   PROC_LOCK(p);
                   mtx_lock_spin(&sched_lock);
                   if (mode == SINGLE_EXIT)
                           remaining = p->p_numthreads;
                   else if (mode == SINGLE_BOUNDARY)
                           remaining = p->p_numthreads - p->p_boundary_count;
                   else
                           remaining = p->p_numthreads - p->p_suspcount;
           }
           if (mode == SINGLE_EXIT) {
                   /*
                    * We have gotten rid of all the other threads and we
                    * are about to either exit or exec. In either case,
                    * we try our utmost  to revert to being a non-threaded
                    * process.
                    */
                   p->p_singlethread = NULL;
                   p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT);
                   thread_unthread(td);
           }
           mtx_unlock_spin(&sched_lock);
           return (0);
   }
   
   /*
    * Called in from locations that can safely check to see
    * whether we have to suspend or at least throttle for a
    * single-thread event (e.g. fork).
    *
    * Such locations include userret().
    * If the "return_instead" argument is non zero, the thread must be able to
    * accept 0 (caller may continue), or 1 (caller must abort) as a result.
    *
    * The 'return_instead' argument tells the function if it may do a
    * thread_exit() or suspend, or whether the caller must abort and back
    * out instead.
    *
    * If the thread that set the single_threading request has set the
    * P_SINGLE_EXIT bit in the process flags then this call will never return
    * if 'return_instead' is false, but will exit.
    *
    * P_SINGLE_EXIT | return_instead == 0| return_instead != 0
    *---------------+--------------------+---------------------
    *       0       | returns 0          |   returns 0 or 1
    *               | when ST ends       |   immediatly
    *---------------+--------------------+---------------------
    *       1       | thread exits       |   returns 1
    *               |                    |  immediatly
    * 0 = thread_exit() or suspension ok,
    * other = return error instead of stopping the thread.
    *
    * While a full suspension is under effect, even a single threading
    * thread would be suspended if it made this call (but it shouldn't).
    * This call should only be made from places where
    * thread_exit() would be safe as that may be the outcome unless
    * return_instead is set.
    */
   int
   thread_suspend_check(int return_instead)
   {
           struct thread *td;
           struct proc *p;
   
           td = curthread;
           p = td->td_proc;
           mtx_assert(&Giant, MA_NOTOWNED);
           PROC_LOCK_ASSERT(p, MA_OWNED);
           while (P_SHOULDSTOP(p) ||
                 ((p->p_flag & P_TRACED) && (td->td_flags & TDF_DBSUSPEND))) {
                   if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
                           KASSERT(p->p_singlethread != NULL,
                               ("singlethread not set"));
                           /*
                            * The only suspension in action is a
                            * single-threading. Single threader need not stop.
                            * XXX Should be safe to access unlocked
                            * as it can only be set to be true by us.
                            */
                           if (p->p_singlethread == td)
                                   return (0);     /* Exempt from stopping. */
                   }
                   if ((p->p_flag & P_SINGLE_EXIT) && return_instead)
                           return (EINTR);
   
                   /* Should we goto user boundary if we didn't come from there? */
                   if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE &&
                       (p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
                           return (ERESTART);
   
                   mtx_lock_spin(&sched_lock);
                   thread_stopped(p);
                   /*
                    * If the process is waiting for us to exit,
                    * this thread should just suicide.
                    * Assumes that P_SINGLE_EXIT implies P_STOPPED_SINGLE.
                    */
                   if ((p->p_flag & P_SINGLE_EXIT) && (p->p_singlethread != td))
                           thread_exit();
   
                   /*
                    * When a thread suspends, it just
                    * moves to the processes's suspend queue
                    * and stays there.
                    */
                   thread_suspend_one(td);
                   if (return_instead == 0) {
                           p->p_boundary_count++;
                           td->td_flags |= TDF_BOUNDARY;
                   }
                   if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
                           if (p->p_numthreads == p->p_suspcount) 
                                   thread_unsuspend_one(p->p_singlethread);
                   }
                   PROC_UNLOCK(p);
                   mi_switch(SW_INVOL, NULL);
                   if (return_instead == 0) {
                           p->p_boundary_count--;
                           td->td_flags &= ~TDF_BOUNDARY;
                   }
                   mtx_unlock_spin(&sched_lock);
                   PROC_LOCK(p);
           }
           return (0);
   }
   
   void
   thread_suspend_one(struct thread *td)
   {
           struct proc *p = td->td_proc;
   
           mtx_assert(&sched_lock, MA_OWNED);
           PROC_LOCK_ASSERT(p, MA_OWNED);
           KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
           p->p_suspcount++;
           TD_SET_SUSPENDED(td);
           TAILQ_INSERT_TAIL(&p->p_suspended, td, td_runq);
   }
   
   void
   thread_unsuspend_one(struct thread *td)
   {
           struct proc *p = td->td_proc;
   
           mtx_assert(&sched_lock, MA_OWNED);
           PROC_LOCK_ASSERT(p, MA_OWNED);
           TAILQ_REMOVE(&p->p_suspended, td, td_runq);
           TD_CLR_SUSPENDED(td);
           p->p_suspcount--;
           setrunnable(td);
   }
   
   /*
    * Allow all threads blocked by single threading to continue running.
    */
   void
   thread_unsuspend(struct proc *p)
   {
           struct thread *td;
   
           mtx_assert(&sched_lock, MA_OWNED);
           PROC_LOCK_ASSERT(p, MA_OWNED);
           if (!P_SHOULDSTOP(p)) {
                   while ((td = TAILQ_FIRST(&p->p_suspended))) {
                           thread_unsuspend_one(td);
                   }
           } else if ((P_SHOULDSTOP(p) == P_STOPPED_SINGLE) &&
               (p->p_numthreads == p->p_suspcount)) {
                   /*
                    * Stopping everything also did the job for the single
                    * threading request. Now we've downgraded to single-threaded,
                    * let it continue.
                    */
                   thread_unsuspend_one(p->p_singlethread);
           }
   }
   
   /*
    * End the single threading mode..
    */
   void
   thread_single_end(void)
   {
           struct thread *td;
           struct proc *p;
   
           td = curthread;
           p = td->td_proc;
           PROC_LOCK_ASSERT(p, MA_OWNED);
          p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY);
          mtx_lock_spin(&sched_lock);
          p->p_singlethread = NULL;
          p->p_procscopegrp = NULL;
          /*
           * If there are other threads they mey now run,
           * unless of course there is a blanket 'stop order'
           * on the process. The single threader must be allowed
           * to continue however as this is a bad place to stop.
           */
          if ((p->p_numthreads != 1) && (!P_SHOULDSTOP(p))) {
                  while ((td = TAILQ_FIRST(&p->p_suspended))) {
                          thread_unsuspend_one(td);
                  }
          }
          mtx_unlock_spin(&sched_lock);
  }
  
  /*
   * Called before going into an interruptible sleep to see if we have been
   * interrupted or requested to exit.
   */
  int
  thread_sleep_check(struct thread *td)
  {
          struct proc *p;
  
          p = td->td_proc;
          mtx_assert(&sched_lock, MA_OWNED);
          if (p->p_flag & P_HADTHREADS) {
                  if (p->p_singlethread != td) {
                          if (p->p_flag & P_SINGLE_EXIT)
                                  return (EINTR);
                          if (p->p_flag & P_SINGLE_BOUNDARY)
                                  return (ERESTART);
                  }
                  if (td->td_flags & TDF_INTERRUPT)
                          return (td->td_intrval);
          }
          return (0);
  }

Cache object: ee8c0ad8cad57fdde39c9335bb7b8817