text: /*-
   * 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 "opt_witness.h"
  #include "opt_kdtrace.h"
  #include "opt_hwpmc_hooks.h"
  
  #include <sys/cdefs.h>
  __FBSDID("$FreeBSD: releng/9.3/sys/kern/kern_thread.c 262057 2014-02-17 13:58:50Z avg $");
  
  #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/rangelock.h>
  #include <sys/resourcevar.h>
  #include <sys/sdt.h>
  #include <sys/smp.h>
  #include <sys/sched.h>
  #include <sys/sleepqueue.h>
  #include <sys/selinfo.h>
  #include <sys/turnstile.h>
  #include <sys/ktr.h>
  #include <sys/rwlock.h>
  #include <sys/umtx.h>
  #include <sys/cpuset.h>
  #ifdef	HWPMC_HOOKS
  #include <sys/pmckern.h>
  #endif
  
  #include <security/audit/audit.h>
  
  #include <vm/vm.h>
  #include <vm/vm_extern.h>
  #include <vm/uma.h>
  #include <sys/eventhandler.h>
  
  SDT_PROVIDER_DECLARE(proc);
  SDT_PROBE_DEFINE(proc, , , lwp__exit);
  
  
  /*
   * thread related storage.
   */
  static uma_zone_t thread_zone;
  
  TAILQ_HEAD(, thread) zombie_threads = TAILQ_HEAD_INITIALIZER(zombie_threads);
  static struct mtx zombie_lock;
  MTX_SYSINIT(zombie_lock, &zombie_lock, "zombie lock", MTX_SPIN);
  
  static void thread_zombie(struct thread *);
  
  #define TID_BUFFER_SIZE	1024
  
  struct mtx tid_lock;
  static struct unrhdr *tid_unrhdr;
  static lwpid_t tid_buffer[TID_BUFFER_SIZE];
  static int tid_head, tid_tail;
  static MALLOC_DEFINE(M_TIDHASH, "tidhash", "thread hash");
  
  struct	tidhashhead *tidhashtbl;
  u_long	tidhash;
  struct	rwlock tidhash_lock;
  
  static lwpid_t
  tid_alloc(void)
  {
  	lwpid_t	tid;
  
  	tid = alloc_unr(tid_unrhdr);
  	if (tid != -1)
  		return (tid);
  	mtx_lock(&tid_lock);
  	if (tid_head == tid_tail) {
  		mtx_unlock(&tid_lock);
  		return (-1);
  	}
  	tid = tid_buffer[tid_head];
  	tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
  	mtx_unlock(&tid_lock);
  	return (tid);
  }
  
  static void
  tid_free(lwpid_t tid)
  {
  	lwpid_t tmp_tid = -1;
  
  	mtx_lock(&tid_lock);
  	if ((tid_tail + 1) % TID_BUFFER_SIZE == tid_head) {
  		tmp_tid = tid_buffer[tid_head];
  		tid_head = (tid_head + 1) % TID_BUFFER_SIZE;
  	}
  	tid_buffer[tid_tail] = tid;
  	tid_tail = (tid_tail + 1) % TID_BUFFER_SIZE;
  	mtx_unlock(&tid_lock);
  	if (tmp_tid != -1)
  		free_unr(tid_unrhdr, tmp_tid);
  }
  
  /*
   * 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 = tid_alloc();
  
  	/*
  	 * 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.
  	 */
  	td->td_critnest = 1;
  	td->td_lend_user_pri = PRI_MAX;
  	EVENTHANDLER_INVOKE(thread_ctor, td);
  #ifdef AUDIT
  	audit_thread_alloc(td);
  #endif
  	umtx_thread_alloc(td);
  	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
  #ifdef AUDIT
  	audit_thread_free(td);
  #endif
  	/* Free all OSD associated to this thread. */
  	osd_thread_exit(td);
  
  	EVENTHANDLER_INVOKE(thread_dtor, td);
  	tid_free(td->td_tid);
  }
  
  /*
   * 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;
  
  	td->td_sleepqueue = sleepq_alloc();
  	td->td_turnstile = turnstile_alloc();
  	td->td_rlqe = NULL;
  	td->td_vp_reserv = 0;
  	EVENTHANDLER_INVOKE(thread_init, td);
  	td->td_sched = (struct td_sched *)&td[1];
  	umtx_thread_init(td);
  	td->td_kstack = 0;
  	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;
  	EVENTHANDLER_INVOKE(thread_fini, td);
  	rlqentry_free(td->td_rlqe);
  	turnstile_free(td->td_turnstile);
  	sleepq_free(td->td_sleepqueue);
  	umtx_thread_fini(td);
  	seltdfini(td);
  }
  
  /*
   * 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_linkup0(struct proc *p, struct thread *td)
  {
  	TAILQ_INIT(&p->p_threads);	     /* all threads in proc */
  	proc_linkup(p, td);
  }
  
  void
  proc_linkup(struct proc *p, struct thread *td)
  {
  
  	sigqueue_init(&p->p_sigqueue, p);
  	p->p_ksi = ksiginfo_alloc(1);
  	if (p->p_ksi != NULL) {
  		/* XXX p_ksi may be null if ksiginfo zone is not ready */
  		p->p_ksi->ksi_flags = KSI_EXT | KSI_INS;
  	}
  	LIST_INIT(&p->p_mqnotifier);
  	p->p_numthreads = 0;
  	thread_link(td, p);
  }
  
  /*
   * Initialize global thread allocation resources.
   */
  void
  threadinit(void)
  {
  
  	mtx_init(&tid_lock, "TID lock", NULL, MTX_DEF);
  
  	/*
  	 * pid_max cannot be greater than PID_MAX.
  	 * leave one number for thread0.
  	 */
  	tid_unrhdr = new_unrhdr(PID_MAX + 2, INT_MAX, &tid_lock);
  
  	thread_zone = uma_zcreate("THREAD", sched_sizeof_thread(),
  	    thread_ctor, thread_dtor, thread_init, thread_fini,
  	    16 - 1, 0);
  	tidhashtbl = hashinit(maxproc / 2, M_TIDHASH, &tidhash);
  	rw_init(&tidhash_lock, "tidhash");
  }
  
  /*
   * Place an unused thread on the zombie list.
   * Use the slpq as that must be unused by now.
   */
  void
  thread_zombie(struct thread *td)
  {
  	mtx_lock_spin(&zombie_lock);
  	TAILQ_INSERT_HEAD(&zombie_threads, td, td_slpq);
  	mtx_unlock_spin(&zombie_lock);
  }
  
  /*
   * Release a thread that has exited after cpu_throw().
   */
  void
  thread_stash(struct thread *td)
  {
  	atomic_subtract_rel_int(&td->td_proc->p_exitthreads, 1);
  	thread_zombie(td);
  }
  
  /*
   * Reap zombie resources.
   */
  void
  thread_reap(void)
  {
  	struct thread *td_first, *td_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)) {
  		mtx_lock_spin(&zombie_lock);
  		td_first = TAILQ_FIRST(&zombie_threads);
  		if (td_first)
  			TAILQ_INIT(&zombie_threads);
  		mtx_unlock_spin(&zombie_lock);
  		while (td_first) {
  			td_next = TAILQ_NEXT(td_first, td_slpq);
  			if (td_first->td_ucred)
  				crfree(td_first->td_ucred);
  			thread_free(td_first);
  			td_first = td_next;
  		}
  	}
  }
  
  /*
   * Allocate a thread.
   */
  struct thread *
  thread_alloc(int pages)
  {
  	struct thread *td;
  
  	thread_reap(); /* check if any zombies to get */
  
  	td = (struct thread *)uma_zalloc(thread_zone, M_WAITOK);
  	KASSERT(td->td_kstack == 0, ("thread_alloc got thread with kstack"));
  	if (!vm_thread_new(td, pages)) {
  		uma_zfree(thread_zone, td);
  		return (NULL);
  	}
  	cpu_thread_alloc(td);
  	return (td);
  }
  
  int
  thread_alloc_stack(struct thread *td, int pages)
  {
  
  	KASSERT(td->td_kstack == 0,
  	    ("thread_alloc_stack called on a thread with kstack"));
  	if (!vm_thread_new(td, pages))
  		return (0);
  	cpu_thread_alloc(td);
  	return (1);
  }
  
  /*
   * Deallocate a thread.
   */
  void
  thread_free(struct thread *td)
  {
  
  	lock_profile_thread_exit(td);
  	if (td->td_cpuset)
  		cpuset_rel(td->td_cpuset);
  	td->td_cpuset = NULL;
  	cpu_thread_free(td);
  	if (td->td_kstack != 0)
  		vm_thread_dispose(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().
   */
  void
  thread_exit(void)
  {
  	uint64_t runtime, new_switchtime;
  	struct thread *td;
  	struct thread *td2;
  	struct proc *p;
  	int wakeup_swapper;
  
  	td = curthread;
  	p = td->td_proc;
  
  	PROC_SLOCK_ASSERT(p, MA_OWNED);
  	mtx_assert(&Giant, MA_NOTOWNED);
  
  	PROC_LOCK_ASSERT(p, MA_OWNED);
  	KASSERT(p != NULL, ("thread exiting without a process"));
  	CTR3(KTR_PROC, "thread_exit: thread %p (pid %ld, %s)", td,
  	    (long)p->p_pid, td->td_name);
  	KASSERT(TAILQ_EMPTY(&td->td_sigqueue.sq_list), ("signal pending"));
  
  #ifdef AUDIT
  	AUDIT_SYSCALL_EXIT(0, td);
  #endif
  	umtx_thread_exit(td);
  	/*
  	 * 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 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);
  			td2 = FIRST_THREAD_IN_PROC(p);
  			sched_exit_thread(td2, td);
  
  			/*
  			 * The test below is NOT true if we are the
  			 * sole exiting thread. P_STOPPED_SINGLE 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_lock(p->p_singlethread);
  					wakeup_swapper = thread_unsuspend_one(
  						p->p_singlethread);
  					thread_unlock(p->p_singlethread);
  					if (wakeup_swapper)
  						kick_proc0();
  				}
  			}
  
  			atomic_add_int(&td->td_proc->p_exitthreads, 1);
  			PCPU_SET(deadthread, td);
  		} else {
  			/*
  			 * The last thread is exiting.. but not through exit()
  			 */
  			panic ("thread_exit: Last thread exiting on its own");
  		}
  	} 
  #ifdef	HWPMC_HOOKS
  	/*
  	 * If this thread is part of a process that is being tracked by hwpmc(4),
  	 * inform the module of the thread's impending exit.
  	 */
  	if (PMC_PROC_IS_USING_PMCS(td->td_proc))
  		PMC_SWITCH_CONTEXT(td, PMC_FN_CSW_OUT);
  #endif
  	PROC_UNLOCK(p);
  
  	/* Do the same timestamp bookkeeping that mi_switch() would do. */
  	new_switchtime = cpu_ticks();
  	runtime = new_switchtime - PCPU_GET(switchtime);
  	td->td_runtime += runtime;
  	td->td_incruntime += runtime;
  	PCPU_SET(switchtime, new_switchtime);
  	PCPU_SET(switchticks, ticks);
  	PCPU_INC(cnt.v_swtch);
  
  	/* Save our resource usage in our process. */
  	td->td_ru.ru_nvcsw++;
  	ruxagg(p, td);
  	rucollect(&p->p_ru, &td->td_ru);
  
  	thread_lock(td);
  	PROC_SUNLOCK(p);
  	td->td_state = TDS_INACTIVE;
  #ifdef WITNESS
  	witness_thread_exit(td);
  #endif
  	CTR1(KTR_PROC, "thread_exit: cpu_throw() thread %p", td);
  	sched_throw(td);
  	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()"));
  	td = FIRST_THREAD_IN_PROC(p);
  	/* Lock the last thread so we spin until it exits cpu_throw(). */
  	thread_lock(td);
  	thread_unlock(td);
  	/* Wait for any remaining threads to exit cpu_throw(). */
  	while (p->p_exitthreads)
  		sched_relinquish(curthread);
  	lock_profile_thread_exit(td);
  	cpuset_rel(td->td_cpuset);
  	td->td_cpuset = 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.
   */
  void
  thread_link(struct thread *td, struct proc *p)
  {
  
  	/*
  	 * XXX This can't be enabled because it's called for proc0 before
  	 * its lock has been created.
  	 * PROC_LOCK_ASSERT(p, MA_OWNED);
  	 */
  	td->td_state    = TDS_INACTIVE;
  	td->td_proc     = p;
  	td->td_flags    = TDF_INMEM;
  
  	LIST_INIT(&td->td_contested);
  	LIST_INIT(&td->td_lprof[0]);
  	LIST_INIT(&td->td_lprof[1]);
  	sigqueue_init(&td->td_sigqueue, p);
  	callout_init(&td->td_slpcallout, CALLOUT_MPSAFE);
  	TAILQ_INSERT_HEAD(&p->p_threads, td, td_plist);
  	p->p_numthreads++;
  }
  
  /*
   * Convert a process with one thread to an unthreaded process.
   */
  void
  thread_unthread(struct thread *td)
  {
  	struct proc *p = td->td_proc;
  
  	KASSERT((p->p_numthreads == 1), ("Unthreading with >1 threads"));
  	p->p_flag &= ~P_HADTHREADS;
  }
  
  /*
   * Called from:
   *  thread_exit()
   */
  void
  thread_unlink(struct thread *td)
  {
  	struct proc *p = td->td_proc;
  
  	PROC_LOCK_ASSERT(p, MA_OWNED);
  	TAILQ_REMOVE(&p->p_threads, td, td_plist);
  	p->p_numthreads--;
  	/* could clear a few other things here */
  	/* Must  NOT clear links to proc! */
  }
  
  static int
  calc_remaining(struct proc *p, int mode)
  {
  	int remaining;
  
  	PROC_LOCK_ASSERT(p, MA_OWNED);
  	PROC_SLOCK_ASSERT(p, MA_OWNED);
  	if (mode == SINGLE_EXIT)
  		remaining = p->p_numthreads;
  	else if (mode == SINGLE_BOUNDARY)
  		remaining = p->p_numthreads - p->p_boundary_count;
  	else if (mode == SINGLE_NO_EXIT)
  		remaining = p->p_numthreads - p->p_suspcount;
  	else
  		panic("calc_remaining: wrong mode %d", mode);
  	return (remaining);
  }
  
  /*
   * 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
   * accelerated 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, wakeup_swapper;
  
  	td = curthread;
  	p = td->td_proc;
  	mtx_assert(&Giant, MA_NOTOWNED);
  	PROC_LOCK_ASSERT(p, MA_OWNED);
  
  	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;
  	PROC_SLOCK(p);
  	p->p_singlethread = td;
  	remaining = calc_remaining(p, mode);
  	while (remaining != 1) {
  		if (P_SHOULDSTOP(p) != P_STOPPED_SINGLE)
  			goto stopme;
  		wakeup_swapper = 0;
  		FOREACH_THREAD_IN_PROC(p, td2) {
  			if (td2 == td)
  				continue;
  			thread_lock(td2);
  			td2->td_flags |= TDF_ASTPENDING | TDF_NEEDSUSPCHK;
  			if (TD_IS_INHIBITED(td2)) {
  				switch (mode) {
  				case SINGLE_EXIT:
  					if (TD_IS_SUSPENDED(td2))
  						wakeup_swapper |=
  						    thread_unsuspend_one(td2);
  					if (TD_ON_SLEEPQ(td2) &&
  					    (td2->td_flags & TDF_SINTR))
  						wakeup_swapper |=
  						    sleepq_abort(td2, EINTR);
  					break;
  				case SINGLE_BOUNDARY:
  					if (TD_IS_SUSPENDED(td2) &&
  					    !(td2->td_flags & TDF_BOUNDARY))
  						wakeup_swapper |=
  						    thread_unsuspend_one(td2);
  					if (TD_ON_SLEEPQ(td2) &&
  					    (td2->td_flags & TDF_SINTR))
  						wakeup_swapper |=
  						    sleepq_abort(td2, ERESTART);
  					break;
  				case SINGLE_NO_EXIT:
  					if (TD_IS_SUSPENDED(td2) &&
  					    !(td2->td_flags & TDF_BOUNDARY))
  						wakeup_swapper |=
  						    thread_unsuspend_one(td2);
  					if (TD_ON_SLEEPQ(td2) &&
  					    (td2->td_flags & TDF_SINTR))
  						wakeup_swapper |=
  						    sleepq_abort(td2, ERESTART);
  					break;
  				default:
  					break;
  				}
  			}
  #ifdef SMP
  			else if (TD_IS_RUNNING(td2) && td != td2) {
  				forward_signal(td2);
  			}
  #endif
  			thread_unlock(td2);
  		}
  		if (wakeup_swapper)
  			kick_proc0();
  		remaining = calc_remaining(p, mode);
  
  		/*
  		 * 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_suspend_switch(td);
  		remaining = calc_remaining(p, mode);
  	}
  	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);
  	}
  	PROC_SUNLOCK(p);
  	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;
  	int wakeup_swapper;
  
  	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_dbgflags & TDB_SUSPEND))) {
  		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);
  
  		/*
  		 * Ignore suspend requests for stop signals if they
  		 * are deferred.
  		 */
  		if (P_SHOULDSTOP(p) == P_STOPPED_SIG &&
  		    td->td_flags & TDF_SBDRY) {
  			KASSERT(return_instead,
  			    ("TDF_SBDRY set for unsafe thread_suspend_check"));
  			return (0);
  		}
  
  		/*
  		 * 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)) {
  			PROC_UNLOCK(p);
  			tidhash_remove(td);
  			PROC_LOCK(p);
  			tdsigcleanup(td);
  			PROC_SLOCK(p);
  			thread_stopped(p);
  			thread_exit();
  		}
  
  		PROC_SLOCK(p);
  		thread_stopped(p);
  		if (P_SHOULDSTOP(p) == P_STOPPED_SINGLE) {
  			if (p->p_numthreads == p->p_suspcount + 1) {
  				thread_lock(p->p_singlethread);
  				wakeup_swapper =
  				    thread_unsuspend_one(p->p_singlethread);
  				thread_unlock(p->p_singlethread);
  				if (wakeup_swapper)
  					kick_proc0();
  			}
  		}
  		PROC_UNLOCK(p);
  		thread_lock(td);
  		/*
  		 * When a thread suspends, it just
  		 * gets taken off all queues.
  		 */
  		thread_suspend_one(td);
  		if (return_instead == 0) {
  			p->p_boundary_count++;
  			td->td_flags |= TDF_BOUNDARY;
  		}
  		PROC_SUNLOCK(p);
  		mi_switch(SW_INVOL | SWT_SUSPEND, NULL);
  		if (return_instead == 0)
  			td->td_flags &= ~TDF_BOUNDARY;
  		thread_unlock(td);
  		PROC_LOCK(p);
  		if (return_instead == 0) {
  			PROC_SLOCK(p);
  			p->p_boundary_count--;
  			PROC_SUNLOCK(p);
  		}
  	}
  	return (0);
  }
  
  void
  thread_suspend_switch(struct thread *td)
  {
  	struct proc *p;
  
  	p = td->td_proc;
  	KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  	PROC_LOCK_ASSERT(p, MA_OWNED);
  	PROC_SLOCK_ASSERT(p, MA_OWNED);
  	/*
  	 * We implement thread_suspend_one in stages here to avoid
  	 * dropping the proc lock while the thread lock is owned.
  	 */
  	thread_stopped(p);
  	p->p_suspcount++;
  	PROC_UNLOCK(p);
  	thread_lock(td);
  	td->td_flags &= ~TDF_NEEDSUSPCHK;
  	TD_SET_SUSPENDED(td);
  	sched_sleep(td, 0);
  	PROC_SUNLOCK(p);
  	DROP_GIANT();
  	mi_switch(SW_VOL | SWT_SUSPEND, NULL);
  	thread_unlock(td);
  	PICKUP_GIANT();
  	PROC_LOCK(p);
  	PROC_SLOCK(p);
  }
  
  void
  thread_suspend_one(struct thread *td)
  {
  	struct proc *p = td->td_proc;
  
  	PROC_SLOCK_ASSERT(p, MA_OWNED);
  	THREAD_LOCK_ASSERT(td, MA_OWNED);
  	KASSERT(!TD_IS_SUSPENDED(td), ("already suspended"));
  	p->p_suspcount++;
  	td->td_flags &= ~TDF_NEEDSUSPCHK;
  	TD_SET_SUSPENDED(td);
  	sched_sleep(td, 0);
  }
  
  int
  thread_unsuspend_one(struct thread *td)
  {
  	struct proc *p = td->td_proc;
  
  	PROC_SLOCK_ASSERT(p, MA_OWNED);
  	THREAD_LOCK_ASSERT(td, MA_OWNED);
  	KASSERT(TD_IS_SUSPENDED(td), ("Thread not suspended"));
  	TD_CLR_SUSPENDED(td);
  	p->p_suspcount--;
  	return (setrunnable(td));
  }
  
  /*
   * Allow all threads blocked by single threading to continue running.
   */
  void
  thread_unsuspend(struct proc *p)
  {
  	struct thread *td;
  	int wakeup_swapper;
  
  	PROC_LOCK_ASSERT(p, MA_OWNED);
  	PROC_SLOCK_ASSERT(p, MA_OWNED);
  	wakeup_swapper = 0;
  	if (!P_SHOULDSTOP(p)) {
                  FOREACH_THREAD_IN_PROC(p, td) {
  			thread_lock(td);
  			if (TD_IS_SUSPENDED(td)) {
  				wakeup_swapper |= thread_unsuspend_one(td);
  			}
  			thread_unlock(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_lock(p->p_singlethread);
  		wakeup_swapper = thread_unsuspend_one(p->p_singlethread);
  		thread_unlock(p->p_singlethread);
  	}
  	if (wakeup_swapper)
  		kick_proc0();
  }
  
  /*
   * End the single threading mode..
   */
  void
  thread_single_end(void)
  {
  	struct thread *td;
  	struct proc *p;
  	int wakeup_swapper;
  
  	td = curthread;
  	p = td->td_proc;
  	PROC_LOCK_ASSERT(p, MA_OWNED);
  	p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY);
  	PROC_SLOCK(p);
  	p->p_singlethread = NULL;
  	wakeup_swapper = 0;
  	/*
  	 * If there are other threads they may 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))) {
                  FOREACH_THREAD_IN_PROC(p, td) {
  			thread_lock(td);
  			if (TD_IS_SUSPENDED(td)) {
  				wakeup_swapper |= thread_unsuspend_one(td);
  			}
  			thread_unlock(td);
  		}
  	}
  	PROC_SUNLOCK(p);
  	if (wakeup_swapper)
  		kick_proc0();
  }
  
  struct thread *
  thread_find(struct proc *p, lwpid_t tid)
  {
  	struct thread *td;
  
  	PROC_LOCK_ASSERT(p, MA_OWNED);
  	FOREACH_THREAD_IN_PROC(p, td) {
  		if (td->td_tid == tid)
  			break;
  	}
  	return (td);
  }
  
  /* Locate a thread by number; return with proc lock held. */
  struct thread *
  tdfind(lwpid_t tid, pid_t pid)
  {
  #define RUN_THRESH	16
  	struct thread *td;
  	int run = 0;
  
  	rw_rlock(&tidhash_lock);
  	LIST_FOREACH(td, TIDHASH(tid), td_hash) {
  		if (td->td_tid == tid) {
  			if (pid != -1 && td->td_proc->p_pid != pid) {
  				td = NULL;
  				break;
  			}
  			PROC_LOCK(td->td_proc);
  			if (td->td_proc->p_state == PRS_NEW) {
  				PROC_UNLOCK(td->td_proc);
  				td = NULL;
  				break;
  			}
  			if (run > RUN_THRESH) {
  				if (rw_try_upgrade(&tidhash_lock)) {
  					LIST_REMOVE(td, td_hash);
  					LIST_INSERT_HEAD(TIDHASH(td->td_tid),
  						td, td_hash);
  					rw_wunlock(&tidhash_lock);
  					return (td);
  				}
  			}
  			break;
  		}
  		run++;
  	}
  	rw_runlock(&tidhash_lock);
  	return (td);
  }
  
  void
  tidhash_add(struct thread *td)
  {
  	rw_wlock(&tidhash_lock);
  	LIST_INSERT_HEAD(TIDHASH(td->td_tid), td, td_hash);
  	rw_wunlock(&tidhash_lock);
  }
  
  void
  tidhash_remove(struct thread *td)
  {
  	rw_wlock(&tidhash_lock);
  	LIST_REMOVE(td, td_hash);
  	rw_wunlock(&tidhash_lock);
  }
  