Unleashed v1.4

[unleashed.git] / kernel / os / lwp.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Copyright (c) 2013, Joyent, Inc. All rights reserved.
 */

#include <sys/param.h>
#include <sys/types.h>
#include <sys/sysmacros.h>
#include <sys/systm.h>
#include <sys/thread.h>
#include <sys/proc.h>
#include <sys/task.h>
#include <sys/project.h>
#include <sys/signal.h>
#include <sys/errno.h>
#include <sys/vmparam.h>
#include <sys/stack.h>
#include <sys/procfs.h>
#include <sys/prsystm.h>
#include <sys/cpuvar.h>
#include <sys/kmem.h>
#include <sys/vtrace.h>
#include <sys/door.h>
#include <vm/seg_kp.h>
#include <sys/debug.h>
#include <sys/tnf.h>
#include <sys/schedctl.h>
#include <sys/poll.h>
#include <sys/copyops.h>
#include <sys/lwp_upimutex_impl.h>
#include <sys/cpupart.h>
#include <sys/lgrp.h>
#include <sys/rctl.h>
#include <sys/contract_impl.h>
#include <sys/cpc_impl.h>
#include <sys/sdt.h>
#include <sys/cmn_err.h>
#include <sys/brand.h>
#include <sys/cyclic.h>
#include <sys/pool.h>

/* hash function for the lwpid hash table, p->p_tidhash[] */
#define TIDHASH(tid, hash_sz)   ((tid) & ((hash_sz) - 1))

void *segkp_lwp;                /* cookie for pool of segkp resources */
extern void reapq_move_lq_to_tq(kthread_t *);
extern void freectx_ctx(struct ctxop *);

/*
 * Create a kernel thread associated with a particular system process.  Give
 * it an LWP so that microstate accounting will be available for it.
 */
kthread_t *
lwp_kernel_create(proc_t *p, void (*proc)(), void *arg, int state, pri_t pri)
{
        klwp_t *lwp;

        VERIFY((p->p_flag & SSYS) != 0);

        lwp = lwp_create(proc, arg, 0, p, state, pri, &t0.t_hold, syscid, 0);

        VERIFY(lwp != NULL);

        return (lwptot(lwp));
}

/*
 * Create a thread that appears to be stopped at sys_rtt.
 */
klwp_t *
lwp_create(void (*proc)(), caddr_t arg, size_t len, proc_t *p,
    int state, int pri, const k_sigset_t *smask, int cid, id_t lwpid)
{
        klwp_t *lwp = NULL;
        kthread_t *t;
        kthread_t *tx;
        cpupart_t *oldpart = NULL;
        size_t  stksize;
        caddr_t lwpdata = NULL;
        processorid_t   binding;
        int err = 0;
        kproject_t *oldkpj, *newkpj;
        void *bufp = NULL;
        klwp_t *curlwp;
        lwpent_t *lep;
        lwpdir_t *old_dir = NULL;
        uint_t old_dirsz = 0;
        tidhash_t *old_hash = NULL;
        uint_t old_hashsz = 0;
        ret_tidhash_t *ret_tidhash = NULL;
        int i;
        int rctlfail = 0;
        boolean_t branded = 0;
        struct ctxop *ctx = NULL;

        ASSERT(cid != sysdccid);        /* system threads must start in SYS */

        ASSERT(p != &p0);               /* No new LWPs in p0. */

        mutex_enter(&p->p_lock);
        mutex_enter(&p->p_zone->zone_nlwps_lock);
        /*
         * don't enforce rctl limits on system processes
         */
        if (!CLASS_KERNEL(cid)) {
                if (p->p_task->tk_nlwps >= p->p_task->tk_nlwps_ctl)
                        if (rctl_test(rc_task_lwps, p->p_task->tk_rctls, p,
                            1, 0) & RCT_DENY)
                                rctlfail = 1;
                if (p->p_task->tk_proj->kpj_nlwps >=
                    p->p_task->tk_proj->kpj_nlwps_ctl)
                        if (rctl_test(rc_project_nlwps,
                            p->p_task->tk_proj->kpj_rctls, p, 1, 0)
                            & RCT_DENY)
                                rctlfail = 1;
                if (p->p_zone->zone_nlwps >= p->p_zone->zone_nlwps_ctl)
                        if (rctl_test(rc_zone_nlwps, p->p_zone->zone_rctls, p,
                            1, 0) & RCT_DENY)
                                rctlfail = 1;
        }
        if (rctlfail) {
                mutex_exit(&p->p_zone->zone_nlwps_lock);
                mutex_exit(&p->p_lock);
                atomic_inc_32(&p->p_zone->zone_ffcap);
                return (NULL);
        }
        p->p_task->tk_nlwps++;
        p->p_task->tk_proj->kpj_nlwps++;
        p->p_zone->zone_nlwps++;
        mutex_exit(&p->p_zone->zone_nlwps_lock);
        mutex_exit(&p->p_lock);

        curlwp = ttolwp(curthread);
        if (curlwp == NULL || (stksize = curlwp->lwp_childstksz) == 0)
                stksize = lwp_default_stksize;

        if (CLASS_KERNEL(cid)) {
                /*
                 * Since we are creating an LWP in an SSYS process, we do not
                 * inherit anything from the current thread's LWP.  We set
                 * stksize and lwpdata to 0 in order to let thread_create()
                 * allocate a regular kernel thread stack for this thread.
                 */
                curlwp = NULL;
                stksize = 0;
                lwpdata = NULL;

        } else if (stksize == lwp_default_stksize) {
                /*
                 * Try to reuse an <lwp,stack> from the LWP deathrow.
                 */
                if (lwp_reapcnt > 0) {
                        mutex_enter(&reaplock);
                        if ((t = lwp_deathrow) != NULL) {
                                ASSERT(t->t_swap);
                                lwp_deathrow = t->t_forw;
                                lwp_reapcnt--;
                                lwpdata = t->t_swap;
                                lwp = t->t_lwp;
                                ctx = t->t_ctx;
                                t->t_swap = NULL;
                                t->t_lwp = NULL;
                                t->t_ctx = NULL;
                                reapq_move_lq_to_tq(t);
                        }
                        mutex_exit(&reaplock);
                        if (lwp != NULL) {
                                lwp_stk_fini(lwp);
                        }
                        if (ctx != NULL) {
                                freectx_ctx(ctx);
                        }
                }
                if (lwpdata == NULL &&
                    (lwpdata = (caddr_t)segkp_cache_get(segkp_lwp)) == NULL) {
                        mutex_enter(&p->p_lock);
                        mutex_enter(&p->p_zone->zone_nlwps_lock);
                        p->p_task->tk_nlwps--;
                        p->p_task->tk_proj->kpj_nlwps--;
                        p->p_zone->zone_nlwps--;
                        mutex_exit(&p->p_zone->zone_nlwps_lock);
                        mutex_exit(&p->p_lock);
                        atomic_inc_32(&p->p_zone->zone_ffnomem);
                        return (NULL);
                }
        } else {
                stksize = roundup(stksize, PAGESIZE);
                if ((lwpdata = (caddr_t)segkp_get(segkp, stksize,
                    (KPD_NOWAIT | KPD_HASREDZONE | KPD_LOCKED))) == NULL) {
                        mutex_enter(&p->p_lock);
                        mutex_enter(&p->p_zone->zone_nlwps_lock);
                        p->p_task->tk_nlwps--;
                        p->p_task->tk_proj->kpj_nlwps--;
                        p->p_zone->zone_nlwps--;
                        mutex_exit(&p->p_zone->zone_nlwps_lock);
                        mutex_exit(&p->p_lock);
                        atomic_inc_32(&p->p_zone->zone_ffnomem);
                        return (NULL);
                }
        }

        /*
         * Create a thread, initializing the stack pointer
         */
        t = thread_create(lwpdata, stksize, NULL, NULL, 0, p, TS_STOPPED, pri);

        /*
         * If a non-NULL stack base is passed in, thread_create() assumes
         * that the stack might be statically allocated (as opposed to being
         * allocated from segkp), and so it does not set t_swap.  Since
         * the lwpdata was allocated from segkp, we must set t_swap to point
         * to it ourselves.
         *
         * This would be less confusing if t_swap had a better name; it really
         * indicates that the stack is allocated from segkp, regardless of
         * whether or not it is swappable.
         */
        if (lwpdata != NULL) {
                ASSERT(!CLASS_KERNEL(cid));
                ASSERT(t->t_swap == NULL);
                t->t_swap = lwpdata;    /* Start of page-able data */
        }

        /*
         * If the stack and lwp can be reused, mark the thread as such.
         * When we get to reapq_add() from resume_from_zombie(), these
         * threads will go onto lwp_deathrow instead of thread_deathrow.
         */
        if (!CLASS_KERNEL(cid) && stksize == lwp_default_stksize)
                t->t_flag |= T_LWPREUSE;

        if (lwp == NULL)
                lwp = kmem_cache_alloc(lwp_cache, KM_SLEEP);
        bzero(lwp, sizeof (*lwp));
        t->t_lwp = lwp;

        t->t_hold = *smask;
        lwp->lwp_thread = t;
        lwp->lwp_procp = p;
        lwp->lwp_sigaltstack.ss_flags = SS_DISABLE;
        if (curlwp != NULL && curlwp->lwp_childstksz != 0)
                lwp->lwp_childstksz = curlwp->lwp_childstksz;

        t->t_stk = lwp_stk_init(lwp, t->t_stk);
        thread_load(t, proc, arg, len);

        /*
         * Allocate the SIGPROF buffer if ITIMER_REALPROF is in effect.
         */
        if (p->p_rprof_cyclic != CYCLIC_NONE)
                t->t_rprof = kmem_zalloc(sizeof (struct rprof), KM_SLEEP);

        if (cid != NOCLASS)
                (void) CL_ALLOC(&bufp, cid, KM_SLEEP);

        /*
         * Allocate an lwp directory entry for the new lwp.
         */
        lep = kmem_zalloc(sizeof (*lep), KM_SLEEP);

        mutex_enter(&p->p_lock);
grow:
        /*
         * Grow the lwp (thread) directory and lwpid hash table if necessary.
         * A note on the growth algorithm:
         *      The new lwp directory size is computed as:
         *              new = 2 * old + 2
         *      Starting with an initial size of 2 (see exec_common()),
         *      this yields numbers that are a power of two minus 2:
         *              2, 6, 14, 30, 62, 126, 254, 510, 1022, ...
         *      The size of the lwpid hash table must be a power of two
         *      and must be commensurate in size with the lwp directory
         *      so that hash bucket chains remain short.  Therefore,
         *      the lwpid hash table size is computed as:
         *              hashsz = (dirsz + 2) / 2
         *      which leads to these hash table sizes corresponding to
         *      the above directory sizes:
         *              2, 4, 8, 16, 32, 64, 128, 256, 512, ...
         * A note on growing the hash table:
         *      For performance reasons, code in lwp_unpark() does not
         *      acquire curproc->p_lock when searching the hash table.
         *      Rather, it calls lwp_hash_lookup_and_lock() which
         *      acquires only the individual hash bucket lock, taking
         *      care to deal with reallocation of the hash table
         *      during the time it takes to acquire the lock.
         *
         *      This is sufficient to protect the integrity of the
         *      hash table, but it requires us to acquire all of the
         *      old hash bucket locks before growing the hash table
         *      and to release them afterwards.  It also requires us
         *      not to free the old hash table because some thread
         *      in lwp_hash_lookup_and_lock() might still be trying
         *      to acquire the old bucket lock.
         *
         *      So we adopt the tactic of keeping all of the retired
         *      hash tables on a linked list, so they can be safely
         *      freed when the process exits or execs.
         *
         *      Because the hash table grows in powers of two, the
         *      total size of all of the hash tables will be slightly
         *      less than twice the size of the largest hash table.
         */
        while (p->p_lwpfree == NULL) {
                uint_t dirsz = p->p_lwpdir_sz;
                lwpdir_t *new_dir;
                uint_t new_dirsz;
                lwpdir_t *ldp;
                tidhash_t *new_hash;
                uint_t new_hashsz;

                mutex_exit(&p->p_lock);

                /*
                 * Prepare to remember the old p_tidhash for later
                 * kmem_free()ing when the process exits or execs.
                 */
                if (ret_tidhash == NULL)
                        ret_tidhash = kmem_zalloc(sizeof (ret_tidhash_t),
                            KM_SLEEP);
                if (old_dir != NULL)
                        kmem_free(old_dir, old_dirsz * sizeof (*old_dir));
                if (old_hash != NULL)
                        kmem_free(old_hash, old_hashsz * sizeof (*old_hash));

                new_dirsz = 2 * dirsz + 2;
                new_dir = kmem_zalloc(new_dirsz * sizeof (lwpdir_t), KM_SLEEP);
                for (ldp = new_dir, i = 1; i < new_dirsz; i++, ldp++)
                        ldp->ld_next = ldp + 1;
                new_hashsz = (new_dirsz + 2) / 2;
                new_hash = kmem_zalloc(new_hashsz * sizeof (tidhash_t),
                    KM_SLEEP);

                mutex_enter(&p->p_lock);
                if (p == curproc)
                        prbarrier(p);

                if (dirsz != p->p_lwpdir_sz || p->p_lwpfree != NULL) {
                        /*
                         * Someone else beat us to it or some lwp exited.
                         * Set up to free our memory and take a lap.
                         */
                        old_dir = new_dir;
                        old_dirsz = new_dirsz;
                        old_hash = new_hash;
                        old_hashsz = new_hashsz;
                } else {
                        /*
                         * For the benefit of lwp_hash_lookup_and_lock(),
                         * called from lwp_unpark(), which searches the
                         * tid hash table without acquiring p->p_lock,
                         * we must acquire all of the tid hash table
                         * locks before replacing p->p_tidhash.
                         */
                        old_hash = p->p_tidhash;
                        old_hashsz = p->p_tidhash_sz;
                        for (i = 0; i < old_hashsz; i++) {
                                mutex_enter(&old_hash[i].th_lock);
                                mutex_enter(&new_hash[i].th_lock);
                        }

                        /*
                         * We simply hash in all of the old directory entries.
                         * This works because the old directory has no empty
                         * slots and the new hash table starts out empty.
                         * This reproduces the original directory ordering
                         * (required for /proc directory semantics).
                         */
                        old_dir = p->p_lwpdir;
                        old_dirsz = p->p_lwpdir_sz;
                        p->p_lwpdir = new_dir;
                        p->p_lwpfree = new_dir;
                        p->p_lwpdir_sz = new_dirsz;
                        for (ldp = old_dir, i = 0; i < old_dirsz; i++, ldp++)
                                lwp_hash_in(p, ldp->ld_entry,
                                    new_hash, new_hashsz, 0);

                        /*
                         * Remember the old hash table along with all
                         * of the previously-remembered hash tables.
                         * We will free them at process exit or exec.
                         */
                        ret_tidhash->rth_tidhash = old_hash;
                        ret_tidhash->rth_tidhash_sz = old_hashsz;
                        ret_tidhash->rth_next = p->p_ret_tidhash;
                        p->p_ret_tidhash = ret_tidhash;

                        /*
                         * Now establish the new tid hash table.
                         * As soon as we assign p->p_tidhash,
                         * code in lwp_unpark() can start using it.
                         */
                        membar_producer();
                        p->p_tidhash = new_hash;

                        /*
                         * It is necessary that p_tidhash reach global
                         * visibility before p_tidhash_sz.  Otherwise,
                         * code in lwp_hash_lookup_and_lock() could
                         * index into the old p_tidhash using the new
                         * p_tidhash_sz and thereby access invalid data.
                         */
                        membar_producer();
                        p->p_tidhash_sz = new_hashsz;

                        /*
                         * Release the locks; allow lwp_unpark() to carry on.
                         */
                        for (i = 0; i < old_hashsz; i++) {
                                mutex_exit(&old_hash[i].th_lock);
                                mutex_exit(&new_hash[i].th_lock);
                        }

                        /*
                         * Avoid freeing these objects below.
                         */
                        ret_tidhash = NULL;
                        old_hash = NULL;
                        old_hashsz = 0;
                }
        }

        /*
         * Block the process against /proc while we manipulate p->p_tlist,
         * unless lwp_create() was called by /proc for the PCAGENT operation.
         * We want to do this early enough so that we don't drop p->p_lock
         * until the thread is put on the p->p_tlist.
         */
        if (p == curproc) {
                prbarrier(p);
                /*
                 * If the current lwp has been requested to stop, do so now.
                 * Otherwise we have a race condition between /proc attempting
                 * to stop the process and this thread creating a new lwp
                 * that was not seen when the /proc PCSTOP request was issued.
                 * We rely on stop() to call prbarrier(p) before returning.
                 */
                while ((curthread->t_proc_flag & TP_PRSTOP) &&
                    !ttolwp(curthread)->lwp_nostop) {
                        /*
                         * We called pool_barrier_enter() before calling
                         * here to lwp_create(). We have to call
                         * pool_barrier_exit() before stopping.
                         */
                        pool_barrier_exit();
                        prbarrier(p);
                        stop(PR_REQUESTED, 0);
                        /*
                         * And we have to repeat the call to
                         * pool_barrier_enter after stopping.
                         */
                        pool_barrier_enter();
                        prbarrier(p);
                }

                /*
                 * If process is exiting, there could be a race between
                 * the agent lwp creation and the new lwp currently being
                 * created. So to prevent this race lwp creation is failed
                 * if the process is exiting.
                 */
                if (p->p_flag & (SEXITLWPS|SKILLED)) {
                        err = 1;
                        goto error;
                }

                /*
                 * Since we might have dropped p->p_lock, the
                 * lwp directory free list might have changed.
                 */
                if (p->p_lwpfree == NULL)
                        goto grow;
        }

        kpreempt_disable();     /* can't grab cpu_lock here */

        /*
         * Inherit processor and processor set bindings from curthread.
         *
         * For kernel LWPs, we do not inherit processor set bindings at
         * process creation time (i.e. when p != curproc).  After the
         * kernel process is created, any subsequent LWPs must be created
         * by threads in the kernel process, at which point we *will*
         * inherit processor set bindings.
         */
        if (CLASS_KERNEL(cid) && p != curproc) {
                t->t_bind_cpu = binding = PBIND_NONE;
                t->t_cpupart = oldpart = &cp_default;
                t->t_bind_pset = PS_NONE;
                t->t_bindflag = (uchar_t)default_binding_mode;
        } else {
                binding = curthread->t_bind_cpu;
                t->t_bind_cpu = binding;
                oldpart = t->t_cpupart;
                t->t_cpupart = curthread->t_cpupart;
                t->t_bind_pset = curthread->t_bind_pset;
                t->t_bindflag = curthread->t_bindflag |
                    (uchar_t)default_binding_mode;
        }

        /*
         * thread_create() initializes this thread's home lgroup to the root.
         * Choose a more suitable lgroup, since this thread is associated
         * with an lwp.
         */
        ASSERT(oldpart != NULL);
        if (binding != PBIND_NONE && t->t_affinitycnt == 0) {
                t->t_bound_cpu = cpu[binding];
                if (t->t_lpl != t->t_bound_cpu->cpu_lpl)
                        lgrp_move_thread(t, t->t_bound_cpu->cpu_lpl, 1);
        } else if (CLASS_KERNEL(cid)) {
                /*
                 * Kernel threads are always in the root lgrp.
                 */
                lgrp_move_thread(t,
                    &t->t_cpupart->cp_lgrploads[LGRP_ROOTID], 1);
        } else {
                lgrp_move_thread(t, lgrp_choose(t, t->t_cpupart), 1);
        }

        kpreempt_enable();

        /*
         * make sure lpl points to our own partition
         */
        ASSERT(t->t_lpl >= t->t_cpupart->cp_lgrploads);
        ASSERT(t->t_lpl < t->t_cpupart->cp_lgrploads +
            t->t_cpupart->cp_nlgrploads);

        /*
         * It is safe to point the thread to the new project without holding it
         * since we're holding the target process' p_lock here and therefore
         * we're guaranteed that it will not move to another project.
         */
        newkpj = p->p_task->tk_proj;
        oldkpj = ttoproj(t);
        if (newkpj != oldkpj) {
                t->t_proj = newkpj;
                (void) project_hold(newkpj);
                project_rele(oldkpj);
        }

        if (cid != NOCLASS) {
                /*
                 * If the lwp is being created in the current process
                 * and matches the current thread's scheduling class,
                 * we should propagate the current thread's scheduling
                 * parameters by calling CL_FORK.  Otherwise just use
                 * the defaults by calling CL_ENTERCLASS.
                 */
                if (p != curproc || curthread->t_cid != cid) {
                        err = CL_ENTERCLASS(t, cid, NULL, NULL, bufp);
                        t->t_pri = pri; /* CL_ENTERCLASS may have changed it */
                        /*
                         * We don't call schedctl_set_cidpri(t) here
                         * because the schedctl data is not yet set
                         * up for the newly-created lwp.
                         */
                } else {
                        t->t_clfuncs = &(sclass[cid].cl_funcs->thread);
                        err = CL_FORK(curthread, t, bufp);
                        t->t_cid = cid;
                }
                if (err) {
                        atomic_inc_32(&p->p_zone->zone_ffmisc);
                        goto error;
                } else {
                        bufp = NULL;
                }
        }

        /*
         * If we were given an lwpid then use it, else allocate one.
         */
        if (lwpid != 0)
                t->t_tid = lwpid;
        else {
                /*
                 * lwp/thread id 0 is never valid; reserved for special checks.
                 * lwp/thread id 1 is reserved for the main thread.
                 * Start again at 2 when INT_MAX has been reached
                 * (id_t is a signed 32-bit integer).
                 */
                id_t prev_id = p->p_lwpid;      /* last allocated tid */

                do {                    /* avoid lwpid duplication */
                        if (p->p_lwpid == INT_MAX) {
                                p->p_flag |= SLWPWRAP;
                                p->p_lwpid = 1;
                        }
                        if ((t->t_tid = ++p->p_lwpid) == prev_id) {
                                /*
                                 * All lwpids are allocated; fail the request.
                                 */
                                err = 1;
                                atomic_inc_32(&p->p_zone->zone_ffnoproc);
                                goto error;
                        }
                        /*
                         * We only need to worry about colliding with an id
                         * that's already in use if this process has
                         * cycled through all available lwp ids.
                         */
                        if ((p->p_flag & SLWPWRAP) == 0)
                                break;
                } while (lwp_hash_lookup(p, t->t_tid) != NULL);
        }

        /*
         * If this is a branded process, let the brand do any necessary lwp
         * initialization.
         */
        if (PROC_IS_BRANDED(p)) {
                if (BROP(p)->b_initlwp(lwp)) {
                        err = 1;
                        atomic_inc_32(&p->p_zone->zone_ffmisc);
                        goto error;
                }
                branded = 1;
        }

        if (t->t_tid == 1) {
                kpreempt_disable();
                ASSERT(t->t_lpl != NULL);
                p->p_t1_lgrpid = t->t_lpl->lpl_lgrpid;
                kpreempt_enable();
                if (p->p_tr_lgrpid != LGRP_NONE &&
                    p->p_tr_lgrpid != p->p_t1_lgrpid) {
                        lgrp_update_trthr_migrations(1);
                }
        }

        p->p_lwpcnt++;
        t->t_waitfor = -1;

        /*
         * Turn microstate accounting on for thread if on for process.
         */
        if (p->p_flag & SMSACCT)
                t->t_proc_flag |= TP_MSACCT;

        /*
         * If the process has watchpoints, mark the new thread as such.
         */
        if (pr_watch_active(p))
                watch_enable(t);

        /*
         * The lwp is being created in the stopped state.
         * We set all the necessary flags to indicate that fact here.
         * We omit the TS_CREATE flag from t_schedflag so that the lwp
         * cannot be set running until the caller is finished with it,
         * even if lwp_continue() is called on it after we drop p->p_lock.
         * When the caller is finished with the newly-created lwp,
         * the caller must call lwp_create_done() to allow the lwp
         * to be set running.  If the TP_HOLDLWP is left set, the
         * lwp will suspend itself after reaching system call exit.
         */
        init_mstate(t, LMS_STOPPED);
        t->t_proc_flag |= TP_HOLDLWP;
        t->t_schedflag |= (TS_ALLSTART & ~(TS_CSTART | TS_CREATE));
        t->t_whystop = PR_SUSPENDED;
        t->t_whatstop = SUSPEND_NORMAL;
        t->t_sig_check = 1;     /* ensure that TP_HOLDLWP is honored */

        /*
         * Set system call processing flags in case tracing or profiling
         * is set.  The first system call will evaluate these and turn
         * them off if they aren't needed.
         */
        t->t_pre_sys = 1;
        t->t_post_sys = 1;

        /*
         * Insert the new thread into the list of all threads.
         */
        if ((tx = p->p_tlist) == NULL) {
                t->t_back = t;
                t->t_forw = t;
                p->p_tlist = t;
        } else {
                t->t_forw = tx;
                t->t_back = tx->t_back;
                tx->t_back->t_forw = t;
                tx->t_back = t;
        }

        /*
         * Insert the new lwp into an lwp directory slot position
         * and into the lwpid hash table.
         */
        lep->le_thread = t;
        lep->le_lwpid = t->t_tid;
        lep->le_start = t->t_start;
        lwp_hash_in(p, lep, p->p_tidhash, p->p_tidhash_sz, 1);

        lwp_fp_init(lwp);

        if (state == TS_RUN) {
                /*
                 * We set the new lwp running immediately.
                 */
                t->t_proc_flag &= ~TP_HOLDLWP;
                lwp_create_done(t);
        }

error:
        if (err) {
                if (CLASS_KERNEL(cid)) {
                        /*
                         * This should only happen if a system process runs
                         * out of lwpids, which shouldn't occur.
                         */
                        panic("Failed to create a system LWP");
                }
                /*
                 * We have failed to create an lwp, so decrement the number
                 * of lwps in the task and let the lgroup load averages know
                 * that this thread isn't going to show up.
                 */
                kpreempt_disable();
                lgrp_move_thread(t, NULL, 1);
                kpreempt_enable();

                ASSERT(MUTEX_HELD(&p->p_lock));
                mutex_enter(&p->p_zone->zone_nlwps_lock);
                p->p_task->tk_nlwps--;
                p->p_task->tk_proj->kpj_nlwps--;
                p->p_zone->zone_nlwps--;
                mutex_exit(&p->p_zone->zone_nlwps_lock);
                if (cid != NOCLASS && bufp != NULL)
                        CL_FREE(cid, bufp);

                if (branded)
                        BROP(p)->b_freelwp(lwp);

                mutex_exit(&p->p_lock);
                t->t_state = TS_FREE;
                thread_rele(t);

                /*
                 * We need to remove t from the list of all threads
                 * because thread_exit()/lwp_exit() isn't called on t.
                 */
                mutex_enter(&pidlock);
                ASSERT(t != t->t_next);         /* t0 never exits */
                t->t_next->t_prev = t->t_prev;
                t->t_prev->t_next = t->t_next;
                mutex_exit(&pidlock);

                thread_free(t);
                kmem_free(lep, sizeof (*lep));
                lwp = NULL;
        } else {
                mutex_exit(&p->p_lock);
        }

        if (old_dir != NULL)
                kmem_free(old_dir, old_dirsz * sizeof (*old_dir));
        if (old_hash != NULL)
                kmem_free(old_hash, old_hashsz * sizeof (*old_hash));
        if (ret_tidhash != NULL)
                kmem_free(ret_tidhash, sizeof (ret_tidhash_t));

        DTRACE_PROC1(lwp__create, kthread_t *, t);
        return (lwp);
}

/*
 * lwp_create_done() is called by the caller of lwp_create() to set the
 * newly-created lwp running after the caller has finished manipulating it.
 */
void
lwp_create_done(kthread_t *t)
{
        proc_t *p = ttoproc(t);

        ASSERT(MUTEX_HELD(&p->p_lock));

        /*
         * We set the TS_CREATE and TS_CSTART flags and call setrun_locked().
         * (The absence of the TS_CREATE flag prevents the lwp from running
         * until we are finished with it, even if lwp_continue() is called on
         * it by some other lwp in the process or elsewhere in the kernel.)
         */
        thread_lock(t);
        ASSERT(t->t_state == TS_STOPPED && !(t->t_schedflag & TS_CREATE));
        /*
         * If TS_CSTART is set, lwp_continue(t) has been called and
         * has already incremented p_lwprcnt; avoid doing this twice.
         */
        if (!(t->t_schedflag & TS_CSTART))
                p->p_lwprcnt++;
        t->t_schedflag |= (TS_CSTART | TS_CREATE);
        setrun_locked(t);
        thread_unlock(t);
}

/*
 * Copy an LWP's active templates, and clear the latest contracts.
 */
void
lwp_ctmpl_copy(klwp_t *dst, klwp_t *src)
{
        int i;

        for (i = 0; i < ct_ntypes; i++) {
                dst->lwp_ct_active[i] = ctmpl_dup(src->lwp_ct_active[i]);
                dst->lwp_ct_latest[i] = NULL;
        }
}

/*
 * Clear an LWP's contract template state.
 */
void
lwp_ctmpl_clear(klwp_t *lwp)
{
        ct_template_t *tmpl;
        int i;

        for (i = 0; i < ct_ntypes; i++) {
                if ((tmpl = lwp->lwp_ct_active[i]) != NULL) {
                        ctmpl_free(tmpl);
                        lwp->lwp_ct_active[i] = NULL;
                }

                if (lwp->lwp_ct_latest[i] != NULL) {
                        contract_rele(lwp->lwp_ct_latest[i]);
                        lwp->lwp_ct_latest[i] = NULL;
                }
        }
}

/*
 * Individual lwp exit.
 * If this is the last lwp, exit the whole process.
 */
void
lwp_exit(void)
{
        kthread_t *t = curthread;
        klwp_t *lwp = ttolwp(t);
        proc_t *p = ttoproc(t);

        ASSERT(MUTEX_HELD(&p->p_lock));

        mutex_exit(&p->p_lock);


        tsd_exit();                     /* free thread specific data */

        kcpc_passivate();               /* Clean up performance counter state */

        pollcleanup();

        if (t->t_door)
                door_slam();

        if (t->t_schedctl != NULL)
                schedctl_lwp_cleanup(t);

        if (t->t_upimutex != NULL)
                upimutex_cleanup();

        /*
         * Perform any brand specific exit processing, then release any
         * brand data associated with the lwp
         */
        if (PROC_IS_BRANDED(p))
                BROP(p)->b_lwpexit(lwp);

        lwp_pcb_exit();

        mutex_enter(&p->p_lock);
        lwp_cleanup();

        /*
         * When this process is dumping core, its lwps are held here
         * until the core dump is finished. Then exitlwps() is called
         * again to release these lwps so that they can finish exiting.
         */
        if (p->p_flag & SCOREDUMP)
                stop(PR_SUSPENDED, SUSPEND_NORMAL);

        /*
         * Block the process against /proc now that we have really acquired
         * p->p_lock (to decrement p_lwpcnt and manipulate p_tlist at least).
         */
        prbarrier(p);

        /*
         * Call proc_exit() if this is the last non-daemon lwp in the process.
         */
        if (!(t->t_proc_flag & TP_DAEMON) &&
            p->p_lwpcnt == p->p_lwpdaemon + 1) {
                mutex_exit(&p->p_lock);
                if (proc_exit(CLD_EXITED, 0) == 0) {
                        /* Restarting init. */
                        return;
                }

                /*
                 * proc_exit() returns a non-zero value when some other
                 * lwp got there first.  We just have to continue in
                 * lwp_exit().
                 */
                mutex_enter(&p->p_lock);
                ASSERT(curproc->p_flag & SEXITLWPS);
                prbarrier(p);
        }

        DTRACE_PROC(lwp__exit);

        /*
         * If the lwp is a detached lwp or if the process is exiting,
         * remove (lwp_hash_out()) the lwp from the lwp directory.
         * Otherwise null out the lwp's le_thread pointer in the lwp
         * directory so that other threads will see it as a zombie lwp.
         */
        prlwpexit(t);           /* notify /proc */
        if (!(t->t_proc_flag & TP_TWAIT) || (p->p_flag & SEXITLWPS))
                lwp_hash_out(p, t->t_tid);
        else {
                ASSERT(!(t->t_proc_flag & TP_DAEMON));
                p->p_lwpdir[t->t_dslot].ld_entry->le_thread = NULL;
                p->p_zombcnt++;
                cv_broadcast(&p->p_lwpexit);
        }
        if (t->t_proc_flag & TP_DAEMON) {
                p->p_lwpdaemon--;
                t->t_proc_flag &= ~TP_DAEMON;
        }
        t->t_proc_flag &= ~TP_TWAIT;

        /*
         * Maintain accurate lwp count for task.max-lwps resource control.
         */
        mutex_enter(&p->p_zone->zone_nlwps_lock);
        p->p_task->tk_nlwps--;
        p->p_task->tk_proj->kpj_nlwps--;
        p->p_zone->zone_nlwps--;
        mutex_exit(&p->p_zone->zone_nlwps_lock);

        CL_EXIT(t);             /* tell the scheduler that t is exiting */
        ASSERT(p->p_lwpcnt != 0);
        p->p_lwpcnt--;

        /*
         * If all remaining non-daemon lwps are waiting in lwp_wait(),
         * wake them up so someone can return EDEADLK.
         * (See the block comment preceeding lwp_wait().)
         */
        if (p->p_lwpcnt == p->p_lwpdaemon + (p->p_lwpwait - p->p_lwpdwait))
                cv_broadcast(&p->p_lwpexit);

        t->t_proc_flag |= TP_LWPEXIT;
        term_mstate(t);

#ifndef NPROBE
        /* Kernel probe */
        if (t->t_tnf_tpdp)
                tnf_thread_exit();
#endif /* NPROBE */

        t->t_forw->t_back = t->t_back;
        t->t_back->t_forw = t->t_forw;
        if (t == p->p_tlist)
                p->p_tlist = t->t_forw;

        /*
         * Clean up the signal state.
         */
        if (t->t_sigqueue != NULL)
                sigdelq(p, t, 0);
        if (lwp->lwp_curinfo != NULL) {
                siginfofree(lwp->lwp_curinfo);
                lwp->lwp_curinfo = NULL;
        }

        /*
         * If we have spymaster information (that is, if we're an agent LWP),
         * free that now.
         */
        if (lwp->lwp_spymaster != NULL) {
                kmem_free(lwp->lwp_spymaster, sizeof (psinfo_t));
                lwp->lwp_spymaster = NULL;
        }

        thread_rele(t);

        /*
         * Terminated lwps are associated with process zero and are put onto
         * death-row by resume().  Avoid preemption after resetting t->t_procp.
         */
        t->t_preempt++;

        if (t->t_ctx != NULL)
                exitctx(t);
        if (p->p_pctx != NULL)
                exitpctx(p);

        t->t_procp = &p0;

        /*
         * Notify the HAT about the change of address space
         */
        hat_thread_exit(t);
        /*
         * When this is the last running lwp in this process and some lwp is
         * waiting for this condition to become true, or this thread was being
         * suspended, then the waiting lwp is awakened.
         *
         * Also, if the process is exiting, we may have a thread waiting in
         * exitlwps() that needs to be notified.
         */
        if (--p->p_lwprcnt == 0 || (t->t_proc_flag & TP_HOLDLWP) ||
            (p->p_flag & SEXITLWPS))
                cv_broadcast(&p->p_holdlwps);

        /*
         * Need to drop p_lock so we can reacquire pidlock.
         */
        mutex_exit(&p->p_lock);
        mutex_enter(&pidlock);

        ASSERT(t != t->t_next);         /* t0 never exits */
        t->t_next->t_prev = t->t_prev;
        t->t_prev->t_next = t->t_next;
        cv_broadcast(&t->t_joincv);     /* wake up anyone in thread_join */
        mutex_exit(&pidlock);

        t->t_state = TS_ZOMB;
        swtch_from_zombie();
        /* never returns */
}


/*
 * Cleanup function for an exiting lwp.
 * Called both from lwp_exit() and from proc_exit().
 * p->p_lock is repeatedly released and grabbed in this function.
 */
void
lwp_cleanup(void)
{
        kthread_t *t = curthread;
        proc_t *p = ttoproc(t);

        ASSERT(MUTEX_HELD(&p->p_lock));

        /* untimeout any lwp-bound realtime timers */
        if (p->p_itimer != NULL)
                timer_lwpexit();

        /*
         * If this is the /proc agent lwp that is exiting, readjust p_lwpid
         * so it appears that the agent never existed, and clear p_agenttp.
         */
        if (t == p->p_agenttp) {
                ASSERT(t->t_tid == p->p_lwpid);
                p->p_lwpid--;
                p->p_agenttp = NULL;
        }

        /*
         * Do lgroup bookkeeping to account for thread exiting.
         */
        kpreempt_disable();
        lgrp_move_thread(t, NULL, 1);
        if (t->t_tid == 1) {
                p->p_t1_lgrpid = LGRP_NONE;
        }
        kpreempt_enable();

        lwp_ctmpl_clear(ttolwp(t));
}

int
lwp_suspend(kthread_t *t)
{
        int tid;
        proc_t *p = ttoproc(t);

        ASSERT(MUTEX_HELD(&p->p_lock));

        /*
         * Set the thread's TP_HOLDLWP flag so it will stop in holdlwp().
         * If an lwp is stopping itself, there is no need to wait.
         */
top:
        t->t_proc_flag |= TP_HOLDLWP;
        if (t == curthread) {
                t->t_sig_check = 1;
        } else {
                /*
                 * Make sure the lwp stops promptly.
                 */
                thread_lock(t);
                t->t_sig_check = 1;
                /*
                 * XXX Should use virtual stop like /proc does instead of
                 * XXX waking the thread to get it to stop.
                 */
                if (ISWAKEABLE(t) || ISWAITING(t)) {
                        setrun_locked(t);
                } else if (t->t_state == TS_ONPROC && t->t_cpu != CPU) {
                        poke_cpu(t->t_cpu->cpu_id);
                }

                tid = t->t_tid;  /* remember thread ID */
                /*
                 * Wait for lwp to stop
                 */
                while (!SUSPENDED(t)) {
                        /*
                         * Drop the thread lock before waiting and reacquire it
                         * afterwards, so the thread can change its t_state
                         * field.
                         */
                        thread_unlock(t);

                        /*
                         * Check if aborted by exitlwps().
                         */
                        if (p->p_flag & SEXITLWPS)
                                lwp_exit();

                        /*
                         * Cooperate with jobcontrol signals and /proc stopping
                         * by calling cv_wait_sig() to wait for the target
                         * lwp to stop.  Just using cv_wait() can lead to
                         * deadlock because, if some other lwp has stopped
                         * by either of these mechanisms, then p_lwprcnt will
                         * never become zero if we do a cv_wait().
                         */
                        if (!cv_wait_sig(&p->p_holdlwps, &p->p_lock))
                                return (EINTR);

                        /*
                         * Check to see if thread died while we were
                         * waiting for it to suspend.
                         */
                        if (idtot(p, tid) == NULL)
                                return (ESRCH);

                        thread_lock(t);
                        /*
                         * If the TP_HOLDLWP flag went away, lwp_continue()
                         * or vfork() must have been called while we were
                         * waiting, so start over again.
                         */
                        if ((t->t_proc_flag & TP_HOLDLWP) == 0) {
                                thread_unlock(t);
                                goto top;
                        }
                }
                thread_unlock(t);
        }
        return (0);
}

/*
 * continue a lwp that's been stopped by lwp_suspend().
 */
void
lwp_continue(kthread_t *t)
{
        proc_t *p = ttoproc(t);
        int was_suspended = t->t_proc_flag & TP_HOLDLWP;

        ASSERT(MUTEX_HELD(&p->p_lock));

        t->t_proc_flag &= ~TP_HOLDLWP;
        thread_lock(t);
        if (SUSPENDED(t) &&
            !(p->p_flag & (SHOLDFORK | SHOLDFORK1 | SHOLDWATCH))) {
                p->p_lwprcnt++;
                t->t_schedflag |= TS_CSTART;
                setrun_locked(t);
        }
        thread_unlock(t);
        /*
         * Wakeup anyone waiting for this thread to be suspended
         */
        if (was_suspended)
                cv_broadcast(&p->p_holdlwps);
}

/*
 * ********************************
 *  Miscellaneous lwp routines    *
 * ********************************
 */
/*
 * When a process is undergoing a forkall(), its p_flag is set to SHOLDFORK.
 * This will cause the process's lwps to stop at a hold point.  A hold
 * point is where a kernel thread has a flat stack.  This is at the
 * return from a system call and at the return from a user level trap.
 *
 * When a process is undergoing a fork1() or vfork(), its p_flag is set to
 * SHOLDFORK1.  This will cause the process's lwps to stop at a modified
 * hold point.  The lwps in the process are not being cloned, so they
 * are held at the usual hold points and also within issig_forreal().
 * This has the side-effect that their system calls do not return
 * showing EINTR.
 *
 * An lwp can also be held.  This is identified by the TP_HOLDLWP flag on
 * the thread.  The TP_HOLDLWP flag is set in lwp_suspend(), where the active
 * lwp is waiting for the target lwp to be stopped.
 */
void
holdlwp(void)
{
        proc_t *p = curproc;
        kthread_t *t = curthread;

        mutex_enter(&p->p_lock);
        /*
         * Don't terminate immediately if the process is dumping core.
         * Once the process has dumped core, all lwps are terminated.
         */
        if (!(p->p_flag & SCOREDUMP)) {
                if ((p->p_flag & SEXITLWPS) || (t->t_proc_flag & TP_EXITLWP))
                        lwp_exit();
        }
        if (!(ISHOLD(p)) && !(p->p_flag & (SHOLDFORK1 | SHOLDWATCH))) {
                mutex_exit(&p->p_lock);
                return;
        }
        /*
         * stop() decrements p->p_lwprcnt and cv_signal()s &p->p_holdlwps
         * when p->p_lwprcnt becomes zero.
         */
        stop(PR_SUSPENDED, SUSPEND_NORMAL);
        if (p->p_flag & SEXITLWPS)
                lwp_exit();
        mutex_exit(&p->p_lock);
}

/*
 * Have all lwps within the process hold at a point where they are
 * cloneable (SHOLDFORK) or just safe w.r.t. fork1 (SHOLDFORK1).
 */
int
holdlwps(int holdflag)
{
        proc_t *p = curproc;

        ASSERT(holdflag == SHOLDFORK || holdflag == SHOLDFORK1);
        mutex_enter(&p->p_lock);
        schedctl_finish_sigblock(curthread);
again:
        while (p->p_flag & (SEXITLWPS | SHOLDFORK | SHOLDFORK1 | SHOLDWATCH)) {
                /*
                 * If another lwp is doing a forkall() or proc_exit(), bail out.
                 */
                if (p->p_flag & (SEXITLWPS | SHOLDFORK)) {
                        mutex_exit(&p->p_lock);
                        return (0);
                }
                /*
                 * Another lwp is doing a fork1() or is undergoing
                 * watchpoint activity.  We hold here for it to complete.
                 */
                stop(PR_SUSPENDED, SUSPEND_NORMAL);
        }
        p->p_flag |= holdflag;
        pokelwps(p);
        --p->p_lwprcnt;
        /*
         * Wait for the process to become quiescent (p->p_lwprcnt == 0).
         */
        while (p->p_lwprcnt > 0) {
                /*
                 * Check if aborted by exitlwps().
                 * Also check if SHOLDWATCH is set; it takes precedence.
                 */
                if (p->p_flag & (SEXITLWPS | SHOLDWATCH)) {
                        p->p_lwprcnt++;
                        p->p_flag &= ~holdflag;
                        cv_broadcast(&p->p_holdlwps);
                        goto again;
                }
                /*
                 * Cooperate with jobcontrol signals and /proc stopping.
                 * If some other lwp has stopped by either of these
                 * mechanisms, then p_lwprcnt will never become zero
                 * and the process will appear deadlocked unless we
                 * stop here in sympathy with the other lwp before
                 * doing the cv_wait() below.
                 *
                 * If the other lwp stops after we do the cv_wait(), it
                 * will wake us up to loop around and do the sympathy stop.
                 *
                 * Since stop() drops p->p_lock, we must start from
                 * the top again on returning from stop().
                 */
                if (p->p_stopsig | (curthread->t_proc_flag & TP_PRSTOP)) {
                        int whystop = p->p_stopsig? PR_JOBCONTROL :
                            PR_REQUESTED;
                        p->p_lwprcnt++;
                        p->p_flag &= ~holdflag;
                        stop(whystop, p->p_stopsig);
                        goto again;
                }
                cv_wait(&p->p_holdlwps, &p->p_lock);
        }
        p->p_lwprcnt++;
        p->p_flag &= ~holdflag;
        mutex_exit(&p->p_lock);
        return (1);
}

/*
 * See comments for holdwatch(), below.
 */
static int
holdcheck(int clearflags)
{
        proc_t *p = curproc;

        /*
         * If we are trying to exit, that takes precedence over anything else.
         */
        if (p->p_flag & SEXITLWPS) {
                p->p_lwprcnt++;
                p->p_flag &= ~clearflags;
                lwp_exit();
        }

        /*
         * If another thread is calling fork1(), stop the current thread so the
         * other can complete.
         */
        if (p->p_flag & SHOLDFORK1) {
                p->p_lwprcnt++;
                stop(PR_SUSPENDED, SUSPEND_NORMAL);
                if (p->p_flag & SEXITLWPS) {
                        p->p_flag &= ~clearflags;
                        lwp_exit();
                }
                return (-1);
        }

        /*
         * If another thread is calling fork(), then indicate we are doing
         * watchpoint activity.  This will cause holdlwps() above to stop the
         * forking thread, at which point we can continue with watchpoint
         * activity.
         */
        if (p->p_flag & SHOLDFORK) {
                p->p_lwprcnt++;
                while (p->p_flag & SHOLDFORK) {
                        p->p_flag |= SHOLDWATCH;
                        cv_broadcast(&p->p_holdlwps);
                        cv_wait(&p->p_holdlwps, &p->p_lock);
                        p->p_flag &= ~SHOLDWATCH;
                }
                return (-1);
        }

        return (0);
}

/*
 * Stop all lwps within the process, holding themselves in the kernel while the
 * active lwp undergoes watchpoint activity.  This is more complicated than
 * expected because stop() relies on calling holdwatch() in order to copyin data
 * from the user's address space.  A double barrier is used to prevent an
 * infinite loop.
 *
 *      o The first thread into holdwatch() is the 'master' thread and does
 *        the following:
 *
 *              - Sets SHOLDWATCH on the current process
 *              - Sets TP_WATCHSTOP on the current thread
 *              - Waits for all threads to be either stopped or have
 *                TP_WATCHSTOP set.
 *              - Sets the SWATCHOK flag on the process
 *              - Unsets TP_WATCHSTOP
 *              - Waits for the other threads to completely stop
 *              - Unsets SWATCHOK
 *
 *      o If SHOLDWATCH is already set when we enter this function, then another
 *        thread is already trying to stop this thread.  This 'slave' thread
 *        does the following:
 *
 *              - Sets TP_WATCHSTOP on the current thread
 *              - Waits for SWATCHOK flag to be set
 *              - Calls stop()
 *
 *      o If SWATCHOK is set on the process, then this function immediately
 *        returns, as we must have been called via stop().
 *
 * In addition, there are other flags that take precedence over SHOLDWATCH:
 *
 *      o If SEXITLWPS is set, exit immediately.
 *
 *      o If SHOLDFORK1 is set, wait for fork1() to complete.
 *
 *      o If SHOLDFORK is set, then watchpoint activity takes precedence In this
 *        case, set SHOLDWATCH, signalling the forking thread to stop first.
 *
 *      o If the process is being stopped via /proc (TP_PRSTOP is set), then we
 *        stop the current thread.
 *
 * Returns 0 if all threads have been quiesced.  Returns non-zero if not all
 * threads were stopped, or the list of watched pages has changed.
 */
int
holdwatch(void)
{
        proc_t *p = curproc;
        kthread_t *t = curthread;
        int ret = 0;

        mutex_enter(&p->p_lock);

        p->p_lwprcnt--;

        /*
         * Check for bail-out conditions as outlined above.
         */
        if (holdcheck(0) != 0) {
                mutex_exit(&p->p_lock);
                return (-1);
        }

        if (!(p->p_flag & SHOLDWATCH)) {
                /*
                 * We are the master watchpoint thread.  Set SHOLDWATCH and poke
                 * the other threads.
                 */
                p->p_flag |= SHOLDWATCH;
                pokelwps(p);

                /*
                 * Wait for all threads to be stopped or have TP_WATCHSTOP set.
                 */
                while (pr_allstopped(p, 1) > 0) {
                        if (holdcheck(SHOLDWATCH) != 0) {
                                p->p_flag &= ~SHOLDWATCH;
                                mutex_exit(&p->p_lock);
                                return (-1);
                        }

                        cv_wait(&p->p_holdlwps, &p->p_lock);
                }

                /*
                 * All threads are now stopped or in the process of stopping.
                 * Set SWATCHOK and let them stop completely.
                 */
                p->p_flag |= SWATCHOK;
                t->t_proc_flag &= ~TP_WATCHSTOP;
                cv_broadcast(&p->p_holdlwps);

                while (pr_allstopped(p, 0) > 0) {
                        /*
                         * At first glance, it may appear that we don't need a
                         * call to holdcheck() here.  But if the process gets a
                         * SIGKILL signal, one of our stopped threads may have
                         * been awakened and is waiting in exitlwps(), which
                         * takes precedence over watchpoints.
                         */
                        if (holdcheck(SHOLDWATCH | SWATCHOK) != 0) {
                                p->p_flag &= ~(SHOLDWATCH | SWATCHOK);
                                mutex_exit(&p->p_lock);
                                return (-1);
                        }

                        cv_wait(&p->p_holdlwps, &p->p_lock);
                }

                /*
                 * All threads are now completely stopped.
                 */
                p->p_flag &= ~SWATCHOK;
                p->p_flag &= ~SHOLDWATCH;
                p->p_lwprcnt++;

        } else if (!(p->p_flag & SWATCHOK)) {

                /*
                 * SHOLDWATCH is set, so another thread is trying to do
                 * watchpoint activity.  Indicate this thread is stopping, and
                 * wait for the OK from the master thread.
                 */
                t->t_proc_flag |= TP_WATCHSTOP;
                cv_broadcast(&p->p_holdlwps);

                while (!(p->p_flag & SWATCHOK)) {
                        if (holdcheck(0) != 0) {
                                t->t_proc_flag &= ~TP_WATCHSTOP;
                                mutex_exit(&p->p_lock);
                                return (-1);
                        }

                        cv_wait(&p->p_holdlwps, &p->p_lock);
                }

                /*
                 * Once the master thread has given the OK, this thread can
                 * actually call stop().
                 */
                t->t_proc_flag &= ~TP_WATCHSTOP;
                p->p_lwprcnt++;

                stop(PR_SUSPENDED, SUSPEND_NORMAL);

                /*
                 * It's not OK to do watchpoint activity, notify caller to
                 * retry.
                 */
                ret = -1;

        } else {

                /*
                 * The only way we can hit the case where SHOLDWATCH is set and
                 * SWATCHOK is set is if we are triggering this from within a
                 * stop() call.  Assert that this is the case.
                 */

                ASSERT(t->t_proc_flag & TP_STOPPING);
                p->p_lwprcnt++;
        }

        mutex_exit(&p->p_lock);

        return (ret);
}

/*
 * force all interruptible lwps to trap into the kernel.
 */
void
pokelwps(proc_t *p)
{
        kthread_t *t;

        ASSERT(MUTEX_HELD(&p->p_lock));

        t = p->p_tlist;
        do {
                if (t == curthread)
                        continue;
                thread_lock(t);
                aston(t);       /* make thread trap or do post_syscall */
                if (ISWAKEABLE(t) || ISWAITING(t)) {
                        setrun_locked(t);
                } else if (t->t_state == TS_STOPPED) {
                        /*
                         * Ensure that proc_exit() is not blocked by lwps
                         * that were stopped via jobcontrol or /proc.
                         */
                        if (p->p_flag & SEXITLWPS) {
                                p->p_stopsig = 0;
                                t->t_schedflag |= (TS_XSTART | TS_PSTART);
                                setrun_locked(t);
                        }
                        /*
                         * If we are holding lwps for a forkall(),
                         * force lwps that have been suspended via
                         * lwp_suspend() and are suspended inside
                         * of a system call to proceed to their
                         * holdlwp() points where they are clonable.
                         */
                        if ((p->p_flag & SHOLDFORK) && SUSPENDED(t)) {
                                if ((t->t_schedflag & TS_CSTART) == 0) {
                                        p->p_lwprcnt++;
                                        t->t_schedflag |= TS_CSTART;
                                        setrun_locked(t);
                                }
                        }
                } else if (t->t_state == TS_ONPROC) {
                        if (t->t_cpu != CPU)
                                poke_cpu(t->t_cpu->cpu_id);
                }
                thread_unlock(t);
        } while ((t = t->t_forw) != p->p_tlist);
}

/*
 * undo the effects of holdlwps() or holdwatch().
 */
void
continuelwps(proc_t *p)
{
        kthread_t *t;

        /*
         * If this flag is set, then the original holdwatch() didn't actually
         * stop the process.  See comments for holdwatch().
         */
        if (p->p_flag & SWATCHOK) {
                ASSERT(curthread->t_proc_flag & TP_STOPPING);
                return;
        }

        ASSERT(MUTEX_HELD(&p->p_lock));
        ASSERT((p->p_flag & (SHOLDFORK | SHOLDFORK1 | SHOLDWATCH)) == 0);

        t = p->p_tlist;
        do {
                thread_lock(t);         /* SUSPENDED looks at t_schedflag */
                if (SUSPENDED(t) && !(t->t_proc_flag & TP_HOLDLWP)) {
                        p->p_lwprcnt++;
                        t->t_schedflag |= TS_CSTART;
                        setrun_locked(t);
                }
                thread_unlock(t);
        } while ((t = t->t_forw) != p->p_tlist);
}

/*
 * Force all other LWPs in the current process other than the caller to exit,
 * and then cv_wait() on p_holdlwps for them to exit.  The exitlwps() function
 * is typically used in these situations:
 *
 *   (a) prior to an exec() system call
 *   (b) prior to dumping a core file
 *   (c) prior to a uadmin() shutdown
 *
 * If the 'coredump' flag is set, other LWPs are quiesced but not destroyed.
 * Multiple threads in the process can call this function at one time by
 * triggering execs or core dumps simultaneously, so the SEXITLWPS bit is used
 * to declare one particular thread the winner who gets to kill the others.
 * If a thread wins the exitlwps() dance, zero is returned; otherwise an
 * appropriate errno value is returned to caller for its system call to return.
 */
int
exitlwps(int coredump)
{
        proc_t *p = curproc;
        int heldcnt;

        if (curthread->t_door)
                door_slam();
        if (p->p_door_list)
                door_revoke_all();
        if (curthread->t_schedctl != NULL)
                schedctl_lwp_cleanup(curthread);

        /*
         * Ensure that before starting to wait for other lwps to exit,
         * cleanup all upimutexes held by curthread. Otherwise, some other
         * lwp could be waiting (uninterruptibly) for a upimutex held by
         * curthread, and the call to pokelwps() below would deadlock.
         * Even if a blocked upimutex_lock is made interruptible,
         * curthread's upimutexes need to be unlocked: do it here.
         */
        if (curthread->t_upimutex != NULL)
                upimutex_cleanup();

        /*
         * Grab p_lock in order to check and set SEXITLWPS to declare a winner.
         * We must also block any further /proc access from this point forward.
         */
        mutex_enter(&p->p_lock);
        prbarrier(p);

        if (p->p_flag & SEXITLWPS) {
                mutex_exit(&p->p_lock);
                aston(curthread);       /* force a trip through post_syscall */
                return (set_errno(EINTR));
        }

        p->p_flag |= SEXITLWPS;
        if (coredump)           /* tell other lwps to stop, not exit */
                p->p_flag |= SCOREDUMP;

        /*
         * Give precedence to exitlwps() if a holdlwps() is
         * in progress. The lwp doing the holdlwps() operation
         * is aborted when it is awakened.
         */
        while (p->p_flag & (SHOLDFORK | SHOLDFORK1 | SHOLDWATCH)) {
                cv_broadcast(&p->p_holdlwps);
                cv_wait(&p->p_holdlwps, &p->p_lock);
                prbarrier(p);
        }
        p->p_flag |= SHOLDFORK;
        pokelwps(p);

        /*
         * Wait for process to become quiescent.
         */
        --p->p_lwprcnt;
        while (p->p_lwprcnt > 0) {
                cv_wait(&p->p_holdlwps, &p->p_lock);
                prbarrier(p);
        }
        p->p_lwprcnt++;
        ASSERT(p->p_lwprcnt == 1);

        /*
         * The SCOREDUMP flag puts the process into a quiescent
         * state.  The process's lwps remain attached to this
         * process until exitlwps() is called again without the
         * 'coredump' flag set, then the lwps are terminated
         * and the process can exit.
         */
        if (coredump) {
                p->p_flag &= ~(SCOREDUMP | SHOLDFORK | SEXITLWPS);
                goto out;
        }

        /*
         * Determine if there are any lwps left dangling in
         * the stopped state.  This happens when exitlwps()
         * aborts a holdlwps() operation.
         */
        p->p_flag &= ~SHOLDFORK;
        if ((heldcnt = p->p_lwpcnt) > 1) {
                kthread_t *t;
                for (t = curthread->t_forw; --heldcnt > 0; t = t->t_forw) {
                        t->t_proc_flag &= ~TP_TWAIT;
                        lwp_continue(t);
                }
        }

        /*
         * Wait for all other lwps to exit.
         */
        --p->p_lwprcnt;
        while (p->p_lwpcnt > 1) {
                cv_wait(&p->p_holdlwps, &p->p_lock);
                prbarrier(p);
        }
        ++p->p_lwprcnt;
        ASSERT(p->p_lwpcnt == 1 && p->p_lwprcnt == 1);

        p->p_flag &= ~SEXITLWPS;
        curthread->t_proc_flag &= ~TP_TWAIT;

out:
        if (!coredump && p->p_zombcnt) {        /* cleanup the zombie lwps */
                lwpdir_t *ldp;
                lwpent_t *lep;
                int i;

                for (ldp = p->p_lwpdir, i = 0; i < p->p_lwpdir_sz; i++, ldp++) {
                        lep = ldp->ld_entry;
                        if (lep != NULL && lep->le_thread != curthread) {
                                ASSERT(lep->le_thread == NULL);
                                p->p_zombcnt--;
                                lwp_hash_out(p, lep->le_lwpid);
                        }
                }
                ASSERT(p->p_zombcnt == 0);
        }

        /*
         * If some other LWP in the process wanted us to suspend ourself,
         * then we will not do it.  The other LWP is now terminated and
         * no one will ever continue us again if we suspend ourself.
         */
        curthread->t_proc_flag &= ~TP_HOLDLWP;
        p->p_flag &= ~(SHOLDFORK | SHOLDFORK1 | SHOLDWATCH | SLWPWRAP);
        mutex_exit(&p->p_lock);
        return (0);
}

/*
 * duplicate a lwp.
 */
klwp_t *
forklwp(klwp_t *lwp, proc_t *cp, id_t lwpid)
{
        klwp_t *clwp;
        void *tregs, *tfpu;
        kthread_t *t = lwptot(lwp);
        kthread_t *ct;
        proc_t *p = lwptoproc(lwp);
        int cid;
        void *bufp;
        void *brand_data;
        int val;

        ASSERT(p == curproc);
        ASSERT(t == curthread || (SUSPENDED(t) && lwp->lwp_asleep == 0));


        if (t == curthread)
                /* copy args out of registers first */
                (void) save_syscall_args();

        clwp = lwp_create(cp->p_lwpcnt == 0 ? lwp_rtt_initial : lwp_rtt,
            NULL, 0, cp, TS_STOPPED, t->t_pri, &t->t_hold, NOCLASS, lwpid);
        if (clwp == NULL)
                return (NULL);

        /*
         * most of the parent's lwp can be copied to its duplicate,
         * except for the fields that are unique to each lwp, like
         * lwp_thread, lwp_procp, lwp_regs, and lwp_ap.
         */
        ct = clwp->lwp_thread;
        tregs = clwp->lwp_regs;
        tfpu = clwp->lwp_fpu;
        brand_data = clwp->lwp_brand;

        /*
         * Copy parent lwp to child lwp.  Hold child's p_lock to prevent
         * mstate_aggr_state() from reading stale mstate entries copied
         * from lwp to clwp.
         */
        mutex_enter(&cp->p_lock);
        *clwp = *lwp;

        /* clear microstate and resource usage data in new lwp */
        init_mstate(ct, LMS_STOPPED);
        bzero(&clwp->lwp_ru, sizeof (clwp->lwp_ru));
        mutex_exit(&cp->p_lock);

        /* fix up child's lwp */

        clwp->lwp_pcb.pcb_flags = 0;
        clwp->lwp_cursig = 0;
        clwp->lwp_extsig = 0;
        clwp->lwp_curinfo = NULL;
        clwp->lwp_thread = ct;
        ct->t_sysnum = t->t_sysnum;
        clwp->lwp_regs = tregs;
        clwp->lwp_fpu = tfpu;
        clwp->lwp_brand = brand_data;
        clwp->lwp_ap = clwp->lwp_arg;
        clwp->lwp_procp = cp;
        bzero(clwp->lwp_timer, sizeof (clwp->lwp_timer));
        clwp->lwp_lastfault = 0;
        clwp->lwp_lastfaddr = 0;

        /* copy parent's struct regs to child. */
        lwp_forkregs(lwp, clwp);

        /*
         * Fork thread context ops, if any.
         */
        if (t->t_ctx)
                forkctx(t, ct);

        /* fix door state in the child */
        if (t->t_door)
                door_fork(t, ct);

        /* copy current contract templates, clear latest contracts */
        lwp_ctmpl_copy(clwp, lwp);

        mutex_enter(&cp->p_lock);
        /* lwp_create() set the TP_HOLDLWP flag */
        if (!(t->t_proc_flag & TP_HOLDLWP))
                ct->t_proc_flag &= ~TP_HOLDLWP;
        if (cp->p_flag & SMSACCT)
                ct->t_proc_flag |= TP_MSACCT;
        mutex_exit(&cp->p_lock);

        /* Allow brand to propagate brand-specific state */
        if (PROC_IS_BRANDED(p))
                BROP(p)->b_forklwp(lwp, clwp);

retry:
        cid = t->t_cid;

        val = CL_ALLOC(&bufp, cid, KM_SLEEP);
        ASSERT(val == 0);

        mutex_enter(&p->p_lock);
        if (cid != t->t_cid) {
                /*
                 * Someone just changed this thread's scheduling class,
                 * so try pre-allocating the buffer again.  Hopefully we
                 * don't hit this often.
                 */
                mutex_exit(&p->p_lock);
                CL_FREE(cid, bufp);
                goto retry;
        }

        ct->t_unpark = t->t_unpark;
        ct->t_clfuncs = t->t_clfuncs;
        CL_FORK(t, ct, bufp);
        ct->t_cid = t->t_cid;   /* after data allocated so prgetpsinfo works */
        mutex_exit(&p->p_lock);

        return (clwp);
}

/*
 * Add a new lwp entry to the lwp directory and to the lwpid hash table.
 */
void
lwp_hash_in(proc_t *p, lwpent_t *lep, tidhash_t *tidhash, uint_t tidhash_sz,
    int do_lock)
{
        tidhash_t *thp = &tidhash[TIDHASH(lep->le_lwpid, tidhash_sz)];
        lwpdir_t **ldpp;
        lwpdir_t *ldp;
        kthread_t *t;

        /*
         * Allocate a directory element from the free list.
         * Code elsewhere guarantees a free slot.
         */
        ldp = p->p_lwpfree;
        p->p_lwpfree = ldp->ld_next;
        ASSERT(ldp->ld_entry == NULL);
        ldp->ld_entry = lep;

        if (do_lock)
                mutex_enter(&thp->th_lock);

        /*
         * Insert it into the lwpid hash table.
         */
        ldpp = &thp->th_list;
        ldp->ld_next = *ldpp;
        *ldpp = ldp;

        /*
         * Set the active thread's directory slot entry.
         */
        if ((t = lep->le_thread) != NULL) {
                ASSERT(lep->le_lwpid == t->t_tid);
                t->t_dslot = (int)(ldp - p->p_lwpdir);
        }

        if (do_lock)
                mutex_exit(&thp->th_lock);
}

/*
 * Remove an lwp from the lwpid hash table and free its directory entry.
 * This is done when a detached lwp exits in lwp_exit() or
 * when a non-detached lwp is waited for in lwp_wait() or
 * when a zombie lwp is detached in lwp_detach().
 */
void
lwp_hash_out(proc_t *p, id_t lwpid)
{
        tidhash_t *thp = &p->p_tidhash[TIDHASH(lwpid, p->p_tidhash_sz)];
        lwpdir_t **ldpp;
        lwpdir_t *ldp;
        lwpent_t *lep;

        mutex_enter(&thp->th_lock);
        for (ldpp = &thp->th_list;
            (ldp = *ldpp) != NULL; ldpp = &ldp->ld_next) {
                lep = ldp->ld_entry;
                if (lep->le_lwpid == lwpid) {
                        prlwpfree(p, lep);      /* /proc deals with le_trace */
                        *ldpp = ldp->ld_next;
                        ldp->ld_entry = NULL;
                        ldp->ld_next = p->p_lwpfree;
                        p->p_lwpfree = ldp;
                        kmem_free(lep, sizeof (*lep));
                        break;
                }
        }
        mutex_exit(&thp->th_lock);
}

/*
 * Lookup an lwp in the lwpid hash table by lwpid.
 */
lwpdir_t *
lwp_hash_lookup(proc_t *p, id_t lwpid)
{
        tidhash_t *thp;
        lwpdir_t *ldp;

        /*
         * The process may be exiting, after p_tidhash has been set to NULL in
         * proc_exit() but before prfee() has been called.  Return failure in
         * this case.
         */
        if (p->p_tidhash == NULL)
                return (NULL);

        thp = &p->p_tidhash[TIDHASH(lwpid, p->p_tidhash_sz)];
        for (ldp = thp->th_list; ldp != NULL; ldp = ldp->ld_next) {
                if (ldp->ld_entry->le_lwpid == lwpid)
                        return (ldp);
        }

        return (NULL);
}

/*
 * Same as lwp_hash_lookup(), but acquire and return
 * the tid hash table entry lock on success.
 */
lwpdir_t *
lwp_hash_lookup_and_lock(proc_t *p, id_t lwpid, kmutex_t **mpp)
{
        tidhash_t *tidhash;
        uint_t tidhash_sz;
        tidhash_t *thp;
        lwpdir_t *ldp;

top:
        tidhash_sz = p->p_tidhash_sz;
        membar_consumer();
        if ((tidhash = p->p_tidhash) == NULL)
                return (NULL);

        thp = &tidhash[TIDHASH(lwpid, tidhash_sz)];
        mutex_enter(&thp->th_lock);

        /*
         * Since we are not holding p->p_lock, the tid hash table
         * may have changed.  If so, start over.  If not, then
         * it cannot change until after we drop &thp->th_lock;
         */
        if (tidhash != p->p_tidhash || tidhash_sz != p->p_tidhash_sz) {
                mutex_exit(&thp->th_lock);
                goto top;
        }

        for (ldp = thp->th_list; ldp != NULL; ldp = ldp->ld_next) {
                if (ldp->ld_entry->le_lwpid == lwpid) {
                        *mpp = &thp->th_lock;
                        return (ldp);
                }
        }

        mutex_exit(&thp->th_lock);
        return (NULL);
}

/*
 * Update the indicated LWP usage statistic for the current LWP.
 */
void
lwp_stat_update(lwp_stat_id_t lwp_stat_id, long inc)
{
        klwp_t *lwp = ttolwp(curthread);

        if (lwp == NULL)
                return;

        switch (lwp_stat_id) {
        case LWP_STAT_INBLK:
                lwp->lwp_ru.inblock += inc;
                break;
        case LWP_STAT_OUBLK:
                lwp->lwp_ru.oublock += inc;
                break;
        case LWP_STAT_MSGRCV:
                lwp->lwp_ru.msgrcv += inc;
                break;
        case LWP_STAT_MSGSND:
                lwp->lwp_ru.msgsnd += inc;
                break;
        default:
                panic("lwp_stat_update: invalid lwp_stat_id 0x%x", lwp_stat_id);
        }
}