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kern_lwp.c revision 1.34 
      1 /*	$NetBSD: kern_lwp.c,v 1.34 2006/03/29 23:02:31 cube Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2001 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Nathan J. Williams.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  * 3. All advertising materials mentioning features or use of this software
     19  *    must display the following acknowledgement:
     20  *        This product includes software developed by the NetBSD
     21  *        Foundation, Inc. and its contributors.
     22  * 4. Neither the name of The NetBSD Foundation nor the names of its
     23  *    contributors may be used to endorse or promote products derived
     24  *    from this software without specific prior written permission.
     25  *
     26  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     27  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     28  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     29  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     30  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     31  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     32  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     33  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     34  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     35  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     36  * POSSIBILITY OF SUCH DAMAGE.
     37  */
     38 
     39 #include <sys/cdefs.h>
     40 __KERNEL_RCSID(0, "$NetBSD: kern_lwp.c,v 1.34 2006/03/29 23:02:31 cube Exp $");
     41 
     42 #include "opt_multiprocessor.h"
     43 
     44 #include <sys/param.h>
     45 #include <sys/systm.h>
     46 #include <sys/pool.h>
     47 #include <sys/lock.h>
     48 #include <sys/proc.h>
     49 #include <sys/sa.h>
     50 #include <sys/savar.h>
     51 #include <sys/types.h>
     52 #include <sys/ucontext.h>
     53 #include <sys/resourcevar.h>
     54 #include <sys/mount.h>
     55 #include <sys/syscallargs.h>
     56 
     57 #include <uvm/uvm_extern.h>
     58 
     59 struct lwplist alllwp;
     60 
     61 #define LWP_DEBUG
     62 
     63 #ifdef LWP_DEBUG
     64 int lwp_debug = 0;
     65 #define DPRINTF(x) if (lwp_debug) printf x
     66 #else
     67 #define DPRINTF(x)
     68 #endif
     69 /* ARGSUSED */
     70 int
     71 sys__lwp_create(struct lwp *l, void *v, register_t *retval)
     72 {
     73 	struct sys__lwp_create_args /* {
     74 		syscallarg(const ucontext_t *) ucp;
     75 		syscallarg(u_long) flags;
     76 		syscallarg(lwpid_t *) new_lwp;
     77 	} */ *uap = v;
     78 	struct proc *p = l->l_proc;
     79 	struct lwp *l2;
     80 	vaddr_t uaddr;
     81 	boolean_t inmem;
     82 	ucontext_t *newuc;
     83 	int s, error;
     84 
     85 	if (p->p_flag & P_SA)
     86 		return EINVAL;
     87 
     88 	newuc = pool_get(&lwp_uc_pool, PR_WAITOK);
     89 
     90 	error = copyin(SCARG(uap, ucp), newuc,
     91 	    l->l_proc->p_emul->e_sa->sae_ucsize);
     92 	if (error)
     93 		return (error);
     94 
     95 	/* XXX check against resource limits */
     96 
     97 	inmem = uvm_uarea_alloc(&uaddr);
     98 	if (__predict_false(uaddr == 0)) {
     99 		return (ENOMEM);
    100 	}
    101 
    102 	/* XXX flags:
    103 	 * __LWP_ASLWP is probably needed for Solaris compat.
    104 	 */
    105 
    106 	newlwp(l, p, uaddr, inmem,
    107 	    SCARG(uap, flags) & LWP_DETACHED,
    108 	    NULL, 0, startlwp, newuc, &l2);
    109 
    110 	if ((SCARG(uap, flags) & LWP_SUSPENDED) == 0) {
    111 		SCHED_LOCK(s);
    112 		l2->l_stat = LSRUN;
    113 		setrunqueue(l2);
    114 		p->p_nrlwps++;
    115 		SCHED_UNLOCK(s);
    116 	} else {
    117 		l2->l_stat = LSSUSPENDED;
    118 	}
    119 
    120 	error = copyout(&l2->l_lid, SCARG(uap, new_lwp),
    121 	    sizeof(l2->l_lid));
    122 	if (error)
    123 		return (error);
    124 
    125 	return (0);
    126 }
    127 
    128 
    129 int
    130 sys__lwp_exit(struct lwp *l, void *v, register_t *retval)
    131 {
    132 
    133 	lwp_exit(l);
    134 	/* NOTREACHED */
    135 	return (0);
    136 }
    137 
    138 
    139 int
    140 sys__lwp_self(struct lwp *l, void *v, register_t *retval)
    141 {
    142 
    143 	*retval = l->l_lid;
    144 
    145 	return (0);
    146 }
    147 
    148 
    149 int
    150 sys__lwp_getprivate(struct lwp *l, void *v, register_t *retval)
    151 {
    152 
    153 	*retval = (uintptr_t) l->l_private;
    154 
    155 	return (0);
    156 }
    157 
    158 
    159 int
    160 sys__lwp_setprivate(struct lwp *l, void *v, register_t *retval)
    161 {
    162 	struct sys__lwp_setprivate_args /* {
    163 		syscallarg(void *) ptr;
    164 	} */ *uap = v;
    165 
    166 	l->l_private = SCARG(uap, ptr);
    167 
    168 	return (0);
    169 }
    170 
    171 
    172 int
    173 sys__lwp_suspend(struct lwp *l, void *v, register_t *retval)
    174 {
    175 	struct sys__lwp_suspend_args /* {
    176 		syscallarg(lwpid_t) target;
    177 	} */ *uap = v;
    178 	int target_lid;
    179 	struct proc *p = l->l_proc;
    180 	struct lwp *t;
    181 	struct lwp *t2;
    182 
    183 	if (p->p_flag & P_SA)
    184 		return EINVAL;
    185 
    186 	target_lid = SCARG(uap, target);
    187 
    188 	LIST_FOREACH(t, &p->p_lwps, l_sibling)
    189 		if (t->l_lid == target_lid)
    190 			break;
    191 
    192 	if (t == NULL)
    193 		return (ESRCH);
    194 
    195 	if (t == l) {
    196 		/*
    197 		 * Check for deadlock, which is only possible
    198 		 * when we're suspending ourself.
    199 		 */
    200 		LIST_FOREACH(t2, &p->p_lwps, l_sibling) {
    201 			if ((t2 != l) && (t2->l_stat != LSSUSPENDED))
    202 				break;
    203 		}
    204 
    205 		if (t2 == NULL) /* All other LWPs are suspended */
    206 			return (EDEADLK);
    207 	}
    208 
    209 	return lwp_suspend(l, t);
    210 }
    211 
    212 inline int
    213 lwp_suspend(struct lwp *l, struct lwp *t)
    214 {
    215 	struct proc *p = t->l_proc;
    216 	int s;
    217 
    218 	if (t == l) {
    219 		SCHED_LOCK(s);
    220 		l->l_stat = LSSUSPENDED;
    221 		/* XXX NJWLWP check if this makes sense here: */
    222 		p->p_stats->p_ru.ru_nvcsw++;
    223 		mi_switch(l, NULL);
    224 		SCHED_ASSERT_UNLOCKED();
    225 		splx(s);
    226 	} else {
    227 		switch (t->l_stat) {
    228 		case LSSUSPENDED:
    229 			return (0); /* _lwp_suspend() is idempotent */
    230 		case LSRUN:
    231 			SCHED_LOCK(s);
    232 			remrunqueue(t);
    233 			t->l_stat = LSSUSPENDED;
    234 			p->p_nrlwps--;
    235 			SCHED_UNLOCK(s);
    236 			break;
    237 		case LSSLEEP:
    238 			t->l_stat = LSSUSPENDED;
    239 			break;
    240 		case LSIDL:
    241 		case LSZOMB:
    242 			return (EINTR); /* It's what Solaris does..... */
    243 		case LSSTOP:
    244 			panic("_lwp_suspend: Stopped LWP in running process!");
    245 			break;
    246 		case LSONPROC:
    247 			/* XXX multiprocessor LWPs? Implement me! */
    248 			return (EINVAL);
    249 		}
    250 	}
    251 
    252 	return (0);
    253 }
    254 
    255 
    256 int
    257 sys__lwp_continue(struct lwp *l, void *v, register_t *retval)
    258 {
    259 	struct sys__lwp_continue_args /* {
    260 		syscallarg(lwpid_t) target;
    261 	} */ *uap = v;
    262 	int s, target_lid;
    263 	struct proc *p = l->l_proc;
    264 	struct lwp *t;
    265 
    266 	if (p->p_flag & P_SA)
    267 		return EINVAL;
    268 
    269 	target_lid = SCARG(uap, target);
    270 
    271 	LIST_FOREACH(t, &p->p_lwps, l_sibling)
    272 		if (t->l_lid == target_lid)
    273 			break;
    274 
    275 	if (t == NULL)
    276 		return (ESRCH);
    277 
    278 	SCHED_LOCK(s);
    279 	lwp_continue(t);
    280 	SCHED_UNLOCK(s);
    281 
    282 	return (0);
    283 }
    284 
    285 void
    286 lwp_continue(struct lwp *l)
    287 {
    288 
    289 	DPRINTF(("lwp_continue of %d.%d (%s), state %d, wchan %p\n",
    290 	    l->l_proc->p_pid, l->l_lid, l->l_proc->p_comm, l->l_stat,
    291 	    l->l_wchan));
    292 
    293 	if (l->l_stat != LSSUSPENDED)
    294 		return;
    295 
    296 	if (l->l_wchan == 0) {
    297 		/* LWP was runnable before being suspended. */
    298 		setrunnable(l);
    299 	} else {
    300 		/* LWP was sleeping before being suspended. */
    301 		l->l_stat = LSSLEEP;
    302 	}
    303 }
    304 
    305 int
    306 sys__lwp_wakeup(struct lwp *l, void *v, register_t *retval)
    307 {
    308 	struct sys__lwp_wakeup_args /* {
    309 		syscallarg(lwpid_t) target;
    310 	} */ *uap = v;
    311 	lwpid_t target_lid;
    312 	struct lwp *t;
    313 	struct proc *p;
    314 	int error;
    315 	int s;
    316 
    317 	p = l->l_proc;
    318 	target_lid = SCARG(uap, target);
    319 
    320 	SCHED_LOCK(s);
    321 
    322 	LIST_FOREACH(t, &p->p_lwps, l_sibling)
    323 		if (t->l_lid == target_lid)
    324 			break;
    325 
    326 	if (t == NULL) {
    327 		error = ESRCH;
    328 		goto exit;
    329 	}
    330 
    331 	if (t->l_stat != LSSLEEP) {
    332 		error = ENODEV;
    333 		goto exit;
    334 	}
    335 
    336 	if ((t->l_flag & L_SINTR) == 0) {
    337 		error = EBUSY;
    338 		goto exit;
    339 	}
    340 	/*
    341 	 * Tell ltsleep to wakeup.
    342 	 */
    343 	t->l_flag |= L_CANCELLED;
    344 
    345 	setrunnable(t);
    346 	error = 0;
    347 exit:
    348 	SCHED_UNLOCK(s);
    349 
    350 	return error;
    351 }
    352 
    353 int
    354 sys__lwp_wait(struct lwp *l, void *v, register_t *retval)
    355 {
    356 	struct sys__lwp_wait_args /* {
    357 		syscallarg(lwpid_t) wait_for;
    358 		syscallarg(lwpid_t *) departed;
    359 	} */ *uap = v;
    360 	int error;
    361 	lwpid_t dep;
    362 
    363 	error = lwp_wait1(l, SCARG(uap, wait_for), &dep, 0);
    364 	if (error)
    365 		return (error);
    366 
    367 	if (SCARG(uap, departed)) {
    368 		error = copyout(&dep, SCARG(uap, departed),
    369 		    sizeof(dep));
    370 		if (error)
    371 			return (error);
    372 	}
    373 
    374 	return (0);
    375 }
    376 
    377 
    378 int
    379 lwp_wait1(struct lwp *l, lwpid_t lid, lwpid_t *departed, int flags)
    380 {
    381 	struct proc *p = l->l_proc;
    382 	struct lwp *l2, *l3;
    383 	int nfound, error, wpri;
    384 	static const char waitstr1[] = "lwpwait";
    385 	static const char waitstr2[] = "lwpwait2";
    386 
    387 	DPRINTF(("lwp_wait1: %d.%d waiting for %d.\n",
    388 	    p->p_pid, l->l_lid, lid));
    389 
    390 	if (lid == l->l_lid)
    391 		return (EDEADLK); /* Waiting for ourselves makes no sense. */
    392 
    393 	wpri = PWAIT |
    394 	    ((flags & LWPWAIT_EXITCONTROL) ? PNOEXITERR : PCATCH);
    395  loop:
    396 	nfound = 0;
    397 	LIST_FOREACH(l2, &p->p_lwps, l_sibling) {
    398 		if ((l2 == l) || (l2->l_flag & L_DETACHED) ||
    399 		    ((lid != 0) && (lid != l2->l_lid)))
    400 			continue;
    401 
    402 		nfound++;
    403 		if (l2->l_stat == LSZOMB) {
    404 			if (departed)
    405 				*departed = l2->l_lid;
    406 
    407 			simple_lock(&p->p_lock);
    408 			LIST_REMOVE(l2, l_sibling);
    409 			p->p_nlwps--;
    410 			p->p_nzlwps--;
    411 			simple_unlock(&p->p_lock);
    412 			/* XXX decrement limits */
    413 
    414 			pool_put(&lwp_pool, l2);
    415 
    416 			return (0);
    417 		} else if (l2->l_stat == LSSLEEP ||
    418 		           l2->l_stat == LSSUSPENDED) {
    419 			/* Deadlock checks.
    420 			 * 1. If all other LWPs are waiting for exits
    421 			 *    or suspended, we would deadlock.
    422 			 */
    423 
    424 			LIST_FOREACH(l3, &p->p_lwps, l_sibling) {
    425 				if (l3 != l && (l3->l_stat != LSSUSPENDED) &&
    426 				    !(l3->l_stat == LSSLEEP &&
    427 					l3->l_wchan == (caddr_t) &p->p_nlwps))
    428 					break;
    429 			}
    430 			if (l3 == NULL) /* Everyone else is waiting. */
    431 				return (EDEADLK);
    432 
    433 			/* XXX we'd like to check for a cycle of waiting
    434 			 * LWPs (specific LID waits, not any-LWP waits)
    435 			 * and detect that sort of deadlock, but we don't
    436 			 * have a good place to store the lwp that is
    437 			 * being waited for. wchan is already filled with
    438 			 * &p->p_nlwps, and putting the lwp address in
    439 			 * there for deadlock tracing would require
    440 			 * exiting LWPs to call wakeup on both their
    441 			 * own address and &p->p_nlwps, to get threads
    442 			 * sleeping on any LWP exiting.
    443 			 *
    444 			 * Revisit later. Maybe another auxillary
    445 			 * storage location associated with sleeping
    446 			 * is in order.
    447 			 */
    448 		}
    449 	}
    450 
    451 	if (nfound == 0)
    452 		return (ESRCH);
    453 
    454 	if ((error = tsleep((caddr_t) &p->p_nlwps, wpri,
    455 	    (lid != 0) ? waitstr1 : waitstr2, 0)) != 0)
    456 		return (error);
    457 
    458 	goto loop;
    459 }
    460 
    461 
    462 int
    463 newlwp(struct lwp *l1, struct proc *p2, vaddr_t uaddr, boolean_t inmem,
    464     int flags, void *stack, size_t stacksize,
    465     void (*func)(void *), void *arg, struct lwp **rnewlwpp)
    466 {
    467 	struct lwp *l2;
    468 	int s;
    469 
    470 	l2 = pool_get(&lwp_pool, PR_WAITOK);
    471 
    472 	l2->l_stat = LSIDL;
    473 	l2->l_forw = l2->l_back = NULL;
    474 	l2->l_proc = p2;
    475 
    476 	memset(&l2->l_startzero, 0,
    477 	       (unsigned) ((caddr_t)&l2->l_endzero -
    478 			   (caddr_t)&l2->l_startzero));
    479 	memcpy(&l2->l_startcopy, &l1->l_startcopy,
    480 	       (unsigned) ((caddr_t)&l2->l_endcopy -
    481 			   (caddr_t)&l2->l_startcopy));
    482 
    483 #if !defined(MULTIPROCESSOR)
    484 	/*
    485 	 * In the single-processor case, all processes will always run
    486 	 * on the same CPU.  So, initialize the child's CPU to the parent's
    487 	 * now.  In the multiprocessor case, the child's CPU will be
    488 	 * initialized in the low-level context switch code when the
    489 	 * process runs.
    490 	 */
    491 	KASSERT(l1->l_cpu != NULL);
    492 	l2->l_cpu = l1->l_cpu;
    493 #else
    494 	/*
    495 	 * zero child's CPU pointer so we don't get trash.
    496 	 */
    497 	l2->l_cpu = NULL;
    498 #endif /* ! MULTIPROCESSOR */
    499 
    500 	l2->l_flag = inmem ? L_INMEM : 0;
    501 	l2->l_flag |= (flags & LWP_DETACHED) ? L_DETACHED : 0;
    502 
    503 	callout_init(&l2->l_tsleep_ch);
    504 
    505 	if (rnewlwpp != NULL)
    506 		*rnewlwpp = l2;
    507 
    508 	l2->l_addr = (struct user *)uaddr;
    509 	uvm_lwp_fork(l1, l2, stack, stacksize, func,
    510 	    (arg != NULL) ? arg : l2);
    511 
    512 	simple_lock(&p2->p_lock);
    513 	l2->l_lid = ++p2->p_nlwpid;
    514 	LIST_INSERT_HEAD(&p2->p_lwps, l2, l_sibling);
    515 	p2->p_nlwps++;
    516 	simple_unlock(&p2->p_lock);
    517 
    518 	/* XXX should be locked differently... */
    519 	s = proclist_lock_write();
    520 	LIST_INSERT_HEAD(&alllwp, l2, l_list);
    521 	proclist_unlock_write(s);
    522 
    523 	if (p2->p_emul->e_lwp_fork)
    524 		(*p2->p_emul->e_lwp_fork)(l1, l2);
    525 
    526 	return (0);
    527 }
    528 
    529 
    530 /*
    531  * Quit the process. This will call cpu_exit, which will call cpu_switch,
    532  * so this can only be used meaningfully if you're willing to switch away.
    533  * Calling with l!=curlwp would be weird.
    534  */
    535 void
    536 lwp_exit(struct lwp *l)
    537 {
    538 	struct proc *p = l->l_proc;
    539 	int s;
    540 
    541 	DPRINTF(("lwp_exit: %d.%d exiting.\n", p->p_pid, l->l_lid));
    542 	DPRINTF((" nlwps: %d nrlwps %d nzlwps: %d\n",
    543 	    p->p_nlwps, p->p_nrlwps, p->p_nzlwps));
    544 
    545 	if (p->p_emul->e_lwp_exit)
    546 		(*p->p_emul->e_lwp_exit)(l);
    547 
    548 	/*
    549 	 * If we are the last live LWP in a process, we need to exit
    550 	 * the entire process (if that's not already going on). We do
    551 	 * so with an exit status of zero, because it's a "controlled"
    552 	 * exit, and because that's what Solaris does.
    553 	 */
    554 	if (((p->p_nlwps - p->p_nzlwps) == 1) && ((p->p_flag & P_WEXIT) == 0)) {
    555 		DPRINTF(("lwp_exit: %d.%d calling exit1()\n",
    556 		    p->p_pid, l->l_lid));
    557 		exit1(l, 0);
    558 		/* NOTREACHED */
    559 	}
    560 
    561 	s = proclist_lock_write();
    562 	LIST_REMOVE(l, l_list);
    563 	proclist_unlock_write(s);
    564 
    565 	/* Free MD LWP resources */
    566 #ifndef __NO_CPU_LWP_FREE
    567 	cpu_lwp_free(l, 0);
    568 #endif
    569 
    570 	pmap_deactivate(l);
    571 
    572 	if (l->l_flag & L_DETACHED) {
    573 		simple_lock(&p->p_lock);
    574 		LIST_REMOVE(l, l_sibling);
    575 		p->p_nlwps--;
    576 		simple_unlock(&p->p_lock);
    577 
    578 		curlwp = NULL;
    579 		l->l_proc = NULL;
    580 	}
    581 
    582 	SCHED_LOCK(s);
    583 	p->p_nrlwps--;
    584 	l->l_stat = LSDEAD;
    585 	SCHED_UNLOCK(s);
    586 
    587 	/* This LWP no longer needs to hold the kernel lock. */
    588 	KERNEL_PROC_UNLOCK(l);
    589 
    590 	/* cpu_exit() will not return */
    591 	cpu_exit(l);
    592 }
    593 
    594 /*
    595  * We are called from cpu_exit() once it is safe to schedule the
    596  * dead process's resources to be freed (i.e., once we've switched to
    597  * the idle PCB for the current CPU).
    598  *
    599  * NOTE: One must be careful with locking in this routine.  It's
    600  * called from a critical section in machine-dependent code, so
    601  * we should refrain from changing any interrupt state.
    602  */
    603 void
    604 lwp_exit2(struct lwp *l)
    605 {
    606 	struct proc *p;
    607 
    608 	KERNEL_LOCK(LK_EXCLUSIVE);
    609 	/*
    610 	 * Free the VM resources we're still holding on to.
    611 	 */
    612 	uvm_lwp_exit(l);
    613 
    614 	if (l->l_flag & L_DETACHED) {
    615 		/* Nobody waits for detached LWPs. */
    616 		pool_put(&lwp_pool, l);
    617 		KERNEL_UNLOCK();
    618 	} else {
    619 		l->l_stat = LSZOMB;
    620 		p = l->l_proc;
    621 		p->p_nzlwps++;
    622 		KERNEL_UNLOCK();
    623 		wakeup(&p->p_nlwps);
    624 	}
    625 }
    626 
    627 /*
    628  * Pick a LWP to represent the process for those operations which
    629  * want information about a "process" that is actually associated
    630  * with a LWP.
    631  */
    632 struct lwp *
    633 proc_representative_lwp(struct proc *p)
    634 {
    635 	struct lwp *l, *onproc, *running, *sleeping, *stopped, *suspended;
    636 	struct lwp *signalled;
    637 
    638 	/* Trivial case: only one LWP */
    639 	if (p->p_nlwps == 1)
    640 		return (LIST_FIRST(&p->p_lwps));
    641 
    642 	switch (p->p_stat) {
    643 	case SSTOP:
    644 	case SACTIVE:
    645 		/* Pick the most live LWP */
    646 		onproc = running = sleeping = stopped = suspended = NULL;
    647 		signalled = NULL;
    648 		LIST_FOREACH(l, &p->p_lwps, l_sibling) {
    649 			if (l->l_lid == p->p_sigctx.ps_lwp)
    650 				signalled = l;
    651 			switch (l->l_stat) {
    652 			case LSONPROC:
    653 				onproc = l;
    654 				break;
    655 			case LSRUN:
    656 				running = l;
    657 				break;
    658 			case LSSLEEP:
    659 				sleeping = l;
    660 				break;
    661 			case LSSTOP:
    662 				stopped = l;
    663 				break;
    664 			case LSSUSPENDED:
    665 				suspended = l;
    666 				break;
    667 			}
    668 		}
    669 		if (signalled)
    670 			return signalled;
    671 		if (onproc)
    672 			return onproc;
    673 		if (running)
    674 			return running;
    675 		if (sleeping)
    676 			return sleeping;
    677 		if (stopped)
    678 			return stopped;
    679 		if (suspended)
    680 			return suspended;
    681 		break;
    682 	case SZOMB:
    683 		/* Doesn't really matter... */
    684 		return (LIST_FIRST(&p->p_lwps));
    685 #ifdef DIAGNOSTIC
    686 	case SIDL:
    687 		/* We have more than one LWP and we're in SIDL?
    688 		 * How'd that happen?
    689 		 */
    690 		panic("Too many LWPs (%d) in SIDL process %d (%s)",
    691 		    p->p_nrlwps, p->p_pid, p->p_comm);
    692 	default:
    693 		panic("Process %d (%s) in unknown state %d",
    694 		    p->p_pid, p->p_comm, p->p_stat);
    695 #endif
    696 	}
    697 
    698 	panic("proc_representative_lwp: couldn't find a lwp for process"
    699 		" %d (%s)", p->p_pid, p->p_comm);
    700 	/* NOTREACHED */
    701 	return NULL;
    702 }
    703