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kern_lwp.c revision 1.8.2.7 
      1 /*	$NetBSD: kern_lwp.c,v 1.8.2.7 2005/12/11 10:29:11 christos 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 1.8.2.7 2005/12/11 10:29:11 christos 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, sizeof(*newuc));
     91 	if (error)
     92 		return (error);
     93 
     94 	/* XXX check against resource limits */
     95 
     96 	inmem = uvm_uarea_alloc(&uaddr);
     97 	if (__predict_false(uaddr == 0)) {
     98 		return (ENOMEM);
     99 	}
    100 
    101 	/* XXX flags:
    102 	 * __LWP_ASLWP is probably needed for Solaris compat.
    103 	 */
    104 
    105 	newlwp(l, p, uaddr, inmem,
    106 	    SCARG(uap, flags) & LWP_DETACHED,
    107 	    NULL, 0, startlwp, newuc, &l2);
    108 
    109 	if ((SCARG(uap, flags) & LWP_SUSPENDED) == 0) {
    110 		SCHED_LOCK(s);
    111 		l2->l_stat = LSRUN;
    112 		setrunqueue(l2);
    113 		p->p_nrlwps++;
    114 		SCHED_UNLOCK(s);
    115 	} else {
    116 		l2->l_stat = LSSUSPENDED;
    117 	}
    118 
    119 	error = copyout(&l2->l_lid, SCARG(uap, new_lwp),
    120 	    sizeof(l2->l_lid));
    121 	if (error)
    122 		return (error);
    123 
    124 	return (0);
    125 }
    126 
    127 
    128 int
    129 sys__lwp_exit(struct lwp *l, void *v, register_t *retval)
    130 {
    131 
    132 	lwp_exit(l);
    133 	/* NOTREACHED */
    134 	return (0);
    135 }
    136 
    137 
    138 int
    139 sys__lwp_self(struct lwp *l, void *v, register_t *retval)
    140 {
    141 
    142 	*retval = l->l_lid;
    143 
    144 	return (0);
    145 }
    146 
    147 
    148 int
    149 sys__lwp_getprivate(struct lwp *l, void *v, register_t *retval)
    150 {
    151 
    152 	*retval = (uintptr_t) l->l_private;
    153 
    154 	return (0);
    155 }
    156 
    157 
    158 int
    159 sys__lwp_setprivate(struct lwp *l, void *v, register_t *retval)
    160 {
    161 	struct sys__lwp_setprivate_args /* {
    162 		syscallarg(void *) ptr;
    163 	} */ *uap = v;
    164 
    165 	l->l_private = SCARG(uap, ptr);
    166 
    167 	return (0);
    168 }
    169 
    170 
    171 int
    172 sys__lwp_suspend(struct lwp *l, void *v, register_t *retval)
    173 {
    174 	struct sys__lwp_suspend_args /* {
    175 		syscallarg(lwpid_t) target;
    176 	} */ *uap = v;
    177 	int target_lid;
    178 	struct proc *p = l->l_proc;
    179 	struct lwp *t;
    180 	struct lwp *t2;
    181 
    182 	if (p->p_flag & P_SA)
    183 		return EINVAL;
    184 
    185 	target_lid = SCARG(uap, target);
    186 
    187 	LIST_FOREACH(t, &p->p_lwps, l_sibling)
    188 		if (t->l_lid == target_lid)
    189 			break;
    190 
    191 	if (t == NULL)
    192 		return (ESRCH);
    193 
    194 	if (t == l) {
    195 		/*
    196 		 * Check for deadlock, which is only possible
    197 		 * when we're suspending ourself.
    198 		 */
    199 		LIST_FOREACH(t2, &p->p_lwps, l_sibling) {
    200 			if ((t2 != l) && (t2->l_stat != LSSUSPENDED))
    201 				break;
    202 		}
    203 
    204 		if (t2 == NULL) /* All other LWPs are suspended */
    205 			return (EDEADLK);
    206 	}
    207 
    208 	return lwp_suspend(l, t);
    209 }
    210 
    211 inline int
    212 lwp_suspend(struct lwp *l, struct lwp *t)
    213 {
    214 	struct proc *p = t->l_proc;
    215 	int s;
    216 
    217 	if (t == l) {
    218 		SCHED_LOCK(s);
    219 		l->l_stat = LSSUSPENDED;
    220 		/* XXX NJWLWP check if this makes sense here: */
    221 		p->p_stats->p_ru.ru_nvcsw++;
    222 		mi_switch(l, NULL);
    223 		SCHED_ASSERT_UNLOCKED();
    224 		splx(s);
    225 	} else {
    226 		switch (t->l_stat) {
    227 		case LSSUSPENDED:
    228 			return (0); /* _lwp_suspend() is idempotent */
    229 		case LSRUN:
    230 			SCHED_LOCK(s);
    231 			remrunqueue(t);
    232 			t->l_stat = LSSUSPENDED;
    233 			p->p_nrlwps--;
    234 			SCHED_UNLOCK(s);
    235 			break;
    236 		case LSSLEEP:
    237 			t->l_stat = LSSUSPENDED;
    238 			break;
    239 		case LSIDL:
    240 		case LSZOMB:
    241 			return (EINTR); /* It's what Solaris does..... */
    242 		case LSSTOP:
    243 			panic("_lwp_suspend: Stopped LWP in running process!");
    244 			break;
    245 		case LSONPROC:
    246 			/* XXX multiprocessor LWPs? Implement me! */
    247 			return (EINVAL);
    248 		}
    249 	}
    250 
    251 	return (0);
    252 }
    253 
    254 
    255 int
    256 sys__lwp_continue(struct lwp *l, void *v, register_t *retval)
    257 {
    258 	struct sys__lwp_continue_args /* {
    259 		syscallarg(lwpid_t) target;
    260 	} */ *uap = v;
    261 	int s, target_lid;
    262 	struct proc *p = l->l_proc;
    263 	struct lwp *t;
    264 
    265 	if (p->p_flag & P_SA)
    266 		return EINVAL;
    267 
    268 	target_lid = SCARG(uap, target);
    269 
    270 	LIST_FOREACH(t, &p->p_lwps, l_sibling)
    271 		if (t->l_lid == target_lid)
    272 			break;
    273 
    274 	if (t == NULL)
    275 		return (ESRCH);
    276 
    277 	SCHED_LOCK(s);
    278 	lwp_continue(t);
    279 	SCHED_UNLOCK(s);
    280 
    281 	return (0);
    282 }
    283 
    284 void
    285 lwp_continue(struct lwp *l)
    286 {
    287 
    288 	DPRINTF(("lwp_continue of %d.%d (%s), state %d, wchan %p\n",
    289 	    l->l_proc->p_pid, l->l_lid, l->l_proc->p_comm, l->l_stat,
    290 	    l->l_wchan));
    291 
    292 	if (l->l_stat != LSSUSPENDED)
    293 		return;
    294 
    295 	if (l->l_wchan == 0) {
    296 		/* LWP was runnable before being suspended. */
    297 		setrunnable(l);
    298 	} else {
    299 		/* LWP was sleeping before being suspended. */
    300 		l->l_stat = LSSLEEP;
    301 	}
    302 }
    303 
    304 int
    305 sys__lwp_wakeup(struct lwp *l, void *v, register_t *retval)
    306 {
    307 	struct sys__lwp_wakeup_args /* {
    308 		syscallarg(lwpid_t) target;
    309 	} */ *uap = v;
    310 	lwpid_t target_lid;
    311 	struct lwp *t;
    312 	struct proc *p;
    313 	int error;
    314 	int s;
    315 
    316 	p = l->l_proc;
    317 	target_lid = SCARG(uap, target);
    318 
    319 	SCHED_LOCK(s);
    320 
    321 	LIST_FOREACH(t, &p->p_lwps, l_sibling)
    322 		if (t->l_lid == target_lid)
    323 			break;
    324 
    325 	if (t == NULL) {
    326 		error = ESRCH;
    327 		goto exit;
    328 	}
    329 
    330 	if (t->l_stat != LSSLEEP) {
    331 		error = ENODEV;
    332 		goto exit;
    333 	}
    334 
    335 	if ((t->l_flag & L_SINTR) == 0) {
    336 		error = EBUSY;
    337 		goto exit;
    338 	}
    339 	/*
    340 	 * Tell ltsleep to wakeup.
    341 	 */
    342 	t->l_flag |= L_CANCELLED;
    343 
    344 	setrunnable(t);
    345 	error = 0;
    346 exit:
    347 	SCHED_UNLOCK(s);
    348 
    349 	return error;
    350 }
    351 
    352 int
    353 sys__lwp_wait(struct lwp *l, void *v, register_t *retval)
    354 {
    355 	struct sys__lwp_wait_args /* {
    356 		syscallarg(lwpid_t) wait_for;
    357 		syscallarg(lwpid_t *) departed;
    358 	} */ *uap = v;
    359 	int error;
    360 	lwpid_t dep;
    361 
    362 	error = lwp_wait1(l, SCARG(uap, wait_for), &dep, 0);
    363 	if (error)
    364 		return (error);
    365 
    366 	if (SCARG(uap, departed)) {
    367 		error = copyout(&dep, SCARG(uap, departed),
    368 		    sizeof(dep));
    369 		if (error)
    370 			return (error);
    371 	}
    372 
    373 	return (0);
    374 }
    375 
    376 
    377 int
    378 lwp_wait1(struct lwp *l, lwpid_t lid, lwpid_t *departed, int flags)
    379 {
    380 	struct proc *p = l->l_proc;
    381 	struct lwp *l2, *l3;
    382 	int nfound, error, wpri;
    383 	static const char waitstr1[] = "lwpwait";
    384 	static const char waitstr2[] = "lwpwait2";
    385 
    386 	DPRINTF(("lwp_wait1: %d.%d waiting for %d.\n",
    387 	    p->p_pid, l->l_lid, lid));
    388 
    389 	if (lid == l->l_lid)
    390 		return (EDEADLK); /* Waiting for ourselves makes no sense. */
    391 
    392 	wpri = PWAIT |
    393 	    ((flags & LWPWAIT_EXITCONTROL) ? PNOEXITERR : PCATCH);
    394  loop:
    395 	nfound = 0;
    396 	LIST_FOREACH(l2, &p->p_lwps, l_sibling) {
    397 		if ((l2 == l) || (l2->l_flag & L_DETACHED) ||
    398 		    ((lid != 0) && (lid != l2->l_lid)))
    399 			continue;
    400 
    401 		nfound++;
    402 		if (l2->l_stat == LSZOMB) {
    403 			if (departed)
    404 				*departed = l2->l_lid;
    405 
    406 			simple_lock(&p->p_lock);
    407 			LIST_REMOVE(l2, l_sibling);
    408 			p->p_nlwps--;
    409 			p->p_nzlwps--;
    410 			simple_unlock(&p->p_lock);
    411 			/* XXX decrement limits */
    412 
    413 			pool_put(&lwp_pool, l2);
    414 
    415 			return (0);
    416 		} else if (l2->l_stat == LSSLEEP ||
    417 		           l2->l_stat == LSSUSPENDED) {
    418 			/* Deadlock checks.
    419 			 * 1. If all other LWPs are waiting for exits
    420 			 *    or suspended, we would deadlock.
    421 			 */
    422 
    423 			LIST_FOREACH(l3, &p->p_lwps, l_sibling) {
    424 				if (l3 != l && (l3->l_stat != LSSUSPENDED) &&
    425 				    !(l3->l_stat == LSSLEEP &&
    426 					l3->l_wchan == (caddr_t) &p->p_nlwps))
    427 					break;
    428 			}
    429 			if (l3 == NULL) /* Everyone else is waiting. */
    430 				return (EDEADLK);
    431 
    432 			/* XXX we'd like to check for a cycle of waiting
    433 			 * LWPs (specific LID waits, not any-LWP waits)
    434 			 * and detect that sort of deadlock, but we don't
    435 			 * have a good place to store the lwp that is
    436 			 * being waited for. wchan is already filled with
    437 			 * &p->p_nlwps, and putting the lwp address in
    438 			 * there for deadlock tracing would require
    439 			 * exiting LWPs to call wakeup on both their
    440 			 * own address and &p->p_nlwps, to get threads
    441 			 * sleeping on any LWP exiting.
    442 			 *
    443 			 * Revisit later. Maybe another auxillary
    444 			 * storage location associated with sleeping
    445 			 * is in order.
    446 			 */
    447 		}
    448 	}
    449 
    450 	if (nfound == 0)
    451 		return (ESRCH);
    452 
    453 	if ((error = tsleep((caddr_t) &p->p_nlwps, wpri,
    454 	    (lid != 0) ? waitstr1 : waitstr2, 0)) != 0)
    455 		return (error);
    456 
    457 	goto loop;
    458 }
    459 
    460 
    461 int
    462 newlwp(struct lwp *l1, struct proc *p2, vaddr_t uaddr, boolean_t inmem,
    463     int flags, void *stack, size_t stacksize,
    464     void (*func)(void *), void *arg, struct lwp **rnewlwpp)
    465 {
    466 	struct lwp *l2;
    467 	int s;
    468 
    469 	l2 = pool_get(&lwp_pool, PR_WAITOK);
    470 
    471 	l2->l_stat = LSIDL;
    472 	l2->l_forw = l2->l_back = NULL;
    473 	l2->l_proc = p2;
    474 
    475 	memset(&l2->l_startzero, 0,
    476 	       (unsigned) ((caddr_t)&l2->l_endzero -
    477 			   (caddr_t)&l2->l_startzero));
    478 	memcpy(&l2->l_startcopy, &l1->l_startcopy,
    479 	       (unsigned) ((caddr_t)&l2->l_endcopy -
    480 			   (caddr_t)&l2->l_startcopy));
    481 
    482 #if !defined(MULTIPROCESSOR)
    483 	/*
    484 	 * In the single-processor case, all processes will always run
    485 	 * on the same CPU.  So, initialize the child's CPU to the parent's
    486 	 * now.  In the multiprocessor case, the child's CPU will be
    487 	 * initialized in the low-level context switch code when the
    488 	 * process runs.
    489 	 */
    490 	KASSERT(l1->l_cpu != NULL);
    491 	l2->l_cpu = l1->l_cpu;
    492 #else
    493 	/*
    494 	 * zero child's CPU pointer so we don't get trash.
    495 	 */
    496 	l2->l_cpu = NULL;
    497 #endif /* ! MULTIPROCESSOR */
    498 
    499 	l2->l_flag = inmem ? L_INMEM : 0;
    500 	l2->l_flag |= (flags & LWP_DETACHED) ? L_DETACHED : 0;
    501 
    502 	callout_init(&l2->l_tsleep_ch);
    503 
    504 	if (rnewlwpp != NULL)
    505 		*rnewlwpp = l2;
    506 
    507 	l2->l_addr = (struct user *)uaddr;
    508 	uvm_lwp_fork(l1, l2, stack, stacksize, func,
    509 	    (arg != NULL) ? arg : l2);
    510 
    511 	simple_lock(&p2->p_lock);
    512 	l2->l_lid = ++p2->p_nlwpid;
    513 	LIST_INSERT_HEAD(&p2->p_lwps, l2, l_sibling);
    514 	p2->p_nlwps++;
    515 	simple_unlock(&p2->p_lock);
    516 
    517 	/* XXX should be locked differently... */
    518 	s = proclist_lock_write();
    519 	LIST_INSERT_HEAD(&alllwp, l2, l_list);
    520 	proclist_unlock_write(s);
    521 
    522 	if (p2->p_emul->e_lwp_fork)
    523 		(*p2->p_emul->e_lwp_fork)(l1, l2);
    524 
    525 	return (0);
    526 }
    527 
    528 
    529 /*
    530  * Quit the process. This will call cpu_exit, which will call cpu_switch,
    531  * so this can only be used meaningfully if you're willing to switch away.
    532  * Calling with l!=curlwp would be weird.
    533  */
    534 void
    535 lwp_exit(struct lwp *l)
    536 {
    537 	struct proc *p = l->l_proc;
    538 	int s;
    539 
    540 	DPRINTF(("lwp_exit: %d.%d exiting.\n", p->p_pid, l->l_lid));
    541 	DPRINTF((" nlwps: %d nrlwps %d nzlwps: %d\n",
    542 	    p->p_nlwps, p->p_nrlwps, p->p_nzlwps));
    543 
    544 	if (p->p_emul->e_lwp_exit)
    545 		(*p->p_emul->e_lwp_exit)(l);
    546 
    547 	/*
    548 	 * If we are the last live LWP in a process, we need to exit
    549 	 * the entire process (if that's not already going on). We do
    550 	 * so with an exit status of zero, because it's a "controlled"
    551 	 * exit, and because that's what Solaris does.
    552 	 */
    553 	if (((p->p_nlwps - p->p_nzlwps) == 1) && ((p->p_flag & P_WEXIT) == 0)) {
    554 		DPRINTF(("lwp_exit: %d.%d calling exit1()\n",
    555 		    p->p_pid, l->l_lid));
    556 		exit1(l, 0);
    557 		/* NOTREACHED */
    558 	}
    559 
    560 	s = proclist_lock_write();
    561 	LIST_REMOVE(l, l_list);
    562 	proclist_unlock_write(s);
    563 
    564 	/* Free MD LWP resources */
    565 #ifndef __NO_CPU_LWP_FREE
    566 	cpu_lwp_free(l, 0);
    567 #endif
    568 
    569 	pmap_deactivate(l);
    570 
    571 	if (l->l_flag & L_DETACHED) {
    572 		simple_lock(&p->p_lock);
    573 		LIST_REMOVE(l, l_sibling);
    574 		p->p_nlwps--;
    575 		simple_unlock(&p->p_lock);
    576 
    577 		curlwp = NULL;
    578 		l->l_proc = NULL;
    579 	}
    580 
    581 	SCHED_LOCK(s);
    582 	p->p_nrlwps--;
    583 	l->l_stat = LSDEAD;
    584 	SCHED_UNLOCK(s);
    585 
    586 	/* This LWP no longer needs to hold the kernel lock. */
    587 	KERNEL_PROC_UNLOCK(l);
    588 
    589 	/* cpu_exit() will not return */
    590 	cpu_exit(l);
    591 }
    592 
    593 /*
    594  * We are called from cpu_exit() once it is safe to schedule the
    595  * dead process's resources to be freed (i.e., once we've switched to
    596  * the idle PCB for the current CPU).
    597  *
    598  * NOTE: One must be careful with locking in this routine.  It's
    599  * called from a critical section in machine-dependent code, so
    600  * we should refrain from changing any interrupt state.
    601  */
    602 void
    603 lwp_exit2(struct lwp *l)
    604 {
    605 	struct proc *p;
    606 
    607 	KERNEL_LOCK(LK_EXCLUSIVE);
    608 	/*
    609 	 * Free the VM resources we're still holding on to.
    610 	 */
    611 	uvm_lwp_exit(l);
    612 
    613 	if (l->l_flag & L_DETACHED) {
    614 		/* Nobody waits for detached LWPs. */
    615 		pool_put(&lwp_pool, l);
    616 		KERNEL_UNLOCK();
    617 	} else {
    618 		l->l_stat = LSZOMB;
    619 		p = l->l_proc;
    620 		p->p_nzlwps++;
    621 		KERNEL_UNLOCK();
    622 		wakeup(&p->p_nlwps);
    623 	}
    624 }
    625 
    626 /*
    627  * Pick a LWP to represent the process for those operations which
    628  * want information about a "process" that is actually associated
    629  * with a LWP.
    630  */
    631 struct lwp *
    632 proc_representative_lwp(struct proc *p)
    633 {
    634 	struct lwp *l, *onproc, *running, *sleeping, *stopped, *suspended;
    635 	struct lwp *signalled;
    636 
    637 	/* Trivial case: only one LWP */
    638 	if (p->p_nlwps == 1)
    639 		return (LIST_FIRST(&p->p_lwps));
    640 
    641 	switch (p->p_stat) {
    642 	case SSTOP:
    643 	case SACTIVE:
    644 		/* Pick the most live LWP */
    645 		onproc = running = sleeping = stopped = suspended = NULL;
    646 		signalled = NULL;
    647 		LIST_FOREACH(l, &p->p_lwps, l_sibling) {
    648 			if (l->l_lid == p->p_sigctx.ps_lwp)
    649 				signalled = l;
    650 			switch (l->l_stat) {
    651 			case LSONPROC:
    652 				onproc = l;
    653 				break;
    654 			case LSRUN:
    655 				running = l;
    656 				break;
    657 			case LSSLEEP:
    658 				sleeping = l;
    659 				break;
    660 			case LSSTOP:
    661 				stopped = l;
    662 				break;
    663 			case LSSUSPENDED:
    664 				suspended = l;
    665 				break;
    666 			}
    667 		}
    668 		if (signalled)
    669 			return signalled;
    670 		if (onproc)
    671 			return onproc;
    672 		if (running)
    673 			return running;
    674 		if (sleeping)
    675 			return sleeping;
    676 		if (stopped)
    677 			return stopped;
    678 		if (suspended)
    679 			return suspended;
    680 		break;
    681 	case SZOMB:
    682 		/* Doesn't really matter... */
    683 		return (LIST_FIRST(&p->p_lwps));
    684 #ifdef DIAGNOSTIC
    685 	case SIDL:
    686 		/* We have more than one LWP and we're in SIDL?
    687 		 * How'd that happen?
    688 		 */
    689 		panic("Too many LWPs (%d) in SIDL process %d (%s)",
    690 		    p->p_nrlwps, p->p_pid, p->p_comm);
    691 	default:
    692 		panic("Process %d (%s) in unknown state %d",
    693 		    p->p_pid, p->p_comm, p->p_stat);
    694 #endif
    695 	}
    696 
    697 	panic("proc_representative_lwp: couldn't find a lwp for process"
    698 		" %d (%s)", p->p_pid, p->p_comm);
    699 	/* NOTREACHED */
    700 	return NULL;
    701 }
    702