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kern_lwp.c revision 1.20 
      1 /*	$NetBSD: kern_lwp.c,v 1.20 2004/01/11 19:39:48 jdolecek 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 1.20 2004/01/11 19:39:48 jdolecek 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 	newuc = pool_get(&lwp_uc_pool, PR_WAITOK);
     86 
     87 	error = copyin(SCARG(uap, ucp), newuc, sizeof(*newuc));
     88 	if (error)
     89 		return (error);
     90 
     91 	/* XXX check against resource limits */
     92 
     93 	inmem = uvm_uarea_alloc(&uaddr);
     94 	if (__predict_false(uaddr == 0)) {
     95 		return (ENOMEM);
     96 	}
     97 
     98 	/* XXX flags:
     99 	 * __LWP_ASLWP is probably needed for Solaris compat.
    100 	 */
    101 
    102 	newlwp(l, p, uaddr, inmem,
    103 	    SCARG(uap, flags) & LWP_DETACHED,
    104 	    NULL, 0, startlwp, newuc, &l2);
    105 
    106 	if ((SCARG(uap, flags) & LWP_SUSPENDED) == 0) {
    107 		SCHED_LOCK(s);
    108 		l2->l_stat = LSRUN;
    109 		setrunqueue(l2);
    110 		SCHED_UNLOCK(s);
    111 		simple_lock(&p->p_lock);
    112 		p->p_nrlwps++;
    113 		simple_unlock(&p->p_lock);
    114 	} else {
    115 		l2->l_stat = LSSUSPENDED;
    116 	}
    117 
    118 	error = copyout(&l2->l_lid, SCARG(uap, new_lwp),
    119 	    sizeof(l2->l_lid));
    120 	if (error)
    121 		return (error);
    122 
    123 	return (0);
    124 }
    125 
    126 
    127 int
    128 sys__lwp_exit(struct lwp *l, void *v, register_t *retval)
    129 {
    130 
    131 	lwp_exit(l);
    132 	/* NOTREACHED */
    133 	return (0);
    134 }
    135 
    136 
    137 int
    138 sys__lwp_self(struct lwp *l, void *v, register_t *retval)
    139 {
    140 
    141 	*retval = l->l_lid;
    142 
    143 	return (0);
    144 }
    145 
    146 
    147 int
    148 sys__lwp_getprivate(struct lwp *l, void *v, register_t *retval)
    149 {
    150 
    151 	*retval = (uintptr_t) l->l_private;
    152 
    153 	return (0);
    154 }
    155 
    156 
    157 int
    158 sys__lwp_setprivate(struct lwp *l, void *v, register_t *retval)
    159 {
    160 	struct sys__lwp_setprivate_args /* {
    161 		syscallarg(void *) ptr;
    162 	} */ *uap = v;
    163 
    164 	l->l_private = SCARG(uap, ptr);
    165 
    166 	return (0);
    167 }
    168 
    169 
    170 int
    171 sys__lwp_suspend(struct lwp *l, void *v, register_t *retval)
    172 {
    173 	struct sys__lwp_suspend_args /* {
    174 		syscallarg(lwpid_t) target;
    175 	} */ *uap = v;
    176 	int target_lid;
    177 	struct proc *p = l->l_proc;
    178 	struct lwp *t;
    179 	struct lwp *t2;
    180 
    181 	target_lid = SCARG(uap, target);
    182 
    183 	LIST_FOREACH(t, &p->p_lwps, l_sibling)
    184 		if (t->l_lid == target_lid)
    185 			break;
    186 
    187 	if (t == NULL)
    188 		return (ESRCH);
    189 
    190 	if (t == l) {
    191 		/*
    192 		 * Check for deadlock, which is only possible
    193 		 * when we're suspending ourself.
    194 		 */
    195 		LIST_FOREACH(t2, &p->p_lwps, l_sibling) {
    196 			if ((t2 != l) && (t2->l_stat != LSSUSPENDED))
    197 				break;
    198 		}
    199 
    200 		if (t2 == NULL) /* All other LWPs are suspended */
    201 			return (EDEADLK);
    202 	}
    203 
    204 	return lwp_suspend(l, t);
    205 }
    206 
    207 inline int
    208 lwp_suspend(l, t)
    209 	struct lwp *l;
    210 	struct lwp *t;
    211 {
    212 	struct proc *p = t->l_proc;
    213 	int s;
    214 
    215 	if (t == l) {
    216 		SCHED_LOCK(s);
    217 		l->l_stat = LSSUSPENDED;
    218 		/* XXX NJWLWP check if this makes sense here: */
    219 		p->p_stats->p_ru.ru_nvcsw++;
    220 		mi_switch(l, NULL);
    221 		SCHED_ASSERT_UNLOCKED();
    222 		splx(s);
    223 	} else {
    224 		switch (t->l_stat) {
    225 		case LSSUSPENDED:
    226 			return (0); /* _lwp_suspend() is idempotent */
    227 		case LSRUN:
    228 			SCHED_LOCK(s);
    229 			remrunqueue(t);
    230 			t->l_stat = LSSUSPENDED;
    231 			SCHED_UNLOCK(s);
    232 			simple_lock(&p->p_lock);
    233 			p->p_nrlwps--;
    234 			simple_unlock(&p->p_lock);
    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 			panic("XXX multiprocessor LWPs? Implement me!");
    247 			break;
    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 	target_lid = SCARG(uap, target);
    266 
    267 	LIST_FOREACH(t, &p->p_lwps, l_sibling)
    268 		if (t->l_lid == target_lid)
    269 			break;
    270 
    271 	if (t == NULL)
    272 		return (ESRCH);
    273 
    274 	SCHED_LOCK(s);
    275 	lwp_continue(t);
    276 	SCHED_UNLOCK(s);
    277 
    278 	return (0);
    279 }
    280 
    281 void
    282 lwp_continue(struct lwp *l)
    283 {
    284 
    285 	DPRINTF(("lwp_continue of %d.%d (%s), state %d, wchan %p\n",
    286 	    l->l_proc->p_pid, l->l_lid, l->l_proc->p_comm, l->l_stat,
    287 	    l->l_wchan));
    288 
    289 	if (l->l_stat != LSSUSPENDED)
    290 		return;
    291 
    292 	if (l->l_wchan == 0) {
    293 		/* LWP was runnable before being suspended. */
    294 		setrunnable(l);
    295 	} else {
    296 		/* LWP was sleeping before being suspended. */
    297 		l->l_stat = LSSLEEP;
    298 	}
    299 }
    300 
    301 int
    302 sys__lwp_wakeup(struct lwp *l, void *v, register_t *retval)
    303 {
    304 	struct sys__lwp_wakeup_args /* {
    305 		syscallarg(lwpid_t) wakeup;
    306 	} */ *uap = v;
    307 	lwpid_t target_lid;
    308 	struct lwp *t;
    309 	struct proc *p;
    310 	int error;
    311 	int s;
    312 
    313 	p = l->l_proc;
    314 	target_lid = SCARG(uap, target);
    315 
    316 	SCHED_LOCK(s);
    317 
    318 
    319 	LIST_FOREACH(t, &p->p_lwps, l_sibling)
    320 		if (t->l_lid == target_lid)
    321 			break;
    322 
    323 	if (t == NULL) {
    324 		error = ESRCH;
    325 		goto exit;
    326 	}
    327 
    328 	if (t->l_stat != LSSLEEP) {
    329 		error = ENODEV;
    330 		goto exit;
    331 	}
    332 
    333 	if ((t->l_flag & L_SINTR) == 0) {
    334 		error = EBUSY;
    335 		goto exit;
    336 	}
    337 	/*
    338 	 * Tell ltsleep to wakeup.
    339 	 */
    340 	t->l_flag |= L_CANCELLED;
    341 
    342 	setrunnable(t);
    343 	error = 0;
    344 exit:
    345 	SCHED_UNLOCK(s);
    346 
    347 
    348 	return error;
    349 }
    350 
    351 int
    352 sys__lwp_wait(struct lwp *l, void *v, register_t *retval)
    353 {
    354 	struct sys__lwp_wait_args /* {
    355 		syscallarg(lwpid_t) wait_for;
    356 		syscallarg(lwpid_t *) departed;
    357 	} */ *uap = v;
    358 	int error;
    359 	lwpid_t dep;
    360 
    361 	error = lwp_wait1(l, SCARG(uap, wait_for), &dep, 0);
    362 	if (error)
    363 		return (error);
    364 
    365 	if (SCARG(uap, departed)) {
    366 		error = copyout(&dep, SCARG(uap, departed),
    367 		    sizeof(dep));
    368 		if (error)
    369 			return (error);
    370 	}
    371 
    372 	return (0);
    373 }
    374 
    375 
    376 int
    377 lwp_wait1(struct lwp *l, lwpid_t lid, lwpid_t *departed, int flags)
    378 {
    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 
    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 
    513 	simple_lock(&p2->p_lock);
    514 	l2->l_lid = ++p2->p_nlwpid;
    515 	LIST_INSERT_HEAD(&p2->p_lwps, l2, l_sibling);
    516 	p2->p_nlwps++;
    517 	simple_unlock(&p2->p_lock);
    518 
    519 	/* XXX should be locked differently... */
    520 	s = proclist_lock_write();
    521 	LIST_INSERT_HEAD(&alllwp, l2, l_list);
    522 	proclist_unlock_write(s);
    523 
    524 	if (p2->p_emul->e_lwp_fork)
    525 		(*p2->p_emul->e_lwp_fork)(l1, l2);
    526 
    527 	return (0);
    528 }
    529 
    530 
    531 /*
    532  * Quit the process. This will call cpu_exit, which will call cpu_switch,
    533  * so this can only be used meaningfully if you're willing to switch away.
    534  * Calling with l!=curlwp would be weird.
    535  */
    536 void
    537 lwp_exit(struct lwp *l)
    538 {
    539 	struct proc *p = l->l_proc;
    540 	int s;
    541 
    542 	DPRINTF(("lwp_exit: %d.%d exiting.\n", p->p_pid, l->l_lid));
    543 	DPRINTF((" nlwps: %d nrlwps %d nzlwps: %d\n",
    544 	    p->p_nlwps, p->p_nrlwps, p->p_nzlwps));
    545 
    546 	if (p->p_emul->e_lwp_exit)
    547 		(*p->p_emul->e_lwp_exit)(l);
    548 
    549 	/*
    550 	 * If we are the last live LWP in a process, we need to exit
    551 	 * the entire process (if that's not already going on). We do
    552 	 * so with an exit status of zero, because it's a "controlled"
    553 	 * exit, and because that's what Solaris does.
    554 	 */
    555 	if (((p->p_nlwps - p->p_nzlwps) == 1) && ((p->p_flag & P_WEXIT) == 0)) {
    556 		DPRINTF(("lwp_exit: %d.%d calling exit1()\n",
    557 		    p->p_pid, l->l_lid));
    558 		exit1(l, 0);
    559 		/* NOTREACHED */
    560 	}
    561 
    562 	s = proclist_lock_write();
    563 	LIST_REMOVE(l, l_list);
    564 	proclist_unlock_write(s);
    565 
    566 	/* Free MD LWP resources */
    567 #ifndef __NO_CPU_LWP_FREE
    568 	cpu_lwp_free(l, 0);
    569 #endif
    570 
    571 	simple_lock(&p->p_lock);
    572 	p->p_nrlwps--;
    573 	simple_unlock(&p->p_lock);
    574 
    575 	l->l_stat = LSDEAD;
    576 
    577 	/* This LWP no longer needs to hold the kernel lock. */
    578 	KERNEL_PROC_UNLOCK(l);
    579 
    580 	/* cpu_exit() will not return */
    581 	cpu_exit(l);
    582 
    583 }
    584 
    585 /*
    586  * We are called from cpu_exit() once it is safe to schedule the
    587  * dead process's resources to be freed (i.e., once we've switched to
    588  * the idle PCB for the current CPU).
    589  *
    590  * NOTE: One must be careful with locking in this routine.  It's
    591  * called from a critical section in machine-dependent code, so
    592  * we should refrain from changing any interrupt state.
    593  */
    594 void
    595 lwp_exit2(struct lwp *l)
    596 {
    597 	struct proc *p;
    598 
    599 	/*
    600 	 * Free the VM resources we're still holding on to.
    601 	 */
    602 	uvm_lwp_exit(l);
    603 
    604 	l->l_stat = LSZOMB;
    605 	if (l->l_flag & L_DETACHED) {
    606 		/* Nobody waits for detached LWPs. */
    607 		LIST_REMOVE(l, l_sibling);
    608 
    609 		if ((l->l_flag & L_PROCEXIT) == 0) {
    610 			p = l->l_proc;
    611 			p->p_nlwps--;
    612 		}
    613 
    614 		pool_put(&lwp_pool, l);
    615 	} else {
    616 		p = l->l_proc;
    617 		p->p_nzlwps++;
    618 		wakeup(&p->p_nlwps);
    619 	}
    620 }
    621 
    622 /*
    623  * Pick a LWP to represent the process for those operations which
    624  * want information about a "process" that is actually associated
    625  * with a LWP.
    626  */
    627 struct lwp *
    628 proc_representative_lwp(p)
    629 	struct proc *p;
    630 {
    631 	struct lwp *l, *onproc, *running, *sleeping, *stopped, *suspended;
    632 
    633 	/* Trivial case: only one LWP */
    634 	if (p->p_nlwps == 1)
    635 		return (LIST_FIRST(&p->p_lwps));
    636 
    637 	switch (p->p_stat) {
    638 	case SSTOP:
    639 	case SACTIVE:
    640 		/* Pick the most live LWP */
    641 		onproc = running = sleeping = stopped = suspended = NULL;
    642 		LIST_FOREACH(l, &p->p_lwps, l_sibling) {
    643 			switch (l->l_stat) {
    644 			case LSONPROC:
    645 				onproc = l;
    646 				break;
    647 			case LSRUN:
    648 				running = l;
    649 				break;
    650 			case LSSLEEP:
    651 				sleeping = l;
    652 				break;
    653 			case LSSTOP:
    654 				stopped = l;
    655 				break;
    656 			case LSSUSPENDED:
    657 				suspended = l;
    658 				break;
    659 			}
    660 		}
    661 		if (onproc)
    662 			return onproc;
    663 		if (running)
    664 			return running;
    665 		if (sleeping)
    666 			return sleeping;
    667 		if (stopped)
    668 			return stopped;
    669 		if (suspended)
    670 			return suspended;
    671 		break;
    672 	case SZOMB:
    673 		/* Doesn't really matter... */
    674 		return (LIST_FIRST(&p->p_lwps));
    675 #ifdef DIAGNOSTIC
    676 	case SIDL:
    677 		/* We have more than one LWP and we're in SIDL?
    678 		 * How'd that happen?
    679 		 */
    680 		panic("Too many LWPs (%d) in SIDL process %d (%s)",
    681 		    p->p_nrlwps, p->p_pid, p->p_comm);
    682 	default:
    683 		panic("Process %d (%s) in unknown state %d",
    684 		    p->p_pid, p->p_comm, p->p_stat);
    685 #endif
    686 	}
    687 
    688 	panic("proc_representative_lwp: couldn't find a lwp for process"
    689 		" %d (%s)", p->p_pid, p->p_comm);
    690 	/* NOTREACHED */
    691 	return NULL;
    692 }
    693