freebsd-dev/sys/kern/kern_lock.c

718 lines
19 KiB
C

/*-
* Copyright (c) 1995
* The Regents of the University of California. All rights reserved.
*
* Copyright (C) 1997
* John S. Dyson. All rights reserved.
*
* This code contains ideas from software contributed to Berkeley by
* Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating
* System project at Carnegie-Mellon University.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* @(#)kern_lock.c 8.18 (Berkeley) 5/21/95
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include "opt_ddb.h"
#include "opt_global.h"
#include <sys/param.h>
#include <sys/kdb.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/lockmgr.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/systm.h>
#include <sys/lock_profile.h>
#ifdef DEBUG_LOCKS
#include <sys/stack.h>
#endif
#ifdef DDB
#include <ddb/ddb.h>
static void db_show_lockmgr(struct lock_object *lock);
#endif
static void lock_lockmgr(struct lock_object *lock, int how);
static int unlock_lockmgr(struct lock_object *lock);
struct lock_class lock_class_lockmgr = {
.lc_name = "lockmgr",
.lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
#ifdef DDB
.lc_ddb_show = db_show_lockmgr,
#endif
.lc_lock = lock_lockmgr,
.lc_unlock = unlock_lockmgr,
};
/*
* Locking primitives implementation.
* Locks provide shared/exclusive sychronization.
*/
void
lock_lockmgr(struct lock_object *lock, int how)
{
panic("lockmgr locks do not support sleep interlocking");
}
int
unlock_lockmgr(struct lock_object *lock)
{
panic("lockmgr locks do not support sleep interlocking");
}
#define COUNT(td, x) if ((td)) (td)->td_locks += (x)
#define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
LK_SHARE_NONZERO | LK_WAIT_NONZERO)
static int acquire(struct lock **lkpp, int extflags, int wanted, int *contested, uint64_t *waittime);
static int acquiredrain(struct lock *lkp, int extflags) ;
static __inline void
sharelock(struct thread *td, struct lock *lkp, int incr) {
lkp->lk_flags |= LK_SHARE_NONZERO;
lkp->lk_sharecount += incr;
COUNT(td, incr);
}
static __inline void
shareunlock(struct thread *td, struct lock *lkp, int decr) {
KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
COUNT(td, -decr);
if (lkp->lk_sharecount == decr) {
lkp->lk_flags &= ~LK_SHARE_NONZERO;
if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
wakeup(lkp);
}
lkp->lk_sharecount = 0;
} else {
lkp->lk_sharecount -= decr;
}
}
static int
acquire(struct lock **lkpp, int extflags, int wanted, int *contested, uint64_t *waittime)
{
struct lock *lkp = *lkpp;
int error;
CTR3(KTR_LOCK,
"acquire(): lkp == %p, extflags == 0x%x, wanted == 0x%x",
lkp, extflags, wanted);
if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted))
return EBUSY;
error = 0;
if ((lkp->lk_flags & wanted) != 0)
lock_profile_obtain_lock_failed(&lkp->lk_object, contested, waittime);
while ((lkp->lk_flags & wanted) != 0) {
CTR2(KTR_LOCK,
"acquire(): lkp == %p, lk_flags == 0x%x sleeping",
lkp, lkp->lk_flags);
lkp->lk_flags |= LK_WAIT_NONZERO;
lkp->lk_waitcount++;
error = msleep(lkp, lkp->lk_interlock, lkp->lk_prio,
lkp->lk_wmesg,
((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
lkp->lk_waitcount--;
if (lkp->lk_waitcount == 0)
lkp->lk_flags &= ~LK_WAIT_NONZERO;
if (error)
break;
if (extflags & LK_SLEEPFAIL) {
error = ENOLCK;
break;
}
if (lkp->lk_newlock != NULL) {
mtx_lock(lkp->lk_newlock->lk_interlock);
mtx_unlock(lkp->lk_interlock);
if (lkp->lk_waitcount == 0)
wakeup((void *)(&lkp->lk_newlock));
*lkpp = lkp = lkp->lk_newlock;
}
}
mtx_assert(lkp->lk_interlock, MA_OWNED);
return (error);
}
/*
* Set, change, or release a lock.
*
* Shared requests increment the shared count. Exclusive requests set the
* LK_WANT_EXCL flag (preventing further shared locks), and wait for already
* accepted shared locks and shared-to-exclusive upgrades to go away.
*/
int
_lockmgr(struct lock *lkp, u_int flags, struct mtx *interlkp,
struct thread *td, char *file, int line)
{
int error;
struct thread *thr;
int extflags, lockflags;
int contested = 0;
uint64_t waitstart = 0;
error = 0;
if (td == NULL)
thr = LK_KERNPROC;
else
thr = td;
if ((flags & LK_INTERNAL) == 0)
mtx_lock(lkp->lk_interlock);
CTR6(KTR_LOCK,
"lockmgr(): lkp == %p (lk_wmesg == \"%s\"), owner == %p, exclusivecount == %d, flags == 0x%x, "
"td == %p", lkp, lkp->lk_wmesg, lkp->lk_lockholder,
lkp->lk_exclusivecount, flags, td);
#ifdef DEBUG_LOCKS
{
struct stack stack; /* XXX */
stack_save(&stack);
CTRSTACK(KTR_LOCK, &stack, 0, 1);
}
#endif
if (flags & LK_INTERLOCK) {
mtx_assert(interlkp, MA_OWNED | MA_NOTRECURSED);
mtx_unlock(interlkp);
}
if ((flags & (LK_NOWAIT|LK_RELEASE)) == 0)
WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK,
&lkp->lk_interlock->lock_object,
"Acquiring lockmgr lock \"%s\"", lkp->lk_wmesg);
if (panicstr != NULL) {
mtx_unlock(lkp->lk_interlock);
return (0);
}
if ((lkp->lk_flags & LK_NOSHARE) &&
(flags & LK_TYPE_MASK) == LK_SHARED) {
flags &= ~LK_TYPE_MASK;
flags |= LK_EXCLUSIVE;
}
extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
switch (flags & LK_TYPE_MASK) {
case LK_SHARED:
/*
* If we are not the exclusive lock holder, we have to block
* while there is an exclusive lock holder or while an
* exclusive lock request or upgrade request is in progress.
*
* However, if TDP_DEADLKTREAT is set, we override exclusive
* lock requests or upgrade requests ( but not the exclusive
* lock itself ).
*/
if (lkp->lk_lockholder != thr) {
lockflags = LK_HAVE_EXCL;
if (td != NULL && !(td->td_pflags & TDP_DEADLKTREAT))
lockflags |= LK_WANT_EXCL | LK_WANT_UPGRADE;
error = acquire(&lkp, extflags, lockflags, &contested, &waitstart);
if (error)
break;
sharelock(td, lkp, 1);
if (lkp->lk_sharecount == 1)
lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
#if defined(DEBUG_LOCKS)
stack_save(&lkp->lk_stack);
#endif
break;
}
/*
* We hold an exclusive lock, so downgrade it to shared.
* An alternative would be to fail with EDEADLK.
*/
sharelock(td, lkp, 1);
if (lkp->lk_sharecount == 1)
lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
/* FALLTHROUGH downgrade */
case LK_DOWNGRADE:
KASSERT(lkp->lk_lockholder == thr && lkp->lk_exclusivecount != 0,
("lockmgr: not holding exclusive lock "
"(owner thread (%p) != thread (%p), exlcnt (%d) != 0",
lkp->lk_lockholder, thr, lkp->lk_exclusivecount));
sharelock(td, lkp, lkp->lk_exclusivecount);
COUNT(td, -lkp->lk_exclusivecount);
lkp->lk_exclusivecount = 0;
lkp->lk_flags &= ~LK_HAVE_EXCL;
lkp->lk_lockholder = LK_NOPROC;
if (lkp->lk_waitcount)
wakeup((void *)lkp);
break;
case LK_EXCLUPGRADE:
/*
* If another process is ahead of us to get an upgrade,
* then we want to fail rather than have an intervening
* exclusive access.
*/
if (lkp->lk_flags & LK_WANT_UPGRADE) {
shareunlock(td, lkp, 1);
error = EBUSY;
break;
}
/* FALLTHROUGH normal upgrade */
case LK_UPGRADE:
/*
* Upgrade a shared lock to an exclusive one. If another
* shared lock has already requested an upgrade to an
* exclusive lock, our shared lock is released and an
* exclusive lock is requested (which will be granted
* after the upgrade). If we return an error, the file
* will always be unlocked.
*/
if (lkp->lk_lockholder == thr)
panic("lockmgr: upgrade exclusive lock");
if (lkp->lk_sharecount <= 0)
panic("lockmgr: upgrade without shared");
shareunlock(td, lkp, 1);
if (lkp->lk_sharecount == 0)
lock_profile_release_lock(&lkp->lk_object);
/*
* If we are just polling, check to see if we will block.
*/
if ((extflags & LK_NOWAIT) &&
((lkp->lk_flags & LK_WANT_UPGRADE) ||
lkp->lk_sharecount > 1)) {
error = EBUSY;
break;
}
if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
/*
* We are first shared lock to request an upgrade, so
* request upgrade and wait for the shared count to
* drop to zero, then take exclusive lock.
*/
lkp->lk_flags |= LK_WANT_UPGRADE;
error = acquire(&lkp, extflags, LK_SHARE_NONZERO, &contested, &waitstart);
lkp->lk_flags &= ~LK_WANT_UPGRADE;
if (error) {
if ((lkp->lk_flags & ( LK_WANT_EXCL | LK_WAIT_NONZERO)) == (LK_WANT_EXCL | LK_WAIT_NONZERO))
wakeup((void *)lkp);
break;
}
if (lkp->lk_exclusivecount != 0)
panic("lockmgr: non-zero exclusive count");
lkp->lk_flags |= LK_HAVE_EXCL;
lkp->lk_lockholder = thr;
lkp->lk_exclusivecount = 1;
COUNT(td, 1);
lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
#if defined(DEBUG_LOCKS)
stack_save(&lkp->lk_stack);
#endif
break;
}
/*
* Someone else has requested upgrade. Release our shared
* lock, awaken upgrade requestor if we are the last shared
* lock, then request an exclusive lock.
*/
if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
LK_WAIT_NONZERO)
wakeup((void *)lkp);
/* FALLTHROUGH exclusive request */
case LK_EXCLUSIVE:
if (lkp->lk_lockholder == thr && thr != LK_KERNPROC) {
/*
* Recursive lock.
*/
if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0)
panic("lockmgr: locking against myself");
if ((extflags & LK_CANRECURSE) != 0) {
lkp->lk_exclusivecount++;
COUNT(td, 1);
break;
}
}
/*
* If we are just polling, check to see if we will sleep.
*/
if ((extflags & LK_NOWAIT) &&
(lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
error = EBUSY;
break;
}
/*
* Try to acquire the want_exclusive flag.
*/
error = acquire(&lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL), &contested, &waitstart);
if (error)
break;
lkp->lk_flags |= LK_WANT_EXCL;
/*
* Wait for shared locks and upgrades to finish.
*/
error = acquire(&lkp, extflags, LK_HAVE_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO, &contested, &waitstart);
lkp->lk_flags &= ~LK_WANT_EXCL;
if (error) {
if (lkp->lk_flags & LK_WAIT_NONZERO)
wakeup((void *)lkp);
break;
}
lkp->lk_flags |= LK_HAVE_EXCL;
lkp->lk_lockholder = thr;
if (lkp->lk_exclusivecount != 0)
panic("lockmgr: non-zero exclusive count");
lkp->lk_exclusivecount = 1;
COUNT(td, 1);
lock_profile_obtain_lock_success(&lkp->lk_object, contested, waitstart, file, line);
#if defined(DEBUG_LOCKS)
stack_save(&lkp->lk_stack);
#endif
break;
case LK_RELEASE:
if (lkp->lk_exclusivecount != 0) {
if (lkp->lk_lockholder != thr &&
lkp->lk_lockholder != LK_KERNPROC) {
panic("lockmgr: thread %p, not %s %p unlocking",
thr, "exclusive lock holder",
lkp->lk_lockholder);
}
if (lkp->lk_lockholder != LK_KERNPROC)
COUNT(td, -1);
if (lkp->lk_exclusivecount == 1) {
lkp->lk_flags &= ~LK_HAVE_EXCL;
lkp->lk_lockholder = LK_NOPROC;
lkp->lk_exclusivecount = 0;
lock_profile_release_lock(&lkp->lk_object);
} else {
lkp->lk_exclusivecount--;
}
} else if (lkp->lk_flags & LK_SHARE_NONZERO)
shareunlock(td, lkp, 1);
else {
printf("lockmgr: thread %p unlocking unheld lock\n",
thr);
kdb_backtrace();
}
if (lkp->lk_flags & LK_WAIT_NONZERO)
wakeup((void *)lkp);
break;
case LK_DRAIN:
/*
* Check that we do not already hold the lock, as it can
* never drain if we do. Unfortunately, we have no way to
* check for holding a shared lock, but at least we can
* check for an exclusive one.
*/
if (lkp->lk_lockholder == thr)
panic("lockmgr: draining against myself");
error = acquiredrain(lkp, extflags);
if (error)
break;
lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
lkp->lk_lockholder = thr;
lkp->lk_exclusivecount = 1;
COUNT(td, 1);
#if defined(DEBUG_LOCKS)
stack_save(&lkp->lk_stack);
#endif
break;
default:
mtx_unlock(lkp->lk_interlock);
panic("lockmgr: unknown locktype request %d",
flags & LK_TYPE_MASK);
/* NOTREACHED */
}
if ((lkp->lk_flags & LK_WAITDRAIN) &&
(lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
lkp->lk_flags &= ~LK_WAITDRAIN;
wakeup((void *)&lkp->lk_flags);
}
mtx_unlock(lkp->lk_interlock);
return (error);
}
static int
acquiredrain(struct lock *lkp, int extflags) {
int error;
if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
return EBUSY;
}
while (lkp->lk_flags & LK_ALL) {
lkp->lk_flags |= LK_WAITDRAIN;
error = msleep(&lkp->lk_flags, lkp->lk_interlock, lkp->lk_prio,
lkp->lk_wmesg,
((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
if (error)
return error;
if (extflags & LK_SLEEPFAIL) {
return ENOLCK;
}
}
return 0;
}
/*
* Transfer any waiting processes from one lock to another.
*/
void
transferlockers(from, to)
struct lock *from;
struct lock *to;
{
KASSERT(from != to, ("lock transfer to self"));
KASSERT((from->lk_flags&LK_WAITDRAIN) == 0, ("transfer draining lock"));
mtx_lock(from->lk_interlock);
if (from->lk_waitcount == 0) {
mtx_unlock(from->lk_interlock);
return;
}
from->lk_newlock = to;
wakeup((void *)from);
msleep(&from->lk_newlock, from->lk_interlock, from->lk_prio,
"lkxfer", 0);
from->lk_newlock = NULL;
from->lk_flags &= ~(LK_WANT_EXCL | LK_WANT_UPGRADE);
KASSERT(from->lk_waitcount == 0, ("active lock"));
mtx_unlock(from->lk_interlock);
}
/*
* Initialize a lock; required before use.
*/
void
lockinit(lkp, prio, wmesg, timo, flags)
struct lock *lkp;
int prio;
const char *wmesg;
int timo;
int flags;
{
CTR5(KTR_LOCK, "lockinit(): lkp == %p, prio == %d, wmesg == \"%s\", "
"timo == %d, flags = 0x%x\n", lkp, prio, wmesg, timo, flags);
lkp->lk_interlock = mtx_pool_alloc(mtxpool_lockbuilder);
lkp->lk_flags = (flags & LK_EXTFLG_MASK);
lkp->lk_sharecount = 0;
lkp->lk_waitcount = 0;
lkp->lk_exclusivecount = 0;
lkp->lk_prio = prio;
lkp->lk_timo = timo;
lkp->lk_lockholder = LK_NOPROC;
lkp->lk_newlock = NULL;
#ifdef DEBUG_LOCKS
stack_zero(&lkp->lk_stack);
#endif
lock_init(&lkp->lk_object, &lock_class_lockmgr, wmesg, NULL,
LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE);
}
/*
* Destroy a lock.
*/
void
lockdestroy(lkp)
struct lock *lkp;
{
CTR2(KTR_LOCK, "lockdestroy(): lkp == %p (lk_wmesg == \"%s\")",
lkp, lkp->lk_wmesg);
lock_destroy(&lkp->lk_object);
}
/*
* Determine the status of a lock.
*/
int
lockstatus(lkp, td)
struct lock *lkp;
struct thread *td;
{
int lock_type = 0;
int interlocked;
if (!kdb_active) {
interlocked = 1;
mtx_lock(lkp->lk_interlock);
} else
interlocked = 0;
if (lkp->lk_exclusivecount != 0) {
if (td == NULL || lkp->lk_lockholder == td)
lock_type = LK_EXCLUSIVE;
else
lock_type = LK_EXCLOTHER;
} else if (lkp->lk_sharecount != 0)
lock_type = LK_SHARED;
if (interlocked)
mtx_unlock(lkp->lk_interlock);
return (lock_type);
}
/*
* Determine the number of holders of a lock.
*/
int
lockcount(lkp)
struct lock *lkp;
{
int count;
mtx_lock(lkp->lk_interlock);
count = lkp->lk_exclusivecount + lkp->lk_sharecount;
mtx_unlock(lkp->lk_interlock);
return (count);
}
/*
* Determine the number of waiters on a lock.
*/
int
lockwaiters(lkp)
struct lock *lkp;
{
int count;
mtx_lock(lkp->lk_interlock);
count = lkp->lk_waitcount;
mtx_unlock(lkp->lk_interlock);
return (count);
}
/*
* Print out information about state of a lock. Used by VOP_PRINT
* routines to display status about contained locks.
*/
void
lockmgr_printinfo(lkp)
struct lock *lkp;
{
if (lkp->lk_sharecount)
printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
lkp->lk_sharecount);
else if (lkp->lk_flags & LK_HAVE_EXCL)
printf(" lock type %s: EXCL (count %d) by thread %p (pid %d)",
lkp->lk_wmesg, lkp->lk_exclusivecount,
lkp->lk_lockholder, lkp->lk_lockholder->td_proc->p_pid);
if (lkp->lk_waitcount > 0)
printf(" with %d pending", lkp->lk_waitcount);
#ifdef DEBUG_LOCKS
stack_print(&lkp->lk_stack);
#endif
}
#ifdef DDB
/*
* Check to see if a thread that is blocked on a sleep queue is actually
* blocked on a 'struct lock'. If so, output some details and return true.
* If the lock has an exclusive owner, return that in *ownerp.
*/
int
lockmgr_chain(struct thread *td, struct thread **ownerp)
{
struct lock *lkp;
lkp = td->td_wchan;
/* Simple test to see if wchan points to a lockmgr lock. */
if (LOCK_CLASS(&lkp->lk_object) == &lock_class_lockmgr &&
lkp->lk_wmesg == td->td_wmesg)
goto ok;
/*
* If this thread is doing a DRAIN, then it would be asleep on
* &lkp->lk_flags rather than lkp.
*/
lkp = (struct lock *)((char *)td->td_wchan -
offsetof(struct lock, lk_flags));
if (LOCK_CLASS(&lkp->lk_object) == &lock_class_lockmgr &&
lkp->lk_wmesg == td->td_wmesg && (lkp->lk_flags & LK_WAITDRAIN))
goto ok;
/* Doen't seem to be a lockmgr lock. */
return (0);
ok:
/* Ok, we think we have a lockmgr lock, so output some details. */
db_printf("blocked on lk \"%s\" ", lkp->lk_wmesg);
if (lkp->lk_sharecount) {
db_printf("SHARED (count %d)\n", lkp->lk_sharecount);
*ownerp = NULL;
} else {
db_printf("EXCL (count %d)\n", lkp->lk_exclusivecount);
*ownerp = lkp->lk_lockholder;
}
return (1);
}
void
db_show_lockmgr(struct lock_object *lock)
{
struct thread *td;
struct lock *lkp;
lkp = (struct lock *)lock;
db_printf(" lock type: %s\n", lkp->lk_wmesg);
db_printf(" state: ");
if (lkp->lk_sharecount)
db_printf("SHARED (count %d)\n", lkp->lk_sharecount);
else if (lkp->lk_flags & LK_HAVE_EXCL) {
td = lkp->lk_lockholder;
db_printf("EXCL (count %d) %p ", lkp->lk_exclusivecount, td);
db_printf("(tid %d, pid %d, \"%s\")\n", td->td_tid,
td->td_proc->p_pid, td->td_proc->p_comm);
} else
db_printf("UNLOCKED\n");
if (lkp->lk_waitcount > 0)
db_printf(" waiters: %d\n", lkp->lk_waitcount);
}
#endif