FreeBSD-5.3/sys/kern/kern_lock.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: src/sys/kern/kern_lock.c,v 1.74.2.2 2004/09/03 15:45:31 kan Exp $");
#include <sys/param.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>
/*
* Locking primitives implementation.
* Locks provide shared/exclusive sychronization.
*/
#define LOCK_WAIT_TIME 100
#define LOCK_SAMPLE_WAIT 7
#if defined(DIAGNOSTIC)
#define LOCK_INLINE
#else
#define LOCK_INLINE __inline
#endif
#define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
LK_SHARE_NONZERO | LK_WAIT_NONZERO)
/*
* Mutex array variables. Rather than each lockmgr lock having its own mutex,
* share a fixed (at boot time) number of mutexes across all lockmgr locks in
* order to keep sizeof(struct lock) down.
*/
static struct mtx lock_mtx;
static int acquire(struct lock **lkpp, int extflags, int wanted);
static int apause(struct lock *lkp, int flags);
static int acquiredrain(struct lock *lkp, int extflags) ;
static void
lockmgr_init(void *dummy __unused)
{
mtx_init(&lock_mtx, "lockmgr", NULL, MTX_DEF);
}
SYSINIT(lmgrinit, SI_SUB_LOCKMGR, SI_ORDER_FIRST, lockmgr_init, NULL)
static LOCK_INLINE void
sharelock(struct lock *lkp, int incr) {
lkp->lk_flags |= LK_SHARE_NONZERO;
lkp->lk_sharecount += incr;
}
static LOCK_INLINE void
shareunlock(struct lock *lkp, int decr) {
KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < 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;
}
}
/*
* This is the waitloop optimization.
*/
static int
apause(struct lock *lkp, int flags)
{
#ifdef SMP
int i, lock_wait;
#endif
if ((lkp->lk_flags & flags) == 0)
return 0;
#ifdef SMP
for (lock_wait = LOCK_WAIT_TIME; lock_wait > 0; lock_wait--) {
mtx_unlock(lkp->lk_interlock);
for (i = LOCK_SAMPLE_WAIT; i > 0; i--)
if ((lkp->lk_flags & flags) == 0)
break;
mtx_lock(lkp->lk_interlock);
if ((lkp->lk_flags & flags) == 0)
return 0;
}
#endif
return 1;
}
static int
acquire(struct lock **lkpp, int extflags, int wanted) {
struct lock *lkp = *lkpp;
int s, 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;
}
if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) {
error = apause(lkp, wanted);
if (error == 0)
return 0;
}
s = splhigh();
while ((lkp->lk_flags & wanted) != 0) {
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));
if (lkp->lk_waitcount == 1) {
lkp->lk_flags &= ~LK_WAIT_NONZERO;
lkp->lk_waitcount = 0;
} else {
lkp->lk_waitcount--;
}
if (error) {
splx(s);
return error;
}
if (extflags & LK_SLEEPFAIL) {
splx(s);
return ENOLCK;
}
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;
}
}
splx(s);
return 0;
}
/*
* 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
#ifndef DEBUG_LOCKS
lockmgr(lkp, flags, interlkp, td)
#else
debuglockmgr(lkp, flags, interlkp, td, name, file, line)
#endif
struct lock *lkp;
u_int flags;
struct mtx *interlkp;
struct thread *td;
#ifdef DEBUG_LOCKS
const char *name; /* Name of lock function */
const char *file; /* Name of file call is from */
int line; /* Line number in file */
#endif
{
int error;
struct thread *thr;
int extflags, lockflags;
CTR5(KTR_LOCK,
"lockmgr(): lkp == %p (lk_wmesg == \"%s\"), flags == 0x%x, "
"interlkp == %p, td == %p", lkp, lkp->lk_wmesg, flags, interlkp, td);
error = 0;
if (td == NULL)
thr = LK_KERNPROC;
else
thr = td;
if ((flags & LK_INTERNAL) == 0)
mtx_lock(lkp->lk_interlock);
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->mtx_object,
"Acquiring lockmgr lock \"%s\"", lkp->lk_wmesg);
if (panicstr != NULL) {
mtx_unlock(lkp->lk_interlock);
return (0);
}
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);
if (error)
break;
sharelock(lkp, 1);
#if defined(DEBUG_LOCKS)
lkp->lk_slockholder = thr;
lkp->lk_sfilename = file;
lkp->lk_slineno = line;
lkp->lk_slockername = name;
#endif
break;
}
/*
* We hold an exclusive lock, so downgrade it to shared.
* An alternative would be to fail with EDEADLK.
*/
sharelock(lkp, 1);
/* 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(lkp, 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(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) || (lkp->lk_sharecount <= 0))
panic("lockmgr: upgrade exclusive lock");
shareunlock(lkp, 1);
/*
* 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);
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;
}
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;
#if defined(DEBUG_LOCKS)
lkp->lk_filename = file;
lkp->lk_lineno = line;
lkp->lk_lockername = name;
#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++;
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));
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);
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;
#if defined(DEBUG_LOCKS)
lkp->lk_filename = file;
lkp->lk_lineno = line;
lkp->lk_lockername = name;
#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_exclusivecount == 1) {
lkp->lk_flags &= ~LK_HAVE_EXCL;
lkp->lk_lockholder = LK_NOPROC;
lkp->lk_exclusivecount = 0;
} else {
lkp->lk_exclusivecount--;
}
} else if (lkp->lk_flags & LK_SHARE_NONZERO)
shareunlock(lkp, 1);
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;
#if defined(DEBUG_LOCKS)
lkp->lk_filename = file;
lkp->lk_lineno = line;
lkp->lk_lockername = name;
#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;
}
error = apause(lkp, LK_ALL);
if (error == 0)
return 0;
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"));
if (from->lk_waitcount == 0)
return;
from->lk_newlock = to;
wakeup((void *)from);
msleep(&from->lk_newlock, NULL, 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"));
}
/*
* 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_wmesg = wmesg;
lkp->lk_timo = timo;
lkp->lk_lockholder = LK_NOPROC;
lkp->lk_newlock = NULL;
#ifdef DEBUG_LOCKS
lkp->lk_filename = "none";
lkp->lk_lockername = "never exclusive locked";
lkp->lk_lineno = 0;
lkp->lk_slockholder = LK_NOPROC;
lkp->lk_sfilename = "none";
lkp->lk_slockername = "never share locked";
lkp->lk_slineno = 0;
#endif
}
/*
* Destroy a lock.
*/
void
lockdestroy(lkp)
struct lock *lkp;
{
CTR2(KTR_LOCK, "lockdestroy(): lkp == %p (lk_wmesg == \"%s\")",
lkp, lkp->lk_wmesg);
}
/*
* Determine the status of a lock.
*/
int
lockstatus(lkp, td)
struct lock *lkp;
struct thread *td;
{
int lock_type = 0;
mtx_lock(lkp->lk_interlock);
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;
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);
}
/*
* 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);
}