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track number of simple locks
[unix-history] / usr / src / sys / kern / kern_lock.c
/*
* Copyright (c) 1995
* The Regents of the University of California. 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.
*
* %sccs.include.redist.c%
*
* @(#)kern_lock.c 8.14 (Berkeley) %G%
*/
#include <sys/param.h>
#include <sys/proc.h>
#include <sys/lock.h>
#include <machine/cpu.h>
/*
* Locking primitives implementation.
* Locks provide shared/exclusive sychronization.
*/
#ifdef DEBUG
#define COUNT(p, x) if (p) (p)->p_locks += (x)
#else
#define COUNT(p, x)
#endif
#if NCPUS > 1
/*
* For multiprocessor system, try spin lock first.
*
* This should be inline expanded below, but we cannot have #if
* inside a multiline define.
*/
int lock_wait_time = 100;
#define PAUSE(lkp, wanted) \
if (lock_wait_time > 0) { \
int i; \
\
simple_unlock(&lkp->lk_interlock); \
for (i = lock_wait_time; i > 0; i--) \
if (!(wanted)) \
break; \
simple_lock(&lkp->lk_interlock); \
} \
if (!(wanted)) \
break;
#else /* NCPUS == 1 */
/*
* It is an error to spin on a uniprocessor as nothing will ever cause
* the simple lock to clear while we are executing.
*/
#define PAUSE(lkp, wanted)
#endif /* NCPUS == 1 */
/*
* Acquire a resource.
*/
#define ACQUIRE(lkp, error, extflags, wanted) \
PAUSE(lkp, wanted); \
for (error = 0; wanted; ) { \
(lkp)->lk_waitcount++; \
simple_unlock(&(lkp)->lk_interlock); \
error = tsleep((void *)lkp, (lkp)->lk_prio, \
(lkp)->lk_wmesg, (lkp)->lk_timo); \
simple_lock(&(lkp)->lk_interlock); \
(lkp)->lk_waitcount--; \
if (error) \
break; \
if ((extflags) & LK_SLEEPFAIL) { \
error = ENOLCK; \
break; \
} \
}
/*
* Initialize a lock; required before use.
*/
void
lockinit(lkp, prio, wmesg, timo, flags)
struct lock *lkp;
int prio;
char *wmesg;
int timo;
int flags;
{
bzero(lkp, sizeof(struct lock));
simple_lock_init(&lkp->lk_interlock);
lkp->lk_flags = flags & LK_EXTFLG_MASK;
lkp->lk_prio = prio;
lkp->lk_timo = timo;
lkp->lk_wmesg = wmesg;
lkp->lk_lockholder = LK_NOPROC;
}
/*
* Determine the status of a lock.
*/
int
lockstatus(lkp)
struct lock *lkp;
{
int lock_type = 0;
simple_lock(&lkp->lk_interlock);
if (lkp->lk_exclusivecount != 0)
lock_type = LK_EXCLUSIVE;
else if (lkp->lk_sharecount != 0)
lock_type = LK_SHARED;
simple_unlock(&lkp->lk_interlock);
return (lock_type);
}
/*
* 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(lkp, flags, interlkp, p)
__volatile struct lock *lkp;
u_int flags;
struct simplelock *interlkp;
struct proc *p;
{
int error;
pid_t pid;
int extflags;
error = 0;
if (p)
pid = p->p_pid;
else
pid = LK_KERNPROC;
simple_lock(&lkp->lk_interlock);
if (flags & LK_INTERLOCK)
simple_unlock(interlkp);
extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
#ifdef DIAGNOSTIC
/*
* Once a lock has drained, the LK_DRAINING flag is set and an
* exclusive lock is returned. The only valid operation thereafter
* is a single release of that exclusive lock. This final release
* clears the LK_DRAINING flag and sets the LK_DRAINED flag. Any
* further requests of any sort will result in a panic. The bits
* selected for these two flags are chosen so that they will be set
* in memory that is freed (freed memory is filled with 0xdeadbeef).
*/
if (lkp->lk_flags & (LK_DRAINING|LK_DRAINED)) {
if (lkp->lk_flags & LK_DRAINED)
panic("lockmgr: using decommissioned lock");
if ((flags & LK_TYPE_MASK) != LK_RELEASE ||
lkp->lk_lockholder != pid)
panic("lockmgr: non-release on draining lock: %d\n",
flags & LK_TYPE_MASK);
lkp->lk_flags &= ~LK_DRAINING;
lkp->lk_flags |= LK_DRAINED;
}
#endif DIAGNOSTIC
switch (flags & LK_TYPE_MASK) {
case LK_SHARED:
if (lkp->lk_lockholder != pid) {
/*
* If just polling, check to see if we will block.
*/
if ((extflags & LK_NOWAIT) && (lkp->lk_flags &
(LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE))) {
error = EBUSY;
break;
}
/*
* Wait for exclusive locks and upgrades to clear.
*/
ACQUIRE(lkp, error, extflags, lkp->lk_flags &
(LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE));
if (error)
break;
lkp->lk_sharecount++;
COUNT(p, 1);
break;
}
/*
* We hold an exclusive lock, so downgrade it to shared.
* An alternative would be to fail with EDEADLK.
*/
lkp->lk_sharecount++;
COUNT(p, 1);
/* fall into downgrade */
case LK_DOWNGRADE:
if (lkp->lk_lockholder != pid || lkp->lk_exclusivecount == 0)
panic("lockmgr: not holding exclusive lock");
lkp->lk_sharecount += 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) {
lkp->lk_sharecount--;
COUNT(p, -1);
error = EBUSY;
break;
}
/* fall into 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 == pid || lkp->lk_sharecount <= 0)
panic("lockmgr: upgrade exclusive lock");
lkp->lk_sharecount--;
COUNT(p, -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;
ACQUIRE(lkp, error, extflags, lkp->lk_sharecount);
lkp->lk_flags &= ~LK_WANT_UPGRADE;
if (error)
break;
lkp->lk_flags |= LK_HAVE_EXCL;
lkp->lk_lockholder = pid;
if (lkp->lk_exclusivecount != 0)
panic("lockmgr: non-zero exclusive count");
lkp->lk_exclusivecount = 1;
COUNT(p, 1);
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_sharecount == 0 && lkp->lk_waitcount)
wakeup((void *)lkp);
/* fall into exclusive request */
case LK_EXCLUSIVE:
if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) {
/*
* Recursive lock.
*/
if ((extflags & LK_CANRECURSE) == 0)
panic("lockmgr: locking against myself");
lkp->lk_exclusivecount++;
COUNT(p, 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)) ||
lkp->lk_sharecount != 0)) {
error = EBUSY;
break;
}
/*
* Try to acquire the want_exclusive flag.
*/
ACQUIRE(lkp, error, extflags, lkp->lk_flags &
(LK_HAVE_EXCL | LK_WANT_EXCL));
if (error)
break;
lkp->lk_flags |= LK_WANT_EXCL;
/*
* Wait for shared locks and upgrades to finish.
*/
ACQUIRE(lkp, error, extflags, lkp->lk_sharecount != 0 ||
(lkp->lk_flags & LK_WANT_UPGRADE));
lkp->lk_flags &= ~LK_WANT_EXCL;
if (error)
break;
lkp->lk_flags |= LK_HAVE_EXCL;
lkp->lk_lockholder = pid;
if (lkp->lk_exclusivecount != 0)
panic("lockmgr: non-zero exclusive count");
lkp->lk_exclusivecount = 1;
COUNT(p, 1);
break;
case LK_RELEASE:
if (lkp->lk_exclusivecount != 0) {
if (pid != lkp->lk_lockholder)
panic("lockmgr: pid %d, not %s %d unlocking",
pid, "exclusive lock holder",
lkp->lk_lockholder);
lkp->lk_exclusivecount--;
COUNT(p, -1);
if (lkp->lk_exclusivecount == 0) {
lkp->lk_flags &= ~LK_HAVE_EXCL;
lkp->lk_lockholder = LK_NOPROC;
}
} else if (lkp->lk_sharecount != 0) {
lkp->lk_sharecount--;
COUNT(p, -1);
}
if (lkp->lk_waitcount)
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 == pid)
panic("lockmgr: draining against myself");
/*
* 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)) ||
lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0)) {
error = EBUSY;
break;
}
PAUSE(lkp, ((lkp->lk_flags &
(LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) ||
lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0));
for (error = 0; ((lkp->lk_flags &
(LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) ||
lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0); ) {
lkp->lk_flags |= LK_WAITDRAIN;
simple_unlock(&lkp->lk_interlock);
if (error = tsleep((void *)&lkp->lk_flags, lkp->lk_prio,
lkp->lk_wmesg, lkp->lk_timo))
return (error);
if ((extflags) & LK_SLEEPFAIL)
return (ENOLCK);
simple_lock(&lkp->lk_interlock);
}
lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
lkp->lk_lockholder = pid;
lkp->lk_exclusivecount = 1;
COUNT(p, 1);
break;
default:
simple_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)) == 0 &&
lkp->lk_sharecount == 0 && lkp->lk_waitcount == 0)) {
lkp->lk_flags &= ~LK_WAITDRAIN;
wakeup((void *)&lkp->lk_flags);
}
simple_unlock(&lkp->lk_interlock);
return (error);
}
/*
* Print out information about state of a lock. Used by VOP_PRINT
* routines to display ststus about contained locks.
*/
lockmgr_printinfo(lkp)
struct lock *lkp;
{
if (lkp->lk_sharecount)
printf(" lock type %s: SHARED", lkp->lk_wmesg);
else if (lkp->lk_flags & LK_HAVE_EXCL)
printf(" lock type %s: EXCL by pid %d", lkp->lk_wmesg,
lkp->lk_lockholder);
if (lkp->lk_waitcount > 0)
printf(" with %d pending", lkp->lk_waitcount);
}
#if defined(DEBUG) && NCPUS == 1
#include <sys/kernel.h>
#include <vm/vm.h>
#include <sys/sysctl.h>
int lockpausetime = 1;
struct ctldebug debug2 = { "lockpausetime", &lockpausetime };
/*
* Simple lock functions so that the debugger can see from whence
* they are being called.
*/
void
simple_lock_init(alp)
struct simplelock *alp;
{
alp->lock_data = 0;
}
void
_simple_lock(alp, id, l)
__volatile struct simplelock *alp;
const char *id;
int l;
{
if (alp->lock_data == 1) {
if (lockpausetime == -1)
panic("%s:%d: simple_lock: lock held", id, l);
if (lockpausetime == 0) {
printf("%s:%d: simple_lock: lock held\n", id, l);
BACKTRACE(curproc);
} else if (lockpausetime > 0) {
printf("%s:%d: simple_lock: lock held...", id, l);
tsleep(&lockpausetime, PCATCH | PPAUSE, "slock",
lockpausetime * hz);
printf(" continuing\n");
}
}
alp->lock_data = 1;
if (curproc)
curproc->p_simple_locks++;
}
int
_simple_lock_try(alp, id, l)
__volatile struct simplelock *alp;
const char *id;
int l;
{
/*
if (alp->lock_data == 1) {
if (lockpausetime == -1)
panic("%s:%d: simple_lock_try: lock held", id, l);
if (lockpausetime == 0) {
printf("%s:%d: simple_lock_try: lock held\n", id, l);
BACKTRACE(curproc);
} else if (lockpausetime > 0) {
printf("%s:%d: simple_lock_try: lock held...", id, l);
tsleep(&lockpausetime, PCATCH | PPAUSE, "slock",
lockpausetime * hz);
printf(" continuing\n");
}
}
*/
if (alp->lock_data)
return (0);
alp->lock_data = 1;
if (curproc)
curproc->p_simple_locks++;
return (1);
}
void
_simple_unlock(alp, id, l)
__volatile struct simplelock *alp;
const char *id;
int l;
{
if (alp->lock_data == 0) {
if (lockpausetime == -1)
panic("%s:%d: simple_unlock: lock not held", id, l);
if (lockpausetime == 0) {
printf("%s:%d: simple_unlock: lock not held\n", id, l);
BACKTRACE(curproc);
} else if (lockpausetime > 0) {
printf("%s:%d: simple_unlock: lock not held...", id, l);
tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock",
lockpausetime * hz);
printf(" continuing\n");
}
}
alp->lock_data = 0;
if (curproc)
curproc->p_simple_locks--;
}
#endif /* DEBUG && NCPUS == 1 */
Continuous source code history from original PDP-7 UNIX to FreeBSD 2, the first fully unencumbered FreeBSD release.