projects / unix-history / blob
? search:
summary | tags | clone url | shortlog | log | commit | commitdiff | tree
blame | history | raw | HEAD
atomic_lock => simple_lock
[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 8.7 (Berkeley) %G%
*/
#include <sys/param.h>
#include <sys/proc.h>
#include <sys/lock.h>
/*
* Locking primitives implementation.
* Locks provide shared/exclusive sychronization.
*/
#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)
/*
* Panic messages for inline expanded simple locks.
* Put text here to avoid hundreds of copies.
*/
const char *simple_lock_held = "simple_lock: lock held";
const char *simple_lock_not_held = "simple_lock: lock not held";
#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
lock_init(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, p)
volatile struct lock *lkp;
u_int flags;
struct proc *p;
{
int error;
pid_t pid;
volatile int extflags;
error = 0;
pid = p->p_pid;
simple_lock(&lkp->lk_interlock);
extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
if (lkp->lk_flags & LK_DRAINED)
panic("lockmgr: using decommissioned lock");
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++;
break;
}
/*
* We hold an exclusive lock, so downgrade it to shared.
* An alternative would be to fail with EDEADLK.
*/
lkp->lk_sharecount++;
/* 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--;
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--;
/*
* 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;
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) {
/*
* Recursive lock.
*/
if ((extflags & LK_CANRECURSE) == 0)
panic("lockmgr: locking against myself");
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)) ||
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;
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--;
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--;
if (lkp->lk_waitcount)
wakeup((void *)lkp);
break;
case LK_DRAIN:
/*
* 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_DRAINED;
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);
}
Continuous source code history from original PDP-7 UNIX to FreeBSD 2, the first fully unencumbered FreeBSD release.