Fix kern_lock so that it will work. Additionally, clean-up some of the

VM systems usage of the kernel lock (lockmgr) code.  This is a first
pass implementation, and is expected to evolve as needed.  The API
for the lock manager code has not changed, but the underlying implementation
has changed significantly.  This change should not materially affect
our current SMP or UP code without non-standard parameters being used.

1 files changed, 144 insertions, 132 deletions

diff --git a/sys/kern/kern_lock.c b/sys/kern/kern_lock.c
index 9fbbb74..32c30c5 100644
--- a/sys/kern/kern_lock.c
+++ b/sys/kern/kern_lock.c
@@ -2,6 +2,9 @@
  * 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.
@@ -35,7 +38,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)kern_lock.c	8.18 (Berkeley) 5/21/95
- * $Id: kern_lock.c,v 1.1 1997/08/04 17:46:51 smp Exp smp $
+ * $Id: kern_lock.c,v 1.7 1997/08/04 19:11:12 fsmp Exp $
  */
 
 #include <sys/param.h>
@@ -54,58 +57,123 @@
 #define COUNT(p, x)
 #endif
 
-#if NCPUS > 1
+#define LOCK_WAIT_TIME 100
+#define LOCK_SAMPLE_WAIT 7
 
-/*
- * 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;
+#if defined(DIAGNOSTIC)
+#define LOCK_INLINE
+#else
+#define LOCK_INLINE inline
+#endif
 
-#else /* NCPUS == 1 */
+static int acquire(struct lock *lkp, int extflags, int wanted);
 
-/*
- * 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)
+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) {
+#if defined(DIAGNOSTIC)
+	if (lkp->lk_sharecount < decr)
+#if defined(DDB)
+		Debugger("shareunlock: count < decr");
+#else
+		panic("shareunlock: count < decr");
+#endif
+#endif
 
-#endif /* NCPUS == 1 */
+	lkp->lk_sharecount -= decr;
+	if (lkp->lk_sharecount == 0)
+		lkp->lk_flags &= ~LK_SHARE_NONZERO;
+}
 
-/*
- * 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;						\
-		}							\
+static int
+apause(struct lock *lkp, int flags) {
+	int lock_wait;
+	lock_wait = LOCK_WAIT_TIME;
+	for (; lock_wait > 0; lock_wait--) {
+		int i;
+		if ((lkp->lk_flags & flags) == 0)
+			return 0;
+		simple_unlock(&lkp->lk_interlock);
+		for (i = LOCK_SAMPLE_WAIT; i > 0; i--) {
+			if ((lkp->lk_flags & flags) == 0) {
+				simple_lock(&lkp->lk_interlock);
+				if ((lkp->lk_flags & flags) == 0)
+					return 0;
+				break;
+			}
+		}
+	}
+	return 1;
+}
+
+
+static int
+acquire(struct lock *lkp, int extflags, int wanted) {
+	int error;
+	int lock_wait;
+
+	if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
+		return EBUSY;
 	}
 
+	error = apause(lkp, wanted);
+	if (error == 0)
+		return 0;
+
+	while ((lkp->lk_flags & wanted) != 0) {
+		lkp->lk_flags |= LK_WAIT_NONZERO;
+		lkp->lk_waitcount++;
+		simple_unlock(&lkp->lk_interlock);
+		error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg, lkp->lk_timo);
+		simple_lock(&lkp->lk_interlock);
+		lkp->lk_waitcount--;
+		if (lkp->lk_waitcount == 0)
+			lkp->lk_flags &= ~LK_WAIT_NONZERO;
+		if (error)
+			return error;
+		if (extflags & LK_SLEEPFAIL) {
+			return ENOLCK;
+		}
+	}
+	return 0;
+}
+
+#define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
+	LK_SHARE_NONZERO | LK_WAIT_NONZERO)
+
+static int
+acquiredrain(struct lock *lkp, int extflags) {
+	int error;
+	int lock_wait;
+
+	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;
+		simple_unlock(&lkp->lk_interlock);
+		error = tsleep(&lkp->lk_flags, lkp->lk_prio,
+			lkp->lk_wmesg, lkp->lk_timo);
+		simple_lock(&lkp->lk_interlock);
+		if (error)
+			return error;
+		if (extflags & LK_SLEEPFAIL) {
+			return ENOLCK;
+		}
+	}
+	return 0;
+}
+
 /*
  * Initialize a lock; required before use.
  */
@@ -119,7 +187,7 @@ lockinit(lkp, prio, wmesg, timo, flags)
 {
 
 	simple_lock_init(&lkp->lk_interlock);
-	lkp->lk_flags = flags & LK_EXTFLG_MASK;
+	lkp->lk_flags = (flags & LK_EXTFLG_MASK);
 	lkp->lk_sharecount = 0;
 	lkp->lk_waitcount = 0;
 	lkp->lk_exclusivecount = 0;
@@ -166,59 +234,25 @@ lockmgr(lkp, flags, interlkp, p)
 	int extflags;
 
 	error = 0;
-	if (p)
-		pid = p->p_pid;
-	else
-		pid = LK_KERNPROC;
+	if (p == NULL)
+		panic("lockmgr: called with null process");
+	pid = p->p_pid;
+
 	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).
-	 * The final release is permitted to give a new lease on life to
-	 * the lock by specifying LK_REENABLE.
-	 */
-	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;
-		if ((flags & LK_REENABLE) == 0)
-			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));
+			error = acquire(lkp, extflags,
+				LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE);
 			if (error)
 				break;
-			lkp->lk_sharecount++;
+			sharelock(lkp, 1);
 			COUNT(p, 1);
 			break;
 		}
@@ -226,14 +260,14 @@ lockmgr(lkp, flags, interlkp, p)
 		 * We hold an exclusive lock, so downgrade it to shared.
 		 * An alternative would be to fail with EDEADLK.
 		 */
-		lkp->lk_sharecount++;
+		sharelock(lkp, 1);
 		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;
+		sharelock(lkp, lkp->lk_exclusivecount);
 		lkp->lk_exclusivecount = 0;
 		lkp->lk_flags &= ~LK_HAVE_EXCL;
 		lkp->lk_lockholder = LK_NOPROC;
@@ -248,7 +282,7 @@ lockmgr(lkp, flags, interlkp, p)
 		 * exclusive access.
 		 */
 		if (lkp->lk_flags & LK_WANT_UPGRADE) {
-			lkp->lk_sharecount--;
+			shareunlock(lkp, 1);
 			COUNT(p, -1);
 			error = EBUSY;
 			break;
@@ -264,9 +298,9 @@ lockmgr(lkp, flags, interlkp, p)
 		 * after the upgrade). If we return an error, the file
 		 * will always be unlocked.
 		 */
-		if (lkp->lk_lockholder == pid || lkp->lk_sharecount <= 0)
+		if ((lkp->lk_lockholder == pid) || (lkp->lk_sharecount <= 0))
 			panic("lockmgr: upgrade exclusive lock");
-		lkp->lk_sharecount--;
+		shareunlock(lkp, 1);
 		COUNT(p, -1);
 		/*
 		 * If we are just polling, check to see if we will block.
@@ -284,7 +318,7 @@ lockmgr(lkp, flags, interlkp, p)
 			 * drop to zero, then take exclusive lock.
 			 */
 			lkp->lk_flags |= LK_WANT_UPGRADE;
-			ACQUIRE(lkp, error, extflags, lkp->lk_sharecount);
+			error = acquire(lkp, extflags , LK_SHARE_NONZERO);
 			lkp->lk_flags &= ~LK_WANT_UPGRADE;
 			if (error)
 				break;
@@ -301,7 +335,8 @@ lockmgr(lkp, flags, interlkp, p)
 		 * lock, awaken upgrade requestor if we are the last shared
 		 * lock, then request an exclusive lock.
 		 */
-		if (lkp->lk_sharecount == 0 && lkp->lk_waitcount)
+		if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
+			LK_WAIT_NONZERO)
 			wakeup((void *)lkp);
 		/* fall into exclusive request */
 
@@ -319,25 +354,22 @@ lockmgr(lkp, flags, interlkp, p)
 		/*
 		 * 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)) {
+		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.
 		 */
-		ACQUIRE(lkp, error, extflags, lkp->lk_flags &
-		    (LK_HAVE_EXCL | LK_WANT_EXCL));
+		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.
 		 */
-		ACQUIRE(lkp, error, extflags, lkp->lk_sharecount != 0 ||
-		       (lkp->lk_flags & LK_WANT_UPGRADE));
+		error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO);
 		lkp->lk_flags &= ~LK_WANT_EXCL;
 		if (error)
 			break;
@@ -361,11 +393,11 @@ lockmgr(lkp, flags, interlkp, p)
 				lkp->lk_flags &= ~LK_HAVE_EXCL;
 				lkp->lk_lockholder = LK_NOPROC;
 			}
-		} else if (lkp->lk_sharecount != 0) {
-			lkp->lk_sharecount--;
+		} else if (lkp->lk_flags & LK_SHARE_NONZERO) {
+			shareunlock(lkp, 1);
 			COUNT(p, -1);
 		}
-		if (lkp->lk_waitcount)
+		if (lkp->lk_flags & LK_WAIT_NONZERO)
 			wakeup((void *)lkp);
 		break;
 
@@ -378,30 +410,10 @@ lockmgr(lkp, flags, interlkp, p)
 		 */
 		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;
+
+		error = acquiredrain(lkp, extflags);
+		if (error)
 			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;
@@ -414,9 +426,9 @@ lockmgr(lkp, flags, interlkp, p)
 		    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)) {
+	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);
 	}