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diff --git a/kern/lock.c b/kern/lock.c
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+/*
+ * Mach Operating System
+ * Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University.
+ * Copyright (c) 1993,1994 The University of Utah and
+ * the Computer Systems Laboratory (CSL).
+ * All rights reserved.
+ *
+ * Permission to use, copy, modify and distribute this software and its
+ * documentation is hereby granted, provided that both the copyright
+ * notice and this permission notice appear in all copies of the
+ * software, derivative works or modified versions, and any portions
+ * thereof, and that both notices appear in supporting documentation.
+ *
+ * CARNEGIE MELLON, THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF
+ * THIS SOFTWARE IN ITS "AS IS" CONDITION, AND DISCLAIM ANY LIABILITY
+ * OF ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF
+ * THIS SOFTWARE.
+ *
+ * Carnegie Mellon requests users of this software to return to
+ *
+ *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
+ *  School of Computer Science
+ *  Carnegie Mellon University
+ *  Pittsburgh PA 15213-3890
+ *
+ * any improvements or extensions that they make and grant Carnegie Mellon
+ * the rights to redistribute these changes.
+ */
+/*
+ *	File:	kern/lock.c
+ *	Author:	Avadis Tevanian, Jr., Michael Wayne Young
+ *	Date:	1985
+ *
+ *	Locking primitives implementation
+ */
+
+#include <cpus.h>
+#include <mach_kdb.h>
+
+#include <kern/lock.h>
+#include <kern/thread.h>
+#include <kern/sched_prim.h>
+#if	MACH_KDB
+#include <machine/db_machdep.h>
+#include <ddb/db_sym.h>
+#endif
+
+
+#if	NCPUS > 1
+
+/*
+ *	Module:		lock
+ *	Function:
+ *		Provide reader/writer sychronization.
+ *	Implementation:
+ *		Simple interlock on a bit.  Readers first interlock,
+ *		increment the reader count, then let go.  Writers hold
+ *		the interlock (thus preventing further readers), and
+ *		wait for already-accepted readers to go away.
+ */
+
+/*
+ *	The simple-lock routines are the primitives out of which
+ *	the lock package is built.  The implementation is left
+ *	to the machine-dependent code.
+ */
+
+#ifdef	notdef
+/*
+ *	A sample implementation of simple locks.
+ *	assumes:
+ *		boolean_t test_and_set(boolean_t *)
+ *			indivisibly sets the boolean to TRUE
+ *			and returns its old value
+ *		and that setting a boolean to FALSE is indivisible.
+ */
+/*
+ *	simple_lock_init initializes a simple lock.  A simple lock
+ *	may only be used for exclusive locks.
+ */
+
+void simple_lock_init(simple_lock_t l)
+{
+	*(boolean_t *)l = FALSE;
+}
+
+void simple_lock(simple_lock_t l)
+{
+	while (test_and_set((boolean_t *)l))
+		continue;
+}
+
+void simple_unlock(simple_lock_t l)
+{
+	*(boolean_t *)l = FALSE;
+}
+
+boolean_t simple_lock_try(simple_lock_t l)
+{
+    	return (!test_and_set((boolean_t *)l));
+}
+#endif	/* notdef */
+#endif	/* NCPUS > 1 */
+
+#if	NCPUS > 1
+int lock_wait_time = 100;
+#else	/* NCPUS > 1 */
+
+	/*
+	 * 	It is silly to spin on a uni-processor as if we
+	 *	thought something magical would happen to the
+	 *	want_write bit while we are executing.
+	 */
+int lock_wait_time = 0;
+#endif	/* NCPUS > 1 */
+
+#if	MACH_SLOCKS && NCPUS == 1
+/*
+ *	This code does not protect simple_locks_taken and simple_locks_info.
+ *	It works despite the fact that interrupt code does use simple locks.
+ *	This is because interrupts use locks in a stack-like manner.
+ *	Each interrupt releases all the locks it acquires, so the data
+ *	structures end up in the same state after the interrupt as before.
+ *	The only precaution necessary is that simple_locks_taken be
+ *	incremented first and decremented last, so that interrupt handlers
+ *	don't over-write active slots in simple_locks_info.
+ */
+
+unsigned int simple_locks_taken = 0;
+
+#define	NSLINFO	1000		/* maximum number of locks held */
+
+struct simple_locks_info {
+	simple_lock_t l;
+	unsigned int ra;
+} simple_locks_info[NSLINFO];
+
+void check_simple_locks(void)
+{
+	assert(simple_locks_taken == 0);
+}
+
+/* Need simple lock sanity checking code if simple locks are being
+   compiled in, and we are compiling for a uniprocessor. */
+
+void simple_lock_init(
+	simple_lock_t l)
+{
+	l->lock_data = 0;
+}
+
+void simple_lock(
+	simple_lock_t l)
+{
+	struct simple_locks_info *info;
+
+	assert(l->lock_data == 0);
+
+	l->lock_data = 1;
+
+	info = &simple_locks_info[simple_locks_taken++];
+	info->l = l;
+	/* XXX we want our return address, if possible */
+#ifdef	i386
+	info->ra = *((unsigned int *)&l - 1);
+#endif	/* i386 */
+}
+
+boolean_t simple_lock_try(
+	simple_lock_t l)
+{
+	struct simple_locks_info *info;
+
+	if (l->lock_data != 0)
+		return FALSE;
+
+	l->lock_data = 1;
+
+	info = &simple_locks_info[simple_locks_taken++];
+	info->l = l;
+	/* XXX we want our return address, if possible */
+#ifdef	i386
+	info->ra = *((unsigned int *)&l - 1);
+#endif	/* i386 */
+
+	return TRUE;
+}
+
+void simple_unlock(
+	simple_lock_t l)
+{
+	assert(l->lock_data != 0);
+
+	l->lock_data = 0;
+
+	if (simple_locks_info[simple_locks_taken-1].l != l) {
+		unsigned int i = simple_locks_taken;
+
+		/* out-of-order unlocking */
+
+		do
+			if (i == 0)
+				panic("simple_unlock");
+		while (simple_locks_info[--i].l != l);
+
+		simple_locks_info[i] = simple_locks_info[simple_locks_taken-1];
+	}
+	simple_locks_taken--;
+}
+
+#endif	/* MACH_SLOCKS && NCPUS == 1 */
+
+/*
+ *	Routine:	lock_init
+ *	Function:
+ *		Initialize a lock; required before use.
+ *		Note that clients declare the "struct lock"
+ *		variables and then initialize them, rather
+ *		than getting a new one from this module.
+ */
+void lock_init(
+	lock_t		l,
+	boolean_t	can_sleep)
+{
+	bzero((char *)l, sizeof(lock_data_t));
+	simple_lock_init(&l->interlock);
+	l->want_write = FALSE;
+	l->want_upgrade = FALSE;
+	l->read_count = 0;
+	l->can_sleep = can_sleep;
+	l->thread = (struct thread *)-1;	/* XXX */
+	l->recursion_depth = 0;
+}
+
+void lock_sleepable(
+	lock_t		l,
+	boolean_t	can_sleep)
+{
+	simple_lock(&l->interlock);
+	l->can_sleep = can_sleep;
+	simple_unlock(&l->interlock);
+}
+
+
+/*
+ *	Sleep locks.  These use the same data structure and algorithm
+ *	as the spin locks, but the process sleeps while it is waiting
+ *	for the lock.  These work on uniprocessor systems.
+ */
+
+void lock_write(
+	register lock_t	l)
+{
+	register int	i;
+
+	check_simple_locks();
+	simple_lock(&l->interlock);
+
+	if (l->thread == current_thread()) {
+		/*
+		 *	Recursive lock.
+		 */
+		l->recursion_depth++;
+		simple_unlock(&l->interlock);
+		return;
+	}
+
+	/*
+	 *	Try to acquire the want_write bit.
+	 */
+	while (l->want_write) {
+		if ((i = lock_wait_time) > 0) {
+			simple_unlock(&l->interlock);
+			while (--i > 0 && l->want_write)
+				continue;
+			simple_lock(&l->interlock);
+		}
+
+		if (l->can_sleep && l->want_write) {
+			l->waiting = TRUE;
+			thread_sleep(l,
+				simple_lock_addr(l->interlock), FALSE);
+			simple_lock(&l->interlock);
+		}
+	}
+	l->want_write = TRUE;
+
+	/* Wait for readers (and upgrades) to finish */
+
+	while ((l->read_count != 0) || l->want_upgrade) {
+		if ((i = lock_wait_time) > 0) {
+			simple_unlock(&l->interlock);
+			while (--i > 0 && (l->read_count != 0 ||
+					l->want_upgrade))
+				continue;
+			simple_lock(&l->interlock);
+		}
+
+		if (l->can_sleep && (l->read_count != 0 || l->want_upgrade)) {
+			l->waiting = TRUE;
+			thread_sleep(l,
+				simple_lock_addr(l->interlock), FALSE);
+			simple_lock(&l->interlock);
+		}
+	}
+	simple_unlock(&l->interlock);
+}
+
+void lock_done(
+	register lock_t	l)
+{
+	simple_lock(&l->interlock);
+
+	if (l->read_count != 0)
+		l->read_count--;
+	else
+	if (l->recursion_depth != 0)
+		l->recursion_depth--;
+	else
+	if (l->want_upgrade)
+	 	l->want_upgrade = FALSE;
+	else
+	 	l->want_write = FALSE;
+
+	/*
+	 *	There is no reason to wakeup a waiting thread
+	 *	if the read-count is non-zero.  Consider:
+	 *		we must be dropping a read lock
+	 *		threads are waiting only if one wants a write lock
+	 *		if there are still readers, they can't proceed
+	 */
+
+	if (l->waiting && (l->read_count == 0)) {
+		l->waiting = FALSE;
+		thread_wakeup(l);
+	}
+
+	simple_unlock(&l->interlock);
+}
+
+void lock_read(
+	register lock_t	l)
+{
+	register int	i;
+
+	check_simple_locks();
+	simple_lock(&l->interlock);
+
+	if (l->thread == current_thread()) {
+		/*
+		 *	Recursive lock.
+		 */
+		l->read_count++;
+		simple_unlock(&l->interlock);
+		return;
+	}
+
+	while (l->want_write || l->want_upgrade) {
+		if ((i = lock_wait_time) > 0) {
+			simple_unlock(&l->interlock);
+			while (--i > 0 && (l->want_write || l->want_upgrade))
+				continue;
+			simple_lock(&l->interlock);
+		}
+
+		if (l->can_sleep && (l->want_write || l->want_upgrade)) {
+			l->waiting = TRUE;
+			thread_sleep(l,
+				simple_lock_addr(l->interlock), FALSE);
+			simple_lock(&l->interlock);
+		}
+	}
+
+	l->read_count++;
+	simple_unlock(&l->interlock);
+}
+
+/*
+ *	Routine:	lock_read_to_write
+ *	Function:
+ *		Improves a read-only lock to one with
+ *		write permission.  If another reader has
+ *		already requested an upgrade to a write lock,
+ *		no lock is held upon return.
+ *
+ *		Returns TRUE if the upgrade *failed*.
+ */
+boolean_t lock_read_to_write(
+	register lock_t	l)
+{
+	register int	i;
+
+	check_simple_locks();
+	simple_lock(&l->interlock);
+
+	l->read_count--;
+
+	if (l->thread == current_thread()) {
+		/*
+		 *	Recursive lock.
+		 */
+		l->recursion_depth++;
+		simple_unlock(&l->interlock);
+		return(FALSE);
+	}
+
+	if (l->want_upgrade) {
+		/*
+		 *	Someone else has requested upgrade.
+		 *	Since we've released a read lock, wake
+		 *	him up.
+		 */
+		if (l->waiting && (l->read_count == 0)) {
+			l->waiting = FALSE;
+			thread_wakeup(l);
+		}
+
+		simple_unlock(&l->interlock);
+		return TRUE;
+	}
+
+	l->want_upgrade = TRUE;
+
+	while (l->read_count != 0) {
+		if ((i = lock_wait_time) > 0) {
+			simple_unlock(&l->interlock);
+			while (--i > 0 && l->read_count != 0)
+				continue;
+			simple_lock(&l->interlock);
+		}
+
+		if (l->can_sleep && l->read_count != 0) {
+			l->waiting = TRUE;
+			thread_sleep(l,
+				simple_lock_addr(l->interlock), FALSE);
+			simple_lock(&l->interlock);
+		}
+	}
+
+	simple_unlock(&l->interlock);
+	return FALSE;
+}
+
+void lock_write_to_read(
+	register lock_t	l)
+{
+	simple_lock(&l->interlock);
+
+	l->read_count++;
+	if (l->recursion_depth != 0)
+		l->recursion_depth--;
+	else
+	if (l->want_upgrade)
+		l->want_upgrade = FALSE;
+	else
+	 	l->want_write = FALSE;
+
+	if (l->waiting) {
+		l->waiting = FALSE;
+		thread_wakeup(l);
+	}
+
+	simple_unlock(&l->interlock);
+}
+
+
+/*
+ *	Routine:	lock_try_write
+ *	Function:
+ *		Tries to get a write lock.
+ *
+ *		Returns FALSE if the lock is not held on return.
+ */
+
+boolean_t lock_try_write(
+	register lock_t	l)
+{
+	simple_lock(&l->interlock);
+
+	if (l->thread == current_thread()) {
+		/*
+		 *	Recursive lock
+		 */
+		l->recursion_depth++;
+		simple_unlock(&l->interlock);
+		return TRUE;
+	}
+
+	if (l->want_write || l->want_upgrade || l->read_count) {
+		/*
+		 *	Can't get lock.
+		 */
+		simple_unlock(&l->interlock);
+		return FALSE;
+	}
+
+	/*
+	 *	Have lock.
+	 */
+
+	l->want_write = TRUE;
+	simple_unlock(&l->interlock);
+	return TRUE;
+}
+
+/*
+ *	Routine:	lock_try_read
+ *	Function:
+ *		Tries to get a read lock.
+ *
+ *		Returns FALSE if the lock is not held on return.
+ */
+
+boolean_t lock_try_read(
+	register lock_t	l)
+{
+	simple_lock(&l->interlock);
+
+	if (l->thread == current_thread()) {
+		/*
+		 *	Recursive lock
+		 */
+		l->read_count++;
+		simple_unlock(&l->interlock);
+		return TRUE;
+	}
+
+	if (l->want_write || l->want_upgrade) {
+		simple_unlock(&l->interlock);
+		return FALSE;
+	}
+
+	l->read_count++;
+	simple_unlock(&l->interlock);
+	return TRUE;
+}
+
+/*
+ *	Routine:	lock_try_read_to_write
+ *	Function:
+ *		Improves a read-only lock to one with
+ *		write permission.  If another reader has
+ *		already requested an upgrade to a write lock,
+ *		the read lock is still held upon return.
+ *
+ *		Returns FALSE if the upgrade *failed*.
+ */
+boolean_t lock_try_read_to_write(
+	register lock_t	l)
+{
+	check_simple_locks();
+	simple_lock(&l->interlock);
+
+	if (l->thread == current_thread()) {
+		/*
+		 *	Recursive lock
+		 */
+		l->read_count--;
+		l->recursion_depth++;
+		simple_unlock(&l->interlock);
+		return TRUE;
+	}
+
+	if (l->want_upgrade) {
+		simple_unlock(&l->interlock);
+		return FALSE;
+	}
+	l->want_upgrade = TRUE;
+	l->read_count--;
+
+	while (l->read_count != 0) {
+		l->waiting = TRUE;
+		thread_sleep(l,
+			simple_lock_addr(l->interlock), FALSE);
+		simple_lock(&l->interlock);
+	}
+
+	simple_unlock(&l->interlock);
+	return TRUE;
+}
+
+/*
+ *	Allow a process that has a lock for write to acquire it
+ *	recursively (for read, write, or update).
+ */
+void lock_set_recursive(
+	lock_t		l)
+{
+	simple_lock(&l->interlock);
+	if (!l->want_write) {
+		panic("lock_set_recursive: don't have write lock");
+	}
+	l->thread = current_thread();
+	simple_unlock(&l->interlock);
+}
+
+/*
+ *	Prevent a lock from being re-acquired.
+ */
+void lock_clear_recursive(
+	lock_t		l)
+{
+	simple_lock(&l->interlock);
+	if (l->thread != current_thread()) {
+		panic("lock_clear_recursive: wrong thread");
+	}
+	if (l->recursion_depth == 0)
+		l->thread = (struct thread *)-1;	/* XXX */
+	simple_unlock(&l->interlock);
+}
+
+#if	MACH_KDB
+#if	MACH_SLOCKS && NCPUS == 1
+void db_show_all_slocks(void)
+{
+	int i;
+	struct simple_locks_info *info;
+	simple_lock_t l;
+
+	for (i = 0; i < simple_locks_taken; i++) {
+		info = &simple_locks_info[i];
+		db_printf("%d: ", i);
+		db_printsym(info->l, DB_STGY_ANY);
+#if i386
+		db_printf(" locked by ");
+		db_printsym(info->ra, DB_STGY_PROC);
+#endif
+		db_printf("\n");
+	}
+}
+#else	/* MACH_SLOCKS && NCPUS == 1 */
+void db_show_all_slocks(void)
+{
+	db_printf("simple lock info not available\n");
+}
+#endif	/* MACH_SLOCKS && NCPUS == 1 */
+#endif	/* MACH_KDB */