From a7039a1d4287a42fb7c72d2a2a68c8fa86baae32 Mon Sep 17 00:00:00 2001
From: Matthew Dillon <dillon@FreeBSD.org>
Date: Sun, 24 Jan 1999 01:05:15 +0000
Subject: [PATCH]     Add invariants to vm_page_busy() and vm_page_wakeup() to
 check for     PG_BUSY stupidity.

---
 sys/vm/vm_page.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/sys/vm/vm_page.h b/sys/vm/vm_page.h
index 685c53b66d6d..c74af825a7e8 100644
--- a/sys/vm/vm_page.h
+++ b/sys/vm/vm_page.h
@@ -61,7 +61,7 @@
  * any improvements or extensions that they make and grant Carnegie the
  * rights to redistribute these changes.
  *
- * $Id: vm_page.h,v 1.50 1999/01/21 08:29:12 dillon Exp $
+ * $Id: vm_page.h,v 1.51 1999/01/21 10:06:24 dillon Exp $
  */
 
 /*
@@ -312,6 +312,7 @@ vm_page_assert_wait(vm_page_t m, int interruptible)
 static __inline void
 vm_page_busy(vm_page_t m)
 {
+	KASSERT((m->flags & PG_BUSY) == 0, ("vm_page_busy: page already busy!!!"));
 	vm_page_flag_set(m, PG_BUSY);
 }
 
@@ -341,6 +342,7 @@ vm_page_flash(vm_page_t m)
 static __inline void
 vm_page_wakeup(vm_page_t m)
 {
+	KASSERT(m->flags & PG_BUSY, ("vm_page_wakeup: page not busy!!!"));
 	vm_page_flag_clear(m, PG_BUSY);
 	vm_page_flash(m);
 }
@@ -426,6 +428,15 @@ vm_page_unhold(vm_page_t mem)
 	KASSERT(mem->hold_count >= 0, ("vm_page_unhold: hold count < 0!!!"));
 }
 
+/*
+ * 	vm_page_protect:
+ *
+ *	Reduce the protection of a page.  This routine never
+ *	raises the protection and therefore can be safely
+ *	called if the page is already at VM_PROT_NONE ( it
+ *	will be a NOP effectively ).
+ */
+
 static __inline void
 vm_page_protect(vm_page_t mem, int prot)
 {