From 41802e2c869ef8b626b1815870a3f7ede579e53f Mon Sep 17 00:00:00 2001
From: kib <kib@FreeBSD.org>
Date: Sat, 9 Aug 2014 05:00:34 +0000
Subject: [PATCH] Adapt vm_page_aflag_set(PGA_WRITEABLE) to the locking of
 pmap_enter(PMAP_ENTER_NOSLEEP).  The PGA_WRITEABLE flag can be set when
 either the page is busied, or the owner object is locked.

Update comments, move all assertions about page state when
PGA_WRITEABLE flag is set, into new helper
vm_page_assert_pga_writeable().

Reviewed by:	alc
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
---
 sys/vm/vm_page.c | 18 ++++++++++++++++++
 sys/vm/vm_page.h | 20 +++++++++-----------
 2 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 4e30a3f5aded..7ce12d63de48 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -3134,6 +3134,24 @@ vm_page_object_lock_assert(vm_page_t m)
 	if (m->object != NULL && !vm_page_xbusied(m))
 		VM_OBJECT_ASSERT_WLOCKED(m->object);
 }
+
+void
+vm_page_assert_pga_writeable(vm_page_t m, uint8_t bits)
+{
+
+	if ((bits & PGA_WRITEABLE) == 0)
+		return;
+
+	/*
+	 * The PGA_WRITEABLE flag can only be set if the page is
+	 * managed, is exclusively busied or the object is locked.
+	 * Currently, this flag is only set by pmap_enter().
+	 */
+	KASSERT((m->oflags & VPO_UNMANAGED) == 0,
+	    ("PGA_WRITEABLE on unmanaged page"));
+	if (!vm_page_xbusied(m))
+		VM_OBJECT_ASSERT_LOCKED(m->object);
+}
 #endif
 
 #include "opt_ddb.h"
diff --git a/sys/vm/vm_page.h b/sys/vm/vm_page.h
index ff61e06adfe5..f12b76c34280 100644
--- a/sys/vm/vm_page.h
+++ b/sys/vm/vm_page.h
@@ -305,10 +305,10 @@ extern struct mtx_padalign pa_lock[];
  * both the MI and MD VM layers.  However, kernel loadable modules should not
  * directly set this flag.  They should call vm_page_reference() instead.
  *
- * PGA_WRITEABLE is set exclusively on managed pages by pmap_enter().  When it
- * does so, the page must be exclusive busied.  The MI VM layer must never
- * access this flag directly.  Instead, it should call
- * pmap_page_is_write_mapped().
+ * PGA_WRITEABLE is set exclusively on managed pages by pmap_enter().
+ * When it does so, the object must be locked, or the page must be
+ * exclusive busied.  The MI VM layer must never access this flag
+ * directly.  Instead, it should call pmap_page_is_write_mapped().
  *
  * PGA_EXECUTABLE may be set by pmap routines, and indicates that a page has
  * at least one executable mapping.  It is not consumed by the MI VM layer.
@@ -533,8 +533,12 @@ void vm_page_lock_assert_KBI(vm_page_t m, int a, const char *file, int line);
 #ifdef INVARIANTS
 void vm_page_object_lock_assert(vm_page_t m);
 #define	VM_PAGE_OBJECT_LOCK_ASSERT(m)	vm_page_object_lock_assert(m)
+void vm_page_assert_pga_writeable(vm_page_t m, uint8_t bits);
+#define	VM_PAGE_ASSERT_PGA_WRITEABLE(m, bits)				\
+	vm_page_assert_pga_writeable(m, bits)
 #else
 #define	VM_PAGE_OBJECT_LOCK_ASSERT(m)	(void)0
+#define	VM_PAGE_ASSERT_PGA_WRITEABLE(m, bits)	(void)0
 #endif
 
 /*
@@ -582,13 +586,7 @@ vm_page_aflag_set(vm_page_t m, uint8_t bits)
 {
 	uint32_t *addr, val;
 
-	/*
-	 * The PGA_WRITEABLE flag can only be set if the page is managed and
-	 * exclusive busied.  Currently, this flag is only set by pmap_enter().
-	 */
-	KASSERT((bits & PGA_WRITEABLE) == 0 ||
-	    ((m->oflags & VPO_UNMANAGED) == 0 && vm_page_xbusied(m)),
-	    ("vm_page_aflag_set: PGA_WRITEABLE and not exclusive busy"));
+	VM_PAGE_ASSERT_PGA_WRITEABLE(m, bits);
 
 	/*
 	 * Access the whole 32-bit word containing the aflags field with an