---
 include/linux/mm.h |    4 +-
 mm/mmap.c          |   89 +++++++++++++++++++++++++++++++----------------------
 2 files changed, 55 insertions(+), 38 deletions(-)

Index: linux-2.6/mm/mmap.c
===================================================================
--- linux-2.6.orig/mm/mmap.c	2008-04-21 14:31:42.000000000 -0700
+++ linux-2.6/mm/mmap.c	2008-04-21 21:37:25.000000000 -0700
@@ -2241,29 +2241,33 @@ int install_special_mapping(struct mm_st
 
 static int cmp_rwsem(const void *a, const void *b)
 {
-	if (a == b)
+	struct rw_semaphore * const *pa = a;
+	struct rw_semaphore * const *pb = b;
+	struct rw_semaphore *va = *pa;
+	struct rw_semaphore *vb = *pb;
+
+	if (va == vb)
 		return 0;
-	if (a > b)
+	if (va > vb)
 		return 1;
 	return -1;
 }
 
 
-static void acquire_locks(struct mm_struct *mm,
-				struct rw_semaphore **locks, int anon)
+static void __scan_locks(struct mm_struct *mm, struct rw_semaphore **locks,
+							int anon, int lock)
 {
 	struct vm_area_struct *vma;
+	struct rw_semaphore *last;
 	int i = 0;
 
 	for (vma = mm->mmap; vma; vma = vma->vm_next) {
-		struct address_space *mapping = vma->vm_file->f_mapping;
-
-		if (mapping) {
-			if (!anon)
-				locks[i++] = &mapping->i_mmap_sem;
-		} else {
-			if (anon)
+		if (anon) {
+			if (vma->anon_vma)
 				locks[i++] = &vma->anon_vma->sem;
+		} else {
+			if (vma->vm_file && vma->vm_file->f_mapping)
+				locks[i++] = &vma->vm_file->f_mapping->i_mmap_sem;
 		}
 	}
 
@@ -2272,9 +2276,34 @@ static void acquire_locks(struct mm_stru
 
 	sort(locks, i, sizeof(struct rw_semaphore *), cmp_rwsem, NULL);
 
-	while (i-- > 0)
-		down_read(locks[i]);
+	last = NULL;
+	while (i-- > 0) {
+		if (last != locks[i]) {
+			if (lock)
+				down_write(locks[i]);
+			else
+				up_write(locks[i]);
+
+			last = locks[i];
+		}
+	}
+}
+
+static int scan_locks(struct mm_struct *mm, int lock)
+{
+	struct rw_semaphore **locks;
+
+	locks = vmalloc(sizeof(struct rw_semaphore *) * mm->map_count);
+	if (!locks)
+		return -ENOMEM;
+
+	__scan_locks(mm, locks, 0, lock);
+	__scan_locks(mm, locks, 1, lock);
+
+	vfree(locks);
+	return 0;
 }
+
 /*
  * This operation locks against the VM for all pte/vma/mm related
  * operations that could ever happen on a certain mm. This includes
@@ -2284,36 +2313,24 @@ static void acquire_locks(struct mm_stru
  */
 int mm_lock(struct mm_struct * mm)
 {
-	struct rw_semaphore **locks;
+	int rc;
 
 	down_write(&mm->mmap_sem);
-	locks = vmalloc(sizeof(struct rw_semaphore *) * mm->map_count);
-	if (!locks) {
-		up_write(&mm->mmap_sem);
-		return -ENOMEM;
-	}
 
-	acquire_locks(mm, locks, 0);
-	acquire_locks(mm, locks, 1);
+	rc = scan_locks(mm, 1);
+	if (rc)
+		up_write(&mm->mmap_sem);
 
-	vfree(locks);
-	return 0;
+	return rc;
 }
 
-void mm_unlock(struct mm_struct *mm)
+int mm_unlock(struct mm_struct *mm)
 {
-	struct vm_area_struct *vma;
+	int rc;
 
-	for (vma = mm->mmap; vma; vma = vma->vm_next) {
-		struct address_space *mapping = vma->vm_file->f_mapping;
-		struct rw_semaphore *sem;
-
-		if (mapping)
-			sem = &mapping->i_mmap_sem;
-		else
-			sem = &vma->anon_vma->sem;
+	rc = scan_locks(mm, 0);
+	if (!rc)
+		up_write(&mm->mmap_sem);
 
-		up_read(sem);
-	}
-	up_write(&mm->mmap_sem);
+	return rc;
 }
Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h	2008-04-21 21:27:32.000000000 -0700
+++ linux-2.6/include/linux/mm.h	2008-04-21 21:27:48.000000000 -0700
@@ -1055,13 +1055,13 @@ extern int install_special_mapping(struc
  * vmaske all mapping to lockout any scans of pages of this address space.
  * This can be used to effectively holding off reclaim from the address space.
  *
- * mm_lock() can fail if there is not enough memory to store a pointer
+ * mm_lock/mm_unlock() can fail if there is not enough memory to store a pointer
  * array to all vmas.
  *
  * mm_lock and mm_unlock are expensive operations that may take a long time.
  */
 extern int mm_lock(struct mm_struct *mm);
-extern void mm_unlock(struct mm_struct *mm);
+extern int mm_unlock(struct mm_struct *mm);
 
 extern unsigned long get_unmapped_area(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);