[PATCH 1/2] mm/mremap: Clean up vma_to_resize()

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>

vma_to_resize() is used in two locations to find and validate the vma
for the mremap location.  One of the two locations already has the vma,
which is then re-found to validate the same vma.

This code can be simplified by moving the vma_lookup() from
vma_to_resize() to mremap_to() and changing the return type to an int
error.

Since the function now just validates the vma, the function is renamed
to mremap_vma_check() to better reflect what it is doing.

Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
---
 mm/mremap.c | 39 +++++++++++++++++++--------------------
 1 file changed, 19 insertions(+), 20 deletions(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index 5917feafe8cc..648c29f568af 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -826,17 +826,12 @@ static unsigned long move_vma(struct vm_area_struct *vma,
 	return new_addr;
 }
 
-static struct vm_area_struct *vma_to_resize(unsigned long addr,
+static int mremap_vma_check(struct vm_area_struct *vma, unsigned long addr,
 	unsigned long old_len, unsigned long new_len, unsigned long flags)
 {
 	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma;
 	unsigned long pgoff;
 
-	vma = vma_lookup(mm, addr);
-	if (!vma)
-		return ERR_PTR(-EFAULT);
-
 	/*
 	 * !old_len is a special case where an attempt is made to 'duplicate'
 	 * a mapping.  This makes no sense for private mappings as it will
@@ -847,37 +842,37 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
 	 */
 	if (!old_len && !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE))) {
 		pr_warn_once("%s (%d): attempted to duplicate a private mapping with mremap.  This is not supported.\n", current->comm, current->pid);
-		return ERR_PTR(-EINVAL);
+		return -EINVAL;
 	}
 
 	if ((flags & MREMAP_DONTUNMAP) &&
 			(vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)))
-		return ERR_PTR(-EINVAL);
+		return -EINVAL;
 
 	/* We can't remap across vm area boundaries */
 	if (old_len > vma->vm_end - addr)
-		return ERR_PTR(-EFAULT);
+		return -EFAULT;
 
 	if (new_len == old_len)
-		return vma;
+		return 0;
 
 	/* Need to be careful about a growing mapping */
 	pgoff = (addr - vma->vm_start) >> PAGE_SHIFT;
 	pgoff += vma->vm_pgoff;
 	if (pgoff + (new_len >> PAGE_SHIFT) < pgoff)
-		return ERR_PTR(-EINVAL);
+		return -EINVAL;
 
 	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
-		return ERR_PTR(-EFAULT);
+		return -EFAULT;
 
 	if (!mlock_future_ok(mm, vma->vm_flags, new_len - old_len))
-		return ERR_PTR(-EAGAIN);
+		return -EAGAIN;
 
 	if (!may_expand_vm(mm, vma->vm_flags,
 				(new_len - old_len) >> PAGE_SHIFT))
-		return ERR_PTR(-ENOMEM);
+		return -ENOMEM;
 
-	return vma;
+	return 0;
 }
 
 static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
@@ -936,7 +931,13 @@ static unsigned long mremap_to(unsigned long addr, unsigned long old_len,
 		old_len = new_len;
 	}
 
-	vma = vma_to_resize(addr, old_len, new_len, flags);
+	vma = vma_lookup(mm, addr);
+	if (!vma) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	mremap_vma_check(vma, addr, old_len, new_len, flags);
 	if (IS_ERR(vma)) {
 		ret = PTR_ERR(vma);
 		goto out;
@@ -1114,11 +1115,9 @@ SYSCALL_DEFINE5(mremap, unsigned long, addr, unsigned long, old_len,
 	/*
 	 * Ok, we need to grow..
 	 */
-	vma = vma_to_resize(addr, old_len, new_len, flags);
-	if (IS_ERR(vma)) {
-		ret = PTR_ERR(vma);
+	ret = mremap_vma_check(vma, addr, old_len, new_len, flags);
+	if (ret)
 		goto out;
-	}
 
 	/* old_len exactly to the end of the area..
 	 */
-- 
2.43.0