[PATCH v2 01/22] mm: Add vma_lookup(), update find_vma_intersection() comments

[Liam Howlett]

Many places in the kernel use find_vma() to get a vma and then check the
start address of the vma to ensure the next vma was not returned.

Other places use the find_vma_intersection() call with add, addr + 1 as
the range; looking for just the vma at a specific address.

The third use of find_vma() is by developers who do not know that the
function starts searching at the provided address upwards for the next
vma.  This results in a bug that is often overlooked for a long time.

Adding the new vma_lookup() function will allow for cleaner code by
removing the find_vma() calls which check limits, making
find_vma_intersection() calls of a single address to be shorter, and
potentially reduce the incorrect uses of find_vma().

Also change find_vma_intersection() comments and declaration to be of
the correct length and add kernel documentation style comment.

Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Reviewed-by: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Davidlohr Bueso <dbueso@xxxxxxx>
---
 include/linux/mm.h | 36 ++++++++++++++++++++++++++++++++----
 1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 25b9041f9925..d5c443993ebe 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2678,17 +2678,45 @@ extern struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long add
 extern struct vm_area_struct * find_vma_prev(struct mm_struct * mm, unsigned long addr,
 					     struct vm_area_struct **pprev);
 
-/* Look up the first VMA which intersects the interval start_addr..end_addr-1,
-   NULL if none.  Assume start_addr < end_addr. */
-static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * mm, unsigned long start_addr, unsigned long end_addr)
+/**
+ * find_vma_intersection() - Look up the first VMA which intersects the interval
+ * @mm: The process address space.
+ * @start_addr: The inclusive start user address.
+ * @end_addr: The exclusive end user address.
+ *
+ * Returns: The first VMA within the provided range, %NULL otherwise.  Assumes
+ * start_addr < end_addr.
+ */
+static inline
+struct vm_area_struct *find_vma_intersection(struct mm_struct *mm,
+					     unsigned long start_addr,
+					     unsigned long end_addr)
 {
-	struct vm_area_struct * vma = find_vma(mm,start_addr);
+	struct vm_area_struct *vma = find_vma(mm, start_addr);
 
 	if (vma && end_addr <= vma->vm_start)
 		vma = NULL;
 	return vma;
 }
 
+/**
+ * vma_lookup() - Find a VMA at a specific address
+ * @mm: The process address space.
+ * @addr: The user address.
+ *
+ * Return: The vm_area_struct at the given address, %NULL otherwise.
+ */
+static inline
+struct vm_area_struct *vma_lookup(struct mm_struct *mm, unsigned long addr)
+{
+	struct vm_area_struct *vma = find_vma(mm, addr);
+
+	if (vma && addr < vma->vm_start)
+		vma = NULL;
+
+	return vma;
+}
+
 static inline unsigned long vm_start_gap(struct vm_area_struct *vma)
 {
 	unsigned long vm_start = vma->vm_start;
-- 
2.30.2