[PATCH 14/30] mm/vma: minor cleanup of expand_[upwards, downwards]()

[Lorenzo Stoakes]

Adjust the stack expansion functions expand_upwards() and
expand_downwards() such that they are expressed in terms of named constant
values, and make use of vma_start_pgoff().

This clearly documents that we are referencing the page offset of the start
of the VMA.

Additionally this cleans up the overflow check in expand_upwards().

No functional change intended.

Signed-off-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>
---
 mm/vma.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/mm/vma.c b/mm/vma.c
index 1e99fe8aa6ef..dc4c2c1077f4 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -3216,13 +3216,12 @@ int expand_upwards(struct vm_area_struct *vma, unsigned long address)
 
 	/* Somebody else might have raced and expanded it already */
 	if (address > vma->vm_end) {
-		unsigned long size, grow;
-
-		size = address - vma->vm_start;
-		grow = (address - vma->vm_end) >> PAGE_SHIFT;
+		const unsigned long size = address - vma->vm_start;
+		const unsigned long grow = (address - vma->vm_end) >> PAGE_SHIFT;
+		const pgoff_t pgoff = vma_start_pgoff(vma);
 
 		error = -ENOMEM;
-		if (vma->vm_pgoff + (size >> PAGE_SHIFT) >= vma->vm_pgoff) {
+		if (pgoff + (size >> PAGE_SHIFT) >= pgoff) {
 			error = acct_stack_growth(vma, size, grow);
 			if (!error) {
 				if (vma_test(vma, VMA_LOCKED_BIT))
@@ -3295,13 +3294,11 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address)
 
 	/* Somebody else might have raced and expanded it already */
 	if (address < vma->vm_start) {
-		unsigned long size, grow;
-
-		size = vma->vm_end - address;
-		grow = (vma->vm_start - address) >> PAGE_SHIFT;
+		const unsigned long size = vma->vm_end - address;
+		const unsigned long grow = (vma->vm_start - address) >> PAGE_SHIFT;
 
 		error = -ENOMEM;
-		if (grow <= vma->vm_pgoff) {
+		if (grow <= vma_start_pgoff(vma)) {
 			error = acct_stack_growth(vma, size, grow);
 			if (!error) {
 				if (vma_test(vma, VMA_LOCKED_BIT))
-- 
2.54.0