[PATCH v2 16/33] 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.

Reviewed-by: Pedro Falcato <pfalcato@xxxxxxx>
Reviewed-by: Gregory Price <gourry@xxxxxxxxxx>
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 7265a054cfa3..5d5e60ea8a25 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))

-- 
2.55.0