It is not enough to just make sure the z3fold header is not larger than the
page size. When z3fold header is equal to PAGE_SIZE, we would underflow
when check alloc size against PAGE_SIZE - ZHDR_SIZE_ALIGNED - CHUNK_SIZE
in z3fold_alloc(). Make sure there has remaining spaces for its buddy to
fix this theoretical issue.
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
This causes the below checkpatch warning:
WARNING: Comparisons should place the constant on the right side of the
test
#31: FILE: mm/z3fold.c:1812:
+ BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE - CHUNK_SIZE);
But I think the error is false positives as all members are constant.
---
mm/z3fold.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/mm/z3fold.c b/mm/z3fold.c
index 04d0e493bd2e..e261e14b7753 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -1805,8 +1805,11 @@ static int __init init_z3fold(void)
{
int ret;
- /* Make sure the z3fold header is not larger than the page size */
- BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE);
+ /*
+ * Make sure the z3fold header is not larger than the page size and
+ * there has remaining spaces for its buddy.
+ */
+ BUILD_BUG_ON(ZHDR_SIZE_ALIGNED > PAGE_SIZE - CHUNK_SIZE);
ret = z3fold_mount();
if (ret)
return ret;
--
2.23.0
