[PATCH mm-unstable 3/4] mm/khugepaged: delay computation of hpage boundaries until use

["Zach O'Keefe" <zokeefe@xxxxxxxxxx>]

Only compute hstart/hend once we've passed all checks that would
cause early return in madvise_collapse().

Fixes: c9d968ffd9ba ("mm/madvise: introduce MADV_COLLAPSE sync hugepage collapse")
Signed-off-by: Zach O'Keefe <zokeefe@xxxxxxxxxx>
---
 mm/khugepaged.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 290422577172..70e9d9950415 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2417,9 +2417,6 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
 	if (!vma->anon_vma || !vma_is_anonymous(vma))
 		return -EINVAL;
 
-	hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
-	hend = end & HPAGE_PMD_MASK;
-
 	if (!hugepage_vma_check(vma, vma->vm_flags, false, false, false))
 		return -EINVAL;
 
@@ -2432,6 +2429,9 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
 	mmgrab(mm);
 	lru_add_drain_all();
 
+	hstart = (start + ~HPAGE_PMD_MASK) & HPAGE_PMD_MASK;
+	hend = end & HPAGE_PMD_MASK;
+
 	for (addr = hstart; addr < hend; addr += HPAGE_PMD_SIZE) {
 		int result = SCAN_FAIL;
 
-- 
2.37.0.170.g444d1eabd0-goog