[PATCH 2/4] mm/hwpoison: fix potential pte_unmap_unlock pte error

[Miaohe Lin]

If the first pte is equal to poisoned_pfn, i.e. check_hwpoisoned_entry()
return 1, the wrong ptep - 1 would be passed to pte_unmap_unlock().

Fixes: ad9c59c24095 ("mm,hwpoison: send SIGBUS with error virutal address")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
 mm/memory-failure.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 052ec9ee7cf6..54f61133bf60 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -632,7 +632,7 @@ static int hwpoison_pte_range(pmd_t *pmdp, unsigned long addr,
 {
 	struct hwp_walk *hwp = (struct hwp_walk *)walk->private;
 	int ret = 0;
-	pte_t *ptep;
+	pte_t *ptep, *mapped_pte;
 	spinlock_t *ptl;
 
 	ptl = pmd_trans_huge_lock(pmdp, walk->vma);
@@ -645,14 +645,15 @@ static int hwpoison_pte_range(pmd_t *pmdp, unsigned long addr,
 	if (pmd_trans_unstable(pmdp))
 		goto out;
 
-	ptep = pte_offset_map_lock(walk->vma->vm_mm, pmdp, addr, &ptl);
+	mapped_pte = ptep = pte_offset_map_lock(walk->vma->vm_mm, pmdp,
+						addr, &ptl);
 	for (; addr != end; ptep++, addr += PAGE_SIZE) {
 		ret = check_hwpoisoned_entry(*ptep, addr, PAGE_SHIFT,
 					     hwp->pfn, &hwp->tk);
 		if (ret == 1)
 			break;
 	}
-	pte_unmap_unlock(ptep - 1, ptl);
+	pte_unmap_unlock(mapped_pte, ptl);
 out:
 	cond_resched();
 	return ret;
-- 
2.23.0