[PATCHv9-rebased2 05/37] khugepaged: recheck pmd after mmap_sem re-acquired

[Kirill A. Shutemov]

Vlastimil noted[1] that pmd can be no longer valid after we drop
mmap_sem. We need recheck it once mmap_sem taken again.

[1] http://lkml.kernel.org/r/12918dcd-a695-c6f4-e06f-69141c5f357f@xxxxxxx

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 mm/huge_memory.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d7ccc8558187..0efdad975659 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2437,6 +2437,9 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 			/* vma is no longer available, don't continue to swapin */
 			if (hugepage_vma_revalidate(mm, address))
 				return false;
+			/* check if the pmd is still valid */
+			if (mm_find_pmd(mm, address) != pmd)
+				return false;
 		}
 		if (ret & VM_FAULT_ERROR) {
 			trace_mm_collapse_huge_page_swapin(mm, swapped_in, 0);
@@ -2522,6 +2525,9 @@ static void collapse_huge_page(struct mm_struct *mm,
 	result = hugepage_vma_revalidate(mm, address);
 	if (result)
 		goto out;
+	/* check if the pmd is still valid */
+	if (mm_find_pmd(mm, address) != pmd)
+		goto out;
 
 	anon_vma_lock_write(vma->anon_vma);
 
-- 
2.8.1