[PATCH v2 05/10] mm/thp: fix page_address_in_vma() on file THP tails

[Hugh Dickins <hughd@google.com>]

From: Jue Wang <juew@google.com>

Anon THP tails were already supported, but memory-failure may need to use
page_address_in_vma() on file THP tails, which its page->mapping check did
not permit: fix it.

hughd adds: no current usage is known to hit the issue, but this does fix
a subtle trap in a general helper: best fixed in stable sooner than later.

Fixes: 800d8c63b2e9 ("shmem: add huge pages support")
Signed-off-by: Jue Wang <juew@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: <stable@vger.kernel.org>
---
 mm/rmap.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 144de54efc1c..e05c300048e6 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -716,11 +716,11 @@ unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
 		if (!vma->anon_vma || !page__anon_vma ||
 		    vma->anon_vma->root != page__anon_vma->root)
 			return -EFAULT;
-	} else if (page->mapping) {
-		if (!vma->vm_file || vma->vm_file->f_mapping != page->mapping)
-			return -EFAULT;
-	} else
+	} else if (!vma->vm_file) {
+		return -EFAULT;
+	} else if (vma->vm_file->f_mapping != compound_head(page)->mapping) {
 		return -EFAULT;
+	}
 
 	return vma_address(page, vma);
 }
-- 
2.26.2