[PATCH v2 2/2] secretmem/gup: don't check if page is secretmem without reference

[Mike Rapoport]

From: Mike Rapoport <r...@linux.ibm.com>

The check in gup_pte_range() whether a page belongs to a secretmem mapping
is performed before grabbing the page reference.

To avoid potential race move the check after try_grab_compound_head().

Signed-off-by: Mike Rapoport <r...@linux.ibm.com>
---
 mm/gup.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index c3a17b189064..4b58c016e949 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2080,13 +2080,13 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, 
unsigned long end,
                VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
                page = pte_page(pte);
 
-               if (page_is_secretmem(page))
-                       goto pte_unmap;
-
                head = try_grab_compound_head(page, 1, flags);
                if (!head)
                        goto pte_unmap;
 
+               if (page_is_secretmem(page))
+                       goto pte_unmap;
+
                if (unlikely(pte_val(pte) != pte_val(*ptep))) {
                        put_compound_head(head, 1, flags);
                        goto pte_unmap;
-- 
2.28.0