[PATCH mm, next-next] Add missing page_count() check to vm_insert_pages().

[Arjun Roy <arjunroy.kdev@gmail.com>]

From: Arjun Roy <arjunroy@google.com>

Add missing page_count() check to vm_insert_pages(), specifically
inside insert_page_in_batch_locked(). This was accidentally forgotten
in the original patchset.

See: https://marc.info/?l=linux-mm&m=158156166403807&w=2

The intention of this patch-set is to reduce atomic ops for
tcp zerocopy receives, which normally hits the same spinlock multiple
times consecutively.

Signed-off-by: Arjun Roy <arjunroy@google.com>

---
 mm/memory.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/memory.c b/mm/memory.c
index f1d5f2264aef..3b4007a6ef7f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1463,8 +1463,11 @@ static int insert_page_into_pte_locked(struct mm_struct *mm, pte_t *pte,
 static int insert_page_in_batch_locked(struct mm_struct *mm, pmd_t *pmd,
 			unsigned long addr, struct page *page, pgprot_t prot)
 {
-	const int err = validate_page_before_insert(page);
+	int err;
 
+	if (!page_count(page))
+		return -EINVAL;
+	err = validate_page_before_insert(page);
 	return err ? err : insert_page_into_pte_locked(
 		mm, pte_offset_map(pmd, addr), addr, page, prot);
 }
-- 
2.25.0.265.gbab2e86ba0-goog