[Resend PATCH 5/6] mm/thp: remove code path which never got into

[Alex Shi <alex.shi@linux.alibaba.com>]

split_huge_page() will never call on a page which isn't on lru list, so
this code never got a chance to run, and should not be run, to add tail
pages on a lru list which head page isn't there.

Although the bug was never triggered, it'better be removed for code
correctness, and add a warn for unexpected calling.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
 mm/huge_memory.c | 13 ++-----------
 1 file changed, 2 insertions(+), 11 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8cecd39bd8b7..d55e3006c63f 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2332,17 +2332,8 @@ static void lru_add_page_tail(struct page *head, struct page *page_tail,
 		/* page reclaim is reclaiming a huge page */
 		get_page(page_tail);
 		list_add_tail(&page_tail->lru, list);
-	} else {
-		/*
-		 * Head page has not yet been counted, as an hpage,
-		 * so we must account for each subpage individually.
-		 *
-		 * Put page_tail on the list at the correct position
-		 * so they all end up in order.
-		 */
-		add_page_to_lru_list_tail(page_tail, lruvec,
-					  page_lru(page_tail));
-	}
+	} else
+		VM_WARN_ON(!PageLRU(head));
 }
 
 static void __split_huge_page_tail(struct page *head, int tail,
-- 
1.8.3.1