linux-kernel - [PATCH 5/8] thp, mm: locking tail page is a bug

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Message-Id: <1373885274-25249-6-git-send-email-kirill.shutemov@linux.intel.com>
Date:	Mon, 15 Jul 2013 13:47:51 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>, Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, Dave Hansen <dave@...1.net>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH 5/8] thp, mm: locking tail page is a bug

From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>

Locking head page means locking entire compound page.
If we try to lock tail page, something went wrong.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
---
 mm/filemap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index f7c4ed5..e59049c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -639,6 +639,7 @@ void __lock_page(struct page *page)
 {
 	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
 
+	VM_BUG_ON(PageTail(page));
 	__wait_on_bit_lock(page_waitqueue(page), &wait, sleep_on_page,
 							TASK_UNINTERRUPTIBLE);
 }
@@ -648,6 +649,7 @@ int __lock_page_killable(struct page *page)
 {
 	DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
 
+	VM_BUG_ON(PageTail(page));
 	return __wait_on_bit_lock(page_waitqueue(page), &wait,
 					sleep_on_page_killable, TASK_KILLABLE);
 }
-- 
1.8.3.2

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