Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932213AbaDVUPw (ORCPT ); Tue, 22 Apr 2014 16:15:52 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:36276 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756756AbaDVUPe (ORCPT ); Tue, 22 Apr 2014 16:15:34 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Vlastimil Babka , Bob Liu , Wanpeng Li , Michel Lespinasse , KOSAKI Motohiro , David Rientjes , Mel Gorman , Hugh Dickins , Joonsoo Kim , Andrew Morton , Linus Torvalds , Kamal Mostafa Subject: [PATCH 3.8 124/133] mm: try_to_unmap_cluster() should lock_page() before mlocking Date: Tue, 22 Apr 2014 13:14:22 -0700 Message-Id: <1398197671-12786-125-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1398197671-12786-1-git-send-email-kamal@canonical.com> References: <1398197671-12786-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.8.13.22 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Vlastimil Babka commit 57e68e9cd65b4b8eb4045a1e0d0746458502554c upstream. A BUG_ON(!PageLocked) was triggered in mlock_vma_page() by Sasha Levin fuzzing with trinity. The call site try_to_unmap_cluster() does not lock the pages other than its check_page parameter (which is already locked). The BUG_ON in mlock_vma_page() is not documented and its purpose is somewhat unclear, but apparently it serializes against page migration, which could otherwise fail to transfer the PG_mlocked flag. This would not be fatal, as the page would be eventually encountered again, but NR_MLOCK accounting would become distorted nevertheless. This patch adds a comment to the BUG_ON in mlock_vma_page() and munlock_vma_page() to that effect. The call site try_to_unmap_cluster() is fixed so that for page != check_page, trylock_page() is attempted (to avoid possible deadlocks as we already have check_page locked) and mlock_vma_page() is performed only upon success. If the page lock cannot be obtained, the page is left without PG_mlocked, which is again not a problem in the whole unevictable memory design. Signed-off-by: Vlastimil Babka Signed-off-by: Bob Liu Reported-by: Sasha Levin Cc: Wanpeng Li Cc: Michel Lespinasse Cc: KOSAKI Motohiro Acked-by: Rik van Riel Cc: David Rientjes Cc: Mel Gorman Cc: Hugh Dickins Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Kamal Mostafa --- mm/mlock.c | 2 ++ mm/rmap.c | 14 ++++++++++++-- 2 files changed, 14 insertions(+), 2 deletions(-) diff --git a/mm/mlock.c b/mm/mlock.c index c9bd528..b6de0e5 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -76,6 +76,7 @@ void clear_page_mlock(struct page *page) */ void mlock_vma_page(struct page *page) { + /* Serialize with page migration */ BUG_ON(!PageLocked(page)); if (!TestSetPageMlocked(page)) { @@ -104,6 +105,7 @@ void mlock_vma_page(struct page *page) */ void munlock_vma_page(struct page *page) { + /* For try_to_munlock() and to serialize with page migration */ BUG_ON(!PageLocked(page)); if (TestClearPageMlocked(page)) { diff --git a/mm/rmap.c b/mm/rmap.c index c208837..da8e2cf 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1414,9 +1414,19 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount, BUG_ON(!page || PageAnon(page)); if (locked_vma) { - mlock_vma_page(page); /* no-op if already mlocked */ - if (page == check_page) + if (page == check_page) { + /* we know we have check_page locked */ + mlock_vma_page(page); ret = SWAP_MLOCK; + } else if (trylock_page(page)) { + /* + * If we can lock the page, perform mlock. + * Otherwise leave the page alone, it will be + * eventually encountered again later. + */ + mlock_vma_page(page); + unlock_page(page); + } continue; /* don't unmap */ } -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/