From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Hugh Dickins , Ashwin Chaugule , Yang Shi , "Kirill A. Shutemov" , "Huang, Ying" , Andrew Morton , Linus Torvalds Subject: [PATCH 4.17 23/63] mm/huge_memory.c: fix data loss when splitting a file pmd Date: Mon, 23 Jul 2018 14:24:29 +0200 Message-Id: <20180723122447.241712157@linuxfoundation.org> In-Reply-To: <20180723122446.351334162@linuxfoundation.org> References: <20180723122446.351334162@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.17-stable review patch. If anyone has any objections, please let me know. ------------------ From: Hugh Dickins commit e1f1b1572e8db87a56609fd05bef76f98f0e456a upstream. __split_huge_pmd_locked() must check if the cleared huge pmd was dirty, and propagate that to PageDirty: otherwise, data may be lost when a huge tmpfs page is modified then split then reclaimed. How has this taken so long to be noticed? Because there was no problem when the huge page is written by a write system call (shmem_write_end() calls set_page_dirty()), nor when the page is allocated for a write fault (fault_dirty_shared_page() calls set_page_dirty()); but when allocated for a read fault (which MAP_POPULATE simulates), no set_page_dirty(). Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1807111741430.1106@eggly.anvils Fixes: d21b9e57c74c ("thp: handle file pages in split_huge_pmd()") Signed-off-by: Hugh Dickins Reported-by: Ashwin Chaugule Reviewed-by: Yang Shi Reviewed-by: Kirill A. Shutemov Cc: "Huang, Ying" Cc: [4.8+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/huge_memory.c | 2 ++ 1 file changed, 2 insertions(+) --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2087,6 +2087,8 @@ static void __split_huge_pmd_locked(stru if (vma_is_dax(vma)) return; page = pmd_page(_pmd); + if (!PageDirty(page) && pmd_dirty(_pmd)) + set_page_dirty(page); if (!PageReferenced(page) && pmd_young(_pmd)) SetPageReferenced(page); page_remove_rmap(page, true);