From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759717Ab0JVTSJ (ORCPT ); Fri, 22 Oct 2010 15:18:09 -0400 Received: from kroah.org ([198.145.64.141]:34046 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759294Ab0JVS4O (ORCPT ); Fri, 22 Oct 2010 14:56:14 -0400 X-Mailbox-Line: From gregkh@clark.site Fri Oct 22 11:52:30 2010 Message-Id: <20101022185230.127872831@clark.site> User-Agent: quilt/0.48-11.2 Date: Fri, 22 Oct 2010 11:51:05 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Hugh Dickins , Andrea Arcangeli Subject: [031/103] ksm: fix bad user data when swapping In-Reply-To: <20101022185455.GA9114@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.35-stable review patch. If anyone has any objections, please let us know. ------------------ From: Hugh Dickins commit 4e31635c367a9e21a43cfbfae4c9deda2e19d1f4 upstream. Building under memory pressure, with KSM on 2.6.36-rc5, collapsed with an internal compiler error: typically indicating an error in swapping. Perhaps there's a timing issue which makes it now more likely, perhaps it's just a long time since I tried for so long: this bug goes back to KSM swapping in 2.6.33. Notice how reuse_swap_page() allows an exclusive page to be reused, but only does SetPageDirty if it can delete it from swap cache right then - if it's currently under Writeback, it has to be left in cache and we don't SetPageDirty, but the page can be reused. Fine, the dirty bit will get set in the pte; but notice how zap_pte_range() does not bother to transfer pte_dirty to page_dirty when unmapping a PageAnon. If KSM chooses to share such a page, it will look like a clean copy of swapcache, and not be written out to swap when its memory is needed; then stale data read back from swap when it's needed again. We could fix this in reuse_swap_page() (or even refuse to reuse a page under writeback), but it's more honest to fix my oversight in KSM's write_protect_page(). Several days of testing on three machines confirms that this fixes the issue they showed. Signed-off-by: Hugh Dickins Cc: Andrew Morton Cc: Andrea Arcangeli Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/ksm.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/mm/ksm.c +++ b/mm/ksm.c @@ -731,7 +731,7 @@ static int write_protect_page(struct vm_ if (!ptep) goto out; - if (pte_write(*ptep)) { + if (pte_write(*ptep) || pte_dirty(*ptep)) { pte_t entry; swapped = PageSwapCache(page); @@ -754,7 +754,9 @@ static int write_protect_page(struct vm_ set_pte_at(mm, addr, ptep, entry); goto out_unlock; } - entry = pte_wrprotect(entry); + if (pte_dirty(entry)) + set_page_dirty(page); + entry = pte_mkclean(pte_wrprotect(entry)); set_pte_at_notify(mm, addr, ptep, entry); } *orig_pte = *ptep;