From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id 8D50F6B0088 for ; Wed, 10 Nov 2010 22:08:43 -0500 (EST) Received: by qyk1 with SMTP id 1so794923qyk.14 for ; Wed, 10 Nov 2010 19:08:42 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20101110190228.e21fdf36.akpm@linux-foundation.org> References: <1289444754-29469-1-git-send-email-lliubbo@gmail.com> <20101110190228.e21fdf36.akpm@linux-foundation.org> Date: Thu, 11 Nov 2010 11:08:41 +0800 Message-ID: Subject: Re: [PATCH v2] fix __set_page_dirty_no_writeback() return value From: Bob Liu Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Andrew Morton Cc: fengguang.wu@intel.com, linux-mm@kvack.org, kenchen@google.com List-ID: On Thu, Nov 11, 2010 at 11:02 AM, Andrew Morton wrote: > On Thu, 11 Nov 2010 11:05:54 +0800 Bob Liu wrote: > >> __set_page_dirty_no_writeback() should return true if it actually transi= tioned >> the page from a clean to dirty state although it seems nobody used its r= eturn >> value now. >> >> Change from v1: >> =C2=A0 =C2=A0 =C2=A0 * preserving cacheline optimisation as Andrew point= ed out >> >> Signed-off-by: Bob Liu >> --- >> =C2=A0mm/page-writeback.c | =C2=A0 =C2=A04 +++- >> =C2=A01 files changed, 3 insertions(+), 1 deletions(-) >> >> diff --git a/mm/page-writeback.c b/mm/page-writeback.c >> index bf85062..ac7018a 100644 >> --- a/mm/page-writeback.c >> +++ b/mm/page-writeback.c >> @@ -1157,8 +1157,10 @@ EXPORT_SYMBOL(write_one_page); >> =C2=A0 */ >> =C2=A0int __set_page_dirty_no_writeback(struct page *page) >> =C2=A0{ >> - =C2=A0 =C2=A0 if (!PageDirty(page)) >> + =C2=A0 =C2=A0 if (!PageDirty(page)) { >> =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 SetPageDirty(page); >> + =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return 1; >> + =C2=A0 =C2=A0 } >> =C2=A0 =C2=A0 =C2=A0 return 0; >> =C2=A0} > > But that has a race. =C2=A0If someone else sets PG_Dirty between the test > and the set, this function will incorrectly return 1. > > Which is why it should use test_and_set if we're going to do this. > Oh, Sorry for that. I will make a new patch soon. --=20 Thanks, --Bob -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: email@kvack.org