From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 8C1826B0069 for ; Fri, 18 Nov 2011 22:27:03 -0500 (EST) Received: by wwf10 with SMTP id 10so5233836wwf.26 for ; Fri, 18 Nov 2011 19:26:59 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20111118113946.6563fd08.akpm@linux-foundation.org> References: <20111118150742.GA23223@tiehlicka.suse.cz> <20111118161128.GC23223@tiehlicka.suse.cz> <20111118113946.6563fd08.akpm@linux-foundation.org> Date: Sat, 19 Nov 2011 11:26:59 +0800 Message-ID: Subject: Re: [PATCH] hugetlb: detect race if fail to COW From: Hillf Danton Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Michal Hocko , Andrea Arcangeli , Johannes Weiner , linux-mm@kvack.org, LKML On Sat, Nov 19, 2011 at 3:39 AM, Andrew Morton wrote: > On Fri, 18 Nov 2011 17:11:28 +0100 > Michal Hocko wrote: > >> On Fri 18-11-11 23:23:12, Hillf Danton wrote: >> > On Fri, Nov 18, 2011 at 11:07 PM, Michal Hocko wrote: >> > > On Fri 18-11-11 22:04:37, Hillf Danton wrote: >> > >> In the error path that we fail to allocate new huge page, before tr= y again, we >> > >> have to check race since page_table_lock is re-acquired. >> > > >> > > I do not think we can race here because we are serialized by >> > > hugetlb_instantiation_mutex AFAIU. Without this lock, however, we co= uld >> > > fall into avoidcopy and shortcut despite the fact that other thread = has >> > > already did the job. >> > > >> > > The mutex usage is not obvious in hugetlb_cow so maybe we want to be >> > > explicit about it (either a comment or do the recheck). >> > > >> > >> > Then the following check is unnecessary, no? >> >> Hmm, thinking about it some more, I guess we have to recheck because we >> can still race with page migration. So we need you patch. >> >> Reviewed-by: Michal Hocko > > So we need a new changelog. =C2=A0How does this look? > Thanks Andrew and Michal:) Best regards Hillf -- 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 internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org