Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753670AbdHKQ7p (ORCPT ); Fri, 11 Aug 2017 12:59:45 -0400 Received: from mx1.redhat.com ([209.132.183.28]:17175 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752724AbdHKQ7n (ORCPT ); Fri, 11 Aug 2017 12:59:43 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 68837DF04 Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=riel@redhat.com Message-ID: <1502470781.6577.49.camel@redhat.com> Subject: Re: [PATCH 2/2] mm,fork: introduce MADV_WIPEONFORK From: Rik van Riel To: Mike Kravetz , Michal Hocko Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, fweimer@redhat.com, colm@allcosts.net, akpm@linux-foundation.org, keescook@chromium.org, luto@amacapital.net, wad@chromium.org, mingo@kernel.org, kirill@shutemov.name, dave.hansen@intel.com Date: Fri, 11 Aug 2017 12:59:41 -0400 In-Reply-To: <6a3e2dbe-6274-4402-0716-88f4fbda73dd@oracle.com> References: <20170806140425.20937-1-riel@redhat.com> <20170806140425.20937-3-riel@redhat.com> <20170810152352.GZ23863@dhcp22.suse.cz> <1502464992.6577.48.camel@redhat.com> <6a3e2dbe-6274-4402-0716-88f4fbda73dd@oracle.com> Organization: Red Hat, Inc Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Fri, 11 Aug 2017 16:59:43 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2141 Lines: 60 On Fri, 2017-08-11 at 09:36 -0700, Mike Kravetz wrote: > On 08/11/2017 08:23 AM, Rik van Riel wrote: > > On Thu, 2017-08-10 at 17:23 +0200, Michal Hocko wrote: > > > On Sun 06-08-17 10:04:25, Rik van Riel wrote: > > > [...] > > > > diff --git a/kernel/fork.c b/kernel/fork.c > > > > index 17921b0390b4..db1fb2802ecc 100644 > > > > --- a/kernel/fork.c > > > > +++ b/kernel/fork.c > > > > @@ -659,6 +659,13 @@ static __latent_entropy int > > > > dup_mmap(struct > > > > mm_struct *mm, > > > >   tmp->vm_flags &= ~(VM_LOCKED | > > > > VM_LOCKONFAULT); > > > >   tmp->vm_next = tmp->vm_prev = NULL; > > > >   file = tmp->vm_file; > > > > + > > > > + /* With VM_WIPEONFORK, the child gets an empty > > > > VMA. */ > > > > + if (tmp->vm_flags & VM_WIPEONFORK) { > > > > + tmp->vm_file = file = NULL; > > > > + tmp->vm_ops = NULL; > > > > + } > > > > > > What about VM_SHARED/|VM)MAYSHARE flags. Is it OK to keep the > > > around? > > > At > > > least do_anonymous_page SIGBUS on !vm_ops && VM_SHARED. Or do I > > > miss > > > where those flags are cleared? > > > > Huh, good spotting.  That makes me wonder why the test case that > > Mike and I ran worked just fine on a MAP_SHARED|MAP_ANONYMOUS VMA, > > and returned zero-filled memory when read by the child process. > > Well, I think I still got a BUG with a MAP_SHARED|MAP_ANONYMOUS vma > on > your v2 patch.  Did not really want to start a discussion on the > implementation until the issue of exactly what VM_WIPEONFORK was > supposed > to do was settled. It worked here, but now I don't understand why :) > > > > OK, I'll do a minimal implementation for now, which will return > > -EINVAL if MADV_WIPEONFORK is called on a VMA with MAP_SHARED > > and/or an mmapped file. > > > > It will work the way it is supposed to with anonymous MAP_PRIVATE > > memory, which is likely the only memory it will be used on, anyway. > > > > Seems reasonable. > > You should also add VM_HUGETLB to those returning -EINVAL.  IIRC, a > VM_HUGETLB vma even without VM_SHARED expects vm_file != NULL. In other words (flags & MAP_SHARED || vma->vm_file) would catch hugetlbfs, too?