Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753431AbdHKPXQ (ORCPT ); Fri, 11 Aug 2017 11:23:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37986 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753148AbdHKPXP (ORCPT ); Fri, 11 Aug 2017 11:23:15 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 91E4D3D3F89 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: <1502464992.6577.48.camel@redhat.com> Subject: Re: [PATCH 2/2] mm,fork: introduce MADV_WIPEONFORK From: Rik van Riel To: Michal Hocko Cc: linux-kernel@vger.kernel.org, mike.kravetz@oracle.com, 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 11:23:12 -0400 In-Reply-To: <20170810152352.GZ23863@dhcp22.suse.cz> References: <20170806140425.20937-1-riel@redhat.com> <20170806140425.20937-3-riel@redhat.com> <20170810152352.GZ23863@dhcp22.suse.cz> 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 15:23:14 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1323 Lines: 35 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. 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.