From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753519AbdHPCS1 (ORCPT ); Tue, 15 Aug 2017 22:18:27 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46450 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753441AbdHPCSV (ORCPT ); Tue, 15 Aug 2017 22:18:21 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 52C6662647 Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx10.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=riel@redhat.com Message-ID: <1502849899.6577.66.camel@redhat.com> Subject: Re: [PATCH 2/2] mm,fork: introduce MADV_WIPEONFORK From: Rik van Riel To: Andrew Morton Cc: linux-kernel@vger.kernel.org, mhocko@kernel.org, mike.kravetz@oracle.com, linux-mm@kvack.org, fweimer@redhat.com, colm@allcosts.net, keescook@chromium.org, luto@amacapital.net, wad@chromium.org, mingo@kernel.org, kirill@shutemov.name, dave.hansen@intel.com, linux-api@vger.kernel.org, torvalds@linux-foundation.org, willy@infradead.org Date: Tue, 15 Aug 2017 22:18:19 -0400 In-Reply-To: <20170815155114.ff9f4164eed28bf02db48fbb@linux-foundation.org> References: <20170811212829.29186-1-riel@redhat.com> <20170811212829.29186-3-riel@redhat.com> <20170815155114.ff9f4164eed28bf02db48fbb@linux-foundation.org> 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 [10.5.110.39]); Wed, 16 Aug 2017 02:18:21 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2017-08-15 at 15:51 -0700, Andrew Morton wrote: > On Fri, 11 Aug 2017 17:28:29 -0400 riel@redhat.com wrote: > > > A further complication is the proliferation of clone flags, > > programs bypassing glibc's functions to call clone directly, > > and programs calling unshare, causing the glibc pthread_atfork > > hook to not get called. > > > > It would be better to have the kernel take care of this > > automatically. > > I'll add "The patch also adds MADV_KEEPONFORK, to undo the effects of > a > prior MADV_WIPEONFORK." here. > > I guess it isn't worth mentioning that these things can cause VMA > merges and splits.  That's the same as every other Linux specific madvise operation. > > --- a/mm/madvise.c > > +++ b/mm/madvise.c > > @@ -80,6 +80,17 @@ static long madvise_behavior(struct > > vm_area_struct *vma, > >   } > >   new_flags &= ~VM_DONTCOPY; > >   break; > > + case MADV_WIPEONFORK: > > + /* MADV_WIPEONFORK is only supported on anonymous > > memory. */ > > + if (vma->vm_file || vma->vm_flags & VM_SHARED) { > > + error = -EINVAL; > > + goto out; > > + } > > + new_flags |= VM_WIPEONFORK; > > + break; > > + case MADV_KEEPONFORK: > > + new_flags &= ~VM_WIPEONFORK; > > + break; > >   case MADV_DONTDUMP: > >   new_flags |= VM_DONTDUMP; > >   break; > > It seems odd to permit MADV_KEEPONFORK against other-than-anon vmas? Given that the only way to set VM_WIPEONFORK is through MADV_WIPEONFORK, calling MADV_KEEPONFORK on an other-than-anon vma would be equivalent to a noop. If new_flags == vma->vm_flags, madvise_behavior() will immediately exit.