From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f200.google.com (mail-qk0-f200.google.com [209.85.220.200]) by kanga.kvack.org (Postfix) with ESMTP id 8D9AB6B025F for ; Fri, 11 Aug 2017 13:07:17 -0400 (EDT) Received: by mail-qk0-f200.google.com with SMTP id d136so20297957qkg.11 for ; Fri, 11 Aug 2017 10:07:17 -0700 (PDT) Received: from userp1040.oracle.com (userp1040.oracle.com. [156.151.31.81]) by mx.google.com with ESMTPS id 140si1134441qkg.455.2017.08.11.10.07.16 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 11 Aug 2017 10:07:16 -0700 (PDT) Subject: Re: [PATCH 2/2] mm,fork: introduce MADV_WIPEONFORK 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> <1502470781.6577.49.camel@redhat.com> From: Mike Kravetz Message-ID: Date: Fri, 11 Aug 2017 10:07:04 -0700 MIME-Version: 1.0 In-Reply-To: <1502470781.6577.49.camel@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel , 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 On 08/11/2017 09:59 AM, Rik van Riel wrote: > 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? Yes, that should catch hugetlbfs. -- Mike Kravetz -- 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/ . Don't email: email@kvack.org