From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4CC66C04E87 for ; Tue, 21 May 2019 10:55:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 18B32217D4 for ; Tue, 21 May 2019 10:55:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1558436108; bh=9MEN2KbBeRSyHZZ/tEW93WclsJlCnlFw4hYl5f3HiOU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=qYsDu9euNz3L+4Kv6zT61W/IqWllI/HHmR4BFlsqf99kvw3ZNtt1NA2/gX6UQnprL YRyPFhm7kTeoeRrdcDVE1G56Vy42bcuIDaWfrVpDalJPKDc/R+zj1WoUyblV9NLO7f yfWMRwVgBNYE0WRQVAbA2Cp5aB+OLI+Y3PU5fzw4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727915AbfEUKzG (ORCPT ); Tue, 21 May 2019 06:55:06 -0400 Received: from mx2.suse.de ([195.135.220.15]:42094 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726750AbfEUKzG (ORCPT ); Tue, 21 May 2019 06:55:06 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 2FCA9ACBC; Tue, 21 May 2019 10:55:04 +0000 (UTC) Date: Tue, 21 May 2019 12:55:03 +0200 From: Michal Hocko To: Minchan Kim Cc: Oleksandr Natalenko , Andrew Morton , LKML , linux-mm , Johannes Weiner , Tim Murray , Joel Fernandes , Suren Baghdasaryan , Daniel Colascione , Shakeel Butt , Sonny Rao , Brian Geffon Subject: Re: [RFC 4/7] mm: factor out madvise's core functionality Message-ID: <20190521105503.GQ32329@dhcp22.suse.cz> References: <20190520035254.57579-1-minchan@kernel.org> <20190520035254.57579-5-minchan@kernel.org> <20190520142633.x5d27gk454qruc4o@butterfly.localdomain> <20190521012649.GE10039@google.com> <20190521063628.x2npirvs75jxjilx@butterfly.localdomain> <20190521104949.GE219653@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190521104949.GE219653@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 21-05-19 19:49:49, Minchan Kim wrote: > On Tue, May 21, 2019 at 08:36:28AM +0200, Oleksandr Natalenko wrote: > > Hi. > > > > On Tue, May 21, 2019 at 10:26:49AM +0900, Minchan Kim wrote: > > > On Mon, May 20, 2019 at 04:26:33PM +0200, Oleksandr Natalenko wrote: > > > > Hi. > > > > > > > > On Mon, May 20, 2019 at 12:52:51PM +0900, Minchan Kim wrote: > > > > > This patch factor out madvise's core functionality so that upcoming > > > > > patch can reuse it without duplication. > > > > > > > > > > It shouldn't change any behavior. > > > > > > > > > > Signed-off-by: Minchan Kim > > > > > --- > > > > > mm/madvise.c | 168 +++++++++++++++++++++++++++------------------------ > > > > > 1 file changed, 89 insertions(+), 79 deletions(-) > > > > > > > > > > diff --git a/mm/madvise.c b/mm/madvise.c > > > > > index 9a6698b56845..119e82e1f065 100644 > > > > > --- a/mm/madvise.c > > > > > +++ b/mm/madvise.c > > > > > @@ -742,7 +742,8 @@ static long madvise_dontneed_single_vma(struct vm_area_struct *vma, > > > > > return 0; > > > > > } > > > > > > > > > > -static long madvise_dontneed_free(struct vm_area_struct *vma, > > > > > +static long madvise_dontneed_free(struct task_struct *tsk, > > > > > + struct vm_area_struct *vma, > > > > > struct vm_area_struct **prev, > > > > > unsigned long start, unsigned long end, > > > > > int behavior) > > > > > @@ -754,8 +755,8 @@ static long madvise_dontneed_free(struct vm_area_struct *vma, > > > > > if (!userfaultfd_remove(vma, start, end)) { > > > > > *prev = NULL; /* mmap_sem has been dropped, prev is stale */ > > > > > > > > > > - down_read(¤t->mm->mmap_sem); > > > > > - vma = find_vma(current->mm, start); > > > > > + down_read(&tsk->mm->mmap_sem); > > > > > + vma = find_vma(tsk->mm, start); > > > > > if (!vma) > > > > > return -ENOMEM; > > > > > if (start < vma->vm_start) { > > > > > @@ -802,7 +803,8 @@ static long madvise_dontneed_free(struct vm_area_struct *vma, > > > > > * Application wants to free up the pages and associated backing store. > > > > > * This is effectively punching a hole into the middle of a file. > > > > > */ > > > > > -static long madvise_remove(struct vm_area_struct *vma, > > > > > +static long madvise_remove(struct task_struct *tsk, > > > > > + struct vm_area_struct *vma, > > > > > struct vm_area_struct **prev, > > > > > unsigned long start, unsigned long end) > > > > > { > > > > > @@ -836,13 +838,13 @@ static long madvise_remove(struct vm_area_struct *vma, > > > > > get_file(f); > > > > > if (userfaultfd_remove(vma, start, end)) { > > > > > /* mmap_sem was not released by userfaultfd_remove() */ > > > > > - up_read(¤t->mm->mmap_sem); > > > > > + up_read(&tsk->mm->mmap_sem); > > > > > } > > > > > error = vfs_fallocate(f, > > > > > FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, > > > > > offset, end - start); > > > > > fput(f); > > > > > - down_read(¤t->mm->mmap_sem); > > > > > + down_read(&tsk->mm->mmap_sem); > > > > > return error; > > > > > } > > > > > > > > > > @@ -916,12 +918,13 @@ static int madvise_inject_error(int behavior, > > > > > #endif > > > > > > > > What about madvise_inject_error() and get_user_pages_fast() in it > > > > please? > > > > > > Good point. Maybe, there more places where assume context is "current" so > > > I'm thinking to limit hints we could allow from external process. > > > It would be better for maintainance point of view in that we could know > > > the workload/usecases when someone ask new advises from external process > > > without making every hints works both contexts. > > > > Well, for madvise_inject_error() we still have a remote variant of > > get_user_pages(), and that should work, no? > > Regardless of madvise_inject_error, it seems to be risky to expose all > of hints for external process, I think. For example, MADV_DONTNEED with > race, it's critical for stability. So, until we could get the way to > prevent the race, I want to restrict hints. Well, if you allow the full ptrace access then you can shoot the target whatever you like. > > Regarding restricting the hints, I'm definitely interested in having > > remote MADV_MERGEABLE/MADV_UNMERGEABLE. But, OTOH, doing it via remote > > madvise() introduces another issue with traversing remote VMAs reliably. > > How is it signifiact when the race happens? It could waste CPU cycle > and make unncessary break of that merged pages but expect it should be > rare so such non-desruptive hint could be exposed via process_madvise, I think. > > If the hint is critical for the race, yes, as Michal suggested, we need a way > to close it and I guess non-cooperative userfaultfd with synchronous support > would help private anonymous vma. If we have a per vma fd approach then we can revalidate atomically and make sure the operation is performed on the range that was really requested. I do not think we want to provide a more specific guarantees. Monitor process has to be careful same way ptrace doesn't want to harm the target. -- Michal Hocko SUSE Labs