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=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 37092C2BA80 for ; Tue, 7 Apr 2020 01:55:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0D44F207FF for ; Tue, 7 Apr 2020 01:55:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="B6Rz7dKm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726591AbgDGBzm (ORCPT ); Mon, 6 Apr 2020 21:55:42 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:50716 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726329AbgDGBzl (ORCPT ); Mon, 6 Apr 2020 21:55:41 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1586224540; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=oItCj2q8YHb63ZBfFyBFQkDD3U/LJfbIS9cHzfIZ+kg=; b=B6Rz7dKmqjP/KZc/yHJLXh5qkViWKUmVdbJHXVWDpYNpF4GSCLOLl5E5YMazBfhaNyFkTf 7ZrCwbnlb4mfKto+XLkIQKRWmcjGxCdPfAGDGvaXqnos+7KVxeJOBDkw6tRlCGKPTc47mR FSrvw5rjSd/jmmk+pa5K4YuaEh4t+Y8= Received: from mail-qt1-f198.google.com (mail-qt1-f198.google.com [209.85.160.198]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-255-2xOz6wj1N22t3dsDwhlmSA-1; Mon, 06 Apr 2020 21:55:38 -0400 X-MC-Unique: 2xOz6wj1N22t3dsDwhlmSA-1 Received: by mail-qt1-f198.google.com with SMTP id n89so1748662qte.15 for ; Mon, 06 Apr 2020 18:55:38 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=oItCj2q8YHb63ZBfFyBFQkDD3U/LJfbIS9cHzfIZ+kg=; b=rAS68Ug9Up1JhHOXOWlTBX1Ta+iH+DNfq0epE4Pd+8yxcYbGfMFReANkGRs+EiDfFA Amr8QnaPrEuIS6qYen1tHu2vDRAvGteSXTBgwGJJqsPRVQ7uSwR5a7k1MPvVrkJY+T5s GwDf4ZVOXB2INzSAZdjo15hNhr81QqjrF6q6tXvxYhmEYZPfRIsSxpms8R0Yra9Cb5Yi w+LHYn/TgfO/YaDOo1AlB9d6iXBMYEUw+j4j4Lh6BQ8JijSf2mNqvnjtld72Ni66kGdn h1ogYc+rRzAbwjcAU29X2RtU7fOKaXWLkZqMnbZxgNpZ0ERwEnXagRcK1+SOHsJsZ2cr VlGA== X-Gm-Message-State: AGi0PuY/AS8Okh8kT51rFT2/MjxEqMs3SxJOzfjHhzIOvKhvsTxOm108 01Nqve61XjeSFBxJD+HrxzSgi7e5mohordfxWJ4odkUfoKMD6Td/pyBMnXYAGHk44gi3LZE3m3q bL2PDsqkV4GbY2XUr+dZUS+VX X-Received: by 2002:ac8:4d8b:: with SMTP id a11mr143478qtw.391.1586224538182; Mon, 06 Apr 2020 18:55:38 -0700 (PDT) X-Google-Smtp-Source: APiQypK+gNlV/6Oyl3ckqIUc2Hc29srtoZnCqrcc5MKHtt+qWVWRdKpz+NvsF8oAGL3g8gWu3juB0g== X-Received: by 2002:ac8:4d8b:: with SMTP id a11mr143461qtw.391.1586224537863; Mon, 06 Apr 2020 18:55:37 -0700 (PDT) Received: from xz-x1 ([2607:9880:19c0:32::3]) by smtp.gmail.com with ESMTPSA id c6sm13998002qkg.88.2020.04.06.18.55.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Apr 2020 18:55:37 -0700 (PDT) Date: Mon, 6 Apr 2020 21:55:35 -0400 From: Peter Xu To: Andrew Morton Cc: syzbot , bgeffon@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, torvalds@linux-foundation.org Subject: Re: BUG: unable to handle kernel paging request in kernel_get_mempolicy Message-ID: <20200407015535.GC48345@xz-x1> References: <0000000000002b25f105a2a3434d@google.com> <20200407004745.GA48345@xz-x1> <20200406183941.38a2e52026e42dbfde239a56@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200406183941.38a2e52026e42dbfde239a56@linux-foundation.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 06, 2020 at 06:39:41PM -0700, Andrew Morton wrote: > On Mon, 6 Apr 2020 20:47:45 -0400 Peter Xu wrote: > > > >From 23800bff6fa346a4e9b3806dc0cfeb74498df757 Mon Sep 17 00:00:00 2001 > > From: Peter Xu > > Date: Mon, 6 Apr 2020 20:40:13 -0400 > > Subject: [PATCH] mm/mempolicy: Allow lookup_node() to handle fatal signal > > > > lookup_node() uses gup to pin the page and get node information. It > > checks against ret>=0 assuming the page will be filled in. However > > it's also possible that gup will return zero, for example, when the > > thread is quickly killed with a fatal signal. Teach lookup_node() to > > gracefully return an error -EFAULT if it happens. > > > > ... > > > > --- a/mm/mempolicy.c > > +++ b/mm/mempolicy.c > > @@ -902,7 +902,10 @@ static int lookup_node(struct mm_struct *mm, unsigned long addr) > > > > int locked = 1; > > err = get_user_pages_locked(addr & PAGE_MASK, 1, 0, &p, &locked); > > - if (err >= 0) { > > + if (err == 0) { > > + /* E.g. GUP interupted by fatal signal */ > > + err = -EFAULT; > > + } else if (err > 0) { > > err = page_to_nid(p); > > put_page(p); > > } > > Doh. Thanks. > > Should it have been -EINTR? It looks ok to me too. I was returning -EFAULT to follow the same value as get_vaddr_frames() (which is the other caller of get_user_pages_locked()). So far the only path that I found can trigger this is when there's a fatal signal pending right after the gup. If so, the userspace won't have a chance to see the -EINTR (or whatever we return) anyways. Thanks, -- Peter Xu