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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham 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 ACF38C6786E for ; Fri, 26 Oct 2018 10:57:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7BA6220856 for ; Fri, 26 Oct 2018 10:57:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7BA6220856 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727503AbeJZTdg (ORCPT ); Fri, 26 Oct 2018 15:33:36 -0400 Received: from mx2.suse.de ([195.135.220.15]:47588 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726275AbeJZTdg (ORCPT ); Fri, 26 Oct 2018 15:33:36 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 76A82AE86; Fri, 26 Oct 2018 10:56:58 +0000 (UTC) Date: Fri, 26 Oct 2018 12:56:56 +0200 From: Michal Hocko To: Matthew Wilcox Cc: miles.chen@mediatek.com, Matthias Brugger , linux-kernel@vger.kernel.org, linux-mm@kvack.org, wsd_upstream@mediatek.com, linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] mm/page_owner: use vmalloc instead of kmalloc Message-ID: <20181026085410.GA8277@dhcp22.suse.cz> References: <1540492481-4144-1-git-send-email-miles.chen@mediatek.com> <20181025192701.GK25444@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181025192701.GK25444@bombadil.infradead.org> 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 Thu 25-10-18 12:27:01, Matthew Wilcox wrote: > On Fri, Oct 26, 2018 at 02:34:41AM +0800, miles.chen@mediatek.com wrote: > > The kbuf used by page owner is allocated by kmalloc(), > > which means it can use only normal memory and there might > > be a "out of memory" issue when we're out of normal memory. > > > > Use vmalloc() so we can also allocate kbuf from highmem > > on 32bit kernel. > > ... hang on, there's a bigger problem here. > > static const struct file_operations proc_page_owner_operations = { > .read = read_page_owner, > }; > > read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) > { > ... > return print_page_owner(buf, count, pfn, page, > page_owner, handle); > } > > static ssize_t > print_page_owner(char __user *buf, size_t count, unsigned long pfn, > struct page *page, struct page_owner *page_owner, > depot_stack_handle_t handle) > { > ... > kbuf = kmalloc(count, GFP_KERNEL); > > So I can force the kernel to make an arbitrary size allocation, triggering > OOMs and forcing swapping if I can get a file handle to this file. > The only saving grace is that (a) this is a debugfs file and (b) it's > root-only (mode 0400). Nevertheless, I feel some clamping is called > for here. Do we really need to output more than 4kB worth of text here? Completely agreed. Let's just clamp it to a single page. Userspace can easily loop around the syscall. -- Michal Hocko SUSE Labs