From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751677AbeDMGJE (ORCPT ); Fri, 13 Apr 2018 02:09:04 -0400 Received: from szxga07-in.huawei.com ([45.249.212.35]:45446 "EHLO huawei.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1750839AbeDMGJD (ORCPT ); Fri, 13 Apr 2018 02:09:03 -0400 Subject: Re: [PATCH] f2fs: set deadline to drop expired inmem pages To: Jaegeuk Kim CC: , , References: <20180408081312.6190-1-yuchao0@huawei.com> <09fd3144-d1c5-ca02-178d-b467d6fbe0e1@huawei.com> <20180413010433.GB51348@jaegeuk-macbookpro.roam.corp.google.com> <20180413040525.GB59368@jaegeuk-macbookpro.roam.corp.google.com> From: Chao Yu Message-ID: <51d2e16a-3a69-71ef-86f5-aee63cd6731c@huawei.com> Date: Fri, 13 Apr 2018 14:08:54 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20180413040525.GB59368@jaegeuk-macbookpro.roam.corp.google.com> Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.134.22.195] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/4/13 12:05, Jaegeuk Kim wrote: > On 04/13, Chao Yu wrote: >> On 2018/4/13 9:04, Jaegeuk Kim wrote: >>> On 04/10, Chao Yu wrote: >>>> Hi Jaegeuk, >>>> >>>> On 2018/4/8 16:13, Chao Yu wrote: >>>>> f2fs doesn't allow abuse on atomic write class interface, so except >>>>> limiting in-mem pages' total memory usage capacity, we need to limit >>>>> start-commit time as well, otherwise we may run into infinite loop >>>>> during foreground GC because target blocks in victim segment are >>>>> belong to atomic opened file for long time. >>>>> >>>>> Now, we will check the condition with f2fs_balance_fs_bg in >>>>> background threads, once if user doesn't commit data exceeding 30 >>>>> seconds, we will drop all cached data, so I expect it can keep our >>>>> system running safely to prevent Dos attack. >>>> >>>> Is it worth to add this patch to avoid abuse on atomic write interface by user? >>> >>> Hmm, hope to see a real problem first in this case. >> >> I think this can be a more critical security leak instead of a potential issue >> which we can wait for someone reporting that can be too late. >> >> For example, user can simply write a huge file whose data spread in all f2fs >> segments, once user open that file as atomic, foreground GC will suffer >> deadloop, causing denying any further service of f2fs. > > How can you guarantee it won't happen within 30sec? If you want to avoid that, Now the value is smaller than generic hang task threshold in order to avoid foreground GC helding gc_mutex too long, we can tune that parameter? > you have to take a look at foreground gc. What do you mean? let GC moves blocks of atomic write opened file? Thanks, > >> >> Thanks, >> >>> >>>> Thanks, >>> >>> . >>> > > . >