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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 7A546C4361B for ; Wed, 9 Dec 2020 01:34:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 436B4238E9 for ; Wed, 9 Dec 2020 01:34:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725974AbgLIBex (ORCPT ); Tue, 8 Dec 2020 20:34:53 -0500 Received: from szxga05-in.huawei.com ([45.249.212.191]:9556 "EHLO szxga05-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725905AbgLIBex (ORCPT ); Tue, 8 Dec 2020 20:34:53 -0500 Received: from DGGEMS402-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4CrKLx3kDKzM22W; Wed, 9 Dec 2020 09:33:29 +0800 (CST) Received: from [10.136.114.67] (10.136.114.67) by smtp.huawei.com (10.3.19.202) with Microsoft SMTP Server (TLS) id 14.3.487.0; Wed, 9 Dec 2020 09:34:07 +0800 Subject: Re: [f2fs-dev] [PATCH v3] f2fs: fix race of pending_pages in decompression To: Jaegeuk Kim , Eric Biggers CC: Daeho Jeong , , , References: <20201205042626.1113600-1-daeho43@gmail.com> From: Chao Yu Message-ID: <55db08c3-6b3f-a78b-c40d-7f61cd7693b7@huawei.com> Date: Wed, 9 Dec 2020 09:34:06 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.136.114.67] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/12/9 7:55, Jaegeuk Kim wrote: > On 12/07, Eric Biggers wrote: >> On Tue, Dec 08, 2020 at 08:51:45AM +0900, Daeho Jeong wrote: >>>> I am trying to review this but it is very hard, as the f2fs compression code is >>>> very hard to understand. >>>> >>>> It looks like a 'struct decompress_io_ctx' represents the work to decompress a >>>> particular cluster. Since the compressed data of the cluster can be read using >>>> multiple bios, there is a reference count of how many pages are remaining to be >>>> read before all the cluster's pages have been read and decompression can start. >>>> >>>> What I don't understand is why that reference counting needs to work differently >>>> depending on whether verity is enabled or not. Shouldn't it be exactly the >>>> same? >>>> >>>> There also seems to be some confusion about the scope of STEP_VERITY. Before >>>> f2fs compression was added, it was a per-bio thing. But now in a compressed >>>> file, it's really a per-cluster thing, since all decompressed pages in a >>>> compressed cluster are verified (or not verified) at once. >>>> >>>> Wouldn't it make a lot more sense to, when a cluster needs both compression and >>>> verity, *not* set STEP_VERITY on the bios, but rather set a similar flag in the >>>> decompress_io_ctx? >>>> >>> >>> Eric, >>> >>> Decompression and verity can be executed in different thread contexts >>> in different timing, so we need separate counts for each. >>> >>> We already use STEP_VERITY for non-compression case, so I think using >>> this flag in here looks more making sense. >>> >>> Thanks, >> >> That didn't really answer my questions. >> >> I gave up trying to review this patch as the compression post-read handling is >> just way too weird and hard to understand. I wrote a patch to clean it all up >> instead, please take a look: >> https://lkml.kernel.org/r/20201208060328.2237091-1-ebiggers@kernel.org > > Eric, > I also tried to review your patch, but it's quite hard to follow quickly and Me too, it needs more time to check whether the cleanup doesn't miss any cases. Thanks, > requires stress tests for a while. Given upcoming merge window and urgency of > the bug, let me apply Daeho's fix first. By any chance, may I ask revisiting > your clean-up on top of the fix in the next cycle? > > Thanks, > >> >> - Eric > > > _______________________________________________ > Linux-f2fs-devel mailing list > Linux-f2fs-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel > . >