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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 EC581C433FE for ; Wed, 9 Dec 2020 03:16:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BE648238E3 for ; Wed, 9 Dec 2020 03:16:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727065AbgLIDQJ (ORCPT ); Tue, 8 Dec 2020 22:16:09 -0500 Received: from mail.kernel.org ([198.145.29.99]:47898 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725789AbgLIDQJ (ORCPT ); Tue, 8 Dec 2020 22:16:09 -0500 Date: Tue, 8 Dec 2020 19:15:26 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1607483728; bh=/4TCF+LoYzcyXRHmzC+6ypXWpRH+zDesJ+YVBcIHubI=; h=From:To:Cc:Subject:References:In-Reply-To:From; b=aLahg2d33CLweu7xhCmj+NyikfQjlTnrdJKNKNP66cL2oBFj417284FYP0Xoy4PCX ewWVdfpu0TGF2ExWeQBjFI4/zZeG1S4H1ZQexJLzmablWlaZYfQZQQMJAgmA3tc4b2 fJRnMMY3nKlT7cFXNukiAmwWEl5tO/3vcYP0OsnveA4bZwKUpFmI3FNN3Zc4Txx3Ku Twxrao+9ZCPEkFowmBomoWD6KXUeyG/ZUi45YtLLRNGG8VpPMn/NneufxlbTnSPobJ g06kc6WSERDwobDJ4kBsnhN+SQKEmkn+geqdsyg84j7Ey29HsfvGrHgyTa+5Zl+SWa 9LlHGZmRCOHbQ== From: Eric Biggers To: Chao Yu Cc: Jaegeuk Kim , Daeho Jeong , kernel-team@android.com, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net Subject: Re: [f2fs-dev] [PATCH v3] f2fs: fix race of pending_pages in decompression Message-ID: References: <20201205042626.1113600-1-daeho43@gmail.com> <55db08c3-6b3f-a78b-c40d-7f61cd7693b7@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55db08c3-6b3f-a78b-c40d-7f61cd7693b7@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 09, 2020 at 09:34:06AM +0800, Chao Yu wrote: > 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, I'm not in a hurry, please just take a look when you have time. - Eric