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=-6.7 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 89D1AC4320E for ; Tue, 27 Jul 2021 15:35:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 77FCD61B55 for ; Tue, 27 Jul 2021 15:35:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229529AbhG0PfB (ORCPT ); Tue, 27 Jul 2021 11:35:01 -0400 Received: from mail.kernel.org ([198.145.29.99]:49704 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236974AbhG0Pen (ORCPT ); Tue, 27 Jul 2021 11:34:43 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 1F65161B30; Tue, 27 Jul 2021 15:33:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1627400016; bh=4PZARTzEx+NyszsOAu6lbi7w9h8FOGeHdmwe6pE+9NE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jMfiwaUj6xWzdeDehxp1Kzifwu3wYRSTIGzv9URGKhVGQ7a5oKrqU5xwTPvM8rNx8 pL33hpdBVSGbU0eDKRD5kdDDGpSsg07OudM+eVRisgp4MLTvCbY68gt6AFwrlEaWeL aopLejmyoFelH+9R0wF/F8FIhMojSeOMTZFJVWxqpP5Rgqa4t4zjqH2VX+AdH5XtWu uSZlHgfJSee0K/66CiOCohm2St51HvN8o1LX6E39pR4NUcaFuF7YLB9uTQuObrvHCe 87yYD/bifuFjreteUYJGN6RMd5ynEbjBdzoY0CxjBKru8RyTZKG4/VRSpIqcus1Gg1 6rq0L0f6sjiKQ== Date: Tue, 27 Jul 2021 08:33:35 -0700 From: "Darrick J. Wong" To: Chao Yu Cc: Eric Biggers , Jaegeuk Kim , linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, Satya Tangirala , Changheun Lee , Matthew Bobrowski Subject: Re: [PATCH 3/9] f2fs: rework write preallocations Message-ID: <20210727153335.GE559212@magnolia> References: <20210716143919.44373-1-ebiggers@kernel.org> <20210716143919.44373-4-ebiggers@kernel.org> <14782036-f6a5-878a-d21f-e7dd7008a285@kernel.org> <70f16fec-02f6-cb19-c407-856101cacc23@kernel.org> <70d9c954-d7f0-bbe2-f078-62273229342f@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <70d9c954-d7f0-bbe2-f078-62273229342f@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Jul 27, 2021 at 04:30:16PM +0800, Chao Yu wrote: > On 2021/7/27 15:38, Eric Biggers wrote: > > That's somewhat helpful, but I've been doing some more investigation and now I'm > > even more confused. How can f2fs support non-overwrite DIO writes at all > > (meaning DIO writes in LFS mode as well as DIO writes to holes in non-LFS mode), > > given that it has no support for unwritten extents? AFAICS, as-is users can > > I'm trying to pick up DAX support patch created by Qiuyang from huawei, and it > looks it faces the same issue, so it tries to fix this by calling sb_issue_zeroout() > in f2fs_map_blocks() before it returns. I really hope you don't, because zeroing the region before memcpy'ing it is absurd. I don't know if f2fs can do that (xfs can't really) without pinning resources during a potentially lengthy memcpy operation, but you /could/ allocate the space in ->iomap_begin, attach some record of that to iomap->private, and only commit the mapping update in ->iomap_end. --D > > easily leak uninitialized disk contents on f2fs by issuing a DIO write that > > won't complete fully (or might not complete fully), then reading back the blocks > > that got allocated but not written to. > > > > I think that f2fs will have to take the ext2 approach of not allowing > > non-overwrite DIO writes at all... > Yes, > > Another option is to enhance f2fs metadata's scalability which needs to update layout > of dnode block or SSA block, after that we can record the status of unwritten data block > there... it's a big change though... > > Thanks, > > > > > - Eric > >