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=-9.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A89E0C4320A for ; Fri, 20 Aug 2021 22:01:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7CD0761178 for ; Fri, 20 Aug 2021 22:01:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231615AbhHTWCG (ORCPT ); Fri, 20 Aug 2021 18:02:06 -0400 Received: from mail.kernel.org ([198.145.29.99]:35854 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229760AbhHTWCF (ORCPT ); Fri, 20 Aug 2021 18:02:05 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 05D6260F39; Fri, 20 Aug 2021 22:01:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1629496887; bh=6Tvf7F8XzySJVAbATDnQkPDRqPuOZ8gtDkb+RLf8JtE=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=a+qXY05sok1kXn0ucTlvGUaXS0cVuG6RW8Rg8+OrzmUosd0h64U4VrkHM1eFmTUpy dOAL54ZWwyNRPd/6Jca3QOL7sFlUk/bYFhCR/LTpU1MF8QOSC121q8pnqQ4kT4IM8N bkXww1I/CT+6LSuFIpsT8/gCJC6nVGSeBxBB/dzUPUY8w35fWNu7XUfRwTbqyhA0ss heOKNv873m4IDcP43HGDZ3GK9vNJA/gEGKExVTlklWmeU4d4cf0klrZQ4r86tv7JW0 AI5PT99NwcZYuuDGtyUDpZyG61xx1a/Wrtl51zW1LgA7GiXFbR0poVZK1WeCjfgOoG ckREQ7e93K7Ow== Subject: Re: [PATCH] f2fs: remove broken support for allocating DIO writes To: Eric Biggers Cc: Jaegeuk Kim , Theodore Ts'o , linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, stable@vger.kernel.org References: <20210728015154.171507-1-ebiggers@kernel.org> From: Chao Yu Message-ID: Date: Sat, 21 Aug 2021 06:01:26 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 2021/8/21 2:11, Eric Biggers wrote: > On Fri, Aug 20, 2021 at 05:35:21PM +0800, Chao Yu wrote: >>>>>> >>>>>> Hmm, I'm still trying to deal with this as a corner case where the writes >>>>>> haven't completed due to an error. How about keeping the preallocated block >>>>>> offsets and releasing them if we get an error? Do we need to handle EIO right? >>>>> >>>>> What about the case that CP + SPO following DIO preallocation? User will >>>>> encounter uninitialized block after recovery. >>>> >>>> I think buffered writes as a workaround can expose the last unwritten block as >>>> well, if SPO happens right after block allocation. We may need to compromise >>>> at certain level? >>>> >>> >>> Freeing preallocated blocks on error would be better than nothing, although note >>> that the preallocated blocks may have filled an arbitrary sequence of holes -- >>> so simply truncating past EOF would *not* be sufficient. >>> >>> But really filesystems need to be designed to never expose uninitialized data, >>> even if I/O errors or a sudden power failure occurs. It is unfortunate that >>> f2fs apparently wasn't designed with that goal in mind. >>> >>> In any case, I don't think we can proceed with any other f2fs direct I/O >>> improvements until this data leakage bug can be solved one way or another. If >>> my patch to remove support for allocating writes isn't acceptable and the >>> desired solution is going to require some more invasive f2fs surgery, are you or >>> Chao going to work on it? I'm not sure there's much I can do here. >> >> I may have time to take look into the implementation as I proposed above, maybe >> just enabling this in FSYNC_MODE_STRICT mode if user concerns unwritten data? >> thoughts? >> > > What does this have to do with fsync? Oops, maybe a separate option is more appropriate. > > - Eric >