From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from dggsgout11.his.huawei.com (unknown [45.249.212.51]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 482382F2F; Fri, 26 Apr 2024 06:24:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.51 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714112673; cv=none; b=h8jMkIBVpaWqbDM7v60xJdZDrwnly9QbweXxZH0rc/g5eQxdwPDeceIf51Yst8+DWANllZaCbn/SwiYKyzYnms6TmAkvo1arrnCsni4hmvpbg/ILSWq/b8OItkjfpGQ9PageBCFdjlZmIKFu7nXQKCe+G8lp88Wjz3uARgvIyys= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714112673; c=relaxed/simple; bh=XQnuMcIYKRdbws5Pv+8e5wtQFLp076vw3Hhu8svUKyo=; h=Subject:To:Cc:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=VeMVRTm6e0zoY+jDBU/ZoI02BKzNPcLQ887cmGYKLN9nZj6MDsUAgE+5ksevZJJxTU6hglo3QXH1/PI6jjzLW6w0uN129Qvm2eHkNq3sBOTo4XW1EPGoOxR57cPbbzMw7xA47ZcaqzY5MWswkWHuapQx5tyjkDysjyTO1FmPmDk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=pass smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=45.249.212.51 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.93.142]) by dggsgout11.his.huawei.com (SkyGuard) with ESMTP id 4VQjNq6HpFz4f3mHy; Fri, 26 Apr 2024 14:24:11 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.112]) by mail.maildlp.com (Postfix) with ESMTP id 29C441A016E; Fri, 26 Apr 2024 14:24:21 +0800 (CST) Received: from [10.174.176.34] (unknown [10.174.176.34]) by APP1 (Coremail) with SMTP id cCh0CgCXaBGTSCtm2W_3Kw--.24233S3; Fri, 26 Apr 2024 14:24:20 +0800 (CST) Subject: Re: [PATCH v5 4/9] xfs: convert delayed extents to unwritten when zeroing post eof blocks To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, hch@infradead.org, brauner@kernel.org, david@fromorbit.com, chandanbabu@kernel.org, tytso@mit.edu, jack@suse.cz, yi.zhang@huawei.com, chengzhihao1@huawei.com, yukuai3@huawei.com References: <20240425131335.878454-1-yi.zhang@huaweicloud.com> <20240425131335.878454-5-yi.zhang@huaweicloud.com> <20240425182904.GA360919@frogsfrogsfrogs> From: Zhang Yi Message-ID: <3be86418-e629-c7e6-fd73-f59f97a73a89@huaweicloud.com> Date: Fri, 26 Apr 2024 14:24:19 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20240425182904.GA360919@frogsfrogsfrogs> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-CM-TRANSID:cCh0CgCXaBGTSCtm2W_3Kw--.24233S3 X-Coremail-Antispam: 1UD129KBjvJXoWxWw47Kw4fXr13JFy8WFWDCFg_yoW7Gr43pF Z3K3W5KF4Dtw1avw1Iv3W5Kw1F93Z3Cr47Ary3Xrn3Za4Yyr1fKF17K3Wjgry8CrZ3A3Wj vFWjg3s293s0vFDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvIb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rwA2F7IY1VAKz4 vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Ar0_tr1l84ACjcxK6xIIjxv20xvEc7Cj xVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x 0267AKxVW0oVCq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG 6I80ewAv7VC0I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFV Cjc4AY6r1j6r4UM4x0Y48IcVAKI48JM4IIrI8v6xkF7I0E8cxan2IY04v7Mxk0xIA0c2IE e2xFo4CEbIxvr21l42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxV Aqx4xG67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q 6r43MIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6x kF7I0E14v26r4j6F4UMIIF0xvE42xK8VAvwI8IcIk0rVWrZr1j6s0DMIIF0xvEx4A2jsIE 14v26r1j6r4UMIIF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf 9x07UWE__UUUUU= X-CM-SenderInfo: d1lo6xhdqjqx5xdzvxpfor3voofrz/ On 2024/4/26 2:29, Darrick J. Wong wrote: > On Thu, Apr 25, 2024 at 09:13:30PM +0800, Zhang Yi wrote: >> From: Zhang Yi >> >> Current clone operation could be non-atomic if the destination of a file >> is beyond EOF, user could get a file with corrupted (zeroed) data on >> crash. >> >> The problem is about preallocations. If you write some data into a file: >> >> [A...B) >> >> and XFS decides to preallocate some post-eof blocks, then it can create >> a delayed allocation reservation: >> >> [A.........D) >> >> The writeback path tries to convert delayed extents to real ones by >> allocating blocks. If there aren't enough contiguous free space, we can >> end up with two extents, the first real and the second still delalloc: >> >> [A....C)[C.D) >> >> After that, both the in-memory and the on-disk file sizes are still B. >> If we clone into the range [E...F) from another file: >> >> [A....C)[C.D) [E...F) >> >> then xfs_reflink_zero_posteof() calls iomap_zero_range() to zero out the >> range [B, E) beyond EOF and flush it. Since [C, D) is still a delalloc >> extent, its pagecache will be zeroed and both the in-memory and on-disk >> size will be updated to D after flushing but before cloning. This is >> wrong, because the user can see the size change and read the zeroes >> while the clone operation is ongoing. >> >> We need to keep the in-memory and on-disk size before the clone >> operation starts, so instead of writing zeroes through the page cache >> for delayed ranges beyond EOF, we convert these ranges to unwritten and >> invalidate any cached data over that range beyond EOF. >> >> Suggested-by: Dave Chinner >> Signed-off-by: Zhang Yi >> --- >> Changes since v4: >> >> Move the delalloc converting hunk before searching the COW fork. Because >> if the file has been reflinked and copied on write, >> xfs_bmap_extsize_align() aligned the range of COW delalloc extent, after >> the writeback, there might be some unwritten extents left over in the >> COW fork that overlaps the delalloc extent we found in data fork. >> >> data fork ...wwww|dddddddddd... >> cow fork |uuuuuuuuuu... >> ^ >> i_size >> >> In my v4, we search the COW fork before checking the delalloc extent, >> goto found_cow tag and return unconverted delalloc srcmap in the above >> case, so the delayed extent in the data fork will have no chance to >> convert to unwritten, it will lead to delalloc extent residue and break >> generic/522 after merging patch 6. > > Hmmm. I suppose that works, but it feels a little funny to convert the > delalloc mapping in the data fork to unwritten /while/ there's unwritten > extents in the cow fork too. Would it make more sense to remap the cow > fork extents here? > Yeah, it looks more reasonable. But from the original scene, the xfs_bmap_extsize_align() aligned the new extent that added to the cow fork could overlaps the unreflinked range, IIUC, I guess that spare range is useless exactly, is there any situation that would use it? > OTOH unwritten extents in the cow fork get changed to written ones by > all the cow remapping functions. Soooo maybe we don't want to go > digging /that/ deep into the system. > Yeah, I think it's okay now unless there's some strong claims. > Reviewed-by: Darrick J. Wong > > --D > >> >> fs/xfs/xfs_iomap.c | 29 +++++++++++++++++++++++++++++ >> 1 file changed, 29 insertions(+) >> >> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c >> index 236ee78aa75b..2857ef1b0272 100644 >> --- a/fs/xfs/xfs_iomap.c >> +++ b/fs/xfs/xfs_iomap.c >> @@ -1022,6 +1022,24 @@ xfs_buffered_write_iomap_begin( >> goto out_unlock; >> } >> >> + /* >> + * For zeroing, trim a delalloc extent that extends beyond the EOF >> + * block. If it starts beyond the EOF block, convert it to an >> + * unwritten extent. >> + */ >> + if ((flags & IOMAP_ZERO) && imap.br_startoff <= offset_fsb && >> + isnullstartblock(imap.br_startblock)) { >> + xfs_fileoff_t eof_fsb = XFS_B_TO_FSB(mp, XFS_ISIZE(ip)); >> + >> + if (offset_fsb >= eof_fsb) >> + goto convert_delay; >> + if (end_fsb > eof_fsb) { >> + end_fsb = eof_fsb; >> + xfs_trim_extent(&imap, offset_fsb, >> + end_fsb - offset_fsb); >> + } >> + } >> + >> /* >> * Search the COW fork extent list even if we did not find a data fork >> * extent. This serves two purposes: first this implements the >> @@ -1167,6 +1185,17 @@ xfs_buffered_write_iomap_begin( >> xfs_iunlock(ip, lockmode); >> return xfs_bmbt_to_iomap(ip, iomap, &imap, flags, 0, seq); >> >> +convert_delay: >> + xfs_iunlock(ip, lockmode); >> + truncate_pagecache(inode, offset); >> + error = xfs_bmapi_convert_delalloc(ip, XFS_DATA_FORK, offset, >> + iomap, NULL); >> + if (error) >> + return error; >> + >> + trace_xfs_iomap_alloc(ip, offset, count, XFS_DATA_FORK, &imap); >> + return 0; >> + >> found_cow: >> seq = xfs_iomap_inode_sequence(ip, 0); >> if (imap.br_startoff <= offset_fsb) { >> -- >> 2.39.2 >> >>