linux-kernel - Re: [PATCH -next v2 1/7] ext4: use reserved metadata blocks when splitting extent on endio

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <c05d7382-27c8-46cb-a008-56c5dc2fde5d@huawei.com>
Date: Wed, 31 Dec 2025 15:34:51 +0800
From: Baokun Li <libaokun1@...wei.com>
To: Zhang Yi <yi.zhang@...weicloud.com>, <linux-ext4@...r.kernel.org>
CC: <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<tytso@....edu>, <adilger.kernel@...ger.ca>, <jack@...e.cz>,
	<ojaswin@...ux.ibm.com>, <ritesh.list@...il.com>, <yi.zhang@...wei.com>,
	<yizhang089@...il.com>, <yangerkun@...wei.com>, <yukuai@...as.com>
Subject: Re: [PATCH -next v2 1/7] ext4: use reserved metadata blocks when
 splitting extent on endio

On 2025-12-23 09:17, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
>
> When performing buffered writes, we may need to split and convert an
> unwritten extent into a written one during the end I/O process. However,
> we do not reserve space specifically for these metadata changes, we only
> reserve 2% of space or 4096 blocks. To address this, we use
> EXT4_GET_BLOCKS_PRE_IO to potentially split extents in advance and
> EXT4_GET_BLOCKS_METADATA_NOFAIL to utilize reserved space if necessary.
>
> These two approaches can reduce the likelihood of running out of space
> and losing data. However, these methods are merely best efforts, we
> could still run out of space, and there is not much difference between
> converting an extent during the writeback process and the end I/O
> process, it won't increase the rick of losing data if we postpone the
> conversion.
>
> Therefore, also use EXT4_GET_BLOCKS_METADATA_NOFAIL in
> ext4_convert_unwritten_extents_endio() to prepare for the buffered I/O
> iomap conversion, which may perform extent conversion during the end I/O
> process.
>
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>
> Reviewed-by: Jan Kara <jack@...e.cz>

Fair point, that is consistent with how
ext4_ext_handle_unwritten_extents() handles it.

Reviewed-by: Baokun Li <libaokun1@...wei.com>

> ---
>  fs/ext4/extents.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 27eb2c1df012..e53959120b04 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3794,6 +3794,8 @@ ext4_convert_unwritten_extents_endio(handle_t *handle, struct inode *inode,
>  	 * illegal.
>  	 */
>  	if (ee_block != map->m_lblk || ee_len > map->m_len) {
> +		int flags = EXT4_GET_BLOCKS_CONVERT |
> +			    EXT4_GET_BLOCKS_METADATA_NOFAIL;
>  #ifdef CONFIG_EXT4_DEBUG
>  		ext4_warning(inode->i_sb, "Inode (%ld) finished: extent logical block %llu,"
>  			     " len %u; IO logical block %llu, len %u",
> @@ -3801,7 +3803,7 @@ ext4_convert_unwritten_extents_endio(handle_t *handle, struct inode *inode,
>  			     (unsigned long long)map->m_lblk, map->m_len);
>  #endif
>  		path = ext4_split_convert_extents(handle, inode, map, path,
> -						EXT4_GET_BLOCKS_CONVERT, NULL);
> +						  flags, NULL);
>  		if (IS_ERR(path))
>  			return path;
>