linux-kernel - Re: [PATCH 2/4] ext4: fix incorrect punch max

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Message-ID: <ykm27jvrnmhgd4spslhn4mano452c6z34fab7r3776dmjkgo7q@cv2lvsiteufa>
Date: Wed, 30 Apr 2025 10:18:58 +0200
From: Jan Kara <jack@...e.cz>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca, jack@...e.cz, 
	wanghaichi0403@...il.com, yi.zhang@...wei.com, libaokun1@...wei.com, yukuai3@...wei.com, 
	yangerkun@...wei.com
Subject: Re: [PATCH 2/4] ext4: fix incorrect punch max_end

On Wed 30-04-25 09:12:59, Zhang Yi wrote:
> From: Zhang Yi <yi.zhang@...wei.com>
> 
> For the extents inodes, the maxbytes should be sb->s_maxbytes instead of
> sbi->s_bitmap_maxbytes. Correct the maxbytes value to correct the
> behavior of punch hole.
> 
> Fixes: 2da376228a24 ("ext4: limit length to bitmap_maxbytes - blocksize in punch_hole")
> Signed-off-by: Zhang Yi <yi.zhang@...wei.com>

Thinking about this some more...

> @@ -4015,6 +4015,12 @@ int ext4_punch_hole(struct file *file, loff_t offset, loff_t length)
>  	trace_ext4_punch_hole(inode, offset, length, 0);
>  	WARN_ON_ONCE(!inode_is_locked(inode));
>  
> +	if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
> +		max_end = sb->s_maxbytes;
> +	else
> +		max_end = EXT4_SB(sb)->s_bitmap_maxbytes;
> +	max_end -= sb->s_blocksize;

I think the -= sb->s_blocksize is needed only for indirect-block based
scheme (due to an implementation quirk in ext4_ind_remove_space()). But
ext4_ext_remove_space() should be fine with punch hole ending right at
sb->s_maxbytes. And since I find it somewhat odd that you can create file
upto s_maxbytes but cannot punch hole to the end, it'd limit that behavior
as much as possible. Ideally we'd fix ext4_ind_remove_space() but I can't
be really bothered for the ancient format...

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR