linux-ext4 - Re: [PATCH v7 3/9] ext4: mark inode dirty before grabbing i_data_sem in ext4

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Message-ID: <20241212215735.dc4ytlkf6mzbnrzd@quack3>
Date: Thu, 12 Dec 2024 22:57:35 +0100
From: Jan Kara <jack@...e.cz>
To: Harshad Shirwadkar <harshadshirwadkar@...il.com>
Cc: linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz,
	harshads@...gle.com
Subject: Re: [PATCH v7 3/9] ext4: mark inode dirty before grabbing i_data_sem
 in ext4_setattr

On Sun 18-08-24 04:03:50, Harshad Shirwadkar wrote:
> Mark inode dirty first and then grab i_data_sem in ext4_setattr().
> 
> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@...il.com>
...

> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index e11f00ff8..c82eba178 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5489,12 +5489,13 @@ int ext4_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
>  					(attr->ia_size > 0 ? attr->ia_size - 1 : 0) >>
>  					inode->i_sb->s_blocksize_bits);
>  
> -			down_write(&EXT4_I(inode)->i_data_sem);
> -			old_disksize = EXT4_I(inode)->i_disksize;
> -			EXT4_I(inode)->i_disksize = attr->ia_size;
>  			rc = ext4_mark_inode_dirty(handle, inode);
>  			if (!error)
>  				error = rc;
> +			down_write(&EXT4_I(inode)->i_data_sem);
> +			old_disksize = EXT4_I(inode)->i_disksize;
> +			EXT4_I(inode)->i_disksize = attr->ia_size;

Well, but this doesn't really work, does it? If you modify inode metadata
*after* calling ext4_mark_inode_dirty() the new metadata will not be copied
into the inode buffer and thus will not be written out... You can move the
ext4_mark_inode_dirty() call to the point where i_data_sem is already
released though. That is perfectly fine.

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