linux-ext4 - Re: [PATCH v6 03/10] ext4: mark inode dirty before grabbing i_data_sem in ext4

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Message-ID: <20240628131518.nxirjq7qqhz3ckh5@quack3>
Date: Fri, 28 Jun 2024 15:15:18 +0200
From: Jan Kara <jack@...e.cz>
To: Harshad Shirwadkar <harshadshirwadkar@...il.com>
Cc: linux-ext4@...r.kernel.org, tytso@....edu, saukad@...gle.com,
	harshads@...gle.com
Subject: Re: [PATCH v6 03/10] ext4: mark inode dirty before grabbing
 i_data_sem in ext4_setattr

On Wed 29-05-24 01:19:56, Harshad Shirwadkar wrote:
> Mark inode dirty first and then grab i_data_sem in ext4_setattr().
> 
> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@...il.com>
> ---
>  fs/ext4/inode.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index aa6440992a55..61ffbdc2fb16 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5410,12 +5410,13 @@ 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;
> +

This is wrong. ext4_mark_inode_dirty() will copy the data to on-disk
buffer. If you set i_disksize after ext4_mark_inode_dirty(), the change
will not get properly logged in the transaction.

What you rather need is calling ext4_mark_inode_dirty() after dropping
i_data_sem which should be completely fine.

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