Re: [PATCH v2 1/5] ext4: prevent data corruption with inline data + DAX

[Jan Kara]

On Mon 11-09-17 23:05:22, Ross Zwisler wrote:
> If an inode has inline data it is currently prevented from using DAX by a
> check in ext4_set_inode_flags().  When the inode grows inline data via
> ext4_create_inline_data() or removes its inline data via
> ext4_destroy_inline_data_nolock(), the value of S_DAX can change.
> 
> Currently these changes are unsafe because we don't hold off page faults
> and I/O, write back dirty radix tree entries and invalidate all mappings.
> There are also issues with mm-level races when changing the value of S_DAX,
> as well as issues with the VM_MIXEDMAP flag:
> 
> https://www.spinics.net/lists/linux-xfs/msg09859.html
> 
> The unsafe transition of S_DAX can reliably cause data corruption, as shown
> by the following fstest:
> 
> https://patchwork.kernel.org/patch/9948381/
> 
> Fix this issue by preventing the DAX mount option from being used on
> filesystems that were created to support inline data.  Inline data is an
> option given to mkfs.ext4.
> 
> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> CC: stable@xxxxxxxxxxxxxxx

Looks good. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza

> ---
>  fs/ext4/inline.c | 10 ----------
>  fs/ext4/super.c  |  5 +++++
>  2 files changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
> index 28c5c3a..fd95019 100644
> --- a/fs/ext4/inline.c
> +++ b/fs/ext4/inline.c
> @@ -302,11 +302,6 @@ static int ext4_create_inline_data(handle_t *handle,
>  	EXT4_I(inode)->i_inline_size = len + EXT4_MIN_INLINE_DATA_SIZE;
>  	ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS);
>  	ext4_set_inode_flag(inode, EXT4_INODE_INLINE_DATA);
> -	/*
> -	 * Propagate changes to inode->i_flags as well - e.g. S_DAX may
> -	 * get cleared
> -	 */
> -	ext4_set_inode_flags(inode);
>  	get_bh(is.iloc.bh);
>  	error = ext4_mark_iloc_dirty(handle, inode, &is.iloc);
>  
> @@ -451,11 +446,6 @@ static int ext4_destroy_inline_data_nolock(handle_t *handle,
>  		}
>  	}
>  	ext4_clear_inode_flag(inode, EXT4_INODE_INLINE_DATA);
> -	/*
> -	 * Propagate changes to inode->i_flags as well - e.g. S_DAX may
> -	 * get set.
> -	 */
> -	ext4_set_inode_flags(inode);
>  
>  	get_bh(is.iloc.bh);
>  	error = ext4_mark_iloc_dirty(handle, inode, &is.iloc);
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index c9e7be5..4251e50 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -3707,6 +3707,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>  	}
>  
>  	if (sbi->s_mount_opt & EXT4_MOUNT_DAX) {
> +		if (ext4_has_feature_inline_data(sb)) {
> +			ext4_msg(sb, KERN_ERR, "Cannot use DAX on a filesystem"
> +					" that may contain inline data");
> +			goto failed_mount;
> +		}
>  		err = bdev_dax_supported(sb, blocksize);
>  		if (err)
>  			goto failed_mount;
> -- 
> 2.9.5
> 
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR