Re: [PATCH 2/2] Btrfs: fix dedupe vs chattr NODATASUM race

[Nikolay Borisov <nborisov@suse.com>]

On 23.05.2018 01:02, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> In btrfs_extent_same(), we must check the NODATASUM flag while the
> inodes are locked. Otherwise, it's possible that btrfs_ioctl_setflags()
> will change the flags after we check. This was correct until a recent
> change.
> 
> Fixes: 0a38effca37c ("Btrfs: split btrfs_extent_same")
> Signed-off-by: Omar Sandoval <osandov@fb.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
>  fs/btrfs/ioctl.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 784e267aad32..c2263bf4d6f5 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -3586,12 +3586,6 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
>  	if (olen == 0)
>  		return 0;
>  
> -	/* don't make the dst file partly checksummed */
> -	if ((BTRFS_I(src)->flags & BTRFS_INODE_NODATASUM) !=
> -	    (BTRFS_I(dst)->flags & BTRFS_INODE_NODATASUM)) {
> -		return -EINVAL;
> -	}
> -
>  	tail_len = olen % BTRFS_MAX_DEDUPE_LEN;
>  	chunk_count = div_u64(olen, BTRFS_MAX_DEDUPE_LEN);
>  	if (chunk_count == 0)
> @@ -3624,6 +3618,13 @@ static int btrfs_extent_same(struct inode *src, u64 loff, u64 olen,
>  	else
>  		btrfs_double_inode_lock(src, dst);
>  
> +	/* don't make the dst file partly checksummed */
> +	if ((BTRFS_I(src)->flags & BTRFS_INODE_NODATASUM) !=
> +	    (BTRFS_I(dst)->flags & BTRFS_INODE_NODATASUM)) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
>  	for (i = 0; i < chunk_count; i++) {
>  		ret = btrfs_extent_same_range(src, loff, BTRFS_MAX_DEDUPE_LEN,
>  					      dst, dst_loff, &cmp);
>