Re: [PATCH] Btrfs: bail out gracefully rather than BUG_ON

[Liu Bo <bo.li.liu@oracle.com>]

On Mon, Oct 30, 2017 at 11:14:38AM -0600, Liu Bo wrote:
> If a file's DIR_ITEM key is invalid (due to memory errors) and gets
> written to disk, a future lookup_path can end up with kernel panic due
> to BUG_ON().
> 
> This gets rid of the BUG_ON(), meanwhile output the corrupted key and
> return ENOENT if it's invalid.
>

The kernel panic is originally

Reported-by: Guillaume Bouchard <bouchard@mercs-eng.com>

Thanks,

-liubo
> Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> ---
> The diff doesn't show the logic well, 'goto out_err' will return with
> assigning 0 to location->objectid, and the caller already has a check
> for (location->objectid == 0) to return -ENOENT.
> 
>  fs/btrfs/inode.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index d94e3f6..916cdc9 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -5500,6 +5500,14 @@ static int btrfs_inode_by_name(struct inode *dir, struct dentry *dentry,
>  		goto out_err;
>  
>  	btrfs_dir_item_key_to_cpu(path->nodes[0], di, location);
> +	if (location->type != BTRFS_INODE_ITEM_KEY &&
> +	    location->type != BTRFS_ROOT_ITEM_KEY) {
> +		btrfs_warn(root->fs_info,
> +	  "%s gets something invalid in DIR_ITEM (name %s, directory ino %llu, location(%llu %u %llu))",
> +			   __func__, name, btrfs_ino(BTRFS_I(dir)),
> +			   location->objectid, location->type, location->offset);
> +		goto out_err;
> +	}
>  out:
>  	btrfs_free_path(path);
>  	return ret;
> @@ -5816,8 +5824,6 @@ struct inode *btrfs_lookup_dentry(struct inode *dir, struct dentry *dentry)
>  		return inode;
>  	}
>  
> -	BUG_ON(location.type != BTRFS_ROOT_ITEM_KEY);
> -
>  	index = srcu_read_lock(&fs_info->subvol_srcu);
>  	ret = fixup_tree_root_location(fs_info, dir, dentry,
>  				       &location, &sub_root);
> -- 
> 2.9.4
> 
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