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

[Nikolay Borisov <nborisov@suse.com>]

On 31.10.2017 23:51, Liu Bo wrote:
> On Tue, Oct 31, 2017 at 10:23:30PM +0200, Nikolay Borisov wrote:
>>
>>
>> On 30.10.2017 19:14, 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.
>>>
>>> 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;
>>
>> If this situation happens it's possible that ret is still 0 so the error
>> handling in btrfs_lookup_dentry might not trigger. How about just
>> setting -EUCLEAN if we execute the if branch?
>>
> 
> Thanks for the comment.  So it's not going to trigger the (ret < 0)
> check, instead it tries to trigger the one following (ret < 0):
> 
>         if (location.objectid == 0)
>                 return ERR_PTR(-ENOENT);
> 
> which is consistent to the case when we didn't find the btrfs_dir_item
> (di is NULL, returned by btrfs_lookup_dir_item()).

You are correct, i should have read 2 lines down ;)


> 
> thanks,
> -liubo
> 
> 
>>> +	}
>>>  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);
>>>
>