Re: [PATCH] Btrfs: don't panic if orphan item already exists

[Miao Xie <miaox@cn.fujitsu.com>]

On 	wed, 14 Dec 2011 10:07:39 +0800, WuBo wrote:
> On 12/14/2011 03:09 AM, Josef Bacik wrote:
>> On Tue, Dec 13, 2011 at 02:03:14PM -0500, Phillip Susi wrote:
>>> On 12/13/2011 12:55 PM, Josef Bacik wrote:
>>>> I've been hitting this BUG_ON() in btrfs_orphan_add when running xfstest 269 in
>>>> a loop.  This is because we will add an orphan item, do the truncate, the
>>>> truncate will fail for whatever reason (*cough*ENOSPC*cough*) and then we're
>>>> left with an orphan item still in the fs.  Then we come back later to do another
>>>> truncate and it blows up because we already have an orphan item.  This is ok so
>>>> just fix the BUG_ON() to only BUG() if ret is not EEXIST.  Thanks,
>>>
>>> Wouldn't it be better to fix the underlying bug, and remove the
>>> orphan item when the truncate fails?
>>>
>>
>> No because we still need the thing to be cleaned up.  If the truncate fails we
>> need to leave the orphan item there so the next time the fs is mounted the inode
>> is cleaned up, that's not a bug.  Thanks,
>>
>> Josef
> 
> Hi, Josef
> 
> I'm digging this issue too, actually xfstests 083 also can trigger this BUG_ON
> while run loops. and I agreed with Phillip's opinion that we'd better "fix the 
> underlying bug". If the btrfs_truncate faild with ENOSPC, we should not even call 
> btrfs_orphan_del to clean the memory orphan list so that the next orphan item
> insert will be skipped.
> 
> But, there is still a trouble. The user will get the fail result while the orphan 
> inode still left in the fs. It's strange. So in the end of the btrfs_truncate,
> if the btrfs_update_inode is successed, I will delete the orphan inode anyway.

Another reason for that we should fix the underlying bug:
File0							| i_size
							v
	+-----------------------------------------------+
	|						|
	+-----------------------------------------------+

The user truncated File0, but failed when doing truncation:
File0				| i_size	| real size
				v		v
	+---------------------------------------+
	|					|
	+---------------------------------------+

The user did pre-allocation for File0 (keep size):
File0				| i_size	| pre-allocated extent	|
				v		v			v
	+---------------------------------------+-----------------------+
	|					|			|
	+---------------------------------------+-----------------------+

And then, the user umounted and mount the file system again. Because we left the orphan item
in the file system, btrfs will drop the pre-allocated extent when mounting it. It is not
the expected result for users.

Thanks
Miao

> 
> what do you think of this idea? I'll make a patch if you do not have any comment.
> 
> BTW, 083 will always make the btrfs_truncate fail with btrfs_truncate_inode_items
> for ENOSPC when the disk is almost full.
> 
> thanks
> wubo
> 
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>