Re: [ 110/180] ext4: dont let i_reserved_meta_blocks go negative

[Brian Foster]

On 10/05/2012 08:37 AM, Willy Tarreau wrote:
> On Fri, Oct 05, 2012 at 07:59:11AM -0400, Brian Foster wrote:
>> On 10/04/2012 05:55 PM, Ben Hutchings wrote:
>>> On Tue, Oct 02, 2012 at 12:53:47AM +0200, Willy Tarreau wrote:
>>>> 2.6.32-longterm review patch.  If anyone has any objections, please let me know.
>>>>
>>>> ------------------
>>>>
>>>> From: Brian Foster <bfoster@xxxxxxxxxx>
>>>>
>>>> commit 97795d2a5b8d3c8dc4365d4bd3404191840453ba upstream.
>>>>
>>>> If we hit a condition where we have allocated metadata blocks that
>>>> were not appropriately reserved, we risk underflow of
>>>> ei->i_reserved_meta_blocks.  In turn, this can throw
>>>> sbi->s_dirtyclusters_counter significantly out of whack and undermine
>>>> the nondelalloc fallback logic in ext4_nonda_switch().  Warn if this
>>>> occurs and set i_allocated_meta_blocks to avoid this problem.
>>>>
>>>> This condition is reproduced by xfstests 270 against ext2 with
>>>> delalloc enabled:
>>>>
>>>> Mar 28 08:58:02 localhost kernel: [  171.526344] EXT4-fs (loop1): delayed block allocation failed for inode 14 at logical offset 64486 with max blocks 64 with error -28
>>>> Mar 28 08:58:02 localhost kernel: [  171.526346] EXT4-fs (loop1): This should not happen!! Data will be lost
>>>>
>>>> 270 ultimately fails with an inconsistent filesystem and requires an
>>>> fsck to repair.  The cause of the error is an underflow in
>>>> ext4_da_update_reserve_space() due to an unreserved meta block
>>>> allocation.
>>> [...]
>>>> +	if (unlikely(ei->i_allocated_meta_blocks > ei->i_reserved_meta_blocks)) {
>>>> +		ext4_msg(inode->i_sb, KERN_NOTICE, "%s: ino %lu, allocated %d "
>>>> +			 "with only %d reserved metadata blocks\n", __func__,
>>>> +			 inode->i_ino, ei->i_allocated_meta_blocks,
>>>> +			 ei->i_reserved_meta_blocks);
>>>> +		WARN_ON(1);
>>>> +		ei->i_allocated_meta_blocks = ei->i_reserved_meta_blocks;
>>>> +	}
>>> [...]
>>>  
>>> This seems to be working around a bug elsewhere.  Has the underlying
>>> bug been fixed in mainline yet?
>>>
>>
>> Yes, the bug was fixed in:
>>
>> 03179fe92318e7934c180d96f12eff2cb36ef7b6
>> ext4: undo ext4_calc_metadata_amount if we fail to claim space
> 
> So should we merge this one instead/too ?
> 

>From the perspective of the bug, I think you would want both patches. I
should probably defer to Ted if he proposed this latter change for stable...

Brian

> Willy
> 

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