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

[Brian Foster]

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

Brian

> Ben.
> 

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