linux-ext4 - Re: [PATCH 2/3] ext4: Update reserved space after the 'correction'

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Date:	Sun, 10 Mar 2013 22:50:16 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org, gnehzuil.liu@...il.com
Subject: Re: [PATCH 2/3] ext4: Update reserved space after the 'correction'

On Fri, Mar 08, 2013 at 09:24:18AM +0100, Lukas Czerner wrote:
> Currently in ext4_ext_map_blocks() in delayed allocation writeback
> we would update the reservation and after that check whether we claimed
> cluster outside of the range of the allocation and if so, we'll give the
> block back to the reservation pool.
> 
> However this also means that if the number of reserved data block
> dropped to zero before the correction, we would release all the metadata
> reservation as well, however we might still need it because the we're
> not done with the delayed allocation and there might be more blocks to
> come. This will result in error messages such as:
> 
> EXT4-fs warning (device sdb): ext4_da_update_reserve_space:361: ino 12,
> allocated 1 with only 0 reserved metadata blocks (releasing 1 blocks
> with reserved 1 data blocks)
> 
> This will only happen on bigalloc file system and it can be easily
> reproduced using fiemap-tester from xfstests like this:
> 
> ./src/fiemap-tester -m DHDHDHDHD -S -p0 /mnt/test/file
> 
> Or using xfstests such as 225.
> 
> Fix this by doing the correction first and updating the reservation
> after that so that we do not accidentally decrease
> i_reserved_data_blocks to zero.
> 
> Signed-off-by: Lukas Czerner <lczerner@...hat.com>

Thanks, applied.

						- Ted
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