On Thu, 31 Jan 2013 11:40:41 -0500, Josef Bacik wrote:
> On Thu, Jan 31, 2013 at 02:23:19AM -0700, Miao Xie wrote:
>> Currently, we can do unlocked dio reads, but the following race
>> is possible:
>>
>> dio_read_task truncate_task
>> ->btrfs_setattr()
>> ->btrfs_direct_IO
>> ->__blockdev_direct_IO
>> ->btrfs_get_block
>> ->btrfs_truncate()
>> #alloc truncated blocks
>> #to other inode
>> ->submit_io()
>> #INFORMATION LEAK
>>
>> In order to avoid this problem, we must serialize unlocked dio reads with
>> truncate by inode_dio_wait().
>>
>
> So I had thinking about this, are we sure we don't want to just lock the
> extent
> range when we truncate? I'm good with this, but it seems like we might as
> well
> and be consistent and use the extent locks. What do you think? Thanks,
But comparing with the current approach, the extent lock has the following
problem:
Dio_Read_Task Truncate_task
truncate file
set isize to 4096
drop pages
lock extent[4096, 8191]
read extent[4096, 8191]
unlock extent[4096, 8191]
lock extent[4096, -1ULL]
truncate item
unlock extent[4096, -1ULL]
lock extent[8192, ...]
read extent[8192, ...]
no extent item
zero the buffer
unlock extent[8192, ...]
we get the data that is mixed with new data.(Punch hole also has this problem,
we need
fix)
Thanks
Miao
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