Re: [URGENT PATCH] ext4: fix potential deadlock in ext4_evict_inode()

[Tao Ma <tm@tao.ma>]

On 08/26/2011 07:35 PM, Theodore Tso wrote:
> 
> On Aug 26, 2011, at 5:17 AM, Christoph Hellwig wrote:
> 
>> The thing I have queued up for 3.2 makes it very simple:  we do not
>> track I/O ends any more at all, outside of the workqueue.
>>
>> For buffered I/O we only mark the page uptodate when all unwritten
>> extent conversion and size updates have finished.  All data integrity
>> callers and inode eviction wait for the pages to be update so we are
>> covered.
>>
>> For direct I/O we only call inode_dio_done and aio_complete once all
>> unwritten extent size updates are done.  Inodes can't be evicted until
>> we drop a reference to the inode, which can't happen until the
>> sync or async dio is done and we drop the inode reference the VFS
>> holds for it.  Sync and fsync are only guaranteed to pick up I/O
>> that has returned to userspace, so we are covered for that as well.
> 
> Long term, I definitely want to make ext4 do something similar. 
> What we have now is just way too fragile…
yeah, actually I have done some basic tests about letting
ext4_free_io_end to clear the page writeback flag for us after the
unwritten extent conversion, and it does have several problems with both
ext4 and jbd2. I will try to write up some solution for review.

Thanks
Tao
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