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

On 08/26/2011 07:35 PM, Theodore Tso wrote:

On Aug 26, 2011, at 5:17 AM, Christoph Hellwig wrote:

quoted

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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