linux-ext4 - Re: [URGENT PATCH] ext4: fix potential deadlock in ext4_evict

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Message-Id: <22BEE903-4141-4D2A-932B-259DF50F14E1@mit.edu>
Date:	Fri, 26 Aug 2011 07:35:24 -0400
From:	Theodore Tso <tytso@....EDU>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Tao Ma <tm@....ma>, Dave Chinner <david@...morbit.com>,
	Jiaying Zhang <jiayingz@...gle.com>, linux-ext4@...r.kernel.org
Subject: Re: [URGENT PATCH] ext4: fix potential deadlock in ext4_evict_inode()


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…

-- Ted

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