On Thu, May 14, 2009 at 05:23:25PM -0400, Theodore Tso wrote:
> On Fri, May 15, 2009 at 06:32:45AM +0930, Kevin Shanahan wrote:
> > Okay, so now I've booted into 2.6.29.3 + check_block_validity patch +
> > short circuit i_cached_extent patch, mounted the fs without
> > nodelalloc. I was able to run the full exchange backup without
> > triggering the check_block_validity error.
>
> Great!
>
> So here's the final fix (it replaces the short circuit i_cached_extent
> patch) which I plan to push to Linus. It should be much less of a
> performance hit than simply short-circuiting i_cached_extent...
>
> Thanks so much for helping to find track this down!!! If ever someone
> deserved an "Ext4 Baker Street Irregulars" T-shirt, it would be
> you....
Hehe, no problem. Will do the final testing shortly (ran out of time
this morning, users are back on the system now). Just one little
correction to your patch below:
> commit 039ed7a483fdcb2dbbc29f00cd0d74c101ab14c5
> Author: Theodore Ts'o <tytso@xxxxxxx>
> Date: Thu May 14 17:09:37 2009 -0400
>
> ext4: Fix race in ext4_inode_info.i_cached_extent
>
> If one CPU is reading from a file while another CPU is writing to the
> same file different locations, there is nothing protecting the
> i_cached_extent structure from being used and updated at the same
> time. This could potentially cause the wrong location on disk to be
> read or written to, including potentially causing the corruption of
> the block group descriptors and/or inode table.
>
> Many thanks to Ken Shannah for helping to track down this problem.
^^^^^^^^^^^
Cheers,
Kevin Shanahan.
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