linux-ext4 - Re: More ext4 acl/xattr corruption

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Date:	Fri, 15 May 2009 07:03:14 +0930
From:	Kevin Shanahan <kmshanah@...b.org.au>
To:	Theodore Tso <tytso@....edu>
Cc:	Andreas Dilger <adilger@....com>, Alex Tomas <bzzz@....com>,
	linux-ext4@...r.kernel.org
Subject: Re: More ext4 acl/xattr corruption - 4th occurence now

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@....edu>
> 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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