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

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Message-ID: <20090515231858.GA5454@kulgan>
Date:	Sat, 16 May 2009 08:48:58 +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 Fri, May 15, 2009 at 07:03:14AM +0930, Kevin Shanahan wrote:
> 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.
>                      ^^^^^^^^^^^

Tested-by: Kevin Shanahan <kmshanah@...b.org.au>

Yes, this patch seems to have fixed the issue. I ran my "exchange
backup to samba share" test on 2.6.29.3 + check_block_validity patch +
the fix race patch with no problems.

Cheers,
Kevin.
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