Re: [BUG ext4?] Working tree getting out of date "spontaneously"

From: Theodore Tso <tytso@mit.edu>
Date: Jun 5, 2009, 18:06 UTC
Message-ID: <20090605180630.GC6442@mit.edu>
In-Reply-To: <20090605150212.GC764@atjola.homenet>

On Fri, Jun 05, 2009 at 05:02:12PM +0200, Björn Steinbrink wrote:

Show 23 quoted lines

> On 2009.06.05 10:55:08 -0400, Theodore Tso wrote:
> > On Fri, Jun 05, 2009 at 03:21:26PM +0200, Björn Steinbrink wrote:
> > > So the ctime got modified. I don't have any fancy indexing stuff
> > > running, and inotify doesn't see any events either while the ctime is
> > > changed.
> > > 
> > > The only thing I changed lately was upgrading to 2.6.30-rc8 and going
> > > from ext3 to ext4. As the ctime change always seems to happen around 30
> > > seconds after the real change, I kind of suspect ext4 to be guilty.
> > > Ted, is that possible?
> > > 
> > > FS is mounted as:
> > > /dev/mapper/vg0-home on /home type ext4 (rw,noatime,nodiratime,barrier=0)
> > > 
> > 
> > I agree it sounds like it's ext4 related, but I'm not able to
> > reproduce it (using 2.6.30-rc8 with the patches planned for the 2.6.31
> > merge window).  This should show the problem, you were seeing, do you
> > agree?
> 
> Yeah, that should do I guess. See my other mail for a simpler, less
> time consuming way to test. And as noted in there, it seems to happen
> only on ext3 filesystems mounted using ext4.

> Filesystem features:      has_journal resize_inode dir_index filetype
>                           needs_recovery sparse_super large_file

Yeah, so you haven't turned on any of the ext4 filesystem features, I assume because you wanted to be easily go back to ext3 if you ran into problems? OK, that's a good starting point.

I'm guessing it's the presence or absence of one of the ext4-specific filesystem features, most probably the extents feature (which is why I had asked you to to send me your dumpe2fs -h output).

So the next step is to create an ext3 filesystem with a git repository on it, and then to gradually turn on various ext4 specific features and see when the bug ends up getting replicated. If I had to guess it's the lack (or absense) of the extents feature, but I'll have to run the test and find out for sure.

Thanks for reporting the bug.  Let me see what I can find.

       	   	     	       	      	  - Ted