Re: ext3 lockdep warning in 2.6.25-rc6

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Sat, 2008-03-22 at 18:34 -0400, Erez Zadok wrote:
> In message <1206207527.6437.83.camel@lappy>, Peter Zijlstra writes:
> > On Sat, 2008-03-22 at 10:37 -0400, Erez Zadok wrote:
> > > I was building a kernel using "make -j 4" inside a unionfs, mounted on top
> > > of ext3.  The kernel is vanilla 2.6.25-rc6 plus unionfs patches.  At some
> > > point I forced a cache flush using "echo 3 > /proc/sys/vm/drop_caches" and I
> > > got the lockdep warning below.  Note that unionfs doesn't appear to be
> > > involved in this lockdep warning at all, so I suspect this is probably an
> > > issue between jbd and ext3 directly.
> > 
> > Known issue, drop_caches isn't production quality.
> 
> Is this a general problem with drop_caches, or its interaction with
> ext3/jbd?  If I get a similar lockdep warning with other file systems,
> should I bother to report this to the respective f/s maintainers?

Its a generic problem with drop_caches. If you look in the lkml archives
you'll find similar reports against XFS and others.

Some time ago Andrew outlined a fix for it, but so far that hasn't
happened:  http://lkml.org/lkml/2007/2/23/46