linux-kernel - Re: LOCKDEP: 3.9-rc1: mount.nfs/4272 still has locks held!

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Message-ID: <20130306010507.GL15816@fieldses.org>
Date:	Tue, 5 Mar 2013 20:05:07 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Mandeep Singh Baines <msb@...omium.org>
Cc:	Tejun Heo <tj@...nel.org>, Jeff Layton <jlayton@...hat.com>,
	"Myklebust, Trond" <Trond.Myklebust@...app.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Ming Lei <ming.lei@...onical.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: LOCKDEP: 3.9-rc1: mount.nfs/4272 still has locks held!

On Tue, Mar 05, 2013 at 04:59:00PM -0800, Mandeep Singh Baines wrote:
> On Tue, Mar 5, 2013 at 3:11 PM, J. Bruce Fields <bfields@...ldses.org> wrote:
> > On Tue, Mar 05, 2013 at 09:49:54AM -0800, Tejun Heo wrote:
> >> On Tue, Mar 05, 2013 at 09:46:48AM -0800, Tejun Heo wrote:
> >> > So, I think this is why implementing freezer as a separate blocking
> >> > mechanism isn't such a good idea.  We're effectively introducing a
> >> > completely new waiting state to a lot of unsuspecting paths which
> >> > generates a lot of risks and eventually extra complexity to work
> >> > around those.  I think we really should update freezer to re-use the
> >> > blocking points we already have - the ones used for signal delivery
> >> > and ptracing.  That way, other code paths don't have to worry about an
> >> > extra stop state and we can confine most complexities to freezer
> >> > proper.
> >>
> >> Also, consolidating those wait states means that we can solve the
> >> event-to-response latency problem for all three cases - signal, ptrace
> >> and freezer, rather than adding separate backing-out strategy for
> >> freezer.
> >
> > Meanwhile, as none of this sounds likely to be done this time
> > around--are we backing out the new lockdep warnings?
> >
> > --b.
> 
> What if we hide it behind a Kconfig? Its finding real bugs.
> 
> http://lkml.org/lkml/2013/3/5/583

If it's really just a 2-line patch to try_to_freeze(), could it just be
carried out-of-tree by people that are specifically working on tracking
down these problems?

But I don't have strong feelings about it--as long as it doesn't result
in the same known issues getting reported again and again....

--b.
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