linux-kernel - Re: circular locking dependency detected panic in filldir when CONFIG_PROVE

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Date:	Sat, 19 Sep 2009 09:23:49 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Trond Myklebust <trond.myklebust@....uio.no>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Joe Korty <joe.korty@...r.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Al Viro <viro@...iv.linux.org.uk>,
	Steve French <sfrench@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: circular locking dependency detected panic in filldir when
	CONFIG_PROVE_LOCKING=y


* Trond Myklebust <trond.myklebust@....uio.no> wrote:

> On Fri, 2009-09-18 at 17:15 -0400, Joe Korty wrote:
> > I experienced a might_fault panic from NFS's use of filldir
> > in a 2.6.31 kernel compiled with CONFIG_PROVE_LOCKING=y.
> > 
> > Looking at filldir, I see it is accessing user space with
> > __put_dir's (which are inatomic) and with one copy_to_user
> > (which is not inatomic).  It is the single copy_to_user
> > which is causing the might_fault panic.
> > 
> > It doesn't make any sense to be mixing use of inatomic
> > and non-inatomic services in filldir.  Either all should be
> > the inatomic version, or none should be.
> > 
> > The might_fault condition being reported by the panic looks
> > real to me, so I suspect the wrong answer is converting
> > everything to the inatomic version, since that just
> > suppresses the circular dependency check while leaving
> > the circular dependency in place.
> 
> Yes. This is known... Please see 
>    http://thread.gmane.org/gmane.linux.nfs/28578
> and
>    http://thread.gmane.org/gmane.linux.nfs/27406
> 
> I'm still hoping the VM folks can see fit to merge Peter's fix at some
> point...

Ouch, those patches at:

  http://programming.kicks-ass.net/kernel-patches/mmap-vs-nfs/

... are 2 years old. Higher intensity prodding needed to get this 
moving?

	Ingo
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