linux-kernel - Re: lockdep warning with 2.6.29-rc6-mm1 (mmotm 24-feb-2009)

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Message-ID: <20090306153808.GA863@balbir.in.ibm.com>
Date:	Fri, 6 Mar 2009 21:08:08 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Eric Paris <eparis@...hat.com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: lockdep warning with 2.6.29-rc6-mm1 (mmotm 24-feb-2009)

* Nick Piggin <npiggin@...e.de> [2009-03-05 08:00:45]:

> On Wed, Mar 04, 2009 at 06:41:15PM +0100, Ingo Molnar wrote:
> > 
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > On Wed, 2009-03-04 at 18:27 +0530, Balbir Singh wrote:
> > > > I see the following on my machine. My understanding is that the
> > > > lockdep warning is complaining about a potential deadlock while
> > > > reclaiming, where we could end up waiting on holding inotify_mutex,
> > > > and we could end up calling reclaim with inotify_mutex held.
> > > > 
> > > > The race seems rare, since one path shows a new inode being created
> > > > and the other one being deleted. It seems like a false positive unless
> > > > the inode's in question turn out to be potentially the same.
> > > 
> > > Its not a false positive until you can guarantee the inodes will _never_
> > > be the same.
> > > 
> > > This thing has been reported numerous times, Ingo even posted 
> > > a potential fix for it, Nick poked the inotify people to speak 
> > > up, but they have so far been silent on the issue :-(
> > 
> > that particular fix is upstream, via:
> > 
> >   3023a3e: inotify: fix GFP_KERNEL related deadlock
> > 
> > so does this reproduce with latest .29-rc7-ish kernels too - or 
> > do we have some other problem in this area too?
> 
> Well as I said, I think it is just a bandaid to shut up lockdep,
> because I think inotify always is guaranteed to have a ref on
> the inode at this point so it should not be subject to reclaim.

I got dropped from the cc and thus could not respond earlier. The
problem can be seen even in 2.6.29-rc7-mm1.

-- 
	Balbir
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