linux-kernel - Re: lockdep: inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM

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Date:	Fri, 15 Jan 2010 13:53:15 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com,
	Christoph Hellwig <hch@...radead.org>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: lockdep: inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-R}
 usage.

On Fri, 2010-01-15 at 23:44 +1100, Dave Chinner wrote:
> 
> > > I can't work out what the <mumble>RECLAIM_FS<mumble> notations are
> > > supposed to mean from the code and they are not documented at
> > > all, so I need someone to explain what this means before I can
> > > determine if it is a valid warning or not....
> > 
> > The <mumble>RECLAIM_FS<mumble> bit means that lock (iprune_sem) was
> > taken from reclaim and is also taken over an allocation.
> 
> So there's an implicit, undocumented requirement that inode reclaim
> during unmount requires a filesystem to do GFP_NOFS allocation? 

Well, I don't know enough about xfs (of filesystems in generic) to say
that with any certainty, but I can imagine inode writeback from the sync
that goes with umount to cause issues.

If this inode reclaim is past all that and the filesystem is basically
RO, then I don't think so and this could be considered a false positive,
in which case we need an annotation for this.

I added hch since he poked at similar reclaim recursions on XFS before
and Nick since he thought up this annotation and knows more about
filesystems than I do.

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