Re: lockdep: inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-R} usage.

[Peter Zijlstra <peterz@infradead.org>]

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.