From f49f9baac8f63de9cbc17a0a84e04060496e8e76 Mon Sep 17 00:00:00 2001
From: Fred Isaman <iisaman@netapp.com>
Date: Thu, 3 Feb 2011 18:28:52 +0000
Subject: [PATCH] pnfs: fix pnfs lock inversion of i_lock and cl_lock

The pnfs code was using throughout the lock order i_lock, cl_lock.
This conflicts with the nfs delegation code.  Rework the pnfs code
to avoid taking both locks simultaneously.

Currently the code takes the double lock to add/remove the layout to a
nfs_client list, while atomically checking that the list of lsegs is
empty.  To avoid this, we rely on existing serializations.  When a
layout is initialized with lseg count equal zero, LAYOUTGET's
openstateid serialization is in effect, making it safe to assume it
stays zero unless we change it.  And once a layout's lseg count drops
to zero, it is set as DESTROYED and so will stay at zero.

Signed-off-by: Fred Isaman <iisaman@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
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