From 080af20cc945d110f9912d01cf6b66f94a375b8d Mon Sep 17 00:00:00 2001
From: Steve Dickson <steved@redhat.com>
Date: Thu, 18 Sep 2014 09:13:17 -0400
Subject: [PATCH] NFSv4: nfs4_state_manager() vs. nfs_server_remove_lists()

There is a race between nfs4_state_manager() and
nfs_server_remove_lists() that happens during a nfsv3 mount.

The v3 mount notices there is already a supper block so
nfs_server_remove_lists() called which uses the nfs_client_lock
spin lock to synchronize access to the client list.

At the same time nfs4_state_manager() is running through
the client list looking for work to do, using the same
lock. When nfs4_state_manager() wins the race to the
list, a v3 client pointer is found and not ignored
properly which causes the panic.

Moving some protocol checks before the state checking
avoids the panic.

CC: Stable Tree <stable@vger.kernel.org>
Signed-off-by: Steve Dickson <steved@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
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