NFS: Convert lookups of the lock context to RCU

Speed up lookups of an existing lock context by avoiding the inode->i_lock,
and using RCU instead.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index a0831e9..d2f4f88 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -62,6 +62,7 @@
 	struct nfs_open_context *open_context;
 	fl_owner_t lockowner;
 	atomic_t io_count;
+	struct rcu_head	rcu_head;
 };
 
 struct nfs4_state;