nfs: per-name sillyunlink exclusion

use d_alloc_parallel() for sillyunlink/lookup exclusion and
explicit rwsem (nfs_rmdir() being a writer and nfs_call_unlink() -
a reader) for rmdir/sillyunlink one.

That ought to make lookup/readdir/!O_CREAT atomic_open really
parallel on NFS.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index d320906..ee8491d 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -1468,10 +1468,10 @@
 };
 
 struct nfs_unlinkdata {
-	struct hlist_node list;
 	struct nfs_removeargs args;
 	struct nfs_removeres res;
-	struct inode *dir;
+	struct dentry *dentry;
+	wait_queue_head_t wq;
 	struct rpc_cred	*cred;
 	struct nfs_fattr dir_attr;
 	long timeout;