proc 2/2: remove struct proc_dir_entry::owner

Setting ->owner as done currently (pde->owner = THIS_MODULE) is racy
as correctly noted at bug #12454. Someone can lookup entry with NULL
->owner, thus not pinning enything, and release it later resulting
in module refcount underflow.

We can keep ->owner and supply it at registration time like ->proc_fops
and ->data.

But this leaves ->owner as easy-manipulative field (just one C assignment)
and somebody will forget to unpin previous/pin current module when
switching ->owner. ->proc_fops is declared as "const" which should give
some thoughts.

->read_proc/->write_proc were just fixed to not require ->owner for
protection.

rmmod'ed directories will be empty and return "." and ".." -- no harm.
And directories with tricky enough readdir and lookup shouldn't be modular.
We definitely don't want such modular code.

Removing ->owner will also make PDE smaller.

So, let's nuke it.

Kudos to Jeff Layton for reminding about this, let's say, oversight.

http://bugzilla.kernel.org/show_bug.cgi?id=12454

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>

net/sunrpc/stats.c

@@ -262,14 +262,8 @@ void
 rpc_proc_init(void)
 {
 	dprintk("RPC:       registering /proc/net/rpc\n");
-	if (!proc_net_rpc) {
-		struct proc_dir_entry *ent;
-		ent = proc_mkdir("rpc", init_net.proc_net);
-		if (ent) {
-			ent->owner = THIS_MODULE;
-			proc_net_rpc = ent;
-		}
-	}
+	if (!proc_net_rpc)
+		proc_net_rpc = proc_mkdir("rpc", init_net.proc_net);
 }
 
 void