dccp_probe: Fix module load dependencies between dccp and dccp_probe

This was just recently reported to me.  When built as modules, the
dccp_probe module has a silent dependency on the dccp module.  This
stems from the fact that the module_init routine of dccp_probe
registers a jprobe on the dccp_sendmsg symbol.  Since the symbol is
only referenced as a text string (the .symbol_name field in the jprobe
struct) rather than the address of the symbol itself, depmod never
picks this dependency up, and so if you load the dccp_probe module
without the dccp module loaded, the register_jprobe call fails with an
-EINVAL, and the whole module load fails.

The fix is pretty easy, we can just wrap the register_jprobe call in a
try_then_request_module call, which forces the dependency to get
satisfied prior to the probe registration.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dccp/probe.c

@@ -163,7 +163,8 @@ static __init int dccpprobe_init(void)
 	if (!proc_net_fops_create(&init_net, procname, S_IRUSR, &dccpprobe_fops))
 		goto err0;
 
-	ret = register_jprobe(&dccp_send_probe);
+	ret = try_then_request_module((register_jprobe(&dccp_send_probe) == 0),
+					"dccp");
 	if (ret)
 		goto err1;