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>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/dccp/probe.c b/net/dccp/probe.c
index dc328425fa20..6fcfe8745043 100644
--- a/net/dccp/probe.c
+++ b/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;