ALSA: seq-oss: Initialize MIDI clients asynchronously

We've got bug reports that the module loading stuck on Debian system
with 3.10 kernel.  The debugging session revealed that the initial
registration of OSS sequencer clients stuck at module loading time,
which involves again with request_module() at the init phase.  This is
triggered only by special --install stuff Debian is using, but it's
still not good to have such loops.

As a workaround, call the registration part asynchronously.  This is a
better approach irrespective of the hang fix, in anyway.

Reported-and-tested-by: Philipp Matthias Hahn <pmhahn@pmhahn.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/seq/oss/seq_oss_init.c

@@ -31,6 +31,7 @@
 #include <linux/export.h>
 #include <linux/moduleparam.h>
 #include <linux/slab.h>
+#include <linux/workqueue.h>
 
 /*
  * common variables
@@ -60,6 +61,14 @@ static void free_devinfo(void *private);
 #define call_ctl(type,rec) snd_seq_kernel_client_ctl(system_client, type, rec)
 
 
+/* call snd_seq_oss_midi_lookup_ports() asynchronously */
+static void async_call_lookup_ports(struct work_struct *work)
+{
+	snd_seq_oss_midi_lookup_ports(system_client);
+}
+
+static DECLARE_WORK(async_lookup_work, async_call_lookup_ports);
+
 /*
  * create sequencer client for OSS sequencer
  */
@@ -85,9 +94,6 @@ snd_seq_oss_create_client(void)
 	system_client = rc;
 	debug_printk(("new client = %d\n", rc));
 
-	/* look up midi devices */
-	snd_seq_oss_midi_lookup_ports(system_client);
-
 	/* create annoucement receiver port */
 	memset(port, 0, sizeof(*port));
 	strcpy(port->name, "Receiver");
@@ -115,6 +121,9 @@ snd_seq_oss_create_client(void)
 	}
 	rc = 0;
 
+	/* look up midi devices */
+	schedule_work(&async_lookup_work);
+
  __error:
 	kfree(port);
 	return rc;
@@ -160,6 +169,7 @@ receive_announce(struct snd_seq_event *ev, int direct, void *private, int atomic
 int
 snd_seq_oss_delete_client(void)
 {
+	cancel_work_sync(&async_lookup_work);
 	if (system_client >= 0)
 		snd_seq_delete_kernel_client(system_client);
 

sound/core/seq/oss/seq_oss_midi.c

@@ -72,7 +72,7 @@ static int send_midi_event(struct seq_oss_devinfo *dp, struct snd_seq_event *ev,
  * look up the existing ports
  * this looks a very exhausting job.
  */
-int __init
+int
 snd_seq_oss_midi_lookup_ports(int client)
 {
 	struct snd_seq_client_info *clinfo;