[PATCH v2] parport: register driver later

[Sudip Mukherjee <sudipm.mukherjee@gmail.com>]

If the parport bus is not yet registered and any device using parallel
port tries to register with the bus we get a stackdump with a message
of Kernel bug.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: <stable@vger.kernel.org> # 4.2+
Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
---

Hi Ross,
Can you please test this patch in your setup. This is a respin of the
previous patch in another way.

 drivers/parport/share.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/parport/share.c b/drivers/parport/share.c
index 3308427..c1eba80 100644
--- a/drivers/parport/share.c
+++ b/drivers/parport/share.c
@@ -135,9 +135,18 @@ static struct bus_type parport_bus_type = {
 	.probe = parport_probe,
 };
 
+static bool is_registered;
+
 int parport_bus_init(void)
 {
-	return bus_register(&parport_bus_type);
+	int ret;
+
+	ret = bus_register(&parport_bus_type);
+	if (ret)
+		return ret;
+
+	is_registered = true;
+	return 0;
 }
 
 void parport_bus_exit(void)
@@ -273,6 +282,9 @@ int __parport_register_driver(struct parport_driver *drv, struct module *owner,
 		/* using device model */
 		int ret;
 
+		if (!is_registered)
+			return -EAGAIN;
+
 		/* initialize common driver fields */
 		drv->driver.name = drv->name;
 		drv->driver.bus = &parport_bus_type;
-- 
1.9.1