sysdev: detect multiple driver registrations

I've just found how easy it is to accidentally register a sysdev_driver for
two different classes.  When this happens, bad things happen as the
sysdev_driver structure keeps has the list entry for the driver
registration.

The following patch makes a WARN_ON() if this happens, although I think
BUG_ON or returning -EAGAIN could also be valid responses to this.

Signed-off-by: Ben Dooks <ben@fluff.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/base/sys.c b/drivers/base/sys.c
index 8e13fd94216..1a06c239371 100644
--- a/drivers/base/sys.c
+++ b/drivers/base/sys.c
@@ -167,6 +167,22 @@ int sysdev_driver_register(struct sysdev_class *cls, struct sysdev_driver *drv)
 {
         int err = 0;
 
+        if (!cls) {
+                printk(KERN_WARNING "sysdev: invalid class passed to "
+                        "sysdev_driver_register!\n");
+                WARN_ON(1);
+                return -EINVAL;
+        }
+
+        /* Check whether this driver has already been added to a class. */
+        if ((drv->entry.next != drv->entry.prev) ||
+            (drv->entry.next != NULL)) {
+                printk(KERN_WARNING "sysdev: class %s: driver (%p) has already"
+                        " been registered to a class, something is wrong, but "
+                        "will forge on!\n", cls->name, drv);
+                WARN_ON(1);
+        }
+
         mutex_lock(&sysdev_drivers_lock);
         if (cls && kset_get(&cls->kset)) {
                 list_add_tail(&drv->entry, &cls->drivers);