Re: pktcdvd oops

[Tejun Heo]

[Greg cc'd]

Peter Osterlund wrote:
> On Mon, 5 Nov 2007, Jens Axboe wrote:
> 
>> Hi Peter,
>>
>> You don't seem to have a bugzilla account, so could not reassign to you.
>> See http://bugzilla.kernel.org/show_bug.cgi?id=9294
> 
> Problem is repeatable on my computer. It dies in __module_get() on this
> line:
> 
>         BUG_ON(module_refcount(module) == 0);
> 
> I think this is because commit 7b595756ec1f49e0049a9e01a1298d53a7faaa15,
> which states: "Note that with this change, userland holding a sysfs node
> does not prevent the backing module from being unloaded."
> 
> Unfortunately, I don't know how this sysfs stuff is supposed to work,
> and therefore don't know how to fix the problem.

Does this fix the problem?

-- 
tejun
diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
index a8130a4..a5ee213 100644
--- a/drivers/block/pktcdvd.c
+++ b/drivers/block/pktcdvd.c
@@ -358,10 +358,19 @@ static ssize_t class_pktcdvd_store_add(struct class *c, const char *buf,
 					size_t count)
 {
 	unsigned int major, minor;
+
 	if (sscanf(buf, "%u:%u", &major, &minor) == 2) {
+		/* pkt_setup_dev() expects caller to hold reference to self */
+		if (!try_module_get(THIS_MODULE))
+			return -ENODEV;
+
 		pkt_setup_dev(MKDEV(major, minor), NULL);
+
+		module_put(THIS_MODULE);
+
 		return count;
 	}
+
 	return -EINVAL;
 }