Subject: Re: [RFC] Suspicious bug in module refcounting

From: Rusty Russell <[email-masked]>
Date: Tue, 10 Feb 2009 13:45:07 +1030

On Tuesday 10 February 2009 01:48:31 Michal Hocko wrote:
> Based on this change, would it make sense to update sys_accept to change
> __module_get to try_module_get like in the following patch?

I don't think so:

>  	/*
> -	 * We don't need try_module_get here, as the listening socket (sock)
> -	 * has the protocol module (sock->ops->owner) held.
> +	 * Socket's owner cannot be in unloading path because there
> +	 * must be at least one listening reference
>  	 */
> -	__module_get(newsock->ops->owner);
> +	if (unlikely(!try_module_get(newsock->ops->owner)))
> +		BUG();

rmmod --wait can make try_module_get fail even if the reference count isn't
zero.  But in this case, we should return an error from the accept call;
presumably the admin really doesn't want us to keep using the module...

Thanks,
Rusty.