netdev - Re: [PATCH net-next-2.6 v2] can: convert protocol handling to RCU

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Message-ID: <20110406153440.GA2277@kurt.e-circ.dyndns.org>
Date:	Wed, 6 Apr 2011 17:34:40 +0200
From:	Kurt Van Dijck <kurt.van.dijck@....be>
To:	Oliver Hartkopp <socketcan@...tkopp.net>
Cc:	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Urs Thuermann <urs@...ogud.escape.de>
Subject: Re: [PATCH net-next-2.6 v2] can: convert protocol handling to RCU

On Wed, Apr 06, 2011 at 04:39:03PM +0200, Oliver Hartkopp wrote:
> On 06.04.2011 11:27, Kurt Van Dijck wrote:
> > On Tue, Apr 05, 2011 at 08:01:16PM +0200, Oliver Hartkopp wrote:
> 
> >>  
> >> +static struct can_proto *can_try_module_get(int protocol)
> >> +{
> >> +	struct can_proto *cp;
> >> +
> >> +	rcu_read_lock();
> >> +	cp = rcu_dereference(proto_tab[protocol]);
> >> +	if (cp && !try_module_get(cp->prot->owner))
> > After the xxx_get, is the 'cp' pointer persistent?
> 
> try_module_get() increases the usage counter of the module - therefore it is.
> It is protected until module_put(cp->prot->owner) at the end of can_create() .
Ok, I understand correctly now.
> 
> >>  	/* check for available protocol and correct usage */
> >>  
> >>  	if (!cp)
> >>  		return -EPROTONOSUPPORT;
> >>  
> >>  	if (cp->type != sock->type) {
> > I don't see how this will evaluate to true?
> > can_proto_register takes care of it.
> 
> This check compares the type of the socket that is to be created with the type
> that's defined for this protocol.
> 
> E.g. if you would give
> 
> s = socket(PF_CAN, SOCK_STREAM, CAN_RAW);
> 
> instead of the correct
> 
> s = socket(PF_CAN, SOCK_RAW, CAN_RAW);
> 
> you will get this error.

Right, I see my mistake now.
> 
> >> -		err = -EPROTONOSUPPORT;
> >> +		err = -EPROTOTYPE;
> >>  		goto errout;
> >>  	}
> >>  
> 
> Regards,
> Oliver

Regards,
Kurt

Acked-by: Kurt Van Dijck <kurt.van.dijck@....be>
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