netdev - Re: [PATCHv3 2/2] IPVS: Add genetlink interface implementation

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Date:	Thu, 14 Aug 2008 15:32:31 +0200 (CEST)
From:	Sven Wegener <sven.wegener@...aler.net>
To:	Julius Volz <juliusv@...gle.com>
cc:	netdev@...r.kernel.org, lvs-devel@...r.kernel.org,
	horms@...ge.net.au, kaber@...sh.net, davem@...emloft.net,
	tgraf@...g.ch, vbusam@...gle.com
Subject: Re: [PATCHv3 2/2] IPVS: Add genetlink interface implementation

On Thu, 14 Aug 2008, Julius Volz wrote:

> On Thu, Aug 14, 2008 at 12:27:19PM +0200, Julius Volz wrote:
> > On Thu, Aug 14, 2008 at 12:04:50PM +0200, Sven Wegener wrote:
> > > On Thu, 14 Aug 2008, Julius Volz wrote:
> > > 
> > > > On Wed, Aug 13, 2008 at 11:51:06PM +0200, Sven Wegener wrote:
> > > > > On Fri, 8 Aug 2008, Julius Volz wrote:
> > > > > > +static int ip_vs_genl_get_cmd(struct sk_buff *skb, struct genl_info *info)
> > > > > > +{
> > > > > > +	struct sk_buff *msg;
> > > > > > +	void *reply;
> > > > > > +	int ret, cmd, reply_cmd;
> > > > > > +
> > > > > > +	mutex_lock(&__ip_vs_mutex);
> > > > > > +
> > > > > > +	cmd = info->genlhdr->cmd;
> > > > > > +
> > > > > > +	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
> > > > > > +	if (!msg) {
> > > > > > +		ret = -ENOMEM;
> > > > > > +		goto out_err;
> > > > > 
> > > > > Here you want out...
> > > > > 
> > > > > > +	}
> > > > > > +
> > > > > > +	if (cmd == IPVS_CMD_GET_SERVICE)
> > > > > > +		reply_cmd = IPVS_CMD_NEW_SERVICE;
> > > > > > +	else if (cmd == IPVS_CMD_GET_INFO)
> > > > > > +		reply_cmd = IPVS_CMD_SET_INFO;
> > > > > > +	else if (cmd == IPVS_CMD_GET_CONFIG)
> > > > > > +		reply_cmd = IPVS_CMD_SET_CONFIG;
> > > > > > +	else {
> > > > > > +		IP_VS_ERR("unknown Generic Netlink command\n");
> > > > > > +		ret = -EINVAL;
> > > > > > +		goto out;
> > > > > 
> > > > > ..and here you want out_error, to not leak msg.
> > > > 
> > > > Ouch, thanks! Fixed this and locked the mutex later. I also removed the
> > > > "if (msg)" from out_err, as it becomes unneeded now. Here's the updated
> > > > patch:
> > > 
> > > You missed the static on the register and unregister functions down at the 
> > > bottom. :) Also see my comments to your change regarding the above issue 
> > > down here.
> > 
> > Hrm, yes!
> > 
> > > > +static int ip_vs_genl_get_cmd(struct sk_buff *skb, struct genl_info *info)
> > > > +{
> > > > +	struct sk_buff *msg;
> > > > +	void *reply;
> > > > +	int ret, cmd, reply_cmd;
> > > > +
> > > > +	cmd = info->genlhdr->cmd;
> > > > +
> > > > +	if (cmd == IPVS_CMD_GET_SERVICE)
> > > > +		reply_cmd = IPVS_CMD_NEW_SERVICE;
> > > > +	else if (cmd == IPVS_CMD_GET_INFO)
> > > > +		reply_cmd = IPVS_CMD_SET_INFO;
> > > > +	else if (cmd == IPVS_CMD_GET_CONFIG)
> > > > +		reply_cmd = IPVS_CMD_SET_CONFIG;
> > > > +	else {
> > > > +		IP_VS_ERR("unknown Generic Netlink command\n");
> > > > +		ret = -EINVAL;
> > > > +		goto out;
> > > > +	}
> > > > +
> > > > +	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
> > > > +	if (!msg) {
> > > > +		ret = -ENOMEM;
> > > > +		goto out;
> > > > +	}
> > > > +
> > > > +	reply = genlmsg_put_reply(msg, info, &ip_vs_genl_family, 0, reply_cmd);
> > > > +	if (reply == NULL)
> > > > +		goto nla_put_failure;
> > > 
> > > These gotos now unlock a not locked mutex down in the error path.
> > 
> > What did they put into my water supply :-/ Thanks!
> 
> Ok, fixed this up. The mutex is not completely moved down to make the
> code look a bit nicer (nla_put_failure assumes locked mutex). There
> should not be much concurrency anyways since this mutex only locks the
> userspace interface, which is mainly used by ipvsadm.

True, it was just a hint for an optimization. Looks good to me.

Acked-by: Sven Wegener <sven.wegener@...aler.net>

Should we get this into 2.6.27? It's a new interface, currently unused, so 
the chance of breaking anything is marginal.

Sven
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