netdev - Re: [patch v2 04/11] nf_conntrack_netlink: pass nf_conntrack_netlink module to netlink_dump

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Date:	Wed, 26 Sep 2012 17:04:30 +0200
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Gao feng <gaofeng@...fujitsu.com>
Cc:	davem@...emloft.net, eric.dumazet@...il.com,
	steffen.klassert@...unet.com, netfilter-devel@...r.kernel.org,
	linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
	linux-crypto@...r.kernel.org, stephen.hemminger@...tta.com,
	jengelh@...i.de
Subject: Re: [patch v2 04/11] nf_conntrack_netlink: pass
 nf_conntrack_netlink module to netlink_dump_start

On Wed, Sep 26, 2012 at 08:35:53PM +0800, Gao feng wrote:
> 于 2012年09月26日 17:58, Pablo Neira Ayuso 写道:
> > On Wed, Sep 26, 2012 at 05:42:31PM +0800, Gao feng wrote:
> >> Hi Pablo:
> >>
> >> 于 2012年09月26日 17:26, Pablo Neira Ayuso 写道:
> >>> On Wed, Sep 26, 2012 at 04:41:21PM +0800, Gao feng wrote:
> >>>> use proper netlink_dump_control.done and .module to avoid panic.
> >>>>
> >>>> Signed-off-by: Gao feng <gaofeng@...fujitsu.com>
> >>>> ---
> >>>>  net/netfilter/nf_conntrack_netlink.c |    8 ++++++++
> >>>>  1 files changed, 8 insertions(+), 0 deletions(-)
> >>>>
> >>>> diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
> >>>> index 9807f32..509a257 100644
> >>>> --- a/net/netfilter/nf_conntrack_netlink.c
> >>>> +++ b/net/netfilter/nf_conntrack_netlink.c
> >>>> @@ -706,6 +706,7 @@ static int ctnetlink_done(struct netlink_callback *cb)
> >>>>  		nf_ct_put((struct nf_conn *)cb->args[1]);
> >>>>  	if (cb->data)
> >>>>  		kfree(cb->data);
> >>>> +	netlink_dump_done(cb);
> >>>
> >>> I think you can call netlink_dump_done from af_netlink.c:
> >>>
> >>> static int netlink_dump(struct sock *sk) 
> >>>         ...
> >>>         if (cb->done) {
> >>>                 cb->done(cb);
> >>>                 netlink_dump_done(...);
> >>>         }
> >>>
> >>> Thus, you don't need to change netlink_dump_control in every netlink
> >>> subsystem.
> >>
> >> because cb->done is called by netlink_sock_destruct too,it's very usefully
> >> when userspace program only send dump request to kernel without reading
> >> data from kernel.
> > 
> > Then add that to netlink_sock_destruct as well. If possible, I prefer
> > if this remains in the netlink core to avoid leaking module refcount
> > if you forget to call netlink_dump_done.
> 
> make sense, I will update it in next version.
> Thanks!

Great. Remove also netlink_dump_done and just use module_put instead
after cb->done. That new function you added is so small that there is
no way to justify its addition.

> > 
> >>>
> >>>>  	return 0;
> >>>>  }
> >>>>  
> >>>> @@ -1022,6 +1023,7 @@ ctnetlink_get_conntrack(struct sock *ctnl, struct sk_buff *skb,
> >>>>  		struct netlink_dump_control c = {
> >>>>  			.dump = ctnetlink_dump_table,
> >>>>  			.done = ctnetlink_done,
> >>>> +			.module = THIS_MODULE,
> >>>
> >>> You can do something similar to:
> >>>
> >>> 9f00d97 netlink: hide struct module parameter in netlink_kernel_create
> >>>
> >>> by definiting netlink_dump_start as static inline and using
> >>> THIS_MODULE from there.
> >>>
> >>> If I'm not missing anything, with those two changes, you will not need
> >>> to modify any caller and it will result one single patch.
> >>>
> >>
> >> You can see the patch [11/11], THIS_MODULE in infiniband/core/cma.c
> >> means module rdma_cm,but we call netlink_dump_start in infiniband/core/netlink.c
> > 
> > You can still use __netlink_dump_start for that case, which allows you
> > to specify a custom struct module * parameter. But for most cases,
> > netlink_dump_start (which hides THIS_MODULE) should be fine.
> 
> I don't know how to deal with module_put in this way.
> and I think my  way is simple enough.

Not sure what problem with module_put you're refering to.

I think you can make this patchset way smaller with the change I'm
proposing.
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