netdev - Re: [RFC] bpf: offload: report device information for offloaded programs

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Date:   Thu, 30 Nov 2017 18:05:56 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        oss-drivers@...ronome.com, alexei.starovoitov@...il.com,
        daniel@...earbox.net, "Eric W . Biederman" <ebiederm@...ssion.com>
Subject: Re: [RFC] bpf: offload: report device information for offloaded
 programs

Hi Kirill,

On Thu, 30 Nov 2017 16:19:13 +0300, Kirill Tkhai wrote:
> > @@ -164,6 +166,38 @@ int bpf_prog_offload_compile(struct bpf_prog *prog)
> >  	return bpf_prog_offload_translate(prog);
> >  }
> >  
> > +int bpf_prog_offload_info_fill(struct bpf_prog_info *info,
> > +			       struct bpf_prog *prog)
> > +{
> > +	struct bpf_dev_offload *offload = prog->aux->offload;
> > +	struct inode *ns_inode;
> > +	struct path ns_path;
> > +	struct net *net;
> > +	int ret = 0;
> > +	void *ptr;
> > +
> > +	info->dev_bound = 1;
> > +
> > +	rtnl_lock();  
> 
> rtnl_lock() is too big lock and it is already overused in kernel.
> Can't we use smaller lock in this driver to protect bpf_prog_offload_devs?
> I suppose rwlock would be appropriate for that.
> 
> (Then, we may completely remove rtnl_lock() from bpf_prog_offload_init()
> and use readlocked dev_base_lock for __dev_get_by_index() instead and
> the new small_rwlock to link in the list.
> 
> Not sure about bpf_prog_offload_verifier_prep() and bpf_prog_offload_translate()
> and which context expect net_device_ops->ndo_bpf users. Either they need rtnl
> or not).

Thanks for the comments, removing the use of rtnl_lock is definitely on
my todo list!