Re: freeze with interface rename & SIOCGIFNAME

[Eric Dumazet <eric.dumazet@gmail.com>]

On Tue, 2013-06-25 at 18:27 +0200, Nicolas Schichan wrote:
> On 06/25/2013 06:15 PM, Eric Dumazet wrote:
> > Nice catch !
> >
> > Please add a helper so that we can use it as well from
> > sock_getbindtodevice(), and submit an official patch ?
> 
> Sure, I'll do that.
> 
> > int netdev_get_name(char *name, int ifindex)
> > {
> > 	struct net_device *dev;
> > 	unsigned int seq;
> >
> > retry:
> >          seq = read_seqcount_begin(&devnet_rename_seq);
> 
> raw_seqcount_begin is required here here. read_seqcount_begin will spin 
> forever as the s->sequence & 1 check will always be true in 
> __read_seqcount_begin(). This will incur some unneed work if a rename is in 
> progress, but that's better than locking the system up.

I am not sure it's needed, because the writer holds a spinlock and is
not allowed to sleep or being preempted.

If it's needed, there is a bug somewhere else...