netdev - Re: [PATCH net-next] sock: Reset dst when changing sk

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Date:   Wed, 7 Nov 2018 17:07:32 -0600
From:   David Barmann <david.barmann@...ckpath.com>
To:     netdev@...r.kernel.org
Cc:     Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net-next] sock: Reset dst when changing sk_mark via
 setsockopt

> On 11/07/2018 02:33 PM, David Barmann wrote:

> > When setting the SO_MARK socket option, the dst needs to be reset so
> > that a new route lookup is performed.
> > 
> > This fixes the case where an application wants to change routing by
> > setting a new sk_mark.  If this is done after some packets have already
> > been sent, the dst is cached and has no effect.
> > 

> > +		} else {
> > +			struct dst_entry *dst = sk_dst_get(sk);
> >  			sk->sk_mark = val;
> > +			sk_dst_reset(sk);
> 
> 
> sk_dst_get() and dst_release() seems extra overhead ?
> 
> net/ipv4/ip_sockglue.c do_ip_setsockopt() has a similar handling for IP_TOS,
> and it only calls sk_dst_reset() (If the new TOS is different than the current one)
> 
> 
> 
> So I would suggest :
> 
> 	if (!ns_capable(...)) {
>         	ret = -EPERM;
> 	} else if (val != sk->sk_mark) {
> 		sk->sk_mark = val;
> 		sk_dst_reset(sk);
> 	}


Thanks Eric, I'll redo that and resubmit.

-David