netdev - Re: [PATCH net 3/3] ipv6: Fix dst_entry refcnt bugs in ip6

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Date:	Wed, 02 Sep 2015 16:46:22 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Martin KaFai Lau <kafai@...com>
Cc:	netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Kernel Team <kernel-team@...com>
Subject: Re: [PATCH net 3/3] ipv6: Fix dst_entry refcnt bugs in ip6_tunnel

On Wed, 2015-09-02 at 16:10 -0700, Martin KaFai Lau wrote:
> On Wed, Sep 02, 2015 at 03:48:57PM -0700, Eric Dumazet wrote:
> > On Wed, 2015-09-02 at 14:52 -0700, Martin KaFai Lau wrote:
> > > On Wed, Sep 02, 2015 at 02:30:45PM -0700, Eric Dumazet wrote:
> > > > Object cannot be freed until all cpus have exited their RCU sections.
> > > You meant the dst_destroy() here will wait for all cpus exited their RCU sections?
> > >
> > > static inline void dst_free(struct dst_entry *dst)
> > > {
> > > 	if (dst->obsolete > 0)
> > > 		return;
> > > 	if (!atomic_read(&dst->__refcnt)) {
> > > 		dst = dst_destroy(dst);
> > > 		if (!dst)
> > > 			return;
> > > 	}
> > > 	__dst_free(dst);
> > > }
> >
> > dst_free() is called after RCU grace period, in the case you are
> > interested in.
> >
> > Look at dst_rcu_free() and rt_free()
> Yes for IPv4 FIB
> 
> Not for IPv6 FIB. F.e. rt6_release()
> The IPv6 FIB is protected by rwlock now.

Oh well. I gave you a hint. I was not saying that it was currently used
in IPv6.

Are you telling me that IPv6 needs to continue to use techniques from
1990 ?

Surely we can use modern stuff, like proper RCU and/or seqlocks.

Since you are fixing a day-0 bug, I do not believe there is a particular
hurry to be conservative.




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