Re: [PATCH] can: Fix kernel panic at security_sock_rcv_skb

[Liu Shuo]

On Thu 12.Jan'17 at 17:33:38 +0100, Oliver Hartkopp wrote:
> On 01/12/2017 02:01 PM, Eric Dumazet wrote:
> > On Thu, 2017-01-12 at 09:22 +0100, Oliver Hartkopp wrote:
>
> > > But my main concern is:
> > >
> > > The reason why can_rx_delete_receiver() was introduced was the need to
> > > remove a huge number of receivers with can_rx_unregister().
> > >
> > > When you call synchronize_rcu() after each receiver removal this would
> > > potentially lead to a big performance issue when e.g. closing CAN_RAW
> > > sockets with a high number of receivers.
> > >
> > > So the idea was to remove/unlink the receiver hlist_del_rcu(&r->list)
> > > and also kmem_cache_free(rcv_cache, r) by some rcu mechanism - so that
> > > all elements are cleaned up by rcu at a later point.
> > >
> > > Is it possible that the problems emerge due to hlist_del_rcu(&r->list)
> > > and you accidently fix it with your introduced synchronize_rcu()?
> >
> > I agree this patch does not fix the root cause.
> >
> > The main problem seems that the sockets themselves are not RCU
> > protected.
> >
> > If CAN uses RCU for delivery, then sockets should be freed only after
> > one RCU grace period.
> >
> > On recent kernels, following patch could help :
>
> Thanks Eric!
>
> @Liu ShuoX: Can you check if Eric's suggestion fixes the issue in your 
> setup?
Sorry for late reply. I was OOO yesterday.
With Eric's hint, i just found his patch that "net: add SOCK_RCU_FREE
socket flag" in the latest kernel. With backporting this one plus Eric's
following patch, it fixs my failure.

Thanks Eric and Oliver!

Shuo
> Best regards,
> Oliver