kernels >= v4.12 oops/crash with ipsec-traffic: partly bisected

[Wolfgang Walter <linux@stwm.de>]

Hello,

kernels >= 4.12 do not work on one of our main routers. They crash as soon as 
ipsec-tunnels are configured and ipsec-traffic actually flows.

Just configuring ipsec (that is starting strongswan) does not trigger the 
oops.

I finally found time to bisect that. Though I have not completed that yet, I 
already narrowed it down to the following commits

good: d24406c85d123df773bc4df88ad5da2233896919
	udp: call dst_hold_safe() in udp_sk_rx_set_dst()
bad: 5b7c9a8ff828287af5aebe93e707271bf1a82cc3
	net: remove dst gc related code

Commits in between are almost all changes to remove dst gc.

Now we have other machines which run just fine with the very same kernels 
doing ipsec. They differ insofar as they have much less cores, do not use the 
ixgbe driver, do not have 10G and terminate only a few tunnels instead of 
hundreds.

I already tested distribution kernels > 4.12 from debian, they also crash.

Regards,
-- 
Wolfgang Walter
Studentenwerk München
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