Re: [bisected] xfrm: TCP connection initiating PMTU discovery stalls on v3.

Wolfgang Walter
2014-12-12T23:47:48Z

Am Freitag, 12. Dezember 2014, 14:31:49 schrieben Sie:
> On Fri, 2014-12-12 at 22:30 +0100, Thomas Jarosch wrote:
> > if it's any help: Disabling TX checksumming prevents the hang
> > even on an unpatched 3.14.x kernel. You could check with your debug
> > statements in place the path of the packets with and without TX
> > checksumming.

I can't disable it as the driver will not allow it:
# ethtool -K eth0 tx off
Cannot change tx-checksumming
Could not change any device features

> Disabling TX checksum automatically disables GSO.
>
> Disabling TSO/GSO is the real 'cure' for the time being, you can keep TX
> checksums.

This does not help here. With GSO disabled (for network device serving the
ipsec traffic, here e.g. eth0) the hang still occurs. tcp_set_skb_tso_segs()
gets called and the else-branch for skb->len <= mss_now is taken.

I tested this serveral times.

Regards,
--
Wolfgang Walter
Studentenwerk München
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