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

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Date:	Sat, 13 Dec 2014 00:47:45 +0100
From:	Wolfgang Walter <linux@...m.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Thomas Jarosch <thomas.jarosch@...ra2net.com>,
	netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Steffen Klassert <steffen.klassert@...unet.com>
Subject: Re: [bisected] xfrm: TCP connection initiating PMTU discovery stalls on v3.

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
Anstalt des öffentlichen Rechts
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