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

From: Thomas Jarosch <[email-masked]>
Date: Fri, 12 Dec 2014 22:30:22 +0100

Wolfgang,

On 12/12/2014 09:31 PM, Wolfgang Walter wrote:
> There is one thing which indicates that there is also a problen in the GSO 
> path, though. As my tests demonstrated disabling GSO on the physical interface 
> serving the ipsec tunnel does not prevent the hangs. It does, though, if sk-
>> sk_gso_max_segs = 1 in sk_setup_caps() if sk_can_gso(sk) returns false. This 
> was the first variation of the patch where sk->sk_gso_max_segs was not set if 
> dst->header_len() is non zero.

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.

HTH,
Thomas