Re: [CRIU] TCP_REPAIR MSS issue

On Tue, 2016-06-14 at 06:03 -0700, Eric Dumazet wrote:

On Tue, 2016-06-14 at 11:40 +0000, Eggert, Lars wrote:

quoted

On 2016-06-14, at 13:28, Pavel Emelyanov [off-list ref] wrote:

quoted

Andrey (in Cc) has played with TCP_REPAIR recently, I guess he can know something.

Thanks for CC'ing him. We looked a little bit more into this:

When TCP_REPAIR is on, tcp_connect() directly calls tcp_finish_connect() before returning, passing NULL for skb, which causes sk_rx_dst_set() to be bypassed. Later, when TCP_REPAIR is being turned off, do_tcp_setsockopt() just does tcp_send_window_probe(), but apparently all the "dst" stuff is being bypassed then also, so the mss remains at TCP_MSS_DEFAULT.

Lars

What gives :

sysctl net/ipv4/ip_no_pmtu_disc net/ipv4/tcp_mtu_probing

Also, is it a regression ? Was this working better with an older linux
version ?