Re: INFO: task hung in bpf_exit_net

On Fri, Dec 22, 2017 at 04:28:07PM -0200, Marcelo Ricardo Leitner wrote:

On Fri, Dec 22, 2017 at 11:58:08AM +0100, Dmitry Vyukov wrote:
...

quoted

quoted

Same with this one, perhaps related to / fixed by:
    http://patchwork.ozlabs.org/patch/850957/

Looking at the log, this one seems to be an infinite loop in SCTP code
with console output in it. Kernel is busy printing gazilion of:

[  176.491099] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too
low, using default minimum of 512
** 110 printk messages dropped **
[  176.503409] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too
low, using default minimum of 512
** 103 printk messages dropped **
...
[  246.742374] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too
low, using default minimum of 512
[  246.742484] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too
low, using default minimum of 512
[  246.742590] sctp: sctp_transport_update_pmtu: Reported pmtu 508 too
low, using default minimum of 512

Looks like a different issue.

Oh. I guess this is caused by the interface having a MTU smaller than
SCTP_DEFAULT_MINSEGMENT (512), as the icmp frag needed handler
(sctp_icmp_frag_needed) will trigger an instant retransmission.
But as the MTU is smaller, SCTP won't update it, but will issue the
retransmission anyway.

I will test this soon. Should be fairly easy to trigger it.

Reproduced it.

netns A veth0(1500) - veth1(1500) B veth2(508) - veth3(508) C

When A sends a sctp packet bigger than 508, it triggers the issue as B
will reply a icmp frag needed with a size that sctp won't accept but
will retransmit anyway.

  Marcelo