Backport recent bbr bugfixes to 4.10 kernel

[SaveTheRbtz]

4.10 kernel is commonly used to test BBR Congestion Control deployments.

Recent net-next pull in 4.13-rc1 had a bunch of fixes for the initial BBR release, namely:
4aea287e90dd61a48268ff2994b56f9799441b62 tcp_bbr: cut pacing rate only if filled pipe
f19fd62dafaf1ed6cf615dba655b82fa9df59074 tcp_bbr: introduce bbr_bw_to_pacing_rate() helper
79135b89b8af304456bd67916b80116ddf03d7b6 tcp_bbr: introduce bbr_init_pacing_rate_from_rtt() helper
1d3648eb5d1fe9ed3d095ed8fa19ad11ca4c8bc0 tcp_bbr: remove sk_pacing_rate=0 transient during init
32984565574da7ed3afa10647bb4020d7a9e6c93 tcp_bbr: init pacing rate on first RTT sample

All of them marked as 'Fixes: 0f8782ea1497 ("tcp_bbr: add BBR congestion control")', which makes them legitimate bugfixes.

All of them constrained to `net/ipv4/tcp_bbr.c` and should be trivial to cherrypick into 4.10.

[Ubuntu Kernel Bot (ubuntu-kernel-bot)]

This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:

apport-collect 1708604

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Vinson Lee (vlee)]

Please backport these tcp_bbr patches to ubuntu-zesty 4.10 kernel. These patches have already landed in linux-stable kernels in 4.9.42 and 4.12.6.

[Kleber Sacilotto de Souza (kleber-souza)]

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-zesty' to 'verification-done-zesty'. If the problem still exists, change the tag 'verification-needed-zesty' to 'verification-failed-zesty'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

[Kleber Sacilotto de Souza (kleber-souza)]

I'm setting the Xenial task to invalid, since these patches are only for 4.10. Xenial/hwe kernel will get these patches automatically.

[Kleber Sacilotto de Souza (kleber-souza)]

Hi @savetherbtz,

Could you please verify the fix with the Zesty kernel currently in -proposed?

Thank you!

[SaveTheRbtz (savetherbtz)]

Sadly, we've already workedaround that problem with a custom-built module. Let me see if my colleagues can test the kernel.

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux - 4.10.0-38.42

---------------
linux (4.10.0-38.42) zesty; urgency=low

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    - md: MD_CLOSING needs to be cleared after called md_set_readonly or
      do_md_stop

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    (LP: #1718397)
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