update cwnd in both convex and concave regions like comment stated.

[rscheff]

Summary

The current cubic code has an oversight that it missed updating cwnd
in the convex region. However, the comment in the code states, that
cwnd should be updated similarly in both convex and concave regions.

This has been reported by Vidhi Goel in Bug Report 238478.

Test Plan

Track the evolution of cwnd throuhg tcp friendly, concave
and convex regions and verify the behavior matches what RFC8312
(TCP Cubic) prescribes.

[rgrimes]

So, is FreeBSD getting close to a proper Cubic yet?

sys/netinet/cc/cc_cubic.c

179 ↗

(On Diff #71254)

I am only going to "NOTE" a style 9 issue here, I do not expect it fixed, as it was an existing issue, and it may be the whole file is this way, but we usually write "} else {" or "} else if {" and I am not sure why these extra new lines are here.

[rscheff]

• style fix

[rscheff]

Re-inspecting the suggested fix. The concave region is where cubic_wnd < cwnd_max, and the convex region is cubic_cwnd > cwnd_max.

However, this if bracket is only preventing snd_cwnd from shrinking.

Will adjust the style and make a comment.

[rscheff]

• only update style and comment. logic was ok before.