Good catch! I run without group scheduling and therefore didn't notice these
stray defines earlier. For 5.1 it should merge cleanly; adding this on top of
the pending 5.2 BFQ patches required a small context fixup in hunk #1 due to
"block, bfq: do not idle for lowest-weight queues".
I'm hesitant to apply this, since the group scheduling stuff has obviously never
been tested.
This is simply a regression in 5.1 caused by 73d58118498b - nothing else,
and as such this fix needs to go into 5.1 as well. I'm sure Paolo will agree.
What you so ominously call "the group scheduling stuff" has been there and
shipping in mainline since day 1 of the BFQ merge, and it works fine in 5.0.
If that's the case (I didn't check how far back it went), then yes, it should
of course go into 5.1.
The ominous nature of my reply I'll chalk up to your interpretation