blk-wbt / wbt_rqw_done logic?

Hi Jens,

While looking into a deadlock that Jan has fixed:

https://lore.kernel.org/linux-block/CA+8F9hggf7jOcGRxvBoa8FYxQs8ZV+XueVAd9BodpQQP_+8Pdw@mail.gmail.com/T/ (local)

I noticed this line of code in blk-wbt.c (L164):

-               if (!inflight || diff >= rwb->wb_background / 2)

And based on the preceding logic calculating `limit` and the comment
in the "no wakeup" check above which references "normal limit" and
decides based on `limit`, it's not clear why `rwb->wb_background` is
used here as there's no comment.

Should this be:

+               if (!inflight || diff >= limit / 2)

I traced the history of the line back to 4.20rc but it hasn't changed
since being added.

Thanks!

Regards,
Omar