mxl.txt

Probably you have this:

upstream: A---B---C
origin:   A
           \
branch:     D

You want to go:
upstream: A---B---C
origin:   A---B---C
                   \
branch:             D


git checkout master
git pull # origin
git fetch upstream
git rebase upstream/master
git push # your origin/master is same as upstream/master
git checkout branch
git rebase origin/master
git push -f origin branch

make a PR