Comment 4 for bug 1821564

Ok, I failed to find where the regression comes from.

Would it be possible for you to do a kernel bisection?

First, find the last good -rc kernel and the first bad -rc kernel from http://kernel.ubuntu.com/~kernel-ppa/mainline/

Then,
$ sudo apt build-dep linux
$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
$ cd linux
$ git bisect start
$ git bisect good $(the good version you found)
$ git bisect bad $(the bad version found)
$ make localmodconfig
$ make -j`nproc` deb-pkg
Install the newly built kernel, then reboot with it.
If the issue still happens,
$ git bisect bad
Otherwise,
$ git bisect good
Repeat to "make -j`nproc` deb-pkg" until you find the commit that causes the regression.