Regression in kernel 4.12-rc1 for Powerpc 32 - partially bisected

[Larry Finger]

On my Powerbook G4 aluminum, kernel 4.12-rc1 fails to boot. I cannot save a copy 
of the early printk messages and I will need to summarize.

The kernel finds the hard driver and recognizes the various partitions. All 
seems normal until after the "unused kernel memory is freed" and that "This 
architecture does not have kernel memory protection", which are both normal. The 
next batch of logged messages are

Loading, please wait...
udevd[64]: starting version 175
udevd[64]: Unable to receive ctrl message: Bad address.
modprobe: chdir(4.12-rc1): No such file or directory
udevd[64]: Unable to receive ctrl message: Bad address.
Begin: Loading essential drivers ... modprobe: chdir: chdir(4.12.0-rc1): No such 
file or directory
done.
Begin: Running /scripts/init-premount ... done.
udevd[64]: Begin: Waiting for root file system ... [   11.651175] random: faast 
init done
done.
Gave up waiting for root device. Common problems:
 - Boot args (cat /proc/cmdline)
   - Check rootdelay= (did the system wait long enough?)
   - Check root= (Did the system wait for the right device?)
 - Missing modules (cat /proc/modules; ls /dev)
ALERT! /dev/disk/by-uuid/<UUID> does not exist. Dropping to a shell!
modprobe: chdir(4.12-rc1): No such file or directory <listed 6 times>

BusyBox v1.20.2 (Debian 1:1.20.0-7) built-in shell (ash)
Enter 'help' for a list of built-in commands.

/bin/sh: can't access tty: Job control turned off
(initramfs)

At that point, the system is dead. I have tried bisecting this issue; however, I 
run into a second problem that crashes the bootstrap.

The bisection was normal with a bad commit at ec02268 ("alpha: switch to 
RAW_COPY_USER") and a good commit at ec02268 ("alpha: switch to RAW_COPY_USER")
ec02268. The next trial at commit c1aad8d ("asm-generic: zero in __get_user(), 
not __get_user_fn()") panics in the bootstrap. That panic has apparently been 
fixed, but my attempts to find that fix have not yet been successful.

Sorry that I do not have a better description of where the problem happens.

As usual, any suggestions welcome.

Larry