[Regression 5.7-rc1] Random hangs on 32-bit PowerPC (PowerBook6,7)

[Resending since I messed up the subject, sorry]

Hi, everyone,

Something went wrong between Linux 5.6 and 5.7-rc1. This is an iBook
G4 laptop with 1.5 GiB of RAM running the Debian powerpc port. I
haven't bisected yet, since it's going to take quite a bit of time, so
I'm sending this mostly as a heads-up (and to see if anybody has any
clues about the possible cause). I'm using the following reproducer:

stress-ng --cpu 8 --io 8 --vm 8 --vm-bytes 1G --fork 8 --timeout 10m

On Linux 5.7-rc1, this completely hangs the machine in about 30
seconds. Linux 5.6 survives the test. Let me know if I can provide any
additional info, otherwise I'll just bite the bullet and start
bisecting.

Thanks,
Rui