qemu-user emulator images core dump when emulating `linux/amd64`, `linux/s390x` with `p_rcu_reader->depth != 0`

[maxheld83]

this is crossposted from tonistiigi/binfmt, see there for details/reproducible example.
(Not repeating that here, because ... DRY).

It seems that asahi may be relevant, b/c @tonistiigi could not reproduce the issue on Apple M1 (under macOS).