Kernels between 4.17-rc1 and current master reboot instantly when built with the OpenMandriva toolchain (gcc 8.1, binutils 2.30) and build environment (build command being run:
make -j32 -O LD=x86_64-openmandriva-linux-gnu-ld.bfd all CC=gcc CXX=g++ CFLAGS="-gdwarf-4 -Wstrict-aliasing=2 -pipe -Wformat -Werror=format-security -D_FORTIFY_SOURCE=2 -fstack-protector-strong --param=ssp-buffer-size=4 -fPIC -flto -O3" LDFLAGS="--hash-style=sysv --build-id=none -flto"
git bisect shows the problem starting with commit 0a1756bd2897951c03c1cb671bdfd40729ac2177 - and by reverting it, 4.17.3 and 4.18-rc2 work fine.
Posting this from a box running 4.18-rc2 with
and its followups
reverted (nothing obviously wrong with those; reverting them was the fastest way to resolve merge conflicts).
Bootloader is grub2 2.02 running from UEFI. The reboot has been observed on both Intel and AMD hardware as well as in qemu-system-x86_64.
Given others are booting unpatched 4.17/4.18 kernels on x86_64 without problems, this is almost certainly caused by some interaction of 0a1756bd2897951c03c1cb671bdfd40729ac2177 and toolchain/compiler flags in use that may come back and bite others as they update toolchains.