I found a lockup in single threaded TCG, with OVMF bios, 16 CPUs.
qemu-system-x86_64 --accel tcg,thread=single -smp cpus=16 -bios /usr/share/ovmf/OVMF.fd
Using Ubuntu 18.04 LTS, default gnome desktop. There is no guest OS, there is no hard drive, just the OVMF firmware locks it up. (I narrowed it down to this from a much larger repro)
Peter Maydell helped me bisect it in IRC.
Works fine at commit 1e8a98b53867f61
Fails at commit 9458a9a1df1a4c7
MTTCG works fine all the way up to master.
Configure command line:
../qemu/configure --target-list=x86_64-softmmu,i386-softmmu --audio-drv-list=pa --enable-libusb --disable-libssh --enable-virglrenderer --enable-opengl --enable-debug
The issue occurs without --enable-debug. I didn't strip the configure down though, it may not need all of those configure options exactly.
OVMF from ubuntu package manager, package named ovmf, exact version is 0~20180205.c0d9813c-2ubuntu0.1