arm64: -smp 2 hangs qemu

[Joel Schopp]

It appears that smp is broken on qemu for arm64. I'm looking into the root cause but am curious if others can reproduce in their environments.

Tested with commit f368c33d5ab09dd5656924185cd975b11838cd25 (July 22) from https://github.com/qemu/qemu.git

[root@joelaarch64 ~]# /usr/local/bin/qemu-system-aarch64 --version
QEMU emulator version 2.0.93, Copyright (c) 2003-2008 Fabrice Bellard

works fine:
qemu --enable-kvm -nographic -netdev tap,id=t0,ifname=tap0,script=no,downscript=no,vhost=on -device virtio-net-device,netdev=t0,id=nic0 -kernel /extra/rootfs/boot/Image -drive file=/extra/Styx-Acadia-42-2014-07-07_10-09-27.img,id=fs -device virtio-blk-device,drive=fs -m 1024 -M virt -cpu host -smp 1 -append "console=ttyAMA0 console=ttyS0 root=/dev/vda2"

hangs:
qemu --enable-kvm -nographic -netdev tap,id=t0,ifname=tap0,script=no,downscript=no,vhost=on -device virtio-net-device,netdev=t0,id=nic0 -kernel /extra/rootfs/boot/Image -drive file=/extra/Styx-Acadia-42-2014-07-07_10-09-27.img,id=fs -device virtio-blk-device,drive=fs -m 1024 -M virt -cpu host -smp 2 -append "console=ttyAMA0 console=ttyS0 root=/dev/vda2"

(gdb) t
[Current thread is 1 (Thread 0x3ffb6787cc0 (LWP 7619))]
(gdb) bt
#0 0x000003ffb6e50330 in ppoll () from /lib64/libc.so.6
#1 0x00000000006631a0 in ppoll (__ss=0x0, __timeout=0x0, __nfds=<optimized out>, __fds=<optimized out>) at /usr/include/bits/poll2.h:77
#2 qemu_poll_ns (fds=<optimized out>, nfds=<optimized out>, timeout=<optimized out>) at qemu-timer.c:314
#3 0x0000000000662878 in os_host_main_loop_wait (timeout=<optimized out>) at main-loop.c:229
#4 main_loop_wait (nonblocking=<optimized out>) at main-loop.c:484
#5 0x000000000040fdf4 in main_loop () at vl.c:2010
#6 main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at vl.c:4541
(gdb) t
[Current thread is 1 (Thread 0x3ffb6787cc0 (LWP 7619))]
(gdb) t 2
[Switching to thread 2 (Thread 0x3ffb64beef0 (LWP 7622))]
#0 0x000003ffb6f10a44 in sigwait () from /lib64/libpthread.so.0
(gdb) bt
#0 0x000003ffb6f10a44 in sigwait () from /lib64/libpthread.so.0
#1 0x000000000069d78c in sigwait_compat (opaque=0xd752c0) at util/compatfd.c:36
#2 0x000003ffb6f07c20 in start_thread () from /lib64/libpthread.so.0
#3 0x000003ffb6e5a80c in clone () from /lib64/libc.so.6

[Joel Schopp (joel-schopp)]

The combination of a newer kernel and newer qemu make qemu work with -smp 2 . Rather than go figure out what got fixed let's just be happy it did.