FYI, we noticed the below changes on https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master commit aef79273d3af5d029ed932b8b4487d5e6914a834 ("drm: Move timestamping constants into drm_vblank_crtc") With the commit, the qemu is crashed after the following dmesg in our test. [ 13.118744] [drm] Initialized drm 1.1.0 20060810 [ 13.167245] microcode: CPU0 sig=0x306c1, pf=0x1, revision=0x1 [ 13.169228] microcode: CPU1 sig=0x306c1, pf=0x1, revision=0x1 [ 13.171634] microcode: Microcode Update Driver: v2.00 <tigran(a)aivazian.fsnet.co.uk&gt;, Peter Oruba [ 13.200914] AVX version of gcm_enc/dec engaged. [ 13.202250] AES CTR mode by8 optimization enabled [ 13.220633] [TTM] Zone kernel: Available graphics memory: 506878 kiB [ 13.222202] [TTM] Initializing pool allocator [ 13.223683] [TTM] Initializing DMA pool allocator [ 13.225517] [drm] fb mappable at 0xFC000000 [ 13.226939] [drm] vram aper at 0xFC000000 [ 13.259037] [drm] size 33554432 [ 13.259038] [drm] fb depth is 24 [ 13.259039] [drm] pitch is 3072 Elapsed time: 60 BUG: kernel test crashed qemu-system-x86_64 -enable-kvm -cpu Haswell,+smep,+smap -kernel /pkg/linux/x86_64-rhel/gcc-4.9/aef79273d3af5d029ed932b8b4487d5e6914a834/vmlinuz-4.3.0-rc2-00043-gaef7927 -append 'root=/dev/ram0 user=lkp job=/lkp/scheduled/vm-kbuild-1G-15/bisect_boot-1-debian-x86_64-2015-02-07.cgz-x86_64-rhel-aef79273d3af5d029ed932b8b4487d5e6914a834-20150923-57667-1i8kvtq-1.yaml ARCH=x86_64 kconfig=x86_64-rhel branch=linux-devel/devel-hourly-2015092221 commit=aef79273d3af5d029ed932b8b4487d5e6914a834 BOOT_IMAGE=/pkg/linux/x86_64-rhel/gcc-4.9/aef79273d3af5d029ed932b8b4487d5e6914a834/vmlinuz-4.3.0-rc2-00043-gaef7927 max_uptime=600 RESULT_ROOT=/result/boot/1/vm-kbuild-1G/debian-x86_64-2015-02-07.cgz/x86_64-rhel/gcc-4.9/aef79273d3af5d029ed932b8b4487d5e6914a834/0 LKP_SERVER=inn earlyprintk=ttyS0,115200 systemd.log_level=err debug apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 console=ttyS0,115200 console=tty0 vga=normal rw ip=::::vm-kbuild-1G-15::dhcp' -initrd /fs/sda1/initrd-vm-kbuild-1G-15 -m 1024 -smp 2 -device e1000,netdev=net0 -netdev user,id=net0,hostfwd=tcp::23014-:22 -boot order=nc -no-reboot -watchdog i6300esb -rtc base=localtime -device virtio-scsi-pci,id=scsi0 -drive file=/fs/sda1/disk0-vm-kbuild-1G-15,if=none,id=hd0,media=disk,aio=native,cache=none -device scsi-hd,bus=scsi0.0,drive=hd0,scsi-id=1,lun=0 -drive file=/fs/sda1/disk1-vm-kbuild-1G-15,if=none,id=hd1,media=disk,aio=native,cache=none -device scsi-hd,bus=scsi0.0,drive=hd1,scsi-id=1,lun=1 -drive file=/fs/sda1/disk2-vm-kbuild-1G-15,if=none,id=hd2,media=disk,aio=native,cache=none -device scsi-hd,bus=scsi0.0,drive=hd2,scsi-id=1,lun=2 -drive file=/fs/sda1/disk3-vm-kbuild-1G-15,if=none,id=hd3,media=disk,aio=native,cache=none -device scsi-hd,bus=scsi0.0,drive=hd3,scsi-id=1,lun=3 -drive file=/fs/sda1/disk4-vm-kbuild-1G-15,if=none,id=hd4,media=disk,aio=native,cache=none -device scsi-hd,bus=scsi0.0,drive=hd4,scsi-id=1,lun=4 -pidfile /dev/shm/kboot/pid-vm-kbuild-1G-15 -serial file:/dev/shm/kboot/serial-vm-kbuild-1G-15 -daemonize -display none -monitor null Thanks, Ying Huang