FYI, we noticed the below changes on

git://internal_merge_and_test_tree revert-a580b73412da93a2194037e54342980f2452520d-2657eee793e8b13334860e7953d5aa6e49227521
commit 2657eee793e8b13334860e7953d5aa6e49227521 ("arch/x86: enable task isolation functionality")


+------------------------------------------------+------------+------------+
|                                                | 5f7bb45a98 | 2657eee793 |
+------------------------------------------------+------------+------------+
| boot_successes                                 | 15         | 0          |
| boot_failures                                  | 4          | 15         |
| IP-Config:Auto-configuration_of_network_failed | 4          |            |
| BUG:kernel_boot_hang                           | 0          | 15         |
+------------------------------------------------+------------+------------+


[   14.953363] debug: unmapping init [mem 0x41bd5000-0x41c9bfff]
[   14.953952] Write protecting the kernel text: 8216k
[   14.954381] Write protecting the kernel read-only data: 3068k
[   14.954849] NX-protecting the kernel data: 6120k

Elapsed time: 750
BUG: kernel boot hang
qemu-system-i386 -enable-kvm -cpu Haswell,+smep,+smap -kernel /pkg/linux/i386-randconfig-s0-201539/gcc-4.9/2657eee793e8b13334860e7953d5aa6e49227521/vmlinuz-4.3.0-rc3-00007-g2657eee -append 'root=/dev/ram0 user=lkp job=/lkp/scheduled/vm-vp-quantal-i386-30/bisect_boot-1-quantal-core-i386.cgz-i386-randconfig-s0-201539-2657eee793e8b13334860e7953d5aa6e49227521-20150929-62209-qa4zpx-0.yaml ARCH=i386 kconfig=i386-randconfig-s0-201539 branch=linux-review/Chris-Metcalf/support-task_isolated-mode-for-nohz_full commit=2657eee793e8b13334860e7953d5aa6e49227521 BOOT_IMAGE=/pkg/linux/i386-randconfig-s0-201539/gcc-4.9/2657eee793e8b13334860e7953d5aa6e49227521/vmlinuz-4.3.0-rc3-00007-g2657eee max_uptime=600 RESULT_ROOT=/result/boot/1/vm-vp-quantal-i386/quantal-core-i386.cgz/i386-randconfig-s0-201539/gcc-4.9/2657eee793e8b13334860e7953d5aa6e49227521/0 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-vp-quantal-i386-30::dhcp drbd.minor_count=8'  -initrd /fs/sde1/initrd-vm-vp-quantal-i386-30 -m 360 -smp 1 -device e1000,netdev=net0 -netdev user,id=net0 -boot order=nc -no-reboot -watchdog i6300esb -rtc base=localtime -pidfile /dev/shm/kboot/pid-vm-vp-quantal-i386-30 -serial file:/dev/shm/kboot/serial-vm-vp-quantal-i386-30 -daemonize -display none -monitor null 


Thanks,
Ying Huang