FYI, we noticed the following commit: https://git.kernel.org/pub/scm/linux/kernel/git/jirislaby/linux.git devel commit 7411df6b66594f6eaeac23fe0174aad4aa71d6f9 ("TTY: serial_core, add ->install") on test machine: vm-vp-quantal-x86_64: 2 threads qemu-system-x86_64 -enable-kvm with 360M memory caused below changes: +----------------+------------+------------+ | | 16b6770edb | 7411df6b66 | +----------------+------------+------------+ | boot_successes | 0 | 0 | +----------------+------------+------------+ WARNING: 'debug_locks && !lock_is_held(&(&state->port.mutex)->dep_map)' is true! ------------[ cut here ]------------ ------------[ cut here ]------------ WARNING: CPU: 0 PID: 1 at drivers/tty/serial/serial_core.c:98 uart_install+0xd4/0xe0 WARNING: CPU: 0 PID: 1 at drivers/tty/serial/serial_core.c:98 uart_install+0xd4/0xe0 CPU: 0 PID: 1 Comm: swapper Not tainted 4.7.0-rc2-next-20160609-00023-g7411df6 #1 CPU: 0 PID: 1 Comm: swapper Not tainted 4.7.0-rc2-next-20160609-00023-g7411df6 #1 power_supply test_battery: uevent FYI, raw QEMU command line is: qemu-system-x86_64 -enable-kvm -kernel /pkg/linux/x86_64-randconfig-s1-06091829/gcc-6/7411df6b66594f6eaeac23fe0174aad4aa71d6f9/vmlinuz-4.7.0-rc2-next-20160609-00023-g7411df6 -append 'root=/dev/ram0 user=lkp job=/lkp/scheduled/vm-vp-quantal-x86_64-49/bisect_boot-1-quantal-core-x86_64.cgz-x86_64-randconfig-s1-06091829-7411df6b66594f6eaeac23fe0174aad4aa71d6f9-20160610-12341-j3nm4r-0.yaml~ ARCH=x86_64 kconfig=x86_64-randconfig-s1-06091829 branch=linux-devel/devel-catchup-201606092006 commit=7411df6b66594f6eaeac23fe0174aad4aa71d6f9 BOOT_IMAGE=/pkg/linux/x86_64-randconfig-s1-06091829/gcc-6/7411df6b66594f6eaeac23fe0174aad4aa71d6f9/vmlinuz-4.7.0-rc2-next-20160609-00023-g7411df6 max_uptime=600 RESULT_ROOT=/result/boot/1/vm-vp-quantal-x86_64/quantal-core-x86_64.cgz/x86_64-randconfig-s1-06091829/gcc-6/7411df6b66594f6eaeac23fe0174aad4aa71d6f9/0 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-x86_64-49::dhcp drbd.minor_count=8' -initrd /fs/sdf1/initrd-vm-vp-quantal-x86_64-49 -m 360 -smp 2 -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-x86_64-49 -serial file:/dev/shm/kboot/serial-vm-vp-quantal-x86_64-49 -daemonize -display none -monitor null Thanks, Kernel Test Robot