FYI, we noticed the following commit: https://git.kernel.org/pub/scm/linux/kernel/git/jirislaby/linux.git devel commit acce93619b7f32eb9f2771fbd8e646b927e8fe1c ("TTY: serial_core, add ->install") on test machine: vm-vp-quantal-i386: 1 threads qemu-system-i386 -enable-kvm -cpu Haswell,+smep,+smap with 360M memory caused below changes: +--------------------------------------------------------------+------------+------------+ | | 92c81a6cc4 | acce93619b | +--------------------------------------------------------------+------------+------------+ | boot_successes | 4 | 0 | | boot_failures | 4 | 8 | | IP-Config:Auto-configuration_of_network_failed | 4 | 4 | | WARNING:at_drivers/tty/serial/serial_core.c:#uart_port_check | 0 | 8 | | backtrace:uart_install | 0 | 8 | | backtrace:tty_init_dev | 0 | 8 | | backtrace:do_sys_open | 0 | 8 | | backtrace:SyS_open | 0 | 8 | | backtrace:kernel_init_freeable | 0 | 8 | +--------------------------------------------------------------+------------+------------+ 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_port_check+0x3c/0x49 WARNING: CPU: 0 PID: 1 at drivers/tty/serial/serial_core.c:98 uart_port_check+0x3c/0x49 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.7.0-rc3-next-20160614-00023-gacce936 #1 CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.7.0-rc3-next-20160614-00023-gacce936 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014 00000000 00000000 00200246 00200246 9441fd6c 9441fd6c 8118315d 8118315d 00000000 00000000 812a064a 812a064a 9441fd84 9441fd84 81040ec0 81040ec0 00000062 00000062 94423000 94423000 96072280 96072280 95f3d800 95f3d800 9441fd98 9441fd98 81040f43 81040f43 00000009 00000009 00000000 00000000 00000000 00000000 9441fdac 9441fdac 812a064a 812a064a 81a41ab2 81a41ab2 81aa7101 81aa7101 94423000 94423000 9441fdc0 9441fdc0 812a0a56 812a0a56 Call Trace: Call Trace: [<8118315d>] dump_stack+0x73/0xa5 [<8118315d>] dump_stack+0x73/0xa5 [<812a064a>] ? uart_port_check+0x3c/0x49 [<812a064a>] ? uart_port_check+0x3c/0x49 [<81040ec0>] __warn+0xad/0xc4 [<81040ec0>] __warn+0xad/0xc4 [<81040f43>] warn_slowpath_null+0x11/0x16 [<81040f43>] warn_slowpath_null+0x11/0x16 [<812a064a>] uart_port_check+0x3c/0x49 [<812a064a>] uart_port_check+0x3c/0x49 [<812a0a56>] uart_install+0x1e/0x55 [<812a0a56>] uart_install+0x1e/0x55 [<81299489>] tty_init_dev+0x2f/0x11a [<81299489>] tty_init_dev+0x2f/0x11a [<812998a3>] tty_open+0x32f/0x34a [<812998a3>] tty_open+0x32f/0x34a [<810eaf19>] chrdev_open+0xe0/0x108 [<810eaf19>] chrdev_open+0xe0/0x108 [<810e6505>] do_dentry_open+0x12e/0x1dd [<810e6505>] do_dentry_open+0x12e/0x1dd [<810eae39>] ? cdev_put+0xe/0xe [<810eae39>] ? cdev_put+0xe/0xe [<810e705b>] vfs_open+0x41/0x46 [<810e705b>] vfs_open+0x41/0x46 [<810f1a13>] path_openat+0x532/0x6ab [<810f1a13>] path_openat+0x532/0x6ab [<810f2351>] do_filp_open+0x31/0x77 [<810f2351>] do_filp_open+0x31/0x77 [<81763db0>] ? _raw_spin_unlock+0x1d/0x27 [<81763db0>] ? _raw_spin_unlock+0x1d/0x27 [<810fd4e9>] ? __alloc_fd+0x168/0x173 [<810fd4e9>] ? __alloc_fd+0x168/0x173 [<810e71e2>] do_sys_open+0x54/0xc7 [<810e71e2>] do_sys_open+0x54/0xc7 [<810e726d>] SyS_open+0x18/0x1a [<810e726d>] SyS_open+0x18/0x1a [<81c5ad3e>] kernel_init_freeable+0x10b/0x16a [<81c5ad3e>] kernel_init_freeable+0x10b/0x16a [<8175e345>] kernel_init+0x8/0xd0 [<8175e345>] kernel_init+0x8/0xd0 [<817643a2>] ret_from_kernel_thread+0xe/0x24 [<817643a2>] ret_from_kernel_thread+0xe/0x24 [<8175e33d>] ? rest_init+0x111/0x111 [<8175e33d>] ? rest_init+0x111/0x111 ---[ end trace aefe2ba633a90994 ]--- ---[ end trace aefe2ba633a90994 ]--- FYI, raw QEMU command line is: qemu-system-i386 -enable-kvm -cpu Haswell,+smep,+smap -kernel /pkg/linux/i386-randconfig-n0-201624/gcc-6/acce93619b7f32eb9f2771fbd8e646b927e8fe1c/vmlinuz-4.7.0-rc3-next-20160614-00023-gacce936 -append 'root=/dev/ram0 user=lkp job=/lkp/scheduled/vm-vp-quantal-i386-7/bisect_boot-1-quantal-core-i386.cgz-i386-randconfig-n0-201624-acce93619b7f32eb9f2771fbd8e646b927e8fe1c-20160614-108942-18nrw9a-1.yaml~ ARCH=i386 kconfig=i386-randconfig-n0-201624 branch=jirislaby/devel commit=acce93619b7f32eb9f2771fbd8e646b927e8fe1c BOOT_IMAGE=/pkg/linux/i386-randconfig-n0-201624/gcc-6/acce93619b7f32eb9f2771fbd8e646b927e8fe1c/vmlinuz-4.7.0-rc3-next-20160614-00023-gacce936 max_uptime=600 RESULT_ROOT=/result/boot/1/vm-vp-quantal-i386/quantal-core-i386.cgz/i386-randconfig-n0-201624/gcc-6/acce93619b7f32eb9f2771fbd8e646b927e8fe1c/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-i386-7::dhcp drbd.minor_count=8' -initrd /fs/sde1/initrd-vm-vp-quantal-i386-7 -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-i386-7 -serial file:/dev/shm/kboot/serial-vm-vp-quantal-i386-7 -daemonize -display none -monitor null Thanks, Kernel Test Robot