FYI, we noticed the following commit: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master commit 761ed4a94582ab291aa24dcbea4e01e8936488c8 ("tty: serial_core: convert uart_close to use tty_port_close") in testcase: boot on test machine: qemu-system-x86_64 -enable-kvm -cpu host -smp 2 -m 4G caused below changes: +-------------------------------------------------+------------+------------+ | | b3b5764618 | 761ed4a945 | +-------------------------------------------------+------------+------------+ | boot_successes | 14 | 5 | | boot_failures | 188 | 71 | | BUG:kernel_reboot-without-warning_in_test_stage | 188 | 34 | | BUG:unable_to_handle_kernel | 0 | 37 | | Oops | 0 | 33 | | RIP:serial8250_tx_chars | 0 | 28 | | calltrace:SyS_open | 0 | 4 | | calltrace:SyS_read | 0 | 5 | | calltrace:SyS_newfstat | 0 | 1 | | calltrace:ring_buffer_producer_thread | 0 | 1 | | calltrace:SyS_newstat | 0 | 3 | | calltrace:SyS_sendmsg | 0 | 1 | | calltrace:SyS_readlinkat | 0 | 1 | | calltrace:SyS_readlink | 0 | 1 | | calltrace:schedule | 0 | 1 | | calltrace:schedule_timeout | 0 | 1 | +-------------------------------------------------+------------+------------+ [ 142.283744] systemd-udevd[212]: starting version 215 Starting Copy rules generated while the root was ro... Starting LSB: MD array assembly... [ 143.836086] BUG: unable to handle kernel NULL pointer dereference at 000000000000046c [ 143.845764] IP: [] serial8250_tx_chars+0x5a/0x2a2 [ 143.845764] PGD 0 [ 143.845764] Oops: 0000 [#1] PREEMPT SMP [ 143.845764] Modules linked in: [ 143.845764] CPU: 0 PID: 189 Comm: systemd-journal Not tainted 4.8.0-rc2-00007-g761ed4a #1 [ 143.884224] task: ffff88011f9162c0 task.stack: ffff88011f930000 Thanks, Xiaolong