FYI, we noticed the following commit (built with gcc-7):

commit: 6bd9edcb2ac76742bbe95f962a14bdbdca08fb18 ("n_tty: Protect tty->disc_data using refcount.")
https://github.com/0day-ci/linux UPDATE-20180830-074540/Tetsuo-Handa/n_tty-Protect-tty-disc_data-using-refcount/20180718-214043

in testcase: cpu-hotplug
with following parameters:




on test machine: qemu-system-i386 -enable-kvm -m 256M

caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):


+-------------------------------+------------+------------+
|                               | fefe287e4b | 6bd9edcb2a |
+-------------------------------+------------+------------+
| boot_successes                | 12         | 4          |
| boot_failures                 | 0          | 6          |
| BUG:kernel_hang_in_test_stage | 0          | 6          |
+-------------------------------+------------+------------+



[ 7281.897723] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[ 7282.747789] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
[ 7312.125308] e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
[ 7312.130066] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
[ 7313.051507] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
BUG: kernel hang in test stage

Elapsed time: 7280

#!/bin/bash



To reproduce:

        git clone https://github.com/intel/lkp-tests.git
        cd lkp-tests
        bin/lkp qemu -k <bzImage> job-script # job-script is attached in this email



Thanks,
Rong, Chen