Sysrq trigger g cause system hang on Ubuntu 15.10

[Eric Huang]

I are using kgdb to debug kernel driver. The break point and sysrq work fine on Ubuntu 14.04. But when I upgrade Ubuntu from 14.04 to 15.10, the sysrq trigger g (alt+sysrq+g) doesn't make gdb break and system hangs. It is a regression. The issue only happens after kernel booting up. It is OK during kernel booting.

[Brad Figg (brad-figg)]

This bug is missing log files that will aid in diagnosing the problem. From a terminal window please run:

apport-collect 1558764

and then change the status of the bug to 'Confirmed'.

If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.

This change has been made by an automated script, maintained by the Ubuntu Kernel Team.

[Joseph Salisbury (jsalisbury)]

I'd like to perform a bisect to figure out what commit caused this regression. We need to identify the earliest kernel where the issue started happening as well as the latest kernel that did not have this issue.

Can you test the following kernels and report back? We are looking for the first kernel version that exhibits this bug:

4.2-rc1: http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.2-rc1-unstable/
4.2-rc4: http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.2-rc4-unstable/
4.2 final: http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.2-wily/

You don't have to test every kernel, just up until the kernel that first has this bug.

Thanks in advance!

[Joseph Salisbury (jsalisbury)]

Also, it might be worthwhile to test the latest mainline kernel, to see if this bug is already fixed there. It can be downloaded from:

http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.5-wily/

[Eric Huang (jinhuieric-huang)]

I used the same custom build kernel in both 14.04 and 15.10, so it should not be kernel issue.

[Launchpad Janitor (janitor)]

[Expired for linux (Ubuntu) because there has been no activity for 60 days.]