Comment 0 for bug 1830433

Hi,

I'm reproducing a kernel bug in vmalloc_sync_all() with a 32-bit x86 kernel.

The problem appears in

Linux ubuntu 4.15.0-50-generic #54-Ubuntu SMP Mon May 6 18:45:45 UTC 2019 i686 i686 i686 GNU/Linux

Kernels 4.15.0-49 and prior work fine.
The kernel 4.18.0-20-generic works fine.
This problem has not been experienced with upstream Linux kernels.

It appears that invoking vmalloc_sync_all() a few times end up triggering this issue. This can be triggered by restarting the lttng-sessiond service with lttng-modules-dkms installed (sometimes a few restarts are needed to trigger the bug). This ends up unloading and reloading those modules, which issues a few vmalloc_sync_all() as side-effect.

I'm not reporting this issue with the "ubuntu-bug linux" command because it crashes the system on that kernel (system hangs, no console output).

My test system runs within a kvm virtual machine on a 64-bit host.

lsb release:

Description: Ubuntu 18.04.2 LTS
Release: 18.04

Information about my kernel:

linux-image-4.15.0-50-generic:
  Installed: 4.15.0-50.54
  Candidate: 4.15.0-50.54
  Version table:
 *** 4.15.0-50.54 500
        500 http://ca.archive.ubuntu.com/ubuntu bionic-updates/main i386 Packages
        500 http://security.ubuntu.com/ubuntu bionic-security/main i386 Packages
        100 /var/lib/dpkg/status

Information about lttng-modules-dkms:

lttng-modules-dkms:
  Installed: 2.10.5-1ubuntu1.2
  Candidate: 2.10.5-1ubuntu1.2
  Version table:
 *** 2.10.5-1ubuntu1.2 500
        500 http://ca.archive.ubuntu.com/ubuntu bionic-updates/universe i386 Packages
        100 /var/lib/dpkg/status
     2.10.5-1ubuntu1 500
        500 http://ca.archive.ubuntu.com/ubuntu bionic/universe i386 Packages