[SRU][j,l/linux-azure][PATCH 0/1] Fix kernel panic when removing GPU

[Ioanna Alifieraki]

BugLink: https://bugs.launchpad.net/bugs/2042568

SRU Justification

[Description]

On a VM on Azure with a Tesla gpu it was noticed that when removing
the gpu from the pci the vm would crash. In case the nvidia drivers
are loaded, the machine won't crash. Instead the removing process 
will hang and the machine will crash on reboot.

This is related to bug [1].
The bug reported in [1] regards another driver but the root cause is
the same. It is still investigated whether this is a bug in pci, or
it is a bug of various drivers on how they use pci.

For this case we have identified that removing commit [2] prevents 
the kernel crashes.

Azure has requested to revert this commit, at least for the time 
being. This commit is not in upstream, so it just need to be 
reverted from Ubuntu kernels.

[Test Case]

On an Azure vm with a gpu :

# echo '1' > /sys/bus/pci/devices/0001:00:00.0/remove

where '0001:00:00.0' the pci address of the gpu.
The vm will crash.

[Where things could go wrong]

The commit to be reverted was included in a patchset to address bugs
https://bugs.launchpad.net/bugs/2023071 and 
https://bugs.launchpad.net/bugs/2023594

However this commit just reduces boot time and removing shall not 
introduce any regressions. Side effects will be increase in the boot
time.

[Other]

Only Ubuntu azure kernels are affected :

- Jammy 5.15
- Lunar 6.2

Focal is also affected since it's using 5.15 kernel.
This commit does not appear in Mantic 6.5 kernel.

[1] https://bugzilla.kernel.org/show_bug.cgi?id=215515
[2] https://git.launchpad.net/~canonical-kernel/ubuntu/+source/linux-azure/+git/jammy/commit/?id=75af0c10b370