[bug report] NVMe hotplug bug in kernel 5.15 with CONFIG_INTEL_IOMMU disabled

[Artur Piechocki]

> Hi Artur,
>
> On 7/8/24 1:26 AM, Artur Piechocki wrote:
>> Hi,
>>
>> I am experiencing a repeatable (potential deadlock) issue when
>> hotplugging NVMe devices on kernel 5.15. The problem occurs on a Ubuntu
>> 22.04.4 server environment when Intel IOMMU support is disabled in the
>> kernel configuration (CONFIG_INTEL_IOMMU is not set). This issue is also
>> reproducible on the native kernel 5.15.161 without any Ubuntu patches.
>>
>> System Information:
>>
>>      Distribution: Ubuntu 22.04.4 server
>>      Kernel Version: Ubuntu 5.15.152 (also repeated on native 5.15.161)
>>      Hardware: NVME Micron SSDPE2KX020T8, Intel(R) Xeon(R) Gold 5222
>>
>> Description of the Issue:
>> When hotplugging an NVMe device, the system experiences a potential
> Only for the sake of curiosity, may I have what does NVMe hotplug indicate?
>
> According to the log, the server is a baremetal, not VM (QEMU/KVM).
>
> Jul  5 09:49:11 tarox1 kernel: [    0.374071] Booting paravirtualized kernel on
> bare hardware

This could be due to the fact that the Ubuntu kernel has built-in
support for paravirtualization, but it doesn't necessarily have to use
it when the system is booted directly on bare hardware.

> Is there any method to hotplug NVMe to a running baremetal server?

The hotplug event occurred through the physical removal and reinsertion
of drives in an NVMe JBOD chassis that supports hotplug functionality,
though I’m not sure if you're asking about a different aspect of the
process?

Additionally, the deadlock does not occur on kernel 6.1. However, I
would like to point out that kernel 5.15 is a long-term support (LTS)
kernel, and the issue still persists on that version.

> Thank you very much!
>
> Dongli Zhang