[PATCH 0/2] nvme: add reference counting for transport modules

[John Garry]

> 
>> When the ctrl ops module ref counting was originally introduced, the 
>> commit message mentioned a crash which it solves.
>>
>> So far for this problem we have seen a report that if we remove the 
>> module, the mounted FS will have IOs fail. The same can be experienced 
>> if the admin unbinds the device from the driver. However, I have not 
>> seen a mention of a crash, kernel data corruption, a hang, etc.
>>
> Yes I have also not observed a kernel crash or data corruption.
> Regarding unbinding, this is triggered through the PCI/device-model
> unbind path. The driver unbind callback returns void so the NVMe driver
> has no way to reject or otherwise prevent the unbind operation from the
> driver side. 

There's suppress_bind_attrs, but I don't think that anyone using VFIO 
would be happy if that were set.

> The purpose of this patch is therefore to protect the 
> transport
> module from being unloaded while the multipath head is still open.