CVE-2024-26846: nvme-fc: do not wait in vain when unloading module

In the Linux kernel, the following vulnerability has been resolved:

nvme-fc: do not wait in vain when unloading module

The module exit path has race between deleting all controllers and freeing 'left over IDs'. To prevent double free a synchronization between nvmedeletectrl and idadestroy has been added by the initial commit.

There is some logic around trying to prevent from hanging forever in waitforcompletion, though it does not handling all cases. E.g. blktests is able to reproduce the situation where the module unload hangs forever.

If we completely rely on the cleanup code executed from the nvmedeletectrl path, all IDs will be freed eventually. This makes calling idadestroy unnecessary. We only have to ensure that all nvmedeletectrl code has been executed before we leave nvmefcexitmodule. This is done by flushing the nvmedeletewq workqueue.

While at it, remove the unused nvmefcwq workqueue too.

— NVD