[dpdk-dev] Should we disallow running secondaries after primary has died?

[Burakov, Anatoly]

Hi all,

While investigating this bug:

https://bugs.dpdk.org/show_bug.cgi?id=284

I came across a realization that, when primary process dies, very little 
actually works. There are some documented issues that are already 
present when secondary processes keep running, like memory map becoming 
static, and hotplug not working any more.

What is less known (and documented) is that VFIO also completely stops 
working when initializing processes, because some time since 18.xx 
releases, we've fixed a long standing VFIO-related bug that had to do 
with creating new containers every time a secondary is run - secondary 
processes will now reuse the primary process's container instead.

Meaning, for VFIO devices, secondary process *initialization* will fail 
after primary process has died, because there is no longer a process 
from which we can get the VFIO container from. Things will still sort-of 
work with igb_uio or in vfio-noiommu mode, but again - no memory map 
updates, no hotplug, potentially other things that i don't even know about.

Therefore, while ideally we would like people to have primary process 
always running, the least we can do to avoid documenting a complex 
matrix of "what is supported in which case" is to disallow secondary 
process initialization after primary process has died.

("disallow" as in "explicitly document it as unsupported", although we 
can also outright prevent it if we want - rte_eal_primary_proc_alive() 
will tell us that)

Thoughts?

-- 
Thanks,
Anatoly