[PATCH v5] um: Enable preemption in UML

[Johannes Berg]

On Fri, 2023-09-22 at 08:38 +0100, Anton Ivanov wrote:
> > 
> > I had enabled CONFIG_DEBUG_ATOMIC_SLEEP because that's actually
> > something I'd really like to have in our testing.
> > 
> > But with that issue I don't even know how we get there really. It
> > doesn't even happen every time we fork?
> > 
> > I'll dig a little bit, but did you try enabling
> > CONFIG_DEBUG_ATOMIC_SLEEP also?
> 
> Will do. I have no crashes over here so I need to trigger this one first.
> 
> Though, frankly, if it is a race in a tlb flush it may be subject to local conditions. So it will be difficult to reproduce.
> 

Yes, it might be a race in the fork handler maybe? IOW, whenever we
actually do fork, it depends on what conditions the rest is in? I'm not
sure I fully figured out right now how the fork handler is doing all
this, but I sent my mail before I could since you were discussing :)

But it shouldn't be impossible - while I don't see it for every fork, it
does happen 8 or 9 times in a very simple test that just boots, pings a
bit, and then shuts down, so ...

johannes