Occasional hung with UM after enable VMAP_STACK

[Johannes Berg]

On Tue, 2022-01-04 at 16:26 -0300, Walter Lozano wrote:
> 
> Thank you for your quick response. The Debian configuration on package 
> user-mode-linux have these settings
> 
> CONFIG_HAVE_ARCH_VMAP_STACK=y
> CONFIG_VMAP_STACK=y

OK, so it actually _is_ enabled.

> as you can see in [1]. I did run some tests disabling those settings, 
> which passed without any hung.
> 
> Unfortunately the "occasional" behavior makes this issue a bit tricky to 
> debug.
> 

Right.

Hm. I've been running our tests with it for about three months and
haven't observed any hangs, but I guess that doesn't mean much.

To be honest, I have no particular reason to even want it, other than
that it catches accidental DMA from stack more easily ... so I guess if
we can't find anything, we might as well revert it.

Feels like it _should_ work though, since it's just a different location
for the stack.

johannes