[LTP] [PATCH] Taunt OOM killer in fork12 setup()

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> 
> 
> On Fri, Jan 31, 2020 at 12:13 AM Martin Doucha < mdoucha@suse.cz > wrote:
> 
> 
> On a system with low memory, fork12 can trigger OOM killer before it hits
> any fork() limits. The OOM killer might accidentally kill e.g. the parent
> shell and external testing tools will assume the test failed.
> 
> Set high oom_score_adj on the fork12 process so that the OOM killer focuses
> on it and its children.
> 
> It sounds more like the OOM-Killer defect but not fork12.

Badness score is based on proportion of rss/swap. It doesn't seem like
defect to me, we just quickly spawn many small tasks.

> What we do for that
> is to protect the parent shell and its harness to avoid oom_kill_process()
> acting on them.
> 
> On the other side, if we do raise the oom score of fork12, that would not
> guarantee OOM-Killer do right evaluation but just makes fork12 easily to be
> killed in testing.

fork12 is not an OOM test, so I don't see problem with this. We only need OOM
to kill something we don't care about, in case it triggers.

I'd move oom_score_adj after fork, so only child processes are better target,
not the parent.