Re: [Intel-gfx] [PATCH 2/3] mm, notifier: Catch sleeping/blocking for !blockable

[Tvrtko Ursulin]

On 23/11/2018 13:12, Daniel Vetter wrote:
> On Fri, Nov 23, 2018 at 1:46 PM Michal Hocko <mhocko@xxxxxxxxxx> wrote:
> > On Fri 23-11-18 13:38:38, Daniel Vetter wrote:
> > > On Fri, Nov 23, 2018 at 12:12:37PM +0100, Michal Hocko wrote:
> > > > On Thu 22-11-18 17:51:05, Daniel Vetter wrote:
> > > > > We need to make sure implementations don't cheat and don't have a
> > > > > possible schedule/blocking point deeply burried where review can't
> > > > > catch it.
> > > > >
> > > > > I'm not sure whether this is the best way to make sure all the
> > > > > might_sleep() callsites trigger, and it's a bit ugly in the code flow.
> > > > > But it gets the job done.
> > > >
> > > > Yeah, it is quite ugly. Especially because it makes DEBUG config
> > > > bahavior much different. So is this really worth it? Has this already
> > > > discovered any existing bug?
> > >
> > > Given that we need an oom trigger to hit this we're not hitting this in CI
> > > (oom is just way to unpredictable to even try). I'd kinda like to also add
> > > some debug interface so I can provoke an oom kill of a specially prepared
> > > process, to make sure we can reliably exercise this path without killing
> > > the kernel accidentally. We do similar tricks for our shrinker already.
> >
> > Create a task with oom_score_adj = 1000 and trigger the oom killer via
> > sysrq and you should get a predictable oom invocation and execution.
>
> Ah right. We kinda do that already in an attempt to get the tests
> killed without the runner, for accidental oom. Just didn't think about
> this in the context of intentionally firing the oom. I'll try whether
> I can bake up some new subtest in our userptr/mmu-notifier testcases.

Very handy trick - I think I will think of applying it in the shrinker 
area as well.

Regards,

Tvrtko