Re: [PATCH RFC] memcg: close the race window between OOM detection and killing

[Tejun Heo <tj@kernel.org>]

Hello, Michal.

On Fri, Jun 05, 2015 at 05:21:35PM +0200, Michal Hocko wrote:
...
> > > TIF_MEMDIE but the allocation path hasn't noticed that because it's passed
> > >         /*
> > >          * Go through the zonelist yet one more time, keep very high watermark
> > >          * here, this is only to catch a parallel oom killing, we must fail if
> > >          * we're still under heavy pressure.
> > >          */
> > >         page = get_page_from_freelist(gfp_mask | __GFP_HARDWALL, order,
> > >                                         ALLOC_WMARK_HIGH|ALLOC_CPUSET, ac);
> > > 
> > > and goes on to kill another task because there is no TIF_MEMDIE
> > > anymore.
> > 
> > Why would this be an issue if we disallow parallel killing?
> 
> I am confused. The whole thread has started by fixing a race in memcg
> and I was asking about the global case which is racy currently as well.

Ah, okay, I thought we were still talking about issues w/ making
things synchronous, but anyways, the above isn't a synchronization
race per-se which is what the original patch was trying to address for
memcg OOM path, right?

Thanks.

-- 
tejun

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