Re: OOPSes in mem_cgroup_protected

[Roman Gushchin]

On Tue, Jun 12, 2018 at 09:08:27PM -0700, John Stultz wrote:
> On Tue, Jun 12, 2018 at 6:02 PM, John Stultz <john.stultz@xxxxxxxxxx> wrote:
> > Hey Tejun,
> >   With the current linus/master, I'm able to fairly regularly trip
> > OOPSes (two examples below) in mem_cgroup_protected(), which seems to
> > be new.  I haven't managed to trigger this sort of thing with v4.17.
> >
> > I've not had much time to dig in or bisect it - I only know that
> > enabling most of the memory debuging config options didn't seem to
> > trip anything prior to the issue. So I wanted to send you a heads up
> > to see if there was already known, or if there was anything you might
> > suggest to help chase this down.
> 
> 
> So the line where we're crashing seems to be in mem_cgroup_protected():
>   parent_emin = READ_ONCE(parent->memory.emin);
> 
> where I'm guessing the parent->memory value is null, and emin is at
> the 0x120 offset in the strucutre.
> 
> Reverting the following commits seems to avoid the issue.
> bf8d5d52ffe8 ("memcg: introduce memory.min")
> 5f93ad67436b ("mm: treat memory.low value inclusive")
> 230671533d64 ("mm: memory.low hierarchical behavior")
> 
> I'm guessing I'm tripping over some path where the memory value never
> gets initialized?
> 
> Any ideas or suggestions?

Hi, John!

The patch below should fix the problem.
It's in the mm tree right now, and hopefully will be merged upstream asap.
Sorry for the inconvenience.

Thanks!

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