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Date:   Wed, 13 Jun 2018 12:50:57 -0700
From:   Roman Gushchin <guro@...com>
To:     John Stultz <john.stultz@...aro.org>
CC:     Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...e.com>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: OOPSes in mem_cgroup_protected

On Wed, Jun 13, 2018 at 12:40:23PM -0700, John Stultz wrote:
> On Tue, Jun 12, 2018 at 9:33 PM, Roman Gushchin <guro@...com> wrote:
> > 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@...aro.org> 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.
> 
> No worries, thanks for the quick fix! The patch you sent seems to be
> working well!

Perfect, thanks!

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