Re: [PATCH RESEND] mm: memcg: synchronize objcg lists with a dedicated spinlock

[Roman Gushchin]

On Thu, Feb 03, 2022 at 03:19:12PM -0800, Andrew Morton wrote:
> On Tue, 1 Feb 2022 14:33:04 -0800 Roman Gushchin <guro@xxxxxx> wrote:
> 
> > Alexander reported a circular lock dependency revealed by the mmap1
> > ltp test:
> >   LOCKDEP_CIRCULAR (suite: ltp, case: mtest06 (mmap1))
> > 
> > ...
> >
> > Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API")
> 
> I'm thinking it needs cc:stable.  It sounds unlikely that we'll hit it
> in real life, but lockdep splats are concerning and I expect downstream
> kernel consumers will end up merging this anyway, for this reason.
> 

I agree.

I'm somewhat surprised that we haven't seen any such warnings until recently,
so I guess some recent kmem accounting change made it more probable.

Anyway, it feels like it's a low risk change and I see no reasons
to not backport it to stable.

Thank you!