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

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Message-ID: <Yf6sskyXcffxTA+b@carbon.dhcp.thefacebook.com>
Date:   Sat, 5 Feb 2022 08:58:26 -0800
From:   Roman Gushchin <guro@...com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        Alexander Egorenkov <egorenar@...ux.ibm.com>,
        Waiman Long <longman@...hat.com>, Tejun Heo <tj@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Jeremy Linton <jeremy.linton@....com>,
        <cgroups@...r.kernel.org>
Subject: Re: [PATCH RESEND] mm: memcg: synchronize objcg lists with a
 dedicated spinlock

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@...com> 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!