linux-kernel - Re: BUG: Bad page state in process - page dumped because: page still charged to cgroup

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Date:   Thu, 2 Jul 2020 09:02:31 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>
Cc:     Michal Hocko <mhocko@...nel.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        open list <linux-kernel@...r.kernel.org>,
        lkft-triage@...ts.linaro.org, Chris Down <chris@...isdown.name>
Subject: Re: BUG: Bad page state in process - page dumped because: page still
 charged to cgroup

On Wed, Jul 1, 2020 at 11:46 AM Roman Gushchin <guro@...com> wrote:
...
> --
>
> From c97afecd32c0db5e024be9ba72f43d22974f5bcd Mon Sep 17 00:00:00 2001
> From: Roman Gushchin <guro@...com>
> Date: Wed, 1 Jul 2020 11:05:32 -0700
> Subject: [PATCH] mm: kmem: make memcg_kmem_enabled() irreversible
>
> Historically the kernel memory accounting was an opt-in feature, which
> could be enabled for individual cgroups. But now it's not true, and
> it's on by default both on cgroup v1 and cgroup v2.  And as long as a
> user has at least one non-root memory cgroup, the kernel memory
> accounting is on. So in most setups it's either always on (if memory
> cgroups are in use and kmem accounting is not disabled), either always
> off (otherwise).
>
> memcg_kmem_enabled() is used in many places to guard the kernel memory
> accounting code. If memcg_kmem_enabled() can reverse from returning
> true to returning false (as now), we can't rely on it on release paths
> and have to check if it was on before.
>
> If we'll make memcg_kmem_enabled() irreversible (always returning true
> after returning it for the first time), it'll make the general logic
> more simple and robust. It also will allow to guard some checks which
> otherwise would stay unguarded.
>
> Signed-off-by: Roman Gushchin <guro@...com>

Reviewed-by: Shakeel Butt <shakeelb@...gle.com>