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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20200702171011.GJ18446@dhcp22.suse.cz>
Date:   Thu, 2 Jul 2020 19:10:11 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Roman Gushchin <guro@...com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        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>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: BUG: Bad page state in process - page dumped because: page still
 charged to cgroup

On Thu 02-07-20 18:35:31, Vlastimil Babka wrote:
> On 7/2/20 6:22 PM, Michal Hocko wrote:
> > On Wed 01-07-20 11:45:52, Roman Gushchin 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>
> 
> Fixes: ? or let Andrew squash it to some patch of your series (it's in mmotm I
> think)?

I would rather make it its own patch because this is really subtle.
-- 
Michal Hocko
SUSE Labs