linux-kernel - Re: [PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations from protection checks

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Date:   Fri, 22 May 2020 12:45:44 +0100
From:   Chris Down <chris@...isdown.name>
To:     Naresh Kamboju <naresh.kamboju@...aro.org>
Cc:     Yafang Shao <laoar.shao@...il.com>,
        Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <guro@...com>, linux-mm <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        lkft-triage@...ts.linaro.org
Subject: Re: [PATCH v3 2/2] mm, memcg: Decouple e{low,min} state mutations
 from protection checks

Naresh Kamboju writes:
>This patch is causing oom-killer while running mkfs -t ext4 on i386 kernel
>running on x86_64 machine version linux-next 5.7.0-rc6-next-20200521.

I think I see what's wrong here -- if we bail out early, memory.e{min,low} 
might be uninitialised.

Does this patch fix it, by any chance?

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d3b23c57bed4..aa902b9cbb79 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -5046,6 +5046,9 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
  			memory_cgrp_subsys.broken_hierarchy = true;
  	}
  
+	memcg->memory.emin = 0;
+	memcg->memory.elow = 0;
+
  	/* The following stuff does not apply to the root */
  	if (!parent) {
  #ifdef CONFIG_MEMCG_KMEM
-- 
2.26.2