linux-kernel - Re: [PATCH v4] Print the memcg's name when system-wide OOM happened

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Date:   Wed, 30 May 2018 13:42:56 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     ufo19890607 <ufo19890607@...il.com>
Cc:     mhocko@...e.com, rientjes@...gle.com,
        kirill.shutemov@...ux.intel.com, aarcange@...hat.com,
        penguin-kernel@...ove.SAKURA.ne.jp, guro@...com,
        yang.s@...baba-inc.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        yuzhoujian <yuzhoujian@...ichuxing.com>
Subject: Re: [PATCH v4] Print the memcg's name when system-wide OOM happened

On Mon, 21 May 2018 03:39:46 +0100 ufo19890607 <ufo19890607@...il.com> wrote:

> From: yuzhoujian <yuzhoujian@...ichuxing.com>
> 
> The dump_header does not print the memcg's name when the system
> oom happened. So users cannot locate the certain container which
> contains the task that has been killed by the oom killer.
> 
> System oom report will print the memcg's name after this patch,
> so users can get the memcg's path from the oom report and check
> the certain container more quickly.

lkp-robot is reporting an oops.

> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -433,6 +433,7 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
>  	if (is_memcg_oom(oc))
>  		mem_cgroup_print_oom_info(oc->memcg, p);
>  	else {
> +		mem_cgroup_print_oom_memcg_name(oc->memcg, p);
>  		show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
>  		if (is_dump_unreclaim_slabs())
>  			dump_unreclaimable_slab();

static inline bool is_memcg_oom(struct oom_control *oc)
{
	return oc->memcg != NULL;
}

So in the mem_cgroup_print_oom_memcg_name() call which this patch adds,
oc->memcg is known to be NULL.  How can this possibly work?