linux-kernel - Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when kernel panic

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Date:   Fri, 15 Sep 2017 21:00:43 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Yang Shi <yang.s@...baba-inc.com>, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when kernel
 panic

On 2017/09/15 2:14, Yang Shi wrote:
> @@ -1274,6 +1276,29 @@ static int slab_show(struct seq_file *m, void *p)
>  	return 0;
>  }
>  
> +void show_unreclaimable_slab()
> +{
> +	struct kmem_cache *s = NULL;
> +	struct slabinfo sinfo;
> +
> +	memset(&sinfo, 0, sizeof(sinfo));
> +
> +	printk("Unreclaimable slabs:\n");
> +	mutex_lock(&slab_mutex);

Please avoid sleeping locks which potentially depend on memory allocation.
There are

	mutex_lock(&slab_mutex);
	kmalloc(GFP_KERNEL);
	mutex_unlock(&slab_mutex);

users which will fail to call panic() if they hit this path.

> +	list_for_each_entry(s, &slab_caches, list) {
> +		if (!is_root_cache(s))
> +			continue;
> +
> +		get_slabinfo(s, &sinfo);
> +
> +		if (!is_reclaimable(s) && sinfo.num_objs > 0)
> +			printk("%-17s %luKB\n", cache_name(s), K(sinfo.num_objs * s->size));
> +	}
> +	mutex_unlock(&slab_mutex);
> +}
> +EXPORT_SYMBOL(show_unreclaimable_slab);
> +#undef K
> +
>  #if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
>  void *memcg_slab_start(struct seq_file *m, loff_t *pos)
>  {
>