Re: [PATCH] [23/31] HWPOISON: add memory cgroup filter

[Li Zefan]

> +#ifdef	CONFIG_CGROUP_MEM_RES_CTLR_SWAP
> +u64 hwpoison_filter_memcg;
> +EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
> +static int hwpoison_filter_task(struct page *p)
> +{
> +	struct mem_cgroup *mem;
> +	struct cgroup_subsys_state *css;
> +	unsigned long ino;
> +
> +	if (!hwpoison_filter_memcg)
> +		return 0;
> +
> +	mem = try_get_mem_cgroup_from_page(p);
> +	if (!mem)
> +		return -EINVAL;
> +
> +	css = mem_cgroup_css(mem);
> +	ino = css->cgroup->dentry->d_inode->i_ino;

I have a question, can try_get_mem_cgroup_from_page() return
root_mem_cgroup?

if it can, then css->cgroup->dentry is NULL, if memcg is
not mounted and there is no subdir in memcg. Because the root
cgroup of an inactive subsystem has no dentry.

> +	css_put(css);
> +
> +	if (ino != hwpoison_filter_memcg)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +#else
> +static int hwpoison_filter_task(struct page *p) { return 0; }
> +#endif
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