Re: [PATCH v2] mm/page_alloc: add a helper function to check page before alloc/free

[Michal Hocko]

On Tue 25-08-15 21:26:30, Yaowei Bai wrote:
[...]
>  static inline int check_new_page(struct page *page)
>  {
> -	const char *bad_reason = NULL;
> -	unsigned long bad_flags = 0;
> -
> -	if (unlikely(page_mapcount(page)))
> -		bad_reason = "nonzero mapcount";
> -	if (unlikely(page->mapping != NULL))
> -		bad_reason = "non-NULL mapping";
> -	if (unlikely(atomic_read(&page->_count) != 0))
> -		bad_reason = "nonzero _count";
> -	if (unlikely(page->flags & __PG_HWPOISON)) {
> -		bad_reason = "HWPoisoned (hardware-corrupted)";
> -		bad_flags = __PG_HWPOISON;
> -	}

You have removed this check AFAICS. Now looking at 39ad4f19671d ("mm:
check __PG_HWPOISON separately from PAGE_FLAGS_CHECK_AT_*") I am not
sure it is correct to check it in the free path as it was removed from
the mask by this commit.

> -	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_PREP)) {
> -		bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
> -		bad_flags = PAGE_FLAGS_CHECK_AT_PREP;
> -	}
> -#ifdef CONFIG_MEMCG
> -	if (unlikely(page->mem_cgroup))
> -		bad_reason = "page still charged to cgroup";
> -#endif
> -	if (unlikely(bad_reason)) {
> -		bad_page(page, bad_reason, bad_flags);
> -		return 1;
> -	}
> -	return 0;
> +	return check_one_page(page, PAGE_FLAGS_CHECK_AT_PREP);
>  }
>  
>  static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
> -- 
> 1.9.1
> 

-- 
Michal Hocko
SUSE Labs
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