Re: [Patch v2 3/4] mm/page_alloc.c: pass all bad reasons to bad_page()

[Anshuman Khandual]

On 01/20/2020 08:34 AM, Wei Yang wrote:
> Now we can pass all bad reasons to __dump_page().
> 
> Signed-off-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
> ---
>  mm/page_alloc.c | 52 ++++++++++++++++++++++++++-----------------------
>  1 file changed, 28 insertions(+), 24 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index a43b9d2482f2..a7b793c739fc 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -609,7 +609,7 @@ static inline int __maybe_unused bad_range(struct zone *zone, struct page *page)
>  }
>  #endif
>  
> -static void bad_page(struct page *page, const char *reason,
> +static void bad_page(struct page *page, int nr, const char **reason,
>  		unsigned long bad_flags)
>  {
>  	static unsigned long resume;
> @@ -638,7 +638,7 @@ static void bad_page(struct page *page, const char *reason,
>  
>  	pr_alert("BUG: Bad page state in process %s  pfn:%05lx\n",
>  		current->comm, page_to_pfn(page));
> -	__dump_page(page, 1, &reason);
> +	__dump_page(page, nr, reason);
>  	bad_flags &= page->flags;
>  	if (bad_flags)
>  		pr_alert("bad because of flags: %#lx(%pGp)\n",
> @@ -1027,27 +1027,25 @@ static inline bool page_expected_state(struct page *page,
>  
>  static void free_pages_check_bad(struct page *page)
>  {
> -	const char *bad_reason;
> -	unsigned long bad_flags;
> -
> -	bad_reason = NULL;
> -	bad_flags = 0;
> +	const char *bad_reason[5];

s/5/NR_BAD_PAGE_REASONS


> +	unsigned long bad_flags = 0;
> +	int nr = 0;
>  
>  	if (unlikely(atomic_read(&page->_mapcount) != -1))
> -		bad_reason = "nonzero mapcount";
> +		bad_reason[nr++] = "nonzero mapcount";
>  	if (unlikely(page->mapping != NULL))
> -		bad_reason = "non-NULL mapping";
> +		bad_reason[nr++] = "non-NULL mapping";
>  	if (unlikely(page_ref_count(page) != 0))
> -		bad_reason = "nonzero _refcount";
> +		bad_reason[nr++] = "nonzero _refcount";
>  	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_FREE)) {
> -		bad_reason = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
> +		bad_reason[nr++] = "PAGE_FLAGS_CHECK_AT_FREE flag(s) set";
>  		bad_flags = PAGE_FLAGS_CHECK_AT_FREE;
>  	}
>  #ifdef CONFIG_MEMCG
>  	if (unlikely(page->mem_cgroup))
> -		bad_reason = "page still charged to cgroup";
> +		bad_reason[nr++] = "page still charged to cgroup";
>  #endif
> -	bad_page(page, bad_reason, bad_flags);
> +	bad_page(page, nr, bad_reason, bad_flags);
>  }
>  
>  static inline int free_pages_check(struct page *page)
> @@ -1062,6 +1060,7 @@ static inline int free_pages_check(struct page *page)
>  
>  static int free_tail_pages_check(struct page *head_page, struct page *page)
>  {
> +	const char *reason;
>  	int ret = 1;
>  
>  	/*
> @@ -1078,7 +1077,8 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
>  	case 1:
>  		/* the first tail page: ->mapping may be compound_mapcount() */
>  		if (unlikely(compound_mapcount(page))) {
> -			bad_page(page, "nonzero compound_mapcount", 0);
> +			reason = "nonzero compound_mapcount";
> +			bad_page(page, 1, &reason, 0);
>  			goto out;
>  		}
>  		break;
> @@ -1090,17 +1090,20 @@ static int free_tail_pages_check(struct page *head_page, struct page *page)
>  		break;
>  	default:
>  		if (page->mapping != TAIL_MAPPING) {
> -			bad_page(page, "corrupted mapping in tail page", 0);
> +			reason = "corrupted mapping in tail page";
> +			bad_page(page, 1, &reason, 0);
>  			goto out;
>  		}
>  		break;
>  	}
>  	if (unlikely(!PageTail(page))) {
> -		bad_page(page, "PageTail not set", 0);
> +		reason = "PageTail not set";
> +		bad_page(page, 1, &reason, 0);
>  		goto out;
>  	}
>  	if (unlikely(compound_head(page) != head_page)) {
> -		bad_page(page, "compound_head not consistent", 0);
> +		reason = "compound_head not consistent";
> +		bad_page(page, 1, &reason, 0);
>  		goto out;
>  	}
>  	ret = 0;
> @@ -2041,29 +2044,30 @@ static inline void expand(struct zone *zone, struct page *page,
>  
>  static void check_new_page_bad(struct page *page)
>  {
> -	const char *bad_reason = NULL;
> +	const char *bad_reason[5];

s/5/NR_BAD_PAGE_REASONS 

>  	unsigned long bad_flags = 0;
> +	int nr = 0;
>  
>  	if (unlikely(atomic_read(&page->_mapcount) != -1))
> -		bad_reason = "nonzero mapcount";
> +		bad_reason[nr++] = "nonzero mapcount";
>  	if (unlikely(page->mapping != NULL))
> -		bad_reason = "non-NULL mapping";
> +		bad_reason[nr++] = "non-NULL mapping";
>  	if (unlikely(page_ref_count(page) != 0))
> -		bad_reason = "nonzero _refcount";
> +		bad_reason[nr++] = "nonzero _refcount";
>  	if (unlikely(page->flags & __PG_HWPOISON)) {
>  		/* Don't complain about hwpoisoned pages */
>  		page_mapcount_reset(page); /* remove PageBuddy */
>  		return;
>  	}
>  	if (unlikely(page->flags & PAGE_FLAGS_CHECK_AT_PREP)) {
> -		bad_reason = "PAGE_FLAGS_CHECK_AT_PREP flag set";
> +		bad_reason[nr++] = "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";
> +		bad_reason[nr++] = "page still charged to cgroup";
>  #endif
> -	bad_page(page, bad_reason, bad_flags);
> +	bad_page(page, 1, bad_reason, bad_flags);
This should be 'nr' here instead ?

>  }
>  
>  /*
>