linux-kernel - Re: BUG: Bad page state [was: Strange oopses in 2.6.30]

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Date:	Wed,  1 Jul 2009 08:45:51 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Mel Gorman <mel@....ul.ie>
Cc:	kosaki.motohiro@...fujitsu.com,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Jiri Slaby <jirislaby@...il.com>,
	Maxim Levitsky <maximlevitsky@...il.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>
Subject: Re: BUG: Bad page state [was: Strange oopses in 2.6.30]

> On Tue, Jun 30, 2009 at 09:31:04AM +0900, KOSAKI Motohiro wrote:
> > > -static inline int free_pages_check(struct page *page)
> > > -{
> > > +static inline int free_pages_check(struct page *page, int wasMlocked)
> > > +{
> > > +	if (unlikely(wasMlocked)) {
> > > +		WARN_ONCE(1, KERN_WARNING
> > > +			"Page flag mlocked set for process %s at pfn:%05lx\n"
> > > +			"page:%p flags:0x%lX\n",
> > 
> > 0x%lX is a bit redundunt.
> > %lX insert "0x" string by itself, I think.
> > 
> 
> /me slaps self
> 
> As hnaz pointed out to me on IRC, %#lX would have done the job of
> putting in the 0x automatically.

No. it's my fault. my last mail has typo (i forgot to write '#'), sorry.

> 
> ==== CUT HERE ====
> mm: Warn once when a page is freed with PG_mlocked set
> 
> When a page is freed with the PG_mlocked set, it is considered an unexpected
> but recoverable situation. A counter records how often this event happens
> but it is easy to miss that this event has occured at all. This patch warns
> once when PG_mlocked is set to prompt debuggers to check the counter to see
> how often it is happening.
> 
> Signed-off-by: Mel Gorman <mel@....ul.ie>
> ---
>  mm/page_alloc.c |   16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5d714f8..519ea6e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -495,8 +495,16 @@ static inline void free_page_mlock(struct page *page)
>  static void free_page_mlock(struct page *page) { }
>  #endif
>  
> -static inline int free_pages_check(struct page *page)
> -{
> +static inline int free_pages_check(struct page *page, int wasMlocked)
> +{
> +	if (unlikely(wasMlocked)) {
> +		WARN_ONCE(1, KERN_WARNING
> +			"Page flag mlocked set for process %s at pfn:%05lx\n"
> +			"page:%p flags:%#lX\n",
> +			current->comm, page_to_pfn(page),
> +			page, page->flags|__PG_MLOCKED);
> +	}
> +
>  	if (unlikely(page_mapcount(page) |
>  		(page->mapping != NULL)  |
>  		(atomic_read(&page->_count) != 0) |
> @@ -562,7 +570,7 @@ static void __free_pages_ok(struct page *page, unsigned int order)
>  	kmemcheck_free_shadow(page, order);
>  
>  	for (i = 0 ; i < (1 << order) ; ++i)
> -		bad += free_pages_check(page + i);
> +		bad += free_pages_check(page + i, wasMlocked);
>  	if (bad)
>  		return;
>  
> @@ -1027,7 +1035,7 @@ static void free_hot_cold_page(struct page *page, int cold)
>  
>  	if (PageAnon(page))
>  		page->mapping = NULL;
> -	if (free_pages_check(page))
> +	if (free_pages_check(page, wasMlocked))
>  		return;
>  
>  	if (!PageHighMem(page)) {

OK, looks fine.
	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>


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