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

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Date:	Tue, 30 Jun 2009 17:34:57 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	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.

==== 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)) {
--
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