linux-kernel - Re: 2.6.21-rc3-mm2 (oops in move

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Date:	Wed, 14 Mar 2007 16:13:27 +0000
From:	mel@...net.ie (Mel Gorman)
To:	Bjorn Helgaas <bjorn.helgaas@...com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.21-rc3-mm2 (oops in move_freepages)

On (14/03/07 09:11), Bjorn Helgaas didst pronounce:
> On Wednesday 14 March 2007 03:44, Mel Gorman wrote:
> > Please try the following patch from Yasunori Goto.
> > ...
> > --- current_test.orig/mm/page_alloc.c	2007-03-08 15:44:10.000000000 +0900
> > +++ current_test/mm/page_alloc.c	2007-03-08 16:17:29.000000000 +0900
> > @@ -707,7 +707,7 @@ int move_freepages(struct zone *zone,
> >  	unsigned long order;
> >  	int blocks_moved = 0;
> >  
> > -	BUG_ON(page_zone(start_page) != page_zone(end_page));
> > +	BUG_ON(page_zone(start_page) != page_zone(end_page - 1));
> >  
> 
> I should have mentioned that I already tried this patch.  The
> oops still occurs, although now it's when loading the value
> pointed to by "end_page - 1" instead of "end_page".

Ok. This looks like another case of HOLES_IN_ZONE hilarity with page_zone().
As I take a new look at the BUG_ON check in move_freepages(), it isn't even
necessary as move_freepages_block() already checks the zone boundaries.  At a
later date when the code has survived a while without new bug reports, I'll
submit a patch that simply deletes this check because it should be redundant.
Just in case, I'd like to preserve the check in the non-HOLES_IN_ZONE
case for now.

Can you try this patch please? It should apply on top of Yasunori Goto's
patch.

Signed-off-by: Mel Gorman <mel@....ul.ie>
diff -rup -X /usr/src/patchset-0.6/bin//dontdiff linux-2.6.21-rc3-mm2-goto/mm/page_alloc.c linux-2.6.21-rc3-mm2-bjorn_testfix/mm/page_alloc.c
--- linux-2.6.21-rc3-mm2-goto/mm/page_alloc.c	2007-03-14 16:07:23.000000000 +0000
+++ linux-2.6.21-rc3-mm2-bjorn_testfix/mm/page_alloc.c	2007-03-14 16:01:00.000000000 +0000
@@ -707,7 +707,15 @@ int move_freepages(struct zone *zone,
 	unsigned long order;
 	int blocks_moved = 0;
 
+#ifndef CONFIG_HOLES_IN_ZONE
+	/*
+	 * page_zone is not safe to call in this context when
+	 * CONFIG_HOLES_IN_ZONE is set but this bug check is
+	 * redundant anyway as we check zone boundaries in
+	 * move_freepages_block()
+	 */
 	BUG_ON(page_zone(start_page) != page_zone(end_page - 1));
+#endif
 
 	for (page = start_page; page < end_page;) {
 		if (!PageBuddy(page)) {
-
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