linux-kernel - Re: [PATCH] mm: compaction: Abort compaction if too many pages are isolated and caller is asynchronous

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Message-ID: <20110531143830.GC13418@barrios-laptop>
Date:	Tue, 31 May 2011 23:38:30 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Mel Gorman <mgorman@...e.de>, Mel Gorman <mel@....ul.ie>,
	akpm@...ux-foundation.org, Ury Stankevich <urykhy@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, stable@...nel.org
Subject: Re: [PATCH] mm: compaction: Abort compaction if too many pages are
 isolated and caller is asynchronous

On Tue, May 31, 2011 at 11:37:35PM +0900, Minchan Kim wrote:
> On Tue, May 31, 2011 at 04:14:02PM +0200, Andrea Arcangeli wrote:
> > On Tue, May 31, 2011 at 10:33:40PM +0900, Minchan Kim wrote:
> > > I checked them before sending patch but I got failed to find strange things. :(
> > 
> > My review also doesn't show other bugs in migrate_pages callers like
> > that one.
> > 
> > > Now I am checking the page's SwapBacked flag can be changed
> > > between before and after of migrate_pages so accounting of NR_ISOLATED_XX can
> > > make mistake. I am approaching the failure, too. Hmm.
> > 
> > When I checked that, I noticed the ClearPageSwapBacked in swapcache if
> > radix insertion fails, but that happens before adding the page in the
> > LRU so it shouldn't have a chance to be isolated.
> 
> True.
> 
> > 
> > So far I only noticed an unsafe page_count in
> > vmscan.c:isolate_lru_pages but that should at worst result in a
> > invalid pointer dereference as random result from that page_count is
> > not going to hurt and I think it's only a theoretical issue.
> 
> 
> Yes. You find a new BUG.
> It seems to be related to this problem but it should be solved although

 typo : It doesn't seem to be.


- 
Kind regards
Minchan Kim
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