Date: Tue, 31 May 2011 16:14:02 +0200
From: Andrea Arcangeli <aarcange@redhat.com>
To: Minchan Kim <minchan.kim@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>, Mel Gorman <mel@csn.ul.ie>,
        akpm@linux-foundation.org, Ury Stankevich <urykhy@gmail.com>,
        KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@kernel.org
Subject: Re: [PATCH] mm: compaction: Abort compaction if too many pages are
 isolated and caller is asynchronous
Message-ID: <20110531141402.GK19505@random.random>
References: <20110530131300.GQ5044@csn.ul.ie>
 <20110530143109.GH19505@random.random>
 <20110530153748.GS5044@csn.ul.ie>
 <20110530165546.GC5118@suse.de>
 <20110530175334.GI19505@random.random>
 <20110531121620.GA3490@barrios-laptop>
 <20110531122437.GJ19505@random.random>
 <20110531133340.GB3490@barrios-laptop>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20110531133340.GB3490@barrios-laptop>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1100
Lines: 23

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.

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.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/