From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753203Ab2L1Ctd (ORCPT ); Thu, 27 Dec 2012 21:49:33 -0500 Received: from LGEMRELSE1Q.lge.com ([156.147.1.111]:55663 "EHLO LGEMRELSE1Q.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752287Ab2L1Cta (ORCPT ); Thu, 27 Dec 2012 21:49:30 -0500 X-AuditID: 9c93016f-b7b54ae000000e9e-6e-50dd08b89b53 Date: Fri, 28 Dec 2012 11:49:28 +0900 From: Minchan Kim To: Zlatko Calusic Cc: Andrew Morton , Mel Gorman , Linus Torvalds , Hugh Dickins , linux-mm , Linux Kernel Mailing List , Zhouping Liu , Sedat Dilek Subject: Re: [PATCH] mm: fix null pointer dereference in wait_iff_congested() Message-ID: <20121228024928.GA19720@blaptop> References: <50D24AF3.1050809@iskon.hr> <20121220111208.GD10819@suse.de> <20121220125802.23e9b22d.akpm@linux-foundation.org> <50D601C9.9060803@iskon.hr> <50D71166.6030608@iskon.hr> <50DB129E.7010000@iskon.hr> <50DD0106.7040001@iskon.hr> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50DD0106.7040001@iskon.hr> User-Agent: Mutt/1.5.21 (2010-09-15) X-Brightmail-Tracker: AAAAAA== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Zlatko, On Fri, Dec 28, 2012 at 03:16:38AM +0100, Zlatko Calusic wrote: > From: Zlatko Calusic > > The unintended consequence of commit 4ae0a48b is that > wait_iff_congested() can now be called with NULL struct zone* > producing kernel oops like this: For good description, it would be better to write simple pseudo code flow to show how NULL-zone pass into wait_iff_congested because kswapd code flow is too complex. As I see the code, we have following line above wait_iff_congested. if (!unbalanced_zone || blah blah) break; How can NULL unbalanced_zone reach wait_iff_congested? > > BUG: unable to handle kernel NULL pointer dereference > IP: [] wait_iff_congested+0x59/0x140 > > This trivial patch fixes it. > > Reported-by: Zhouping Liu > Reported-and-tested-by: Sedat Dilek > Cc: Andrew Morton > Cc: Mel Gorman > Cc: Hugh Dickins > Signed-off-by: Zlatko Calusic > --- > mm/vmscan.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 02bcfa3..e55ce55 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -2782,7 +2782,7 @@ loop_again: > if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) { > if (has_under_min_watermark_zone) > count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT); > - else > + else if (unbalanced_zone) > wait_iff_congested(unbalanced_zone, BLK_RW_ASYNC, HZ/10); > } > > -- > 1.8.1.rc3 > > -- > Zlatko > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Kind regards, Minchan Kim