From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id E0DD06B005A for ; Wed, 19 Aug 2009 22:52:07 -0400 (EDT) Date: Thu, 20 Aug 2009 10:52:09 +0800 From: Wu Fengguang Subject: [PATCH] mm: make nr_scan_try_batch() more safe on races Message-ID: <20090820025209.GA24387@localhost> References: <20090820024929.GA19793@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090820024929.GA19793@localhost> Sender: owner-linux-mm@kvack.org To: Andrew Morton , Balbir Singh Cc: KAMEZAWA Hiroyuki , KOSAKI Motohiro , Rik van Riel , Johannes Weiner , Avi Kivity , Andrea Arcangeli , "Dike, Jeffrey G" , Hugh Dickins , Christoph Lameter , Mel Gorman , LKML , linux-mm , "nishimura@mxp.nes.nec.co.jp" , "lizf@cn.fujitsu.com" , "menage@google.com" List-ID: nr_scan_try_batch() can be called concurrently on the same zone and the non-atomic calculations can go wrong. This is not a big problem as long as the errors are small and won't impact the balanced zone aging noticeably. @nr_to_scan could be much larger values than @swap_cluster_max. So don't store such large values to *nr_saved_scan directly, which helps reducing possible errors on races. CC: KOSAKI Motohiro Signed-off-by: Wu Fengguang --- mm/vmscan.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) --- linux.orig/mm/vmscan.c 2009-08-20 10:46:30.000000000 +0800 +++ linux/mm/vmscan.c 2009-08-20 10:49:36.000000000 +0800 @@ -1496,15 +1496,14 @@ static unsigned long nr_scan_try_batch(u unsigned long *nr_saved_scan, unsigned long swap_cluster_max) { - unsigned long nr; - - *nr_saved_scan += nr_to_scan; - nr = *nr_saved_scan; + unsigned long nr = *nr_saved_scan + nr_to_scan; if (nr >= swap_cluster_max) *nr_saved_scan = 0; - else + else { + *nr_saved_scan = nr; nr = 0; + } return nr; } -- 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