From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 9 Oct 2007 18:49:25 +0900 From: KAMEZAWA Hiroyuki Subject: [PATCH][for -mm] Fix and Enhancements for memory cgroup [1/6] fix refcnt race in charge/uncharge Message-Id: <20071009184925.ad8248d4.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20071009184620.8b14cbc6.kamezawa.hiroyu@jp.fujitsu.com> References: <20071009184620.8b14cbc6.kamezawa.hiroyu@jp.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: KAMEZAWA Hiroyuki Cc: "balbir@linux.vnet.ibm.com" , "linux-mm@kvack.org" , "containers@lists.osdl.org" , Andrew Morton List-ID: The logic of uncharging is - decrement refcnt -> lock page cgroup -> remove page cgroup. But the logic of charging is - lock page cgroup -> increment refcnt -> return. Then, one charge will be added to a page_cgroup under being removed. This makes no big trouble (like panic) but one charge is lost. This patch add a test at charging to verify page_cgroup's refcnt is greater than 0. If not, unlock and retry. Signed-off-by: KAMEZAWA Hiroyuki mm/memcontrol.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) Index: linux-2.6.23-rc8-mm2/mm/memcontrol.c =================================================================== --- linux-2.6.23-rc8-mm2.orig/mm/memcontrol.c +++ linux-2.6.23-rc8-mm2/mm/memcontrol.c @@ -271,14 +271,19 @@ int mem_cgroup_charge(struct page *page, * to see if the cgroup page already has a page_cgroup associated * with it */ +retry: lock_page_cgroup(page); pc = page_get_page_cgroup(page); /* * The page_cgroup exists and the page has already been accounted */ if (pc) { - atomic_inc(&pc->ref_cnt); - goto done; + if (unlikely(!atomic_inc_not_zero(&pc->ref_cnt))) { + /* this page is under being uncharge ? */ + unlock_page_cgroup(page); + goto retry; + } else + goto done; } unlock_page_cgroup(page); -- 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