From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with ESMTP id 222886B004D for ; Sun, 22 Mar 2009 19:23:45 -0400 (EDT) Date: Mon, 23 Mar 2009 09:13:37 +0900 From: Daisuke Nishimura Subject: Re: [BUGFIX][PATCH mmotm] memcg: try_get_mem_cgroup_from_swapcache fix Message-Id: <20090323091337.0a800858.nishimura@mxp.nes.nec.co.jp> In-Reply-To: <20090322184015.GE24227@balbir.in.ibm.com> References: <20090323000238.e650c65e.d-nishimura@mtf.biglobe.ne.jp> <20090322184015.GE24227@balbir.in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: balbir@linux.vnet.ibm.com Cc: nishimura@mxp.nes.nec.co.jp, Andrew Morton , KAMEZAWA Hiroyuki , linux-mm List-ID: On Mon, 23 Mar 2009 00:10:15 +0530, Balbir Singh wrote: > * Daisuke Nishimura [2009-03-23 00:02:38]: > > > From: Daisuke Nishimura > > > > css_tryget can be called twice in !PageCgroupUsed case. > > > > Signed-off-by: Daisuke Nishimura > > --- > > This is a fix for cgroups-use-css-id-in-swap-cgroup-for-saving-memory-v5.patch > > > > mm/memcontrol.c | 10 ++++------ > > 1 files changed, 4 insertions(+), 6 deletions(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index 5de6be9..55dea59 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -1027,9 +1027,11 @@ static struct mem_cgroup *try_get_mem_cgroup_from_swapcache(struct page *page) > > /* > > * Used bit of swapcache is solid under page lock. > > */ > > - if (PageCgroupUsed(pc)) > > + if (PageCgroupUsed(pc)) { > > mem = pc->mem_cgroup; > > - else { > > + if (mem && !css_tryget(&mem->css)) > > + mem = NULL; > > + } else { > > ent.val = page_private(page); > > id = lookup_swap_cgroup(ent); > > rcu_read_lock(); > > @@ -1038,10 +1040,6 @@ static struct mem_cgroup *try_get_mem_cgroup_from_swapcache(struct page *page) > > mem = NULL; > > rcu_read_unlock(); > > } > > - if (!mem) > > - return NULL; > > - if (!css_tryget(&mem->css)) > > - return NULL; > > return mem; > > } > > How did you detect the problem? Any test case/steps to reproduce the issue? > I found this when rebasing my patch onto mmotm and reviewing it. I suppose this bug can leads to an unremovable directory. Thanks, Daisuke Nishimura. -- 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