Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755217Ab0DVObo (ORCPT ); Thu, 22 Apr 2010 10:31:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:26801 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754466Ab0DVObn (ORCPT ); Thu, 22 Apr 2010 10:31:43 -0400 Date: Thu, 22 Apr 2010 10:31:05 -0400 From: Vivek Goyal To: Li Zefan Cc: LKML , "containers@lists.osdl.org" , "Paul E. McKenney" , Paul Menage , Andrew Morton , Jens Axboe , Gui Jianfeng Subject: Re: [PATCH 5/5] blk-cgroup: Fix an RCU warning in blkiocg_create() Message-ID: <20100422143105.GA3228@redhat.com> References: <4BD016F4.8060108@cn.fujitsu.com> <4BD017AC.1020209@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4BD017AC.1020209@cn.fujitsu.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1954 Lines: 64 On Thu, Apr 22, 2010 at 05:32:28PM +0800, Li Zefan wrote: > with CONFIG_PROVE_RCU=y, a warning can be triggered: > > # mount -t cgroup -o blkio xxx /mnt > # mkdir /mnt/subgroup > > ... > kernel/cgroup.c:4442 invoked rcu_dereference_check() without protection! > ... > IIUC, so blkiocg_create() is being called with cgroup_mutex held and not with rcu read lock held. Hence rcu_dereference() in css_depth() gives warning. So one easy solution is to don't use css_depth() at all. In this case simple check like cgroup->top_cgroup should suffice. Makese sense to me. Acked-by: Vivek Goyal Thanks Vivek > To fix this, we avoid caling css_depth() here, which is a bit simpler > than the original code. > > Signed-off-by: Li Zefan > --- > block/blk-cgroup.c | 8 ++++---- > 1 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c > index 5fe03de..2cc682b 100644 > --- a/block/blk-cgroup.c > +++ b/block/blk-cgroup.c > @@ -286,16 +286,16 @@ done: > static struct cgroup_subsys_state * > blkiocg_create(struct cgroup_subsys *subsys, struct cgroup *cgroup) > { > - struct blkio_cgroup *blkcg, *parent_blkcg; > + struct blkio_cgroup *blkcg; > + struct cgroup *parent = cgroup->parent; > > - if (!cgroup->parent) { > + if (!parent) { > blkcg = &blkio_root_cgroup; > goto done; > } > > /* Currently we do not support hierarchy deeper than two level (0,1) */ > - parent_blkcg = cgroup_to_blkio_cgroup(cgroup->parent); > - if (css_depth(&parent_blkcg->css) > 0) > + if (parent != cgroup->top_cgroup) > return ERR_PTR(-EINVAL); > > blkcg = kzalloc(sizeof(*blkcg), GFP_KERNEL); > -- > 1.6.3 -- 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/