From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757930Ab3GQXCg (ORCPT ); Wed, 17 Jul 2013 19:02:36 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:56824 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757598Ab3GQW4n (ORCPT ); Wed, 17 Jul 2013 18:56:43 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Li Zefan , Tejun Heo , Luis Henriques Subject: [PATCH 024/145] cgroup: fix umount vs cgroup_cfts_commit() race Date: Wed, 17 Jul 2013 15:45:56 -0700 Message-Id: <1374101277-7915-25-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1374101277-7915-1-git-send-email-kamal@canonical.com> References: <1374101277-7915-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.8.13.5 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Li Zefan commit 084457f284abf6789d90509ee11dae383842b23b upstream. cgroup_cfts_commit() uses dget() to keep cgroup alive after cgroup_mutex is dropped, but dget() won't prevent cgroupfs from being umounted. When the race happens, vfs will see some dentries with non-zero refcnt while umount is in process. Keep running this: mount -t cgroup -o blkio xxx /cgroup umount /cgroup And this: modprobe cfq-iosched rmmod cfs-iosched After a while, the BUG() in shrink_dcache_for_umount_subtree() may be triggered: BUG: Dentry xxx{i=0,n=blkio.yyy} still in use (1) [umount of cgroup cgroup] Signed-off-by: Li Zefan Signed-off-by: Tejun Heo [ luis: backported to 3.8: - fixed build error: added '&' to atomic_inc_not_zero parameter; this was fixed upstream by commit e8c82d20a9f729cf4b9f73043f7fd4e0872bebfd ] Signed-off-by: Luis Henriques --- kernel/cgroup.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 02ddadb..b6a1f62 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2813,13 +2813,17 @@ static void cgroup_cfts_commit(struct cgroup_subsys *ss, { LIST_HEAD(pending); struct cgroup *cgrp, *n; + struct super_block *sb = ss->root->sb; /* %NULL @cfts indicates abort and don't bother if @ss isn't attached */ - if (cfts && ss->root != &rootnode) { + if (cfts && ss->root != &rootnode && + atomic_inc_not_zero(&sb->s_active)) { list_for_each_entry(cgrp, &ss->root->allcg_list, allcg_node) { dget(cgrp->dentry); list_add_tail(&cgrp->cft_q_node, &pending); } + } else { + sb = NULL; } mutex_unlock(&cgroup_mutex); @@ -2842,6 +2846,9 @@ static void cgroup_cfts_commit(struct cgroup_subsys *ss, dput(cgrp->dentry); } + if (sb) + deactivate_super(sb); + mutex_unlock(&cgroup_cft_mutex); } -- 1.8.1.2