From patchwork Thu Jul 11 14:23:49 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Luis Henriques X-Patchwork-Id: 258477 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id 21DDC2C02A5 for ; Fri, 12 Jul 2013 00:26:05 +1000 (EST) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1UxHok-0007gs-4i; Thu, 11 Jul 2013 14:25:58 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1UxHoT-0007WV-95 for kernel-team@lists.ubuntu.com; Thu, 11 Jul 2013 14:25:41 +0000 Received: from bl15-104-132.dsl.telepac.pt ([188.80.104.132] helo=localhost) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1UxHoT-0001aT-1Y; Thu, 11 Jul 2013 14:25:41 +0000 From: Luis Henriques To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Subject: [PATCH 19/98] cgroup: fix umount vs cgroup_cfts_commit() race Date: Thu, 11 Jul 2013 15:23:49 +0100 Message-Id: <1373552708-15235-20-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1373552708-15235-1-git-send-email-luis.henriques@canonical.com> References: <1373552708-15235-1-git-send-email-luis.henriques@canonical.com> X-Extended-Stable: 3.5 Cc: Tejun Heo , Li Zefan X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com 3.5.7.17 -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 3.5: - 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 07ba52a..3b3fa5b 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2771,13 +2771,17 @@ 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); @@ -2800,6 +2804,9 @@ static void cgroup_cfts_commit(struct cgroup_subsys *ss, dput(cgrp->dentry); } + if (sb) + deactivate_super(sb); + mutex_unlock(&cgroup_cft_mutex); }