Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753113AbaF3OSj (ORCPT ); Mon, 30 Jun 2014 10:18:39 -0400 Received: from mail-qc0-f172.google.com ([209.85.216.172]:51877 "EHLO mail-qc0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750952AbaF3OSh (ORCPT ); Mon, 30 Jun 2014 10:18:37 -0400 Date: Mon, 30 Jun 2014 10:18:33 -0400 From: Tejun Heo To: Li Zefan Cc: LKML , Cgroups Subject: Re: [PATCH v3 1/3] cgroup: fix mount failure in a corner case Message-ID: <20140630141833.GA14807@htj.dyndns.org> References: <53B0DE66.5080100@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53B0DE66.5080100@huawei.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Applied with minor updates. Thanks. ------- 8< ------- >From 970317aa48c6ef66cd023c039c2650c897bad927 Mon Sep 17 00:00:00 2001 From: Li Zefan Date: Mon, 30 Jun 2014 11:49:58 +0800 Subject: [PATCH 1/3] cgroup: fix mount failure in a corner case # cat test.sh #! /bin/bash mount -t cgroup -o cpu xxx /cgroup umount /cgroup mount -t cgroup -o cpu,cpuacct xxx /cgroup umount /cgroup # ./test.sh mount: xxx already mounted or /cgroup busy mount: according to mtab, xxx is already mounted on /cgroup It's because the cgroupfs_root of the first mount was under destruction asynchronously. Fix this by delaying and then retrying mount for this case. v3: - put the refcnt immediately after getting it. (Tejun) v2: - use percpu_ref_tryget_live() rather that introducing percpu_ref_alive(). (Tejun) - adjust comment. tj: Updated the comment a bit. Cc: # 3.15 Signed-off-by: Li Zefan Signed-off-by: Tejun Heo --- kernel/cgroup.c | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index d9a8be9..6406866 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1648,10 +1648,12 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, int flags, const char *unused_dev_name, void *data) { + struct cgroup_subsys *ss; struct cgroup_root *root; struct cgroup_sb_opts opts; struct dentry *dentry; int ret; + int i; bool new_sb; /* @@ -1677,6 +1679,27 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, goto out_unlock; } + /* + * Destruction of cgroup root is asynchronous, so subsystems may + * still be dying after the previous unmount. Let's drain the + * dying subsystems. We just need to ensure that the ones + * unmounted previously finish dying and don't care about new ones + * starting. Testing ref liveliness is good enough. + */ + for_each_subsys(ss, i) { + if (!(opts.subsys_mask & (1 << i)) || + ss->root == &cgrp_dfl_root) + continue; + + if (!percpu_ref_tryget_live(&ss->root->cgrp.self.refcnt)) { + mutex_unlock(&cgroup_mutex); + msleep(10); + ret = restart_syscall(); + goto out_free; + } + cgroup_put(&ss->root->cgrp); + } + for_each_root(root) { bool name_match = false; -- 1.9.3 -- 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/