From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756367Ab3HaN7y (ORCPT ); Sat, 31 Aug 2013 09:59:54 -0400 Received: from mail-qc0-f171.google.com ([209.85.216.171]:42317 "EHLO mail-qc0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753103Ab3HaN7x (ORCPT ); Sat, 31 Aug 2013 09:59:53 -0400 Date: Sat, 31 Aug 2013 09:59:49 -0400 From: Tejun Heo To: lizefan@huawei.com Cc: containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 3/9] cgroup: make for_each_subsys() useable under cgroup_root_mutex Message-ID: <20130831135949.GB26539@htj.dyndns.org> References: <1377723829-22814-1-git-send-email-tj@kernel.org> <1377723829-22814-4-git-send-email-tj@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1377723829-22814-4-git-send-email-tj@kernel.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We want to use for_each_subsys() in cgroupfs_root handling where only cgroup_root_mutex is held. The only way cgroup_subsys[] can change is through module load/unload, make cgroup_[un]load_subsys() grab cgroup_root_mutex too and update the lockdep annotation in for_each_subsys() to allow either cgroup_mutex or cgroup_root_mutex. * Lockdep annotation is moved from inner 'if' condition to outer 'for' init caluse. There's no reason to execute the assertion every loop. * Loop index @i is renamed to @ssid. Indices iterating through subsys will be [re]named to @ssid gradually. v2: cgroup_assert_mutex_or_root_locked() caused build failure if !CONFIG_LOCKEDP. Conditionalize its definition. The build failure was reported by kbuild test bot. Signed-off-by: Tejun Heo Cc: kbuild test robot --- kernel/cgroup.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -93,6 +93,14 @@ static DEFINE_MUTEX(cgroup_root_mutex); lockdep_is_held(&cgroup_mutex), \ "cgroup_mutex or RCU read lock required"); +#ifdef CONFIG_LOCKDEP +#define cgroup_assert_mutex_or_root_locked() \ + WARN_ON_ONCE(debug_locks && (!lockdep_is_held(&cgroup_mutex) && \ + !lockdep_is_held(&cgroup_root_mutex))) +#else +#define cgroup_assert_mutex_or_root_locked() do { } while (0) +#endif + /* * Generate an array of cgroup subsystem pointers. At boot time, this is * populated with the built in subsystems, and modular subsystems are @@ -291,14 +299,15 @@ static int notify_on_release(const struc /** * for_each_subsys - iterate all loaded cgroup subsystems * @ss: the iteration cursor - * @i: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end + * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end * - * Should be called under cgroup_mutex. + * Iterates through all loaded subsystems. Should be called under + * cgroup_mutex or cgroup_root_mutex. */ -#define for_each_subsys(ss, i) \ - for ((i) = 0; (i) < CGROUP_SUBSYS_COUNT; (i)++) \ - if (({ lockdep_assert_held(&cgroup_mutex); \ - !((ss) = cgroup_subsys[i]); })) { } \ +#define for_each_subsys(ss, ssid) \ + for (({ cgroup_assert_mutex_or_root_locked(); (ssid) = 0; }); \ + (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++) \ + if (!((ss) = cgroup_subsys[(ssid)])) { } \ else /** @@ -4911,6 +4920,7 @@ int __init_or_module cgroup_load_subsys( cgroup_init_cftsets(ss); mutex_lock(&cgroup_mutex); + mutex_lock(&cgroup_root_mutex); cgroup_subsys[ss->subsys_id] = ss; /* @@ -4966,10 +4976,12 @@ int __init_or_module cgroup_load_subsys( goto err_unload; /* success! */ + mutex_unlock(&cgroup_root_mutex); mutex_unlock(&cgroup_mutex); return 0; err_unload: + mutex_unlock(&cgroup_root_mutex); mutex_unlock(&cgroup_mutex); /* @ss can't be mounted here as try_module_get() would fail */ cgroup_unload_subsys(ss); @@ -4999,6 +5011,7 @@ void cgroup_unload_subsys(struct cgroup_ BUG_ON(ss->root != &cgroup_dummy_root); mutex_lock(&cgroup_mutex); + mutex_lock(&cgroup_root_mutex); offline_css(cgroup_css(cgroup_dummy_top, ss)); @@ -5037,6 +5050,7 @@ void cgroup_unload_subsys(struct cgroup_ ss->css_free(cgroup_css(cgroup_dummy_top, ss)); RCU_INIT_POINTER(cgroup_dummy_top->subsys[ss->subsys_id], NULL); + mutex_unlock(&cgroup_root_mutex); mutex_unlock(&cgroup_mutex); } EXPORT_SYMBOL_GPL(cgroup_unload_subsys);