From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: [PATCH 2/7] cgroup: make for_each_subsys() useable under cgroup_root_mutex Date: Fri, 6 Dec 2013 15:27:47 -0500 Message-ID: <1386361672-27791-3-git-send-email-tj@kernel.org> References: <1386361672-27791-1-git-send-email-tj@kernel.org> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:from:to:cc:subject:date:message-id:in-reply-to:references; bh=xXex/uIlMpRE0I7S0Ey8EOcfZhgIYumHxQyiM9nJ49o=; b=DqKFy16HCT6aM1Qc0uNr9g+C6oHkguHMVMl0oFybBj0LY8XfvV/IaTn0kkIhQjx43v K6CmnvWqwy1TGGLGnlGnIDbFL/z89sudbIzw72KdL8diEePbFqlU/V2IKc26CJqvTi/V HDJI0p4nXnMoXdZnSakUKZwqJw+Q5uiFFiH2qyQ72OrQA1MzpCGg/nwCdeccAnSNxKOf RC9ZOaM6CIGh5DWvuo9/rlROYJ1OVpQEBliDa6punClXj+1qKUmFtREfyDwUqtluLF2c Es7vHf2D+Aj7QwNmWSqII9kexyIpH6x3xO5JiXfi8yBi1JDMdTEd2WLGWIs/7lNGR0ry 6w0A== In-Reply-To: <1386361672-27791-1-git-send-email-tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, vdavydov-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org, Tejun Heo , kbuild test robot 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 Acked-by: Li Zefan Cc: kbuild test robot --- kernel/cgroup.c | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index c22eecb..4a7fb40 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -98,6 +98,14 @@ 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 + /* * cgroup destruction makes heavy use of work items and there can be a lot * of concurrent destructions. Use a separate workqueue so that cgroup @@ -237,14 +245,15 @@ static int notify_on_release(const struct cgroup *cgrp) /** * 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 /** @@ -4592,6 +4601,7 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss) cgroup_init_cftsets(ss); mutex_lock(&cgroup_mutex); + mutex_lock(&cgroup_root_mutex); cgroup_subsys[ss->subsys_id] = ss; /* @@ -4641,10 +4651,12 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss) 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); @@ -4674,6 +4686,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss) BUG_ON(ss->root != &cgroup_dummy_root); mutex_lock(&cgroup_mutex); + mutex_lock(&cgroup_root_mutex); offline_css(cgroup_css(cgroup_dummy_top, ss)); @@ -4708,6 +4721,7 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss) 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); -- 1.8.4.2