From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: [PATCH 12/17] cgroup: introduce CSS_ONLINE flag and on/offline_css() helpers Date: Mon, 12 Nov 2012 19:01:39 -0800 Message-ID: <1352775704-9023-13-git-send-email-tj@kernel.org> References: <1352775704-9023-1-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:x-mailer:in-reply-to :references; bh=iv2CuLbR/fv2GebEAnubKcvSHDDPEMDzVjCy3J5eG5w=; b=jOHNtaPuelgirDzFkQeoluOk20zmOH1iEd0Jx6Ntk/CGs+/7SPWpZ1g24/YT3w4vXN 1AMub2ym+zt5z732r9WoE/DnhpqDlxUdIeexmt8iVSDcqvq8qycXlA7SVAX4vjBIZ84Y IIjyAZVF4rzsiYCrAf1lzBn4jy9vvFnDqvcv3rE4pwT8g4eibg1oZDPtaqpI7Y85akLi mwA56+495ZMbuex8HAqJW1NMvHhGmM1nnqlWSr9iwbZwSyFjy5qWHtUc5OCRvF+d1o5O KWbajlXeFwv8ehWFr+RbfIc9kdwZ3PbXqyZMo5VnCLk09NSo46BOcRCMqNSM/igm5CfO Vn/Q== In-Reply-To: <1352775704-9023-1-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: lizefan@huawei.com, containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Cc: mhocko@suse.cz, glommer@parallels.com, Tejun Heo New helpers on/offline_css() respectively wrap ->post_create() and ->pre_destroy() invocations. online_css() sets CSS_ONLINE after ->post_create() is complete and offline_css() invokes ->pre_destroy() iff CSS_ONLINE is set and clears it while also handling the temporary dropping of cgroup_mutex. This patch doesn't introduce any behavior change at the moment but will be used to improve cgroup_create() failure path and allow ->post_create() to fail. Signed-off-by: Tejun Heo --- include/linux/cgroup.h | 1 + kernel/cgroup.c | 65 ++++++++++++++++++++++++++++++++------------------ 2 files changed, 43 insertions(+), 23 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index e9f07ef..c487315 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -82,6 +82,7 @@ struct cgroup_subsys_state { /* bits in struct cgroup_subsys_state flags field */ enum { CSS_ROOT = (1 << 0), /* this CSS is the root of the subsystem */ + CSS_ONLINE = (1 << 1), /* between ->post_create() and ->pre_destroy() */ }; /* Caller must verify that the css is not for root cgroup */ diff --git a/kernel/cgroup.c b/kernel/cgroup.c index afc47d6..c3087f5 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4035,6 +4035,42 @@ static void init_cgroup_css(struct cgroup_subsys_state *css, INIT_WORK(&css->dput_work, css_dput_fn); } +/* invoke ->post_create() on a new CSS and mark it online */ +static void online_css(struct cgroup_subsys *ss, struct cgroup *cgrp) +{ + lockdep_assert_held(&cgroup_mutex); + + if (ss->post_create) + ss->post_create(cgrp); + cgrp->subsys[ss->subsys_id]->flags |= CSS_ONLINE; +} + +/* if the CSS is online, invoke ->pre_destory() on it and mark it offline */ +static void offline_css(struct cgroup_subsys *ss, struct cgroup *cgrp) + __releases(&cgroup_mutex) __acquires(&cgroup_mutex) +{ + struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id]; + + lockdep_assert_held(&cgroup_mutex); + + if (!(css->flags & CSS_ONLINE)) + return; + + /* + * pre_destroy() should be called with cgroup_mutex unlocked. See + * 3fa59dfbc3 ("cgroup: fix potential deadlock in pre_destroy") for + * details. This temporary unlocking should go away once + * cgroup_mutex is unexported from controllers. + */ + if (ss->pre_destroy) { + mutex_unlock(&cgroup_mutex); + ss->pre_destroy(cgrp); + mutex_lock(&cgroup_mutex); + } + + cgrp->subsys[ss->subsys_id]->flags &= ~CSS_ONLINE; +} + /* * cgroup_create - create a cgroup * @parent: cgroup that will be parent of the new cgroup @@ -4137,8 +4173,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, dget(dentry); /* creation succeeded, notify subsystems */ - if (ss->post_create) - ss->post_create(cgrp); + online_css(ss, cgrp); } err = cgroup_populate_dir(cgrp, true, root->subsys_mask); @@ -4240,18 +4275,9 @@ static int cgroup_destroy_locked(struct cgroup *cgrp) } set_bit(CGRP_REMOVED, &cgrp->flags); - /* - * Tell subsystems to initate destruction. pre_destroy() should be - * called with cgroup_mutex unlocked. See 3fa59dfbc3 ("cgroup: fix - * potential deadlock in pre_destroy") for details. This temporary - * unlocking should go away once cgroup_mutex is unexported from - * controllers. - */ - mutex_unlock(&cgroup_mutex); + /* tell subsystems to initate destruction */ for_each_subsys(cgrp->root, ss) - if (ss->pre_destroy) - ss->pre_destroy(cgrp); - mutex_lock(&cgroup_mutex); + offline_css(ss, cgrp); /* * Put all the base refs. Each css holds an extra reference to the @@ -4354,9 +4380,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss) BUG_ON(!list_empty(&init_task.tasks)); ss->active = 1; - - if (ss->post_create) - ss->post_create(dummytop); + online_css(ss, dummytop); mutex_unlock(&cgroup_mutex); @@ -4469,9 +4493,7 @@ int __init_or_module cgroup_load_subsys(struct cgroup_subsys *ss) write_unlock(&css_set_lock); ss->active = 1; - - if (ss->post_create) - ss->post_create(dummytop); + online_css(ss, dummytop); /* success! */ mutex_unlock(&cgroup_mutex); @@ -4501,12 +4523,9 @@ void cgroup_unload_subsys(struct cgroup_subsys *ss) */ BUG_ON(ss->root != &rootnode); - /* ->pre_destroy() should be called outside cgroup_mutex for now */ - if (ss->pre_destroy) - ss->pre_destroy(dummytop); - mutex_lock(&cgroup_mutex); + offline_css(ss, dummytop); ss->active = 0; if (ss->use_id) { -- 1.7.11.7