From 3c9c825b8b50de7dbb015e6bfc04bb2da79364d9 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 12 Feb 2014 09:29:50 -0500 Subject: [PATCH] cgroup: rename cgroupfs_root->number_of_cgroups to ->nr_cgrps and make it atomic_t root->number_of_cgroups is currently an integer protected with cgroup_mutex. Except for sanity checks and proc reporting, the only place it's used is to check whether the root has any child during remount; however, this is a bit flawed as the counter is not decremented when the cgroup is unlinked but when it's released, meaning that there could be an extended period where all cgroups are removed but remount is still not allowed because some internal objects are lingering. While not perfect either, it'd be better to use emptiness test on root->top_cgroup.children. This patch updates cgroup_remount() to test top_cgroup's children instead, which makes number_of_cgroups only actual usage statistics printing in proc implemented in proc_cgroupstats_show(). Let's shorten its name and make it an atomic_t so that we don't have to worry about its synchronization. It's purely auxiliary at this point. Signed-off-by: Tejun Heo Acked-by: Li Zefan --- include/linux/cgroup.h | 4 ++-- kernel/cgroup.c | 16 +++++++--------- 2 files changed, 9 insertions(+), 11 deletions(-) diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h index 4d6ff7d40cf6..f0e6105bbbc1 100644 --- a/include/linux/cgroup.h +++ b/include/linux/cgroup.h @@ -290,8 +290,8 @@ struct cgroupfs_root { /* The root cgroup for this hierarchy */ struct cgroup top_cgroup; - /* Tracks how many cgroups are currently defined in hierarchy.*/ - int number_of_cgroups; + /* Number of cgroups in the hierarchy, used only for /proc/cgroups */ + atomic_t nr_cgrps; /* A list running through the active hierarchies */ struct list_head root_list; diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 638df032fb94..cffdb6e2ad08 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -758,7 +758,7 @@ static void cgroup_put_root(struct cgroupfs_root *root) } mutex_lock(&cgroup_mutex); - BUG_ON(root->number_of_cgroups != 1); + BUG_ON(atomic_read(&root->nr_cgrps) != 1); BUG_ON(!list_empty(&cgrp->children)); /* Rebind all subsystems back to the default hierarchy */ @@ -928,9 +928,7 @@ static void cgroup_free_fn(struct work_struct *work) { struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work); - mutex_lock(&cgroup_mutex); - cgrp->root->number_of_cgroups--; - mutex_unlock(&cgroup_mutex); + atomic_dec(&cgrp->root->nr_cgrps); /* * We get a ref to the parent, and put the ref when this cgroup is @@ -1320,7 +1318,7 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data) } /* remounting is not allowed for populated hierarchies */ - if (root->number_of_cgroups > 1) { + if (!list_empty(&root->top_cgroup.children)) { ret = -EBUSY; goto out_unlock; } @@ -1360,7 +1358,7 @@ static void init_cgroup_root(struct cgroupfs_root *root) atomic_set(&root->refcnt, 1); INIT_LIST_HEAD(&root->root_list); - root->number_of_cgroups = 1; + atomic_set(&root->nr_cgrps, 1); cgrp->root = root; init_cgroup_housekeeping(cgrp); idr_init(&root->cgroup_idr); @@ -1463,7 +1461,7 @@ static int cgroup_setup_root(struct cgroupfs_root *root) write_unlock(&css_set_lock); BUG_ON(!list_empty(&root_cgrp->children)); - BUG_ON(root->number_of_cgroups != 1); + BUG_ON(atomic_read(&root->nr_cgrps) != 1); kernfs_activate(root_cgrp->kn); ret = 0; @@ -3709,7 +3707,7 @@ static long cgroup_create(struct cgroup *parent, const char *name, /* allocation complete, commit to creation */ list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children); - root->number_of_cgroups++; + atomic_inc(&root->nr_cgrps); /* * Grab a reference on the root and parent so that they don't get @@ -4281,7 +4279,7 @@ static int proc_cgroupstats_show(struct seq_file *m, void *v) for_each_subsys(ss, i) seq_printf(m, "%s\t%d\t%d\t%d\n", ss->name, ss->root->hierarchy_id, - ss->root->number_of_cgroups, !ss->disabled); + atomic_read(&ss->root->nr_cgrps), !ss->disabled); mutex_unlock(&cgroup_mutex); return 0; -- 2.39.2