cgroups: allow cgroup hierarchies to be created with no bound subsystems
This patch removes the restriction that a cgroup hierarchy must have at
least one bound subsystem. The mount option "none" is treated as an
explicit request for no bound subsystems.
A hierarchy with no subsystems can be useful for plain task tracking, and
is also a step towards the support for multiply-bindable subsystems.
As part of this change, the hierarchy id is no longer calculated from the
bitmask of subsystems in the hierarchy (since this is not guaranteed to be
unique) but is allocated via an ida. Reference counts on cgroups from
css_set objects are now taken explicitly one per hierarchy, rather than
one per subsystem.
Example usage:
mount -t cgroup -o none,name=foo cgroup /mnt/cgroup
Based on the "no-op"/"none" subsystem concept proposed by
kamezawa.hiroyu@jp.fujitsu.com
Signed-off-by: Paul Menage <menage@google.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8ba6809..14efffe 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -49,6 +49,7 @@
#include <linux/namei.h>
#include <linux/smp_lock.h>
#include <linux/pid_namespace.h>
+#include <linux/idr.h>
#include <asm/atomic.h>
@@ -77,6 +78,9 @@
*/
unsigned long subsys_bits;
+ /* Unique id for this hierarchy. */
+ int hierarchy_id;
+
/* The bitmask of subsystems currently attached to this hierarchy */
unsigned long actual_subsys_bits;
@@ -147,6 +151,10 @@
static LIST_HEAD(roots);
static int root_count;
+static DEFINE_IDA(hierarchy_ida);
+static int next_hierarchy_id;
+static DEFINE_SPINLOCK(hierarchy_id_lock);
+
/* dummytop is a shorthand for the dummy hierarchy's top cgroup */
#define dummytop (&rootnode.top_cgroup)
@@ -264,42 +272,10 @@
* compiled into their kernel but not actually in use */
static int use_task_css_set_links __read_mostly;
-/* When we create or destroy a css_set, the operation simply
- * takes/releases a reference count on all the cgroups referenced
- * by subsystems in this css_set. This can end up multiple-counting
- * some cgroups, but that's OK - the ref-count is just a
- * busy/not-busy indicator; ensuring that we only count each cgroup
- * once would require taking a global lock to ensure that no
- * subsystems moved between hierarchies while we were doing so.
- *
- * Possible TODO: decide at boot time based on the number of
- * registered subsystems and the number of CPUs or NUMA nodes whether
- * it's better for performance to ref-count every subsystem, or to
- * take a global lock and only add one ref count to each hierarchy.
- */
-
-/*
- * unlink a css_set from the list and free it
- */
-static void unlink_css_set(struct css_set *cg)
+static void __put_css_set(struct css_set *cg, int taskexit)
{
struct cg_cgroup_link *link;
struct cg_cgroup_link *saved_link;
-
- hlist_del(&cg->hlist);
- css_set_count--;
-
- list_for_each_entry_safe(link, saved_link, &cg->cg_links,
- cg_link_list) {
- list_del(&link->cg_link_list);
- list_del(&link->cgrp_link_list);
- kfree(link);
- }
-}
-
-static void __put_css_set(struct css_set *cg, int taskexit)
-{
- int i;
/*
* Ensure that the refcount doesn't hit zero while any readers
* can see it. Similar to atomic_dec_and_lock(), but for an
@@ -312,20 +288,27 @@
write_unlock(&css_set_lock);
return;
}
- unlink_css_set(cg);
- write_unlock(&css_set_lock);
- rcu_read_lock();
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
- struct cgroup *cgrp = rcu_dereference(cg->subsys[i]->cgroup);
+ /* This css_set is dead. unlink it and release cgroup refcounts */
+ hlist_del(&cg->hlist);
+ css_set_count--;
+
+ list_for_each_entry_safe(link, saved_link, &cg->cg_links,
+ cg_link_list) {
+ struct cgroup *cgrp = link->cgrp;
+ list_del(&link->cg_link_list);
+ list_del(&link->cgrp_link_list);
if (atomic_dec_and_test(&cgrp->count) &&
notify_on_release(cgrp)) {
if (taskexit)
set_bit(CGRP_RELEASABLE, &cgrp->flags);
check_for_release(cgrp);
}
+
+ kfree(link);
}
- rcu_read_unlock();
+
+ write_unlock(&css_set_lock);
kfree(cg);
}
@@ -519,6 +502,7 @@
cgrp_link_list);
link->cg = cg;
link->cgrp = cgrp;
+ atomic_inc(&cgrp->count);
list_move(&link->cgrp_link_list, &cgrp->css_sets);
/*
* Always add links to the tail of the list so that the list
@@ -539,7 +523,6 @@
{
struct css_set *res;
struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
- int i;
struct list_head tmp_cg_links;
@@ -578,10 +561,6 @@
write_lock(&css_set_lock);
/* Add reference counts and links from the new css_set. */
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
- struct cgroup *cgrp = res->subsys[i]->cgroup;
- atomic_inc(&cgrp->count);
- }
list_for_each_entry(link, &oldcg->cg_links, cg_link_list) {
struct cgroup *c = link->cgrp;
if (c->root == cgrp->root)
@@ -972,8 +951,11 @@
unsigned long flags;
char *release_agent;
char *name;
+ /* User explicitly requested empty subsystem */
+ bool none;
struct cgroupfs_root *new_root;
+
};
/* Convert a hierarchy specifier into a bitmask of subsystems and
@@ -1002,6 +984,9 @@
if (!ss->disabled)
opts->subsys_bits |= 1ul << i;
}
+ } else if (!strcmp(token, "none")) {
+ /* Explicitly have no subsystems */
+ opts->none = true;
} else if (!strcmp(token, "noprefix")) {
set_bit(ROOT_NOPREFIX, &opts->flags);
} else if (!strncmp(token, "release_agent=", 14)) {
@@ -1051,6 +1036,8 @@
}
}
+ /* Consistency checks */
+
/*
* Option noprefix was introduced just for backward compatibility
* with the old cpuset, so we allow noprefix only if mounting just
@@ -1060,7 +1047,15 @@
(opts->subsys_bits & mask))
return -EINVAL;
- /* We can't have an empty hierarchy */
+
+ /* Can't specify "none" and some subsystems */
+ if (opts->subsys_bits && opts->none)
+ return -EINVAL;
+
+ /*
+ * We either have to specify by name or by subsystems. (So all
+ * empty hierarchies must have a name).
+ */
if (!opts->subsys_bits && !opts->name)
return -EINVAL;
@@ -1141,6 +1136,31 @@
init_cgroup_housekeeping(cgrp);
}
+static bool init_root_id(struct cgroupfs_root *root)
+{
+ int ret = 0;
+
+ do {
+ if (!ida_pre_get(&hierarchy_ida, GFP_KERNEL))
+ return false;
+ spin_lock(&hierarchy_id_lock);
+ /* Try to allocate the next unused ID */
+ ret = ida_get_new_above(&hierarchy_ida, next_hierarchy_id,
+ &root->hierarchy_id);
+ if (ret == -ENOSPC)
+ /* Try again starting from 0 */
+ ret = ida_get_new(&hierarchy_ida, &root->hierarchy_id);
+ if (!ret) {
+ next_hierarchy_id = root->hierarchy_id + 1;
+ } else if (ret != -EAGAIN) {
+ /* Can only get here if the 31-bit IDR is full ... */
+ BUG_ON(ret);
+ }
+ spin_unlock(&hierarchy_id_lock);
+ } while (ret);
+ return true;
+}
+
static int cgroup_test_super(struct super_block *sb, void *data)
{
struct cgroup_sb_opts *opts = data;
@@ -1150,8 +1170,12 @@
if (opts->name && strcmp(opts->name, root->name))
return 0;
- /* If we asked for subsystems then they must match */
- if (opts->subsys_bits && (opts->subsys_bits != root->subsys_bits))
+ /*
+ * If we asked for subsystems (or explicitly for no
+ * subsystems) then they must match
+ */
+ if ((opts->subsys_bits || opts->none)
+ && (opts->subsys_bits != root->subsys_bits))
return 0;
return 1;
@@ -1161,15 +1185,19 @@
{
struct cgroupfs_root *root;
- /* Empty hierarchies aren't supported */
- if (!opts->subsys_bits)
+ if (!opts->subsys_bits && !opts->none)
return NULL;
root = kzalloc(sizeof(*root), GFP_KERNEL);
if (!root)
return ERR_PTR(-ENOMEM);
+ if (!init_root_id(root)) {
+ kfree(root);
+ return ERR_PTR(-ENOMEM);
+ }
init_cgroup_root(root);
+
root->subsys_bits = opts->subsys_bits;
root->flags = opts->flags;
if (opts->release_agent)
@@ -1179,6 +1207,18 @@
return root;
}
+static void cgroup_drop_root(struct cgroupfs_root *root)
+{
+ if (!root)
+ return;
+
+ BUG_ON(!root->hierarchy_id);
+ spin_lock(&hierarchy_id_lock);
+ ida_remove(&hierarchy_ida, root->hierarchy_id);
+ spin_unlock(&hierarchy_id_lock);
+ kfree(root);
+}
+
static int cgroup_set_super(struct super_block *sb, void *data)
{
int ret;
@@ -1188,7 +1228,7 @@
if (!opts->new_root)
return -EINVAL;
- BUG_ON(!opts->subsys_bits);
+ BUG_ON(!opts->subsys_bits && !opts->none);
ret = set_anon_super(sb, NULL);
if (ret)
@@ -1257,7 +1297,7 @@
sb = sget(fs_type, cgroup_test_super, cgroup_set_super, &opts);
if (IS_ERR(sb)) {
ret = PTR_ERR(sb);
- kfree(opts.new_root);
+ cgroup_drop_root(opts.new_root);
goto out_err;
}
@@ -1351,7 +1391,7 @@
* We re-used an existing hierarchy - the new root (if
* any) is not needed
*/
- kfree(opts.new_root);
+ cgroup_drop_root(opts.new_root);
}
simple_set_mnt(mnt, sb);
@@ -1410,7 +1450,7 @@
mutex_unlock(&cgroup_mutex);
kill_litter_super(sb);
- kfree(root);
+ cgroup_drop_root(root);
}
static struct file_system_type cgroup_fs_type = {
@@ -3109,7 +3149,7 @@
/* Add init_css_set to the hash table */
hhead = css_set_hash(init_css_set.subsys);
hlist_add_head(&init_css_set.hlist, hhead);
-
+ BUG_ON(!init_root_id(&rootnode));
err = register_filesystem(&cgroup_fs_type);
if (err < 0)
goto out;
@@ -3164,7 +3204,7 @@
struct cgroup *cgrp;
int count = 0;
- seq_printf(m, "%lu:", root->subsys_bits);
+ seq_printf(m, "%d:", root->hierarchy_id);
for_each_subsys(root, ss)
seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
if (strlen(root->name))
@@ -3210,8 +3250,8 @@
mutex_lock(&cgroup_mutex);
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
- seq_printf(m, "%s\t%lu\t%d\t%d\n",
- ss->name, ss->root->subsys_bits,
+ seq_printf(m, "%s\t%d\t%d\t%d\n",
+ ss->name, ss->root->hierarchy_id,
ss->root->number_of_cgroups, !ss->disabled);
}
mutex_unlock(&cgroup_mutex);
@@ -3929,8 +3969,8 @@
name = c->dentry->d_name.name;
else
name = "?";
- seq_printf(seq, "Root %lu group %s\n",
- c->root->subsys_bits, name);
+ seq_printf(seq, "Root %d group %s\n",
+ c->root->hierarchy_id, name);
}
rcu_read_unlock();
read_unlock(&css_set_lock);