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Subject[PATCH 2/7] cgroups: Allow to bind a subsystem to a cgroup hierarchy
Stephane posted a patchset to add perf_cgroup subsystem, so perf can
be used to monitor all threads belonging to a cgroup.

But if you already mounted a cgroup hierarchy but without perf_cgroup
and the hierarchy has sub-cgroups, you can't bind perf_cgroup to it,
and thus you're not able to use per-cgroup perf feature.

This patchset alleviates the pain, and then a subsytem can be bind/unbind
to/from a hierarchy which has sub-cgroups in it.

For a cgroup subsystem to become bindable, the can_bind flag of
struct cgroup_subsys should be set, and provide ->bind() callback
if necessary.

But for some constraints, not all subsystems can take advantage of
this patch. For example, we can't decide a cgroup's cpuset.mems and
cpuset.cpus automatically, so cpuset is not bindable.

Usage:

# mount -t cgroup -o cpuset xxx /mnt
# mkdir /mnt/tmp
# echo $$ > /mnt/tmp/tasks
(assume cpuacct is bindable, and we add cpuacct to the hierarchy)
# mount -o remount,cpuset,cpuacct xxx /mnt

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
include/linux/cgroup.h | 5 +
kernel/cgroup.c | 225 ++++++++++++++++++++++++++++++++++++++---------
2 files changed, 187 insertions(+), 43 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index e23ded6..49369ff 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -490,6 +490,11 @@ struct cgroup_subsys {
* (not available in early_init time.)
*/
unsigned int use_id:1;
+ /*
+ * Indicate if this subsystem can be bound/unbound to/from a cgroup
+ * hierarchy which has child cgroups.
+ */
+ unsigned int can_bind:1;

#define MAX_CGROUP_TYPE_NAMELEN 32
const char *name;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 6c36750..46df5f8 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -57,6 +57,7 @@
#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
#include <linux/eventfd.h>
#include <linux/poll.h>
+#include <linux/bitops.h>

#include <asm/atomic.h>

@@ -870,18 +871,13 @@ static void remove_dir(struct dentry *d)

static void cgroup_clear_directory(struct dentry *dentry)
{
- struct list_head *node;
+ struct dentry *d, *tmp;

BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
spin_lock(&dcache_lock);
- node = dentry->d_subdirs.next;
- while (node != &dentry->d_subdirs) {
- struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
- list_del_init(node);
- if (d->d_inode) {
- /* This should never be called on a cgroup
- * directory with child cgroups */
- BUG_ON(d->d_inode->i_mode & S_IFDIR);
+ list_for_each_entry_safe(d, tmp, &dentry->d_subdirs, d_u.d_child) {
+ if (d->d_inode && !(d->d_inode->i_mode & S_IFDIR)) {
+ list_del_init(&d->d_u.d_child);
d = dget_locked(d);
spin_unlock(&dcache_lock);
d_delete(d);
@@ -889,7 +885,6 @@ static void cgroup_clear_directory(struct dentry *dentry)
dput(d);
spin_lock(&dcache_lock);
}
- node = dentry->d_subdirs.next;
}
spin_unlock(&dcache_lock);
}
@@ -934,6 +929,145 @@ void cgroup_release_and_wakeup_rmdir(struct cgroup_subsys_state *css)
css_put(css);
}

+static void init_cgroup_css(struct cgroup_subsys_state *css,
+ struct cgroup_subsys *ss,
+ struct cgroup *cgrp)
+{
+ css->cgroup = cgrp;
+ atomic_set(&css->refcnt, 1);
+ css->flags = 0;
+ css->id = NULL;
+ if (cgrp == dummytop)
+ set_bit(CSS_ROOT, &css->flags);
+ BUG_ON(cgrp->subsys[ss->subsys_id]);
+ cgrp->subsys[ss->subsys_id] = css;
+}
+
+/*
+ * cgroup_walk_herarchy - iterate through a cgroup hierarchy
+ * @process_cgroup: callback called on each cgroup in the hierarchy
+ * @data: will be passed to @process_cgroup
+ * @top_cgrp: the root cgroup of the hierarchy
+ *
+ * For such a hierarchy:
+ * a1 c1
+ * / /
+ * Root - a2 - b1 - c2
+ * \
+ * a3
+ *
+ * The iterating order is: a1, a2, b1, c1, c2, a3. So a parent will be
+ * processed before its children.
+ */
+static int cgroup_walk_hierarchy(int (*process_cgroup)(struct cgroup *, void *),
+ void *data, struct cgroup *top_cgrp)
+{
+ struct cgroup *parent = top_cgrp;
+ struct cgroup *child;
+ struct list_head *node;
+ int ret;
+
+ node = parent->children.next;
+repeat:
+ while (node != &parent->children) {
+ child = list_entry(node, struct cgroup, sibling);
+
+ ret = process_cgroup(child, data);
+ if (ret)
+ return ret;
+
+ if (!list_empty(&child->children)) {
+ parent = child;
+ node = parent->children.next;
+ goto repeat;
+ } else
+ node = node->next;
+ }
+
+ if (parent != top_cgrp) {
+ child = parent;
+ parent = child->parent;
+ node = child->sibling.next;
+ goto repeat;
+ }
+
+ return 0;
+}
+
+static int hierarchy_attach_css_failed(struct cgroup *cgrp, void *data)
+{
+ unsigned long added_bits = (unsigned long)data;
+ int i;
+
+ for_each_set_bit(i, &added_bits, CGROUP_SUBSYS_COUNT);
+ if (cgrp->subsys[i])
+ subsys[i]->destroy(subsys[i], cgrp);
+
+ return 0;
+}
+
+static int hierarchy_attach_css(struct cgroup *cgrp, void *data)
+{
+ unsigned long added_bits = (unsigned long)data;
+ int i;
+ int ret = 0;
+
+ for_each_set_bit(i, &added_bits, CGROUP_SUBSYS_COUNT) {
+ struct cgroup_subsys_state *css;
+ struct cgroup_subsys *ss = subsys[i];
+
+ css = ss->create(ss, cgrp);
+ if (IS_ERR(css)) {
+ ret = PTR_ERR(css);
+ break;
+ }
+ init_cgroup_css(css, ss, cgrp);
+
+ if (ss->use_id) {
+ ret = alloc_css_id(ss, cgrp->parent, cgrp);
+ if (ret)
+ break;
+ }
+ }
+
+ if (ret)
+ cgroup_walk_hierarchy(hierarchy_attach_css_failed, data,
+ cgrp->top_cgroup);
+ return ret;
+}
+
+static int hierarchy_update_css_sets(struct cgroup *cgrp, void *data)
+{
+ unsigned long added_bits = (unsigned long)data;
+ int i;
+ struct cg_cgroup_link *link;
+
+ write_lock(&css_set_lock);
+ list_for_each_entry(link, &cgrp->css_sets, cgrp_link_list) {
+ struct css_set *cg = link->cg;
+ struct hlist_head *hhead;
+
+ for_each_set_bit(i, &added_bits, CGROUP_SUBSYS_COUNT)
+ cg->subsys[i] = cgrp->subsys[i];
+
+ /* rehash */
+ hlist_del(&cg->hlist);
+ hhead = css_set_hash(cg->subsys);
+ hlist_add_head(&cg->hlist, hhead);
+ }
+ write_unlock(&css_set_lock);
+
+ return 0;
+}
+
+static int hierarchy_populate_dir(struct cgroup *cgrp, void *data)
+{
+ mutex_lock_nested(&cgrp->dentry->d_inode->i_mutex, I_MUTEX_CHILD);
+ cgroup_populate_dir(cgrp);
+ mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
+ return 0;
+}
+
/*
* Call with cgroup_mutex held. Drops reference counts on modules, including
* any duplicate ones that parse_cgroupfs_options took. If this function
@@ -945,36 +1079,53 @@ static int rebind_subsystems(struct cgroupfs_root *root,
unsigned long added_bits, removed_bits;
struct cgroup *cgrp = &root->top_cgroup;
int i;
+ int err;

BUG_ON(!mutex_is_locked(&cgroup_mutex));

removed_bits = root->actual_subsys_bits & ~final_bits;
added_bits = final_bits & ~root->actual_subsys_bits;
+
/* Check that any added subsystems are currently free */
- for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
- unsigned long bit = 1UL << i;
- struct cgroup_subsys *ss = subsys[i];
- if (!(bit & added_bits))
- continue;
+ for_each_set_bit(i, &added_bits, CGROUP_SUBSYS_COUNT) {
/*
* Nobody should tell us to do a subsys that doesn't exist:
* parse_cgroupfs_options should catch that case and refcounts
* ensure that subsystems won't disappear once selected.
*/
- BUG_ON(ss == NULL);
- if (ss->root != &rootnode) {
+ BUG_ON(subsys[i] == NULL);
+ if (subsys[i]->root != &rootnode) {
/* Subsystem isn't free */
return -EBUSY;
}
}

- /* Currently we don't handle adding/removing subsystems when
- * any child cgroups exist. This is theoretically supportable
- * but involves complex error handling, so it's being left until
- * later */
- if (root->number_of_cgroups > 1)
+ /* removing will be supported later */
+ if (root->number_of_cgroups > 1 && removed_bits)
return -EBUSY;

+ if (root->number_of_cgroups > 1) {
+ for_each_set_bit(i, &added_bits, CGROUP_SUBSYS_COUNT)
+ if (!subsys[i]->can_bind)
+ return -EBUSY;
+
+ for_each_set_bit(i, &added_bits, CGROUP_SUBSYS_COUNT) {
+ BUG_ON(cgrp->subsys[i]);
+ BUG_ON(!dummytop->subsys[i]);
+ BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
+
+ cgrp->subsys[i] = dummytop->subsys[i];
+ cgrp->subsys[i]->cgroup = cgrp;
+ }
+
+ err = cgroup_walk_hierarchy(hierarchy_attach_css,
+ (void *)added_bits, cgrp);
+ if (err)
+ goto failed;
+
+ cgroup_walk_hierarchy(hierarchy_update_css_sets,
+ (void *)added_bits, cgrp);
+
/* Process each subsystem */
for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
struct cgroup_subsys *ss = subsys[i];
@@ -982,12 +1133,7 @@ static int rebind_subsystems(struct cgroupfs_root *root,
if (bit & added_bits) {
/* We're binding this subsystem to this hierarchy */
BUG_ON(ss == NULL);
- BUG_ON(cgrp->subsys[i]);
- BUG_ON(!dummytop->subsys[i]);
- BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
mutex_lock(&ss->hierarchy_mutex);
- cgrp->subsys[i] = dummytop->subsys[i];
- cgrp->subsys[i]->cgroup = cgrp;
list_move(&ss->sibling, &root->subsys_list);
ss->root = root;
if (ss->bind)
@@ -1000,10 +1146,10 @@ static int rebind_subsystems(struct cgroupfs_root *root,
BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
mutex_lock(&ss->hierarchy_mutex);
- if (ss->bind)
- ss->bind(ss, dummytop);
dummytop->subsys[i]->cgroup = dummytop;
cgrp->subsys[i] = NULL;
+ if (ss->bind)
+ ss->bind(ss, dummytop);
subsys[i]->root = &rootnode;
list_move(&ss->sibling, &rootnode.subsys_list);
mutex_unlock(&ss->hierarchy_mutex);
@@ -1030,6 +1176,12 @@ static int rebind_subsystems(struct cgroupfs_root *root,
synchronize_rcu();

return 0;
+
+failed:
+ for_each_set_bit(i, &added_bits, CGROUP_SUBSYS_COUNT)
+ cgrp->subsys[i] = NULL;
+
+ return err;
}

static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
@@ -1285,6 +1437,7 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)

/* (re)populate subsystem files */
cgroup_populate_dir(cgrp);
+ cgroup_walk_hierarchy(hierarchy_populate_dir, NULL, cgrp);

if (opts.release_agent)
strcpy(root->release_agent_path, opts.release_agent);
@@ -3313,20 +3466,6 @@ static int cgroup_populate_dir(struct cgroup *cgrp)
return 0;
}

-static void init_cgroup_css(struct cgroup_subsys_state *css,
- struct cgroup_subsys *ss,
- struct cgroup *cgrp)
-{
- css->cgroup = cgrp;
- atomic_set(&css->refcnt, 1);
- css->flags = 0;
- css->id = NULL;
- if (cgrp == dummytop)
- set_bit(CSS_ROOT, &css->flags);
- BUG_ON(cgrp->subsys[ss->subsys_id]);
- cgrp->subsys[ss->subsys_id] = css;
-}
-
static void cgroup_lock_hierarchy(struct cgroupfs_root *root)
{
/* We need to take each hierarchy_mutex in a consistent order */
--
1.7.0.1


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