[RFC PATCH 2/5] cgroup: Change kernfs_node for directories to store cgroup_subsys_state

Brian Welty
2019-05-01T14:04:35Z

Change the kernfs_node.priv to store the cgroup_subsys_state (CSS) pointer
for directories, instead of storing cgroup pointer. This is done in order
to support files within the cgroup associated with devices. We require
of_css() to return the device-specific CSS pointer for these files.

Cc: cgroups@vger.kernel.org
Signed-off-by: Brian Welty <brian.welty@intel.com>
---
kernel/cgroup/cgroup-v1.c | 10 ++++----
kernel/cgroup/cgroup.c | 48 +++++++++++++++++----------------------
2 files changed, 27 insertions(+), 31 deletions(-)

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index c126b34fd4ff..4fa56cc2b99c 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -723,6 +723,7 @@ int proc_cgroupstats_show(struct seq_file *m, void *v)
int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
{
struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
+ struct cgroup_subsys_state *css;
struct cgroup *cgrp;
struct css_task_iter it;
struct task_struct *tsk;
@@ -740,12 +741,13 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
* @kn->priv is RCU safe. Let's do the RCU dancing.
*/
rcu_read_lock();
- cgrp = rcu_dereference(*(void __rcu __force **)&kn->priv);
- if (!cgrp || cgroup_is_dead(cgrp)) {
+ css = rcu_dereference(*(void __rcu __force **)&kn->priv);
+ if (!css || cgroup_is_dead(css->cgroup)) {
rcu_read_unlock();
mutex_unlock(&cgroup_mutex);
return -ENOENT;
}
+ cgrp = css->cgroup;
rcu_read_unlock();

css_task_iter_start(&cgrp->self, 0, &it);
@@ -851,7 +853,7 @@ void cgroup1_release_agent(struct work_struct *work)
static int cgroup1_rename(struct kernfs_node *kn, struct kernfs_node *new_parent,
const char *new_name_str)
{
- struct cgroup *cgrp = kn->priv;
+ struct cgroup_subsys_state *css = kn->priv;
int ret;

if (kernfs_type(kn) != KERNFS_DIR)
@@ -871,7 +873,7 @@ static int cgroup1_rename(struct kernfs_node *kn, struct kernfs_node *new_parent

ret = kernfs_rename(kn, new_parent, new_name_str);
if (!ret)
- TRACE_CGROUP_PATH(rename, cgrp);
+ TRACE_CGROUP_PATH(rename, css->cgroup);

mutex_unlock(&cgroup_mutex);

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 9b035e728941..1fe4fee502ea 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -595,12 +595,13 @@ static void cgroup_get_live(struct cgroup *cgrp)

struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
{
- struct cgroup *cgrp = of->kn->parent->priv;
+ struct cgroup_subsys_state *css = of->kn->parent->priv;
struct cftype *cft = of_cft(of);

- /* FIXME this needs updating to lookup device-specific CSS */
-
/*
+ * If the cft specifies a subsys and this is not a device file,
+ * then lookup the css, otherwise it is already correct.
+ *
* This is open and unprotected implementation of cgroup_css().
* seq_css() is only called from a kernfs file operation which has
* an active reference on the file. Because all the subsystem
@@ -608,10 +609,9 @@ struct cgroup_subsys_state *of_css(struct kernfs_open_file *of)
* the matching css from the cgroup's subsys table is guaranteed to
* be and stay valid until the enclosing operation is complete.
*/
- if (cft->ss)
- return rcu_dereference_raw(cgrp->subsys[cft->ss->id]);
- else
- return &cgrp->self;
+ if (cft->ss && !css->device)
+ css = rcu_dereference_raw(css->cgroup->subsys[cft->ss->id]);
+ return css;
}
EXPORT_SYMBOL_GPL(of_css);

@@ -1524,12 +1524,14 @@ static u16 cgroup_calc_subtree_ss_mask(u16 subtree_control, u16 this_ss_mask)
*/
void cgroup_kn_unlock(struct kernfs_node *kn)
{
+ struct cgroup_subsys_state *css;
struct cgroup *cgrp;

if (kernfs_type(kn) == KERNFS_DIR)
- cgrp = kn->priv;
+ css = kn->priv;
else
- cgrp = kn->parent->priv;
+ css = kn->parent->priv;
+ cgrp = css->cgroup;

mutex_unlock(&cgroup_mutex);

@@ -1556,12 +1558,14 @@ void cgroup_kn_unlock(struct kernfs_node *kn)
*/
struct cgroup *cgroup_kn_lock_live(struct kernfs_node *kn, bool drain_offline)
{
+ struct cgroup_subsys_state *css;
struct cgroup *cgrp;

if (kernfs_type(kn) == KERNFS_DIR)
- cgrp = kn->priv;
+ css = kn->priv;
else
- cgrp = kn->parent->priv;
+ css = kn->parent->priv;
+ cgrp = css->cgroup;

/*
* We're gonna grab cgroup_mutex which nests outside kernfs
@@ -1652,7 +1656,7 @@ static int cgroup_device_mkdir(struct cgroup_subsys_state *css)
if (WARN_ON_ONCE(ret >= CGROUP_FILE_NAME_MAX))
return 0;

- kn = kernfs_create_dir(cgrp->kn, name, cgrp->kn->mode, cgrp);
+ kn = kernfs_create_dir(cgrp->kn, name, cgrp->kn->mode, css);
if (IS_ERR(kn))
return PTR_ERR(kn);
css->device_kn = kn;
@@ -1662,7 +1666,7 @@ static int cgroup_device_mkdir(struct cgroup_subsys_state *css)
/* FIXME: prefix dev_name with bus_name for uniqueness? */
kn = kernfs_create_dir(css->device_kn,
dev_name(device_css->device),
- cgrp->kn->mode, cgrp);
+ cgrp->kn->mode, device_css);
if (IS_ERR(kn))
return PTR_ERR(kn);
/* FIXME: kernfs_get needed here? */
@@ -2025,7 +2029,7 @@ int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask)
root->kf_root = kernfs_create_root(kf_sops,
KERNFS_ROOT_CREATE_DEACTIVATED |
KERNFS_ROOT_SUPPORT_EXPORTOP,
- root_cgrp);
+ &root_cgrp->self);
if (IS_ERR(root->kf_root)) {
ret = PTR_ERR(root->kf_root);
goto exit_root_id;
@@ -3579,9 +3583,9 @@ static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
size_t nbytes, loff_t off)
{
struct cgroup_namespace *ns = current->nsproxy->cgroup_ns;
- struct cgroup *cgrp = of->kn->parent->priv;
+ struct cgroup_subsys_state *css = of_css(of);
struct cftype *cft = of->kn->priv;
- struct cgroup_subsys_state *css;
+ struct cgroup *cgrp = css->cgroup;
int ret;

/*
@@ -3598,16 +3602,6 @@ static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf,
if (cft->write)
return cft->write(of, buf, nbytes, off);

- /*
- * kernfs guarantees that a file isn't deleted with operations in
- * flight, which means that the matching css is and stays alive and
- * doesn't need to be pinned. The RCU locking is not necessary
- * either. It's just for the convenience of using cgroup_css().
- */
- rcu_read_lock();
- css = cgroup_css(cgrp, cft->ss);
- rcu_read_unlock();
-
if (cft->write_u64) {
unsigned long long v;
ret = kstrtoull(buf, 0, &v);
@@ -5262,7 +5256,7 @@ int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
}

/* create the directory */
- kn = kernfs_create_dir(parent->kn, name, mode, cgrp);
+ kn = kernfs_create_dir(parent->kn, name, mode, &cgrp->self);
if (IS_ERR(kn)) {
ret = PTR_ERR(kn);
goto out_destroy;
--
2.21.0

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