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Subject[PATCH 01/12] cgroup: update cgroup->subsys_mask to ->child_subsys_mask and restore cgroup_root->subsys_mask
Date
944196278d3d ("cgroup: move ->subsys_mask from cgroupfs_root to
cgroup") moved ->subsys_mask from cgroup_root to cgroup to prepare for
the unified hierarhcy; however, it turns out that carrying the
subsys_mask of the children in the parent, instead of itself, is a lot
more natural. This patch restores cgroup_root->subsys_mask and morphs
cgroup->subsys_mask into cgroup->child_subsys_mask.

* Uses of root->cgrp.subsys_mask are restored to root->subsys_mask.

* Remove automatic setting and clearing of cgrp->subsys_mask and
instead just inherit ->child_subsys_mask from the parent during
cgroup creation. Note that this doesn't affect any current
behaviors.

* Undo __kill_css() separation.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
include/linux/cgroup.h | 7 ++++--
kernel/cgroup.c | 64 +++++++++++++++++++++-----------------------------
2 files changed, 32 insertions(+), 39 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index c251585..1b5b2fe 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -173,8 +173,8 @@ struct cgroup {
*/
u64 serial_nr;

- /* The bitmask of subsystems attached to this cgroup */
- unsigned long subsys_mask;
+ /* the bitmask of subsystems enabled on the child cgroups */
+ unsigned long child_subsys_mask;

/* Private pointers for each registered subsystem */
struct cgroup_subsys_state __rcu *subsys[CGROUP_SUBSYS_COUNT];
@@ -282,6 +282,9 @@ enum {
struct cgroup_root {
struct kernfs_root *kf_root;

+ /* The bitmask of subsystems attached to this hierarchy */
+ unsigned long subsys_mask;
+
/* Unique id for this hierarchy. */
int hierarchy_id;

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 9fcdaa7..dd40679 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -529,7 +529,7 @@ static struct css_set *find_existing_css_set(struct css_set *old_cset,
* won't change, so no need for locking.
*/
for_each_subsys(ss, i) {
- if (root->cgrp.subsys_mask & (1UL << i)) {
+ if (root->subsys_mask & (1UL << i)) {
/* Subsystem is in this hierarchy. So we want
* the subsystem state from the new
* cgroup */
@@ -742,7 +742,7 @@ static void cgroup_destroy_root(struct cgroup_root *root)
BUG_ON(!list_empty(&cgrp->children));

/* Rebind all subsystems back to the default hierarchy */
- rebind_subsystems(&cgrp_dfl_root, cgrp->subsys_mask);
+ rebind_subsystems(&cgrp_dfl_root, root->subsys_mask);

/*
* Release all the links from cset_links to this hierarchy's
@@ -1050,8 +1050,11 @@ static int rebind_subsystems(struct cgroup_root *dst_root,
ss->root = dst_root;
css->cgroup = &dst_root->cgrp;

- src_root->cgrp.subsys_mask &= ~(1 << ssid);
- dst_root->cgrp.subsys_mask |= 1 << ssid;
+ src_root->subsys_mask &= ~(1 << ssid);
+ src_root->cgrp.child_subsys_mask &= ~(1 << ssid);
+
+ dst_root->subsys_mask |= 1 << ssid;
+ dst_root->cgrp.child_subsys_mask |= 1 << ssid;

if (ss->bind)
ss->bind(css);
@@ -1069,7 +1072,7 @@ static int cgroup_show_options(struct seq_file *seq,
int ssid;

for_each_subsys(ss, ssid)
- if (root->cgrp.subsys_mask & (1 << ssid))
+ if (root->subsys_mask & (1 << ssid))
seq_printf(seq, ",%s", ss->name);
if (root->flags & CGRP_ROOT_SANE_BEHAVIOR)
seq_puts(seq, ",sane_behavior");
@@ -1273,12 +1276,12 @@ static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data)
if (ret)
goto out_unlock;

- if (opts.subsys_mask != root->cgrp.subsys_mask || opts.release_agent)
+ if (opts.subsys_mask != root->subsys_mask || opts.release_agent)
pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n",
task_tgid_nr(current), current->comm);

- added_mask = opts.subsys_mask & ~root->cgrp.subsys_mask;
- removed_mask = root->cgrp.subsys_mask & ~opts.subsys_mask;
+ added_mask = opts.subsys_mask & ~root->subsys_mask;
+ removed_mask = root->subsys_mask & ~opts.subsys_mask;

/* Don't allow flags or name to change at remount */
if (((opts.flags ^ root->flags) & CGRP_ROOT_OPTION_MASK) ||
@@ -1535,7 +1538,7 @@ retry:
* subsystems) then they must match.
*/
if ((opts.subsys_mask || opts.none) &&
- (opts.subsys_mask != root->cgrp.subsys_mask)) {
+ (opts.subsys_mask != root->subsys_mask)) {
if (!name_match)
continue;
ret = -EBUSY;
@@ -3662,8 +3665,6 @@ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss)
cgroup_get(cgrp);
css_get(css->parent);

- cgrp->subsys_mask |= 1 << ss->id;
-
if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
parent->parent) {
pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
@@ -3784,13 +3785,15 @@ static long cgroup_create(struct cgroup *parent, const char *name,

/* let's create and online css's */
for_each_subsys(ss, ssid) {
- if (root->cgrp.subsys_mask & (1 << ssid)) {
+ if (parent->child_subsys_mask & (1 << ssid)) {
err = create_css(cgrp, ss);
if (err)
goto err_destroy;
}
}

+ cgrp->child_subsys_mask = parent->child_subsys_mask;
+
kernfs_activate(kn);

mutex_unlock(&cgroup_mutex);
@@ -3886,7 +3889,16 @@ static void css_killed_ref_fn(struct percpu_ref *ref)
queue_work(cgroup_destroy_wq, &css->destroy_work);
}

-static void __kill_css(struct cgroup_subsys_state *css)
+/**
+ * kill_css - destroy a css
+ * @css: css to destroy
+ *
+ * This function initiates destruction of @css by removing cgroup interface
+ * files and putting its base reference. ->css_offline() will be invoked
+ * asynchronously once css_tryget() is guaranteed to fail and when the
+ * reference count reaches zero, @css will be released.
+ */
+static void kill_css(struct cgroup_subsys_state *css)
{
lockdep_assert_held(&cgroup_tree_mutex);

@@ -3916,28 +3928,6 @@ static void __kill_css(struct cgroup_subsys_state *css)
}

/**
- * kill_css - destroy a css
- * @css: css to destroy
- *
- * This function initiates destruction of @css by removing cgroup interface
- * files and putting its base reference. ->css_offline() will be invoked
- * asynchronously once css_tryget() is guaranteed to fail and when the
- * reference count reaches zero, @css will be released.
- */
-static void kill_css(struct cgroup_subsys_state *css)
-{
- struct cgroup *cgrp = css->cgroup;
-
- lockdep_assert_held(&cgroup_tree_mutex);
-
- /* if already killed, noop */
- if (cgrp->subsys_mask & (1 << css->ss->id)) {
- cgrp->subsys_mask &= ~(1 << css->ss->id);
- __kill_css(css);
- }
-}
-
-/**
* cgroup_destroy_locked - the first stage of cgroup destruction
* @cgrp: cgroup to be destroyed
*
@@ -4149,7 +4139,7 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss)

BUG_ON(online_css(css));

- cgrp_dfl_root.cgrp.subsys_mask |= 1 << ss->id;
+ cgrp_dfl_root.subsys_mask |= 1 << ss->id;

mutex_unlock(&cgroup_mutex);
mutex_unlock(&cgroup_tree_mutex);
@@ -4306,7 +4296,7 @@ int proc_cgroup_show(struct seq_file *m, void *v)

seq_printf(m, "%d:", root->hierarchy_id);
for_each_subsys(ss, ssid)
- if (root->cgrp.subsys_mask & (1 << ssid))
+ if (root->subsys_mask & (1 << ssid))
seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
if (strlen(root->name))
seq_printf(m, "%sname=%s", count ? "," : "",
--
1.9.0


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