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-rw-r--r--kernel/cgroup_freezer.c40
1 files changed, 29 insertions, 11 deletions
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 6c3154e477f6..2bc4a2256444 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -52,7 +52,7 @@ static inline struct freezer *css_freezer(struct cgroup_subsys_state *css)
static inline struct freezer *task_freezer(struct task_struct *task)
{
- return css_freezer(task_css(task, freezer_subsys_id));
+ return css_freezer(task_css(task, freezer_cgrp_id));
}
static struct freezer *parent_freezer(struct freezer *freezer)
@@ -84,8 +84,6 @@ static const char *freezer_state_strs(unsigned int state)
return "THAWED";
};
-struct cgroup_subsys freezer_subsys;
-
static struct cgroup_subsys_state *
freezer_css_alloc(struct cgroup_subsys_state *parent_css)
{
@@ -189,7 +187,7 @@ static void freezer_attach(struct cgroup_subsys_state *new_css,
* current state before executing the following - !frozen tasks may
* be visible in a FROZEN cgroup and frozen tasks in a THAWED one.
*/
- cgroup_taskset_for_each(task, new_css, tset) {
+ cgroup_taskset_for_each(task, tset) {
if (!(freezer->state & CGROUP_FREEZING)) {
__thaw_task(task);
} else {
@@ -216,6 +214,16 @@ static void freezer_attach(struct cgroup_subsys_state *new_css,
}
}
+/**
+ * freezer_fork - cgroup post fork callback
+ * @task: a task which has just been forked
+ *
+ * @task has just been created and should conform to the current state of
+ * the cgroup_freezer it belongs to. This function may race against
+ * freezer_attach(). Losing to freezer_attach() means that we don't have
+ * to do anything as freezer_attach() will put @task into the appropriate
+ * state.
+ */
static void freezer_fork(struct task_struct *task)
{
struct freezer *freezer;
@@ -224,14 +232,26 @@ static void freezer_fork(struct task_struct *task)
freezer = task_freezer(task);
/*
- * The root cgroup is non-freezable, so we can skip the
- * following check.
+ * The root cgroup is non-freezable, so we can skip locking the
+ * freezer. This is safe regardless of race with task migration.
+ * If we didn't race or won, skipping is obviously the right thing
+ * to do. If we lost and root is the new cgroup, noop is still the
+ * right thing to do.
*/
if (!parent_freezer(freezer))
goto out;
+ /*
+ * Grab @freezer->lock and freeze @task after verifying @task still
+ * belongs to @freezer and it's freezing. The former is for the
+ * case where we have raced against task migration and lost and
+ * @task is already in a different cgroup which may not be frozen.
+ * This isn't strictly necessary as freeze_task() is allowed to be
+ * called spuriously but let's do it anyway for, if nothing else,
+ * documentation.
+ */
spin_lock_irq(&freezer->lock);
- if (freezer->state & CGROUP_FREEZING)
+ if (freezer == task_freezer(task) && (freezer->state & CGROUP_FREEZING))
freeze_task(task);
spin_unlock_irq(&freezer->lock);
out:
@@ -422,7 +442,7 @@ static void freezer_change_state(struct freezer *freezer, bool freeze)
}
static int freezer_write(struct cgroup_subsys_state *css, struct cftype *cft,
- const char *buffer)
+ char *buffer)
{
bool freeze;
@@ -473,13 +493,11 @@ static struct cftype files[] = {
{ } /* terminate */
};
-struct cgroup_subsys freezer_subsys = {
- .name = "freezer",
+struct cgroup_subsys freezer_cgrp_subsys = {
.css_alloc = freezer_css_alloc,
.css_online = freezer_css_online,
.css_offline = freezer_css_offline,
.css_free = freezer_css_free,
- .subsys_id = freezer_subsys_id,
.attach = freezer_attach,
.fork = freezer_fork,
.base_cftypes = files,