Merge branch 'for_linus' of git://cavan.codon.org.uk/platform-drivers-x86

[cascardo/linux.git] / kernel / cgroup_freezer.c

diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 6c3154e..2bc4a22 100644 (file)
--- 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,