1 files changed, 42 insertions, 8 deletions

diff --git a/include/linux/freezer.h b/include/linux/freezer.h
index d09af4b67cf1..ee899329e65a 100644
--- a/include/linux/freezer.h
+++ b/include/linux/freezer.h
@@ -75,28 +75,62 @@ static inline bool cgroup_freezing(struct task_struct *task)
  */
 
 
-/* Tell the freezer not to count the current task as freezable. */
+/**
+ * freezer_do_not_count - tell freezer to ignore %current
+ *
+ * Tell freezers to ignore the current task when determining whether the
+ * target frozen state is reached.  IOW, the current task will be
+ * considered frozen enough by freezers.
+ *
+ * The caller shouldn't do anything which isn't allowed for a frozen task
+ * until freezer_cont() is called.  Usually, freezer[_do_not]_count() pair
+ * wrap a scheduling operation and nothing much else.
+ */
 static inline void freezer_do_not_count(void)
 {
         current->flags |= PF_FREEZER_SKIP;
 }
 
-/*
- * Tell the freezer to count the current task as freezable again and try to
- * freeze it.
+/**
+ * freezer_count - tell freezer to stop ignoring %current
+ *
+ * Undo freezer_do_not_count().  It tells freezers that %current should be
+ * considered again and tries to freeze if freezing condition is already in
+ * effect.
  */
 static inline void freezer_count(void)
 {
         current->flags &= ~PF_FREEZER_SKIP;
+        /*
+         * If freezing is in progress, the following paired with smp_mb()
+         * in freezer_should_skip() ensures that either we see %true
+         * freezing() or freezer_should_skip() sees !PF_FREEZER_SKIP.
+         */
+        smp_mb();
         try_to_freeze();
 }
 
-/*
- * Check if the task should be counted as freezable by the freezer
+/**
+ * freezer_should_skip - whether to skip a task when determining frozen
+ *                       state is reached
+ * @p: task in quesion
+ *
+ * This function is used by freezers after establishing %true freezing() to
+ * test whether a task should be skipped when determining the target frozen
+ * state is reached.  IOW, if this function returns %true, @p is considered
+ * frozen enough.
  */
-static inline int freezer_should_skip(struct task_struct *p)
+static inline bool freezer_should_skip(struct task_struct *p)
 {
-        return !!(p->flags & PF_FREEZER_SKIP);
+        /*
+         * The following smp_mb() paired with the one in freezer_count()
+         * ensures that either freezer_count() sees %true freezing() or we
+         * see cleared %PF_FREEZER_SKIP and return %false.  This makes it
+         * impossible for a task to slip frozen state testing after
+         * clearing %PF_FREEZER_SKIP.
+         */
+        smp_mb();
+        return p->flags & PF_FREEZER_SKIP;
 }
 
 /*