1 files changed, 23 insertions, 0 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 38c8654aaa96..c3ba31f210a9 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -107,13 +107,25 @@ extern unsigned long nr_iowait(void);
 
 #include <asm/processor.h>
 
+/*
+ * Task state bitmask. NOTE! These bits are also
+ * encoded in fs/proc/array.c: get_task_state().
+ *
+ * We have two separate sets of flags: task->state
+ * is about runnability, while task->exit_state are
+ * about the task exiting. Confusing, but this way
+ * modifying one set can't modify the other one by
+ * mistake.
+ */
 #define TASK_RUNNING            0
 #define TASK_INTERRUPTIBLE      1
 #define TASK_UNINTERRUPTIBLE    2
 #define TASK_STOPPED            4
 #define TASK_TRACED             8
+/* in tsk->exit_state */
 #define EXIT_ZOMBIE             16
 #define EXIT_DEAD               32
+/* in tsk->state again */
 #define TASK_NONINTERACTIVE     64
 
 #define __set_task_state(tsk, state_value)              \
@@ -121,6 +133,17 @@ extern unsigned long nr_iowait(void);
 #define set_task_state(tsk, state_value)                \
         set_mb((tsk)->state, (state_value))
 
+/*
+ * set_current_state() includes a barrier so that the write of current->state
+ * is correctly serialised wrt the caller's subsequent test of whether to
+ * actually sleep:
+ *
+ *      set_current_state(TASK_UNINTERRUPTIBLE);
+ *      if (do_i_need_to_sleep())
+ *              schedule();
+ *
+ * If the caller does not need such serialisation then use __set_current_state()
+ */
 #define __set_current_state(state_value)                        \
         do { current->state = (state_value); } while (0)
 #define set_current_state(state_value)          \