sched: Fix comment for sched_info_depart

[~andy/linux] / kernel / sched / stats.h

diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 17d7065c38721a3431e011642e8d6e634d10a40d..c7edee71bce8915f67a3b4427b7f305696834afb 100644 (file)
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -104,8 +104,9 @@ static inline void sched_info_queued(struct task_struct *t)
 }
 
 /*
- * Called when a process ceases being the active-running process, either
- * voluntarily or involuntarily.  Now we can calculate how long we ran.
+ * Called when a process ceases being the active-running process involuntarily
+ * due, typically, to expiring its time slice (this may also be called when
+ * switching to the idle task).  Now we can calculate how long we ran.
  * Also, if the process is still in the TASK_RUNNING state, call
  * sched_info_queued() to mark that it has now again started waiting on
  * the runqueue.
@@ -161,6 +162,39 @@ sched_info_switch(struct task_struct *prev, struct task_struct *next)
  * on CONFIG_SCHEDSTATS.
  */
 
+/**
+ * cputimer_running - return true if cputimer is running
+ *
+ * @tsk:       Pointer to target task.
+ */
+static inline bool cputimer_running(struct task_struct *tsk)
+
+{
+       struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+
+       if (!cputimer->running)
+               return false;
+
+       /*
+        * After we flush the task's sum_exec_runtime to sig->sum_sched_runtime
+        * in __exit_signal(), we won't account to the signal struct further
+        * cputime consumed by that task, even though the task can still be
+        * ticking after __exit_signal().
+        *
+        * In order to keep a consistent behaviour between thread group cputime
+        * and thread group cputimer accounting, lets also ignore the cputime
+        * elapsing after __exit_signal() in any thread group timer running.
+        *
+        * This makes sure that POSIX CPU clocks and timers are synchronized, so
+        * that a POSIX CPU timer won't expire while the corresponding POSIX CPU
+        * clock delta is behind the expiring timer value.
+        */
+       if (unlikely(!tsk->sighand))
+               return false;
+
+       return true;
+}
+
 /**
  * account_group_user_time - Maintain utime for a thread group.
  *
@@ -176,7 +210,7 @@ static inline void account_group_user_time(struct task_struct *tsk,
 {
        struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
 
-       if (!cputimer->running)
+       if (!cputimer_running(tsk))
                return;
 
        raw_spin_lock(&cputimer->lock);
@@ -199,7 +233,7 @@ static inline void account_group_system_time(struct task_struct *tsk,
 {
        struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
 
-       if (!cputimer->running)
+       if (!cputimer_running(tsk))
                return;
 
        raw_spin_lock(&cputimer->lock);
@@ -222,7 +256,7 @@ static inline void account_group_exec_runtime(struct task_struct *tsk,
 {
        struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
 
-       if (!cputimer->running)
+       if (!cputimer_running(tsk))
                return;
 
        raw_spin_lock(&cputimer->lock);