posix-cpu-timers: don't account cpu timer after stopped thread runtime accounting
When tsk->signal->cputimer->running is 1, signal->cputimer (i.e. per process
timer account) and tsk->sum_sched_runtime (i.e. per thread timer account)
increase at the same pace because update_curr() increases both accounting.
However, there is one exception. When thread exiting, __exit_signal() turns
over task's sum_shced_runtime to sig->sum_sched_runtime, but it doesn't stop
signal->cputimer accounting.
This inconsistency makes POSIX timer wake up too early. This patch fixes it.
Original-patch-by: Olivier Langlois <olivier@trillion01.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Olivier Langlois <olivier@trillion01.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 2ef90a5..71bac97 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -162,6 +162,39 @@
*/
/**
+ * 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.
*
* @tsk: Pointer to task structure.
@@ -176,7 +209,7 @@
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
- if (!cputimer->running)
+ if (!cputimer_running(tsk))
return;
raw_spin_lock(&cputimer->lock);
@@ -199,7 +232,7 @@
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
- if (!cputimer->running)
+ if (!cputimer_running(tsk))
return;
raw_spin_lock(&cputimer->lock);
@@ -222,7 +255,7 @@
{
struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
- if (!cputimer->running)
+ if (!cputimer_running(tsk))
return;
raw_spin_lock(&cputimer->lock);
