timers: fix TIMER_ABSTIME for process wide cpu timers

The POSIX timer interface allows for absolute time expiry values through the
TIMER_ABSTIME flag, therefore we have to synchronize the timer to the clock
every time we start it.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 34 insertions, 0 deletions

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index e5d7bfdfa7d4..2313a4cc14ea 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -261,6 +261,40 @@ out:
         rcu_read_unlock();
 }
 
+static void update_gt_cputime(struct task_cputime *a, struct task_cputime *b)
+{
+        if (cputime_gt(b->utime, a->utime))
+                a->utime = b->utime;
+
+        if (cputime_gt(b->stime, a->stime))
+                a->stime = b->stime;
+
+        if (b->sum_exec_runtime > a->sum_exec_runtime)
+                a->sum_exec_runtime = b->sum_exec_runtime;
+}
+
+void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
+{
+        struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+        struct task_cputime sum;
+        unsigned long flags;
+
+        spin_lock_irqsave(&cputimer->lock, flags);
+        if (!cputimer->running) {
+                cputimer->running = 1;
+                /*
+                 * The POSIX timer interface allows for absolute time expiry
+                 * values through the TIMER_ABSTIME flag, therefore we have
+                 * to synchronize the timer to the clock every time we start
+                 * it.
+                 */
+                thread_group_cputime(tsk, &sum);
+                update_gt_cputime(&cputimer->cputime, &sum);
+        }
+        *times = cputimer->cputime;
+        spin_unlock_irqrestore(&cputimer->lock, flags);
+}
+
 /*
  * Sample a process (thread group) clock for the given group_leader task.
  * Must be called with tasklist_lock held for reading.