timers: split process wide cpu clocks/timers, fix

To decrease the chance of a missed enable, always enable the timer when we
sample it, we'll always disable it when we find that there are no active timers
in the jiffy tick.

This fixes a flood of warnings reported by Mike Galbraith.

Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 15 insertions, 28 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 79392916d6c9..5d10fa0b6002 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2209,6 +2209,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
         unsigned long flags;
 
         spin_lock_irqsave(&cputimer->lock, flags);
+        cputimer->running = 1;
         *times = cputimer->cputime;
         spin_unlock_irqrestore(&cputimer->lock, flags);
 }
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index db107c9bbc05..e5d7bfdfa7d4 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -488,7 +488,7 @@ void posix_cpu_timers_exit_group(struct task_struct *tsk)
 {
         struct task_cputime cputime;
 
-        thread_group_cputime(tsk, &cputime);
+        thread_group_cputimer(tsk, &cputime);
         cleanup_timers(tsk->signal->cpu_timers,
                        cputime.utime, cputime.stime, cputime.sum_exec_runtime);
 }
@@ -507,29 +507,6 @@ static void clear_dead_task(struct k_itimer *timer, union cpu_time_count now)
 }
 
 /*
- * Enable the process wide cpu timer accounting.
- *
- * serialized using ->sighand->siglock
- */
-static void start_process_timers(struct task_struct *tsk)
-{
-        tsk->signal->cputimer.running = 1;
-        barrier();
-}
-
-/*
- * Release the process wide timer accounting -- timer stops ticking when
- * nobody cares about it.
- *
- * serialized using ->sighand->siglock
- */
-static void stop_process_timers(struct task_struct *tsk)
-{
-        tsk->signal->cputimer.running = 0;
-        barrier();
-}
-
-/*
  * Insert the timer on the appropriate list before any timers that
  * expire later.  This must be called with the tasklist_lock held
  * for reading, and interrupts disabled.
@@ -549,9 +526,6 @@ static void arm_timer(struct k_itimer *timer, union cpu_time_count now)
         BUG_ON(!irqs_disabled());
         spin_lock(&p->sighand->siglock);
 
-        if (!CPUCLOCK_PERTHREAD(timer->it_clock))
-                start_process_timers(p);
-
         listpos = head;
         if (CPUCLOCK_WHICH(timer->it_clock) == CPUCLOCK_SCHED) {
                 list_for_each_entry(next, head, entry) {
@@ -1021,6 +995,19 @@ static void check_thread_timers(struct task_struct *tsk,
         }
 }
 
+static void stop_process_timers(struct task_struct *tsk)
+{
+        struct thread_group_cputimer *cputimer = &tsk->signal->cputimer;
+        unsigned long flags;
+
+        if (!cputimer->running)
+                return;
+
+        spin_lock_irqsave(&cputimer->lock, flags);
+        cputimer->running = 0;
+        spin_unlock_irqrestore(&cputimer->lock, flags);
+}
+
 /*
  * Check for any per-thread CPU timers that have fired and move them
  * off the tsk->*_timers list onto the firing list.  Per-thread timers
@@ -1427,7 +1414,6 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
         struct list_head *head;
 
         BUG_ON(clock_idx == CPUCLOCK_SCHED);
-        start_process_timers(tsk);
         cpu_timer_sample_group(clock_idx, tsk, &now);
 
         if (oldval) {