Re: sig->cputimer.lock/rq->lock lockdep report

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

On Wed, 2011-10-12 at 23:13 +0300, Ari Savolainen wrote:
> I've got the same problem that Dave reported earlier. I bisected it to
> commit d670ec13178d "posix-cpu-timers: Cure SMP wobbles". 

https://lkml.org/lkml/2011/10/7/282

Does the below work for you? (still not proud of it)

---
 include/linux/sched.h     |    3 +++
 kernel/posix-cpu-timers.c |    6 +++++-
 kernel/sched_stats.h      |    4 ++--
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 41d0237..ad9eafc 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -503,6 +503,7 @@ struct task_cputime {
  * @running:		non-zero when there are timers running and
  * 			@cputime receives updates.
  * @lock:		lock for fields in this struct.
+ * @runtime_lock:	lock for cputime.sum_exec_runtime
  *
  * This structure contains the version of task_cputime, above, that is
  * used for thread group CPU timer calculations.
@@ -511,6 +512,7 @@ struct thread_group_cputimer {
 	struct task_cputime cputime;
 	int running;
 	spinlock_t lock;
+	spinlock_t runtime_lock;
 };
 
 #include <linux/rwsem.h>
@@ -2566,6 +2568,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times);
 static inline void thread_group_cputime_init(struct signal_struct *sig)
 {
 	spin_lock_init(&sig->cputimer.lock);
+	spin_lock_init(&sig->cputimer.runtime_lock);
 }
 
 /*
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index c8008dd..fa189a6 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -284,9 +284,13 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
 		 * it.
 		 */
 		thread_group_cputime(tsk, &sum);
+		spin_lock(&cputimer->runtime_lock);
 		update_gt_cputime(&cputimer->cputime, &sum);
-	}
+	} else
+		spin_lock(&cputimer->runtime_lock);
+
 	*times = cputimer->cputime;
+	spin_unlock(&cputimer->runtime_lock);
 	spin_unlock_irqrestore(&cputimer->lock, flags);
 }
 
diff --git a/kernel/sched_stats.h b/kernel/sched_stats.h
index 331e01b..a7e2c1a 100644
--- a/kernel/sched_stats.h
+++ b/kernel/sched_stats.h
@@ -330,7 +330,7 @@ static inline void account_group_exec_runtime(struct task_struct *tsk,
 	if (!cputimer->running)
 		return;
 
-	spin_lock(&cputimer->lock);
+	spin_lock(&cputimer->runtime_lock);
 	cputimer->cputime.sum_exec_runtime += ns;
-	spin_unlock(&cputimer->lock);
+	spin_unlock(&cputimer->runtime_lock);
 }