locking/lockdep, sched/core: Implement a better lock pinning scheme

The problem with the existing lock pinning is that each pin is of
value 1; this mean you can simply unpin if you know its pinned,
without having any extra information.

This scheme generates a random (16 bit) cookie for each pin and
requires this same cookie to unpin. This means you have to keep the
cookie in context.

No objsize difference for !LOCKDEP kernels.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 6 insertions, 5 deletions

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 738e3c84dfe1..ba53a87bb978 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -670,9 +670,9 @@ static enum hrtimer_restart dl_task_timer(struct hrtimer *timer)
 		 * Nothing relies on rq->lock after this, so its safe to drop
 		 * rq->lock.
 		 */
-		lockdep_unpin_lock(&rq->lock);
+		lockdep_unpin_lock(&rq->lock, rf.cookie);
 		push_dl_task(rq);
-		lockdep_pin_lock(&rq->lock);
+		lockdep_repin_lock(&rq->lock, rf.cookie);
 	}
 #endif
 
@@ -1125,7 +1125,8 @@ static struct sched_dl_entity *pick_next_dl_entity(struct rq *rq,
 	return rb_entry(left, struct sched_dl_entity, rb_node);
 }
 
-struct task_struct *pick_next_task_dl(struct rq *rq, struct task_struct *prev)
+struct task_struct *
+pick_next_task_dl(struct rq *rq, struct task_struct *prev, struct pin_cookie cookie)
 {
 	struct sched_dl_entity *dl_se;
 	struct task_struct *p;
@@ -1140,9 +1141,9 @@ struct task_struct *pick_next_task_dl(struct rq *rq, struct task_struct *prev)
 		 * disabled avoiding further scheduler activity on it and we're
 		 * being very careful to re-start the picking loop.
 		 */
-		lockdep_unpin_lock(&rq->lock);
+		lockdep_unpin_lock(&rq->lock, cookie);
 		pull_dl_task(rq);
-		lockdep_pin_lock(&rq->lock);
+		lockdep_repin_lock(&rq->lock, cookie);
 		/*
 		 * pull_rt_task() can drop (and re-acquire) rq->lock; this
 		 * means a stop task can slip in, in which case we need to