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, 5 insertions, 3 deletions

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index a5eecb1e5e4b..0b6a838e9e73 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1202,7 +1202,8 @@ struct sched_class {
 	 * tasks.
 	 */
 	struct task_struct * (*pick_next_task) (struct rq *rq,
-						struct task_struct *prev);
+						struct task_struct *prev,
+						struct pin_cookie cookie);
 	void (*put_prev_task) (struct rq *rq, struct task_struct *p);
 
 #ifdef CONFIG_SMP
@@ -1453,6 +1454,7 @@ static inline void sched_avg_update(struct rq *rq) { }
 
 struct rq_flags {
 	unsigned long flags;
+	struct pin_cookie cookie;
 };
 
 struct rq *__task_rq_lock(struct task_struct *p, struct rq_flags *rf)
@@ -1464,7 +1466,7 @@ struct rq *task_rq_lock(struct task_struct *p, struct rq_flags *rf)
 static inline void __task_rq_unlock(struct rq *rq, struct rq_flags *rf)
 	__releases(rq->lock)
 {
-	lockdep_unpin_lock(&rq->lock);
+	lockdep_unpin_lock(&rq->lock, rf->cookie);
 	raw_spin_unlock(&rq->lock);
 }
 
@@ -1473,7 +1475,7 @@ task_rq_unlock(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
 	__releases(rq->lock)
 	__releases(p->pi_lock)
 {
-	lockdep_unpin_lock(&rq->lock);
+	lockdep_unpin_lock(&rq->lock, rf->cookie);
 	raw_spin_unlock(&rq->lock);
 	raw_spin_unlock_irqrestore(&p->pi_lock, rf->flags);
 }