[RFC PATCH 03/11] kernel/locking: Add p->blocked_on wrapper

["Connor O'Brien" <connoro@google.com>]

From: Valentin Schneider <valentin.schneider@arm.com>

This lets us assert p->blocked_lock is held whenever we access
p->blocked_on.

XXX: just make a pointer return, so we can also check at get's.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
[fix conflicts]
Signed-off-by: Connor O'Brien <connoro@google.com>
---
 include/linux/sched.h  | 7 +++++++
 kernel/locking/mutex.c | 6 +++---
 2 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index bd995e66d7d6..379e4c052644 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2201,6 +2201,13 @@ static inline int rwlock_needbreak(rwlock_t *lock)
 #endif
 }
 
+static inline void set_task_blocked_on(struct task_struct *p, struct mutex *m)
+{
+	lockdep_assert_held(&p->blocked_lock);
+
+	p->blocked_on = m;
+}
+
 static __always_inline bool need_resched(void)
 {
 	return unlikely(tif_need_resched());
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index f05cd2d216c7..7800380219db 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -645,7 +645,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 			goto err_early_kill;
 	}
 
-	current->blocked_on = lock;
+	set_task_blocked_on(current, lock);
 	set_current_state(state);
 	trace_contention_begin(lock, LCB_F_MUTEX);
 	for (;;) {
@@ -686,7 +686,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 		/*
 		 * Gets reset by ttwu_runnable().
 		 */
-		current->blocked_on = lock;
+		set_task_blocked_on(current, lock);
 		set_current_state(state);
 		/*
 		 * Here we order against unlock; we must either see it change
@@ -720,7 +720,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 	}
 
 	__mutex_remove_waiter(lock, &waiter);
-	current->blocked_on = NULL;
+	set_task_blocked_on(current, NULL);
 
 	debug_mutex_free_waiter(&waiter);
 
-- 
2.38.0.rc1.362.ged0d419d3c-goog