Re: [RFC] RT-patch update to remove the global pi_lock

[Steven Rostedt <rostedt@goodmis.org>]

OK, here it is. Against 2.6.13-rc7-rt1. 

Please, test it well. Make sure to turn off any debugging, especially
CONFIG_RT_DEADLOCK_DETECT.  Since that would use a global trace_lock
that defeats the purpose of removing the pi_lock.

The patch to remove the single pi_lock:

-- Steve

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Index: linux_realtime_goliath/kernel/rt.c
===================================================================
--- linux_realtime_goliath/kernel/rt.c	(revision 304)
+++ linux_realtime_goliath/kernel/rt.c	(working copy)
@@ -22,6 +22,9 @@
  *
  *  Copyright (C) 2005, Kihon Technologies Inc., Steven Rostedt
  *
+ *   (also by Steven Rostedt)
+ *    - Converted single pi_lock to individual task locks.
+ *
  */
 #include <linux/config.h>
 #include <linux/sched.h>
@@ -36,6 +39,26 @@
 #define CAPTURE_LOCK
 
 /*
+ * Lock order:
+ *
+ *  To keep from having a single lock for PI, each task and lock
+ *  has their own locking. The order is as follows:
+ *
+ * blocked task->pi_lock -> lock->wait_lock -> owner task->pi_lock.
+ * 
+ * This is safe since a owner task should never block on a lock that
+ * is owned by a blocking task.  Otherwise you would have a deadlock 
+ * in the normal system.
+ * The same goes for the locks. A lock held by one task, should not be
+ * taken by task that holds a lock that is blocking this lock's owner.
+ *
+ * A task that is about to grab a lock is first considered to be a 
+ * blocking task, even if the task successfully acquires the lock.
+ * This is because the taking of the locks happen before the
+ * task becomes the owner.
+ */
+
+/*
  * These flags are used for allowing of stealing of ownerships.
  */
 #define RT_PENDOWNER	1	/* pending owner on a lock */
@@ -83,14 +106,6 @@
  */
 //#define ALL_TASKS_PI
 
-/*
- * We need a global lock for priority inheritance handling.
- * This is only for the slow path, but still, we might want
- * to optimize it later to be more scalable.
- */
-static __cacheline_aligned_in_smp raw_spinlock_t pi_lock =
-						RAW_SPIN_LOCK_UNLOCKED;
-
 #ifdef CONFIG_RT_DEADLOCK_DETECT
 # define __EIP_DECL__ , unsigned long eip
 # define __EIP__ , eip
@@ -174,6 +189,8 @@
 	if (trace_on) {				\
 		trace_on = 0;			\
 		console_verbose();		\
+		if (spin_is_locked(&current->pi_lock)) \
+			__raw_spin_unlock(&current->pi_lock); \
 		spin_unlock(&trace_lock);	\
 	}					\
 } while (0)
@@ -228,7 +245,6 @@
  */
 void zap_rt_locks(void)
 {
-	spin_lock_init(&pi_lock);
 #ifdef CONFIG_RT_DEADLOCK_DETECT
 	spin_lock_init(&trace_lock);
 #endif
@@ -589,11 +605,11 @@
 			printk("exiting task is not even the owner??\n");
 		goto restart;
 	}
-	__raw_spin_lock(&pi_lock);
+	__raw_spin_lock(&task->pi_lock);
 	plist_for_each(curr1, &task->pi_waiters) {
 		w = plist_entry(curr1, struct rt_mutex_waiter, pi_list);
 		TRACE_OFF();
-		__raw_spin_unlock(&pi_lock);
+		__raw_spin_unlock(&task->pi_lock);
 		trace_unlock_irqrestore(&trace_lock, flags, ti);
 
 		printk("hm, PI interest held at exit time? Task:\n");
@@ -601,7 +617,7 @@
 		printk_waiter(w);
 		return;
 	}
-	__raw_spin_unlock(&pi_lock);
+	__raw_spin_unlock(&task->pi_lock);
 	trace_unlock_irqrestore(&trace_lock, flags, ti);
 }
 
@@ -674,6 +690,7 @@
 	struct rt_mutex_waiter *w;
 	struct plist *curr1;
 
+	__raw_spin_lock(&old_owner->task->pi_lock);
 	plist_for_each(curr1, &old_owner->task->pi_waiters) {
 		w = plist_entry(curr1, struct rt_mutex_waiter, pi_list);
 		if (w->lock == lock) {
@@ -682,9 +699,10 @@
 			printk_waiter(w);
 			printk("\n");
 			TRACE_WARN_ON(1);
-			return;
+			break;
 		}
 	}
+	__raw_spin_unlock(&old_owner->task->pi_lock);
 }
 
 #else
@@ -732,13 +750,24 @@
 
 int pi_walk, pi_null, pi_prio, pi_initialized;
 
-static void pi_setprio(struct rt_mutex *lock, struct task_struct *p, int prio)
+/*
+ * The lock->wait_lock and p->pi_lock must be held.
+ */
+static void pi_setprio(struct rt_mutex *lock, struct task_struct *task, int prio)
 {
+	struct rt_mutex *l = lock;
+	struct task_struct *p = task;
+	/*
+	 * We don't want to release the parameters locks.
+	 */
+
 	if (unlikely(!p->pid)) {
 		pi_null++;
 		return;
 	}
 
+	TRACE_BUG_ON_LOCKED(!spin_is_locked(&lock->wait_lock));
+	TRACE_BUG_ON_LOCKED(!spin_is_locked(&p->pi_lock));
 #ifdef CONFIG_RT_DEADLOCK_DETECT
 	pi_prio++;
 	if (p->policy != SCHED_NORMAL && prio > normal_prio(p)) {
@@ -759,7 +788,6 @@
 	 * If the task is blocked on some other task then boost that
 	 * other task (or tasks) too:
 	 */
-	__raw_spin_lock(&p->pi_lock);
 	for (;;) {
 		struct rt_mutex_waiter *w = p->blocked_on;
 #ifdef CONFIG_RT_DEADLOCK_DETECT
@@ -774,16 +802,27 @@
 		 * it RT, then register the task in the PI list and
 		 * requeue it to the wait list:
 		 */
-		lock = w->lock;
+
+		/*
+		 * Don't unlock the original lock->wait_lock
+		 */
+		if (l != lock)
+			__raw_spin_unlock(&l->wait_lock);
+		l = w->lock;
 		TRACE_BUG_ON_LOCKED(!lock);
-		TRACE_BUG_ON_LOCKED(!lock_owner(lock));
+
+		if (l != lock)
+			__raw_spin_lock(&l->wait_lock);
+
+		TRACE_BUG_ON_LOCKED(!lock_owner(l));
 		if (rt_task(p) && plist_empty(&w->pi_list)) {
+			TRACE_BUG_ON_LOCKED(was_rt);
 			plist_init(&w->pi_list, prio);
-			plist_add(&w->pi_list, &lock_owner(lock)->task->pi_waiters);
+			plist_add(&w->pi_list, &lock_owner(l)->task->pi_waiters);
 
-			plist_del(&w->list, &lock->wait_list);
+			plist_del(&w->list, &l->wait_list);
 			plist_init(&w->list, prio);
-			plist_add(&w->list, &lock->wait_list);
+			plist_add(&w->list, &l->wait_list);
 		}
 		/*
 		 * If the task is blocked on a lock, and we just restored
@@ -795,16 +834,18 @@
 		 */
 		if (!rt_task(p) && !plist_empty(&w->pi_list)) {
 			TRACE_BUG_ON_LOCKED(!was_rt);
-			plist_del(&w->pi_list, &lock_owner(lock)->task->pi_waiters);
-			plist_del(&w->list, &lock->wait_list);
+			plist_del(&w->pi_list, &lock_owner(l)->task->pi_waiters);
+			plist_del(&w->list, &l->wait_list);
 			plist_init(&w->list, prio);
-			plist_add(&w->list, &lock->wait_list);
+			plist_add(&w->list, &l->wait_list);
 		}
 
 		pi_walk++;
+		
+		if (p != task)
+			__raw_spin_unlock(&p->pi_lock);
 
-		__raw_spin_unlock(&p->pi_lock);
-		p = lock_owner(lock)->task;
+		p = lock_owner(l)->task;
 		TRACE_BUG_ON_LOCKED(!p);
 		__raw_spin_lock(&p->pi_lock);
 		/*
@@ -815,7 +856,10 @@
 		if (p->prio <= prio)
 			break;
 	}
-	__raw_spin_unlock(&p->pi_lock);
+	if (l != lock)
+		__raw_spin_unlock(&l->wait_lock);
+	if (p != task)
+		__raw_spin_unlock(&p->pi_lock);
 }
 
 /*
@@ -831,7 +875,9 @@
 	unsigned long flags;
 	int oldprio;
 
-	spin_lock_irqsave(&pi_lock, flags);
+	spin_lock_irqsave(&p->pi_lock,flags);
+	if (p->blocked_on)
+		spin_lock(&p->blocked_on->lock->wait_lock);
 
 	oldprio = p->normal_prio;
 	if (oldprio == prio)
@@ -858,10 +904,17 @@
 	else
 		mutex_setprio(p, prio);
  out:
-	spin_unlock_irqrestore(&pi_lock, flags);
+	if (p->blocked_on)
+		spin_unlock(&p->blocked_on->lock->wait_lock);
 
+	spin_unlock_irqrestore(&p->pi_lock, flags);
+
 }
 
+/*
+ * This is called with both the waiter->task->pi_lock and 
+ * lock->wait_lock held.
+ */
 static void
 task_blocks_on_lock(struct rt_mutex_waiter *waiter, struct thread_info *ti,
 		    struct rt_mutex *lock __EIP_DECL__)
@@ -872,7 +925,6 @@
 	/* mark the current thread as blocked on the lock */
 	waiter->eip = eip;
 #endif
-	__raw_spin_lock(&task->pi_lock);
 	task->blocked_on = waiter;
 	waiter->lock = lock;
 	waiter->ti = ti;
@@ -884,31 +936,24 @@
 	if (!rt_task(task)) {
 		plist_add(&waiter->list, &lock->wait_list);
 		set_lock_owner_pending(lock);
-		__raw_spin_unlock(&task->pi_lock);
 		return;
 	}
 #endif
-	__raw_spin_unlock(&task->pi_lock);
-	__raw_spin_lock(&pi_lock);
+	plist_add(&waiter->pi_list, &lock_owner(lock)->task->pi_waiters);
 	/*
-	 * We could have been added to the pi list from another task
-	 * doing a pi_setprio.
+	 * Add RT tasks to the head:
 	 */
-	if (likely(plist_empty(&waiter->pi_list))) {
-		plist_add(&waiter->pi_list, &lock_owner(lock)->task->pi_waiters);
-		/*
-		 * Add RT tasks to the head:
-		 */
-		plist_add(&waiter->list, &lock->wait_list);
-	}
+	plist_add(&waiter->list, &lock->wait_list);
 	set_lock_owner_pending(lock);
 	/*
 	 * If the waiter has higher priority than the owner
 	 * then temporarily boost the owner:
 	 */
-	if (task->prio < lock_owner(lock)->task->prio)
+	if (task->prio < lock_owner(lock)->task->prio) {
+		__raw_spin_lock(&lock_owner(lock)->task->pi_lock);
 		pi_setprio(lock, lock_owner(lock)->task, task->prio);
-	__raw_spin_unlock(&pi_lock);
+		__raw_spin_unlock(&lock_owner(lock)->task->pi_lock);
+	}
 }
 
 /*
@@ -942,6 +987,10 @@
 }
 EXPORT_SYMBOL(__init_rwsem);
 
+/*
+ * This must be called with both the old_owner and new_owner pi_locks held.
+ * As well as the lock->wait_lock.
+ */
 static inline
 void set_new_owner(struct rt_mutex *lock, struct thread_info *old_owner,
 			struct thread_info *new_owner __EIP_DECL__)
@@ -975,6 +1024,8 @@
 /*
  * handle the lock release when processes blocked on it that can now run
  * - the spinlock must be held by the caller
+ *
+ * The lock->wait_lock must be held, and the lock's owner->pi_lock must not.
  */
 static struct thread_info *
 pick_new_owner(struct rt_mutex *lock, struct thread_info *old_owner,
@@ -990,14 +1041,34 @@
 	 */
 	waiter = plist_first_entry(&lock->wait_list, struct rt_mutex_waiter, list);
 
+ try_again:
 	trace_special_pid(waiter->ti->task->pid, waiter->ti->task->prio, 0);
 
 #ifdef ALL_TASKS_PI
 	check_pi_list_present(lock, waiter, old_owner);
 #endif
 	new_owner = waiter->ti;
+	/*
+	 * The new owner is still blocked on this lock, so we
+	 * must release the lock->wait_lock before grabing 
+	 * the new_owner lock.
+	 */
+	__raw_spin_unlock(&lock->wait_lock);
+	__raw_spin_lock(&new_owner->task->pi_lock);
+	__raw_spin_lock(&lock->wait_lock);
+	/*
+	 * In this split second of releasing the lock, a high priority 
+	 * process could have come along and blocked as well.
+	 */
+	waiter = plist_first_entry(&lock->wait_list, struct rt_mutex_waiter, list);
+	if (unlikely(waiter->ti != new_owner)) {
+		__raw_spin_unlock(&new_owner->task->pi_lock);
+		goto try_again;
+	}
 	plist_del_init(&waiter->list, &lock->wait_list);
 
+	__raw_spin_lock(&old_owner->task->pi_lock);
+
 	plist_del(&waiter->pi_list, &old_owner->task->pi_waiters);
 	plist_init(&waiter->pi_list, waiter->ti->task->prio);
 
@@ -1008,6 +1079,9 @@
 	new_owner->task->blocked_on = NULL;
 	TRACE_WARN_ON(save_state != lock->save_state);
 
+	__raw_spin_unlock(&old_owner->task->pi_lock);
+	__raw_spin_unlock(&new_owner->task->pi_lock);
+
 	return new_owner;
 }
 
@@ -1060,9 +1134,7 @@
 	 * is still sleeping and hasn't woken up to get the lock.
 	 */
 
-	/* Test the simple case first, is it already running? */
-	if (!TASK_PENDING(owner))
-		return 0;
+	TRACE_BUG_ON_LOCKED(!owner);
 
 	/* The owner is pending on a lock, but is it this lock? */
 	if (owner->pending_owner != lock)
@@ -1134,17 +1206,35 @@
 		return 0;
 
 	trace_lock_irqsave(&trace_lock, flags, ti);
+	/*
+	 * We are no longer blocked on the lock, so we are considered a
+	 * owner. So we must grab the lock->wait_lock first.
+	 */
 	__raw_spin_lock(&lock->wait_lock);
+	__raw_spin_lock(&task->pi_lock);
 
 	if (!(task->rt_flags & RT_PENDOWNER)) {
-		/* someone else stole it */
+		/*
+		 * Someone else stole it.
+		 * We are grabbing a lock now, so we must release the
+		 * locks again and retake them in the opposite order.
+		 */
+		__raw_spin_unlock(&task->pi_lock);
+		__raw_spin_unlock(&lock->wait_lock);
+
+		__raw_spin_lock(&task->pi_lock);
+		__raw_spin_lock(&lock->wait_lock);
+
 		old_owner = lock_owner(lock);
 		TRACE_BUG_ON_LOCKED(old_owner == ti);
 		if (likely(!old_owner) || __grab_lock(lock, task, old_owner->task)) {
 			/* we got it back! */
-			__raw_spin_lock(&pi_lock);
-			set_new_owner(lock, old_owner, ti __W_EIP__(waiter));
-			__raw_spin_unlock(&pi_lock);
+			if (old_owner) {
+				__raw_spin_lock(&old_owner->task->pi_lock);
+				set_new_owner(lock, old_owner, ti __W_EIP__(waiter));
+				__raw_spin_unlock(&old_owner->task->pi_lock);
+			} else
+				set_new_owner(lock, old_owner, ti __W_EIP__(waiter));
 			ret = 0;
 		} else {
 			/* Add ourselves back to the list */
@@ -1159,6 +1249,7 @@
 	}
 
 	__raw_spin_unlock(&lock->wait_lock);
+	__raw_spin_unlock(&task->pi_lock);
 	trace_unlock_irqrestore(&trace_lock, flags, ti);
 
 	return ret;
@@ -1196,6 +1287,7 @@
 
 	trace_lock_irqsave(&trace_lock, flags, ti);
 	TRACE_BUG_ON_LOCKED(!raw_irqs_disabled());
+	__raw_spin_lock(&task->pi_lock);
 	__raw_spin_lock(&lock->wait_lock);
 	INIT_WAITER(&waiter);
 
@@ -1205,10 +1297,14 @@
 	if (likely(!old_owner) || __grab_lock(lock, task, old_owner->task)) {
 		/* granted */
 		TRACE_WARN_ON_LOCKED(!plist_empty(&lock->wait_list) && !old_owner);
-		__raw_spin_lock(&pi_lock);
-		set_new_owner(lock, old_owner, ti __EIP__);
-		__raw_spin_unlock(&pi_lock);
+		if (old_owner) {
+			__raw_spin_lock(&old_owner->task->pi_lock);
+			set_new_owner(lock, old_owner, ti __EIP__);
+			__raw_spin_unlock(&old_owner->task->pi_lock);
+		} else
+			set_new_owner(lock, old_owner, ti __EIP__);
 		__raw_spin_unlock(&lock->wait_lock);
+		__raw_spin_unlock(&task->pi_lock);
 		trace_unlock_irqrestore(&trace_lock, flags, ti);
 
 		FREE_WAITER(&waiter);
@@ -1223,6 +1319,7 @@
 	TRACE_BUG_ON_LOCKED(!raw_irqs_disabled());
 	/* we don't need to touch the lock struct anymore */
 	__raw_spin_unlock(&lock->wait_lock);
+	__raw_spin_unlock(&task->pi_lock);
 	trace_unlock_irqrestore(&trace_lock, flags, ti);
 
 	might_sleep();
@@ -1273,6 +1370,7 @@
 
 	trace_lock_irqsave(&trace_lock, flags, ti);
 	TRACE_BUG_ON_LOCKED(!raw_irqs_disabled());
+	__raw_spin_lock(&task->pi_lock);
 	__raw_spin_lock(&lock->wait_lock);
 	INIT_WAITER(&waiter);
 
@@ -1282,10 +1380,14 @@
 	if (likely(!old_owner) || __grab_lock(lock, task, old_owner->task)) {
 		/* granted */
 		TRACE_WARN_ON_LOCKED(!plist_empty(&lock->wait_list) && !old_owner);
-		__raw_spin_lock(&pi_lock);
-		set_new_owner(lock, old_owner, ti __EIP__);
-		__raw_spin_unlock(&pi_lock);
+		if (old_owner) {
+			__raw_spin_lock(&old_owner->task->pi_lock);
+			set_new_owner(lock, old_owner, ti __EIP__);
+			__raw_spin_unlock(&old_owner->task->pi_lock);
+		} else
+			set_new_owner(lock, old_owner, ti __EIP__);
 		__raw_spin_unlock(&lock->wait_lock);
+		__raw_spin_unlock(&task->pi_lock);
 		trace_unlock_irqrestore(&trace_lock, flags, ti);
 
 		FREE_WAITER(&waiter);
@@ -1306,6 +1408,7 @@
 
 	/* we don't need to touch the lock struct anymore */
 	__raw_spin_unlock(&lock->wait_lock);
+	__raw_spin_unlock(&task->pi_lock);
 	trace_unlock(&trace_lock, ti);
 
 	/*
@@ -1396,7 +1499,6 @@
 	TRACE_WARN_ON_LOCKED(list_empty(&lock->held_list));
 	list_del_init(&lock->held_list);
 #endif
-	__raw_spin_lock(&pi_lock);
 
 #ifdef ALL_TASKS_PI
 	if (plist_empty(&lock->wait_list))
@@ -1409,7 +1511,6 @@
 			__up_mutex_waiter_nosavestate(lock __EIP__);
 	} else
 		lock->owner = NULL;
-	__raw_spin_unlock(&pi_lock);
 	__raw_spin_unlock(&lock->wait_lock);
 #ifdef CONFIG_DEBUG_PREEMPT
 	if (current->lock_count < 0 || current->lock_count >= MAX_LOCK_STACK) {
@@ -1640,6 +1741,7 @@
 
 	trace_lock_irqsave(&trace_lock, flags, ti);
 	TRACE_BUG_ON_LOCKED(!raw_irqs_disabled());
+	__raw_spin_lock(&task->pi_lock);
 	__raw_spin_lock(&lock->wait_lock);
 	INIT_WAITER(&waiter);
 
@@ -1649,10 +1751,14 @@
 	if (likely(!old_owner) || __grab_lock(lock, task, old_owner->task)) {
 		/* granted */
 		TRACE_WARN_ON_LOCKED(!plist_empty(&lock->wait_list) && !old_owner);
-		__raw_spin_lock(&pi_lock);
-		set_new_owner(lock, old_owner, ti __EIP__);
-		__raw_spin_unlock(&pi_lock);
+		if (old_owner) {
+			__raw_spin_lock(&old_owner->task->pi_lock);
+			set_new_owner(lock, old_owner, ti __EIP__);
+			__raw_spin_unlock(&old_owner->task->pi_lock);
+		} else
+			set_new_owner(lock, old_owner, ti __EIP__);
 		__raw_spin_unlock(&lock->wait_lock);
+		__raw_spin_unlock(&task->pi_lock);
 		trace_unlock_irqrestore(&trace_lock, flags, ti);
 
 		FREE_WAITER(&waiter);
@@ -1667,6 +1773,7 @@
 	TRACE_BUG_ON_LOCKED(!raw_irqs_disabled());
 	/* we don't need to touch the lock struct anymore */
 	__raw_spin_unlock(&lock->wait_lock);
+	__raw_spin_unlock(&task->pi_lock);
 	trace_unlock_irqrestore(&trace_lock, flags, ti);
 
 	might_sleep();
@@ -1684,6 +1791,7 @@
 			 * didnt get the lock - else return success:
 			 */
 			trace_lock_irq(&trace_lock, ti);
+			__raw_spin_lock(&task->pi_lock);
 			__raw_spin_lock(&lock->wait_lock);
 			if (waiter.ti) {
 				plist_del_init(&waiter.list, &lock->wait_list);
@@ -1692,17 +1800,16 @@
 				 * (No big problem if our PI effect lingers
 				 *  a bit - owner will restore prio.)
 				 */
-				__raw_spin_lock(&pi_lock);
 				TRACE_WARN_ON_LOCKED(waiter.ti != ti);
 				TRACE_WARN_ON_LOCKED(current->blocked_on != &waiter);
 				plist_del(&waiter.pi_list, &task->pi_waiters);
 				plist_init(&waiter.pi_list, task->prio);
 				waiter.ti = NULL;
 				current->blocked_on = NULL;
-				__raw_spin_unlock(&pi_lock);
 				ret = -EINTR;
 			}
 			__raw_spin_unlock(&lock->wait_lock);
+			__raw_spin_unlock(&task->pi_lock);
 			trace_unlock_irq(&trace_lock, ti);
 			break;
 		}
@@ -1741,6 +1848,7 @@
 
 	trace_lock_irqsave(&trace_lock, flags, ti);
 	TRACE_BUG_ON_LOCKED(!raw_irqs_disabled());
+	__raw_spin_lock(&task->pi_lock);
 	__raw_spin_lock(&lock->wait_lock);
 
 	old_owner = lock_owner(lock);
@@ -1749,13 +1857,18 @@
 	if (likely(!old_owner) || __grab_lock(lock, task, old_owner->task)) {
 		/* granted */
 		TRACE_WARN_ON_LOCKED(!plist_empty(&lock->wait_list) && !old_owner);
-		__raw_spin_lock(&pi_lock);
-		set_new_owner(lock, old_owner, ti __EIP__);
-		__raw_spin_unlock(&pi_lock);
+		if (old_owner) {
+			__raw_spin_lock(&old_owner->task->pi_lock);
+			set_new_owner(lock, old_owner, ti __EIP__);
+			__raw_spin_unlock(&old_owner->task->pi_lock);
+		} else
+			set_new_owner(lock, old_owner, ti __EIP__);
+		__raw_spin_unlock(&lock->wait_lock);
+		__raw_spin_unlock(&task->pi_lock);
 		ret = 1;
 	}
-
 	__raw_spin_unlock(&lock->wait_lock);
+	__raw_spin_unlock(&task->pi_lock);
 	trace_unlock_irqrestore(&trace_lock, flags, ti);
 
 	return ret;
@@ -1817,6 +1930,7 @@
 	 * to the previous priority (or to the next highest prio
 	 * waiter's priority):
 	 */
+	__raw_spin_lock(&old_owner->pi_lock);
 	prio = old_owner->normal_prio;
 	if (unlikely(!plist_empty(&old_owner->pi_waiters))) {
 		w = plist_first_entry(&old_owner->pi_waiters, struct rt_mutex_waiter, pi_list);
@@ -1825,6 +1939,7 @@
 	}
 	if (unlikely(prio != old_owner->prio))
 		pi_setprio(lock, old_owner, prio);
+	__raw_spin_unlock(&old_owner->pi_lock);
 #ifdef CAPTURE_LOCK
 	if (lock != &kernel_sem.lock) {
 		new_owner->rt_flags |= RT_PENDOWNER;
@@ -1851,6 +1966,7 @@
 	 * to the previous priority (or to the next highest prio
 	 * waiter's priority):
 	 */
+	__raw_spin_lock(&old_owner->pi_lock);
 	prio = old_owner->normal_prio;
 	if (unlikely(!plist_empty(&old_owner->pi_waiters))) {
 		w = plist_first_entry(&old_owner->pi_waiters, struct rt_mutex_waiter, pi_list);
@@ -1859,6 +1975,7 @@
 	}
 	if (unlikely(prio != old_owner->prio))
 		pi_setprio(lock, old_owner, prio);
+	__raw_spin_unlock(&old_owner->pi_lock);
 #ifdef CAPTURE_LOCK
 	if (lock != &kernel_sem.lock) {
 		new_owner->rt_flags |= RT_PENDOWNER;




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