[PATCH] rtmutex: Propagate priority settings into PI lock chains

When the priority of a task, which is blocked on a lock, changes we must
propagate this change into the PI lock chain.  Therefor the chain walk code
is changed to get rid of the references to current to avoid false positives
in the deadlock detector, as setscheduler might be called by a task which
holds the lock on which the task whose priority is changed is blocked.

Also add some comments about the get/put_task_struct usage to avoid
confusion.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 38 insertions, 6 deletions

diff --git a/kernel/rtmutex.c b/kernel/rtmutex.c
index 3fc0f06..45d6101 100644
--- a/kernel/rtmutex.c
+++ b/kernel/rtmutex.c
@@ -160,7 +160,8 @@ int max_lock_depth = 1024;
 static int rt_mutex_adjust_prio_chain(task_t *task,
 				      int deadlock_detect,
 				      struct rt_mutex *orig_lock,
-				      struct rt_mutex_waiter *orig_waiter
+				      struct rt_mutex_waiter *orig_waiter,
+				      struct task_struct *top_task
 				      __IP_DECL__)
 {
 	struct rt_mutex *lock;
@@ -189,7 +190,7 @@ static int rt_mutex_adjust_prio_chain(task_t *task,
 			prev_max = max_lock_depth;
 			printk(KERN_WARNING "Maximum lock depth %d reached "
 			       "task: %s (%d)\n", max_lock_depth,
-			       current->comm, current->pid);
+			       top_task->comm, top_task->pid);
 		}
 		put_task_struct(task);
 
@@ -229,7 +230,7 @@ static int rt_mutex_adjust_prio_chain(task_t *task,
 	}
 
 	/* Deadlock detection */
-	if (lock == orig_lock || rt_mutex_owner(lock) == current) {
+	if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
 		debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
 		spin_unlock(&lock->wait_lock);
 		ret = deadlock_detect ? -EDEADLK : 0;
@@ -433,6 +434,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 		__rt_mutex_adjust_prio(owner);
 		if (owner->pi_blocked_on) {
 			boost = 1;
+			/* gets dropped in rt_mutex_adjust_prio_chain()! */
 			get_task_struct(owner);
 		}
 		spin_unlock_irqrestore(&owner->pi_lock, flags);
@@ -441,6 +443,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 		spin_lock_irqsave(&owner->pi_lock, flags);
 		if (owner->pi_blocked_on) {
 			boost = 1;
+			/* gets dropped in rt_mutex_adjust_prio_chain()! */
 			get_task_struct(owner);
 		}
 		spin_unlock_irqrestore(&owner->pi_lock, flags);
@@ -450,8 +453,8 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 
 	spin_unlock(&lock->wait_lock);
 
-	res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock,
-					 waiter __IP__);
+	res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
+					 current __IP__);
 
 	spin_lock(&lock->wait_lock);
 
@@ -552,6 +555,7 @@ static void remove_waiter(struct rt_mutex *lock,
 
 		if (owner->pi_blocked_on) {
 			boost = 1;
+			/* gets dropped in rt_mutex_adjust_prio_chain()! */
 			get_task_struct(owner);
 		}
 		spin_unlock_irqrestore(&owner->pi_lock, flags);
@@ -564,12 +568,37 @@ static void remove_waiter(struct rt_mutex *lock,
 
 	spin_unlock(&lock->wait_lock);
 
-	rt_mutex_adjust_prio_chain(owner, 0, lock, NULL __IP__);
+	rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current __IP__);
 
 	spin_lock(&lock->wait_lock);
 }
 
 /*
+ * Recheck the pi chain, in case we got a priority setting
+ *
+ * Called from sched_setscheduler
+ */
+void rt_mutex_adjust_pi(struct task_struct *task)
+{
+	struct rt_mutex_waiter *waiter;
+	unsigned long flags;
+
+	spin_lock_irqsave(&task->pi_lock, flags);
+
+	waiter = task->pi_blocked_on;
+	if (!waiter || waiter->list_entry.prio == task->prio) {
+		spin_unlock_irqrestore(&task->pi_lock, flags);
+		return;
+	}
+
+	/* gets dropped in rt_mutex_adjust_prio_chain()! */
+	get_task_struct(task);
+	spin_unlock_irqrestore(&task->pi_lock, flags);
+
+	rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task __RET_IP__);
+}
+
+/*
  * Slow path lock function:
  */
 static int __sched
@@ -636,6 +665,7 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
 			if (unlikely(ret))
 				break;
 		}
+
 		spin_unlock(&lock->wait_lock);
 
 		debug_rt_mutex_print_deadlock(&waiter);
diff --git a/kernel/sched.c b/kernel/sched.c
index 7a30add..2629c17 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4070,6 +4070,8 @@ recheck:
 	__task_rq_unlock(rq);
 	spin_unlock_irqrestore(&p->pi_lock, flags);
 
+	rt_mutex_adjust_pi(p);
+
 	return 0;
 }
 EXPORT_SYMBOL_GPL(sched_setscheduler);