linux-kernel - Re: [patch 2/2] rtmutex: Detect changes in the pi lock chain

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Date:	Fri, 6 Jun 2014 11:48:59 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...nel.org>, Brad Mouring <bmouring@...com>
Subject: Re: [patch 2/2] rtmutex: Detect changes in the pi lock chain



hehe, I can almost follow this code :-)

How about something like this on top?

---
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -260,6 +260,11 @@ static void rt_mutex_adjust_prio(struct
  */
 int max_lock_depth = 1024;
 
+static inline struct rt_mutex *task_blocked_on(struct task_struct *p)
+{
+	return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
+}
+
 /*
  * Adjust the priority chain. Also used for deadlock detection.
  * Decreases task's usage by one - may thus free the task.
@@ -443,10 +448,7 @@ static int rt_mutex_adjust_prio_chain(st
 	 * blocked itself. If yes we store a pointer to the lock for
 	 * the lock chain change detection above.
 	 */
-	if (task->pi_blocked_on)
-		next_lock = task->pi_blocked_on->lock;
-	else
-		next_lock = NULL;
+	next_lock = task_blocked_on(task);
 
 	raw_spin_unlock_irqrestore(&task->pi_lock, flags);
 
@@ -569,7 +571,7 @@ static int task_blocks_on_rt_mutex(struc
 {
 	struct task_struct *owner = rt_mutex_owner(lock);
 	struct rt_mutex_waiter *top_waiter = waiter;
-	struct rt_mutex *next_lock = NULL;
+	struct rt_mutex *next_lock;
 	unsigned long flags;
 	int chain_walk, res;
 
@@ -614,8 +616,8 @@ static int task_blocks_on_rt_mutex(struc
 	} else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
 		chain_walk = 1;
 	}
-	if (owner->pi_blocked_on)
-		next_lock = owner->pi_blocked_on->lock;
+
+	next_lock = task_blocked_on(owner);
 
 	raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 	if (!chain_walk)
@@ -705,8 +707,7 @@ static void remove_waiter(struct rt_mute
 		}
 		__rt_mutex_adjust_prio(owner);
 
-		if (owner->pi_blocked_on)
-			next_lock = owner->pi_blocked_on->lock;
+		next_lock = task_blocked_on(owner);
 
 		raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
 	}

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