[patch V3 6/7] rtmutex: Cleanup deadlock detector debug logic

[Thomas Gleixner <tglx@linutronix.de>]

[-- Attachment #1: rtmutex-cleanup-deadlock-detector-debug-logic.patch --]
[-- Type: text/plain, Size: 10852 bytes --]

The conditions under which deadlock detection is conducted are unclear
and undocumented.

Add constants instead of using 0/1 and provide a selection function
which hides the additional debug dependency from the calling code.

Add comments where needed.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/locking/rtmutex-debug.c  |    5 +-
 kernel/locking/rtmutex-debug.h  |    7 ++--
 kernel/locking/rtmutex.c        |   69 +++++++++++++++++++++++++++-------------
 kernel/locking/rtmutex.h        |    7 +++-
 kernel/locking/rtmutex_common.h |   15 ++++++++
 5 files changed, 75 insertions(+), 28 deletions(-)

Index: tip/kernel/locking/rtmutex-debug.c
===================================================================
--- tip.orig/kernel/locking/rtmutex-debug.c
+++ tip/kernel/locking/rtmutex-debug.c
@@ -66,12 +66,13 @@ void rt_mutex_debug_task_free(struct tas
  * the deadlock. We print when we return. act_waiter can be NULL in
  * case of a remove waiter operation.
  */
-void debug_rt_mutex_deadlock(int detect, struct rt_mutex_waiter *act_waiter,
+void debug_rt_mutex_deadlock(enum rtmutex_chainwalk chwalk,
+			     struct rt_mutex_waiter *act_waiter,
 			     struct rt_mutex *lock)
 {
 	struct task_struct *task;
 
-	if (!debug_locks || detect || !act_waiter)
+	if (!debug_locks || chwalk || !act_waiter)
 		return;
 
 	task = rt_mutex_owner(act_waiter->lock);
Index: tip/kernel/locking/rtmutex-debug.h
===================================================================
--- tip.orig/kernel/locking/rtmutex-debug.h
+++ tip/kernel/locking/rtmutex-debug.h
@@ -20,14 +20,15 @@ extern void debug_rt_mutex_unlock(struct
 extern void debug_rt_mutex_proxy_lock(struct rt_mutex *lock,
 				      struct task_struct *powner);
 extern void debug_rt_mutex_proxy_unlock(struct rt_mutex *lock);
-extern void debug_rt_mutex_deadlock(int detect, struct rt_mutex_waiter *waiter,
+extern void debug_rt_mutex_deadlock(enum rtmutex_chainwalk chwalk,
+				    struct rt_mutex_waiter *waiter,
 				    struct rt_mutex *lock);
 extern void debug_rt_mutex_print_deadlock(struct rt_mutex_waiter *waiter);
 # define debug_rt_mutex_reset_waiter(w)			\
 	do { (w)->deadlock_lock = NULL; } while (0)
 
-static inline int debug_rt_mutex_detect_deadlock(struct rt_mutex_waiter *waiter,
-						 int detect)
+static inline bool debug_rt_mutex_detect_deadlock(struct rt_mutex_waiterr *waiter,
+						  enum rtmutex_chainwalk walk)
 {
 	return (waiter != NULL);
 }
Index: tip/kernel/locking/rtmutex.c
===================================================================
--- tip.orig/kernel/locking/rtmutex.c
+++ tip/kernel/locking/rtmutex.c
@@ -256,6 +256,25 @@ static void rt_mutex_adjust_prio(struct
 }
 
 /*
+ * Deadlock detection is conditional:
+ *
+ * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
+ * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
+ *
+ * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
+ * conducted independent of the detect argument.
+ *
+ * If the waiter argument is NULL this indicates the deboost path and
+ * deadlock detection is disabled independent of the detect argument
+ * and the config settings.
+ */
+static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
+					  enum rtmutex_chainwalk chwalk)
+{
+	return debug_rt_mutex_detect_deadlock(waiter, chwalk);
+}
+
+/*
  * Max number of times we'll walk the boosting chain:
  */
 int max_lock_depth = 1024;
@@ -328,7 +347,7 @@ static inline struct rt_mutex *task_bloc
  *	goto again;
  */
 static int rt_mutex_adjust_prio_chain(struct task_struct *task,
-				      int deadlock_detect,
+				      enum rtmutex_chainwalk chwalk,
 				      struct rt_mutex *orig_lock,
 				      struct rt_mutex *next_lock,
 				      struct rt_mutex_waiter *orig_waiter,
@@ -336,12 +355,12 @@ static int rt_mutex_adjust_prio_chain(st
 {
 	struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
 	struct rt_mutex_waiter *prerequeue_top_waiter;
-	int detect_deadlock, ret = 0, depth = 0;
+	int ret = 0, depth = 0;
 	struct rt_mutex *lock;
+	bool detect_deadlock;
 	unsigned long flags;
 
-	detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
-							 deadlock_detect);
+	detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
 
 	/*
 	 * The (de)boosting is a step by step approach with a lot of
@@ -449,7 +468,7 @@ static int rt_mutex_adjust_prio_chain(st
 	 * walk, we detected a deadlock.
 	 */
 	if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
-		debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
+		debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
 		raw_spin_unlock(&lock->wait_lock);
 		ret = -EDEADLK;
 		goto out_unlock_pi;
@@ -659,7 +678,7 @@ static int try_to_take_rt_mutex(struct r
 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
 				   struct rt_mutex_waiter *waiter,
 				   struct task_struct *task,
-				   int detect_deadlock)
+				   enum rtmutex_chainwalk chwalk)
 {
 	struct task_struct *owner = rt_mutex_owner(lock);
 	struct rt_mutex_waiter *top_waiter = waiter;
@@ -705,7 +724,7 @@ static int task_blocks_on_rt_mutex(struc
 		__rt_mutex_adjust_prio(owner);
 		if (owner->pi_blocked_on)
 			chain_walk = 1;
-	} else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
+	} else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
 		chain_walk = 1;
 	}
 
@@ -730,7 +749,7 @@ static int task_blocks_on_rt_mutex(struc
 
 	raw_spin_unlock(&lock->wait_lock);
 
-	res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock,
+	res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
 					 next_lock, waiter, task);
 
 	raw_spin_lock(&lock->wait_lock);
@@ -813,7 +832,8 @@ static void remove_waiter(struct rt_mute
 
 	raw_spin_unlock(&lock->wait_lock);
 
-	rt_mutex_adjust_prio_chain(owner, 0, lock, next_lock, NULL, current);
+	rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
+				   next_lock, NULL, current);
 
 	raw_spin_lock(&lock->wait_lock);
 }
@@ -843,7 +863,8 @@ void rt_mutex_adjust_pi(struct task_stru
 	/* gets dropped in rt_mutex_adjust_prio_chain()! */
 	get_task_struct(task);
 
-	rt_mutex_adjust_prio_chain(task, 0, NULL, next_lock, NULL, task);
+	rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL, NULL,
+				   NULL, task);
 }
 
 /**
@@ -921,7 +942,7 @@ static void rt_mutex_handle_deadlock(int
 static int __sched
 rt_mutex_slowlock(struct rt_mutex *lock, int state,
 		  struct hrtimer_sleeper *timeout,
-		  int detect_deadlock)
+		  enum rtmutex_chainwalk chwalk)
 {
 	struct rt_mutex_waiter waiter;
 	int ret = 0;
@@ -947,7 +968,7 @@ rt_mutex_slowlock(struct rt_mutex *lock,
 			timeout->task = NULL;
 	}
 
-	ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
+	ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
 
 	if (likely(!ret))
 		ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
@@ -956,7 +977,7 @@ rt_mutex_slowlock(struct rt_mutex *lock,
 
 	if (unlikely(ret)) {
 		remove_waiter(lock, &waiter);
-		rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter);
+		rt_mutex_handle_deadlock(ret, chwalk, &waiter);
 	}
 
 	/*
@@ -1037,27 +1058,28 @@ static inline int
 rt_mutex_fastlock(struct rt_mutex *lock, int state,
 		  int (*slowfn)(struct rt_mutex *lock, int state,
 				struct hrtimer_sleeper *timeout,
-				int detect_deadlock))
+				enum rtmutex_chainwalk chwalk))
 {
 	if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 		rt_mutex_deadlock_account_lock(lock, current);
 		return 0;
 	} else
-		return slowfn(lock, state, NULL, 0);
+		return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
 }
 
 static inline int
 rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
-			struct hrtimer_sleeper *timeout, int detect_deadlock,
+			struct hrtimer_sleeper *timeout,
+			enum rtmutex_chainwalk chwalk,
 			int (*slowfn)(struct rt_mutex *lock, int state,
 				      struct hrtimer_sleeper *timeout,
-				      int detect_deadlock))
+				      enum rtmutex_chainwalk chwalk))
 {
-	if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
+	if (!chwalk && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
 		rt_mutex_deadlock_account_lock(lock, current);
 		return 0;
 	} else
-		return slowfn(lock, state, timeout, detect_deadlock);
+		return slowfn(lock, state, timeout, chwalk);
 }
 
 static inline int
@@ -1119,7 +1141,8 @@ int __rt_mutex_timed_lock(struct rt_mute
 {
 	might_sleep();
 
-	return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout, 0,
+	return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
+				       RT_MUTEX_FULL_CHAINWALK,
 				       rt_mutex_slowlock);
 }
 
@@ -1141,7 +1164,8 @@ rt_mutex_timed_lock(struct rt_mutex *loc
 {
 	might_sleep();
 
-	return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout, 0,
+	return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
+				       RT_MUTEX_MIN_CHAINWALK,
 				       rt_mutex_slowlock);
 }
 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
@@ -1270,7 +1294,8 @@ int rt_mutex_start_proxy_lock(struct rt_
 	}
 
 	/* We enforce deadlock detection for futexes */
-	ret = task_blocks_on_rt_mutex(lock, waiter, task, 1);
+	ret = task_blocks_on_rt_mutex(lock, waiter, task,
+				      RT_MUTEX_FULL_CHAINWALK);
 
 	if (ret && !rt_mutex_owner(lock)) {
 		/*
Index: tip/kernel/locking/rtmutex.h
===================================================================
--- tip.orig/kernel/locking/rtmutex.h
+++ tip/kernel/locking/rtmutex.h
@@ -22,10 +22,15 @@
 #define debug_rt_mutex_init(m, n)			do { } while (0)
 #define debug_rt_mutex_deadlock(d, a ,l)		do { } while (0)
 #define debug_rt_mutex_print_deadlock(w)		do { } while (0)
-#define debug_rt_mutex_detect_deadlock(w,d)		(d)
 #define debug_rt_mutex_reset_waiter(w)			do { } while (0)
 
 static inline void rt_mutex_print_deadlock(struct rt_mutex_waiter *w)
 {
 	WARN(1, "rtmutex deadlock detected\n");
 }
+
+static inline bool debug_rt_mutex_detect_deadlock(struct rt_mutex_waiter *w,
+						  enum rtmutex_chainwalk walk)
+{
+	return walk == RT_MUTEX_FULL_CHAINWALK;
+}
Index: tip/kernel/locking/rtmutex_common.h
===================================================================
--- tip.orig/kernel/locking/rtmutex_common.h
+++ tip/kernel/locking/rtmutex_common.h
@@ -102,6 +102,21 @@ static inline struct task_struct *rt_mut
 }
 
 /*
+ * Constants for rt mutex functions which have a selectable deadlock
+ * detection.
+ *
+ * RT_MUTEX_MIN_CHAINWALK:	Stops the lock chain walk when there are
+ *				no further PI adjustments to be made.
+ *
+ * RT_MUTEX_FULL_CHAINWALK:	Invoke deadlock detection with a full
+ *				walk of the lock chain.
+ */
+enum rtmutex_chainwalk {
+	RT_MUTEX_MIN_CHAINWALK,
+	RT_MUTEX_FULL_CHAINWALK,
+};
+
+/*
  * PI-futex support (proxy locking functions, etc.):
  */
 extern struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock);