[PATCH 1/3] mutex debug: add generic blocked_on usage

[Daniel Walker]

There are a couple of blocked on type structures. One for mutexes, and one
for rtmutexes, and we also need one for futexes.

Instead of just adding another one to the task struct I combined them all into
a union. Since a waiter can only be blocked on one of the types at any given
time this should be safe.

I also usurped the pi_lock as the lock which protects all the blocked_on types.

Signed-off-by: Daniel Walker <dwalker@xxxxxxxxxx>

---
 include/linux/sched.h |   27 ++++++++++++++++++++++-----
 kernel/fork.c         |    2 --
 kernel/mutex-debug.c  |   23 +++++++++++++++++------
 kernel/mutex-debug.h  |    4 +++-
 kernel/mutex.c        |    7 ++++++-
 5 files changed, 48 insertions(+), 15 deletions(-)

Index: linux-2.6.25/include/linux/sched.h
===================================================================
--- linux-2.6.25.orig/include/linux/sched.h
+++ linux-2.6.25/include/linux/sched.h
@@ -1024,6 +1024,21 @@ struct sched_rt_entity {
 #endif
 };
 
+enum lock_waiter_type {
+	RT_MUTEX_WAITER = 1,
+	MUTEX_WAITER,
+	FUTEX_WAITER,
+};
+
+struct lock_waiter_state {
+	enum lock_waiter_type lock_type;
+	union {
+		struct rt_mutex_waiter *rt_blocked_on;
+		struct mutex_waiter *mutex_blocked_on;
+		struct futex_q *futex_blocked_on;
+	};
+};
+
 struct task_struct {
 	volatile long state;	/* -1 unrunnable, 0 runnable, >0 stopped */
 	void *stack;
@@ -1201,7 +1216,7 @@ struct task_struct {
 /* Protection of (de-)allocation: mm, files, fs, tty, keyrings */
 	spinlock_t alloc_lock;
 
-	/* Protection of the PI data structures: */
+	/* Protects blocked_on field and PI waiters list. */
 	spinlock_t pi_lock;
 
 #ifdef CONFIG_RT_MUTEXES
@@ -1211,10 +1226,12 @@ struct task_struct {
 	struct rt_mutex_waiter *pi_blocked_on;
 #endif
 
-#ifdef CONFIG_DEBUG_MUTEXES
-	/* mutex deadlock detection */
-	struct mutex_waiter *blocked_on;
-#endif
+	/*
+ 	 * Deadlock detection and priority inheritance handling,
+	 * and any other out of line mutex operations
+	 */
+	struct lock_waiter_state *blocked_on;
+
 #ifdef CONFIG_TRACE_IRQFLAGS
 	unsigned int irq_events;
 	int hardirqs_enabled;
Index: linux-2.6.25/kernel/fork.c
===================================================================
--- linux-2.6.25.orig/kernel/fork.c
+++ linux-2.6.25/kernel/fork.c
@@ -1158,9 +1158,7 @@ static struct task_struct *copy_process(
 	p->lockdep_recursion = 0;
 #endif
 
-#ifdef CONFIG_DEBUG_MUTEXES
 	p->blocked_on = NULL; /* not blocked yet */
-#endif
 
 	/* Perform scheduler related setup. Assign this task to a CPU. */
 	sched_fork(p, clone_flags);
Index: linux-2.6.25/kernel/mutex-debug.c
===================================================================
--- linux-2.6.25.orig/kernel/mutex-debug.c
+++ linux-2.6.25/kernel/mutex-debug.c
@@ -52,23 +52,34 @@ void debug_mutex_free_waiter(struct mute
 	memset(waiter, MUTEX_DEBUG_FREE, sizeof(*waiter));
 }
 
-void debug_mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
+void debug_mutex_add_waiter(struct mutex *lock, struct lock_waiter_state *lock_waiter,
 			    struct thread_info *ti)
 {
+	struct task_struct *task = ti->task;
+
 	SMP_DEBUG_LOCKS_WARN_ON(!spin_is_locked(&lock->wait_lock));
 
 	/* Mark the current thread as blocked on the lock: */
-	ti->task->blocked_on = waiter;
-	waiter->lock = lock;
+	lock_waiter->mutex_blocked_on->lock = lock;
+	spin_lock(&task->pi_lock);
+	task->blocked_on = lock_waiter;
+	spin_unlock(&task->pi_lock);
 }
 
 void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
 			 struct thread_info *ti)
 {
+	struct task_struct *task = ti->task;
+
+	spin_lock(&task->pi_lock);
+
 	DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
-	DEBUG_LOCKS_WARN_ON(waiter->task != ti->task);
-	DEBUG_LOCKS_WARN_ON(ti->task->blocked_on != waiter);
-	ti->task->blocked_on = NULL;
+	DEBUG_LOCKS_WARN_ON(waiter->task != task);
+	DEBUG_LOCKS_WARN_ON(task->blocked_on != NULL);
+	DEBUG_LOCKS_WARN_ON(task->blocked_on->mutex_blocked_on != waiter);
+
+	task->blocked_on = NULL;
+	spin_unlock(&task->pi_lock);
 
 	list_del_init(&waiter->list);
 	waiter->task = NULL;
Index: linux-2.6.25/kernel/mutex-debug.h
===================================================================
--- linux-2.6.25.orig/kernel/mutex-debug.h
+++ linux-2.6.25/kernel/mutex-debug.h
@@ -25,10 +25,12 @@ extern void debug_mutex_lock_common(stru
 				    struct mutex_waiter *waiter);
 extern void debug_mutex_wake_waiter(struct mutex *lock,
 				    struct mutex_waiter *waiter);
+
 extern void debug_mutex_free_waiter(struct mutex_waiter *waiter);
 extern void debug_mutex_add_waiter(struct mutex *lock,
-				   struct mutex_waiter *waiter,
+				   struct lock_waiter_state *lock_waiter,
 				   struct thread_info *ti);
+
 extern void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
 				struct thread_info *ti);
 extern void debug_mutex_unlock(struct mutex *lock);
Index: linux-2.6.25/kernel/mutex.c
===================================================================
--- linux-2.6.25.orig/kernel/mutex.c
+++ linux-2.6.25/kernel/mutex.c
@@ -131,11 +131,16 @@ __mutex_lock_common(struct mutex *lock, 
 	unsigned int old_val;
 	unsigned long flags;
 
+#ifdef CONFIG_DEBUG_MUTEXES
+	struct lock_waiter_state lock_waiter =
+		{ .lock_type = MUTEX_WAITER, { .mutex_blocked_on = &waiter} };
+#endif
+
 	spin_lock_mutex(&lock->wait_lock, flags);
 
 	debug_mutex_lock_common(lock, &waiter);
 	mutex_acquire(&lock->dep_map, subclass, 0, ip);
-	debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
+	debug_mutex_add_waiter(lock, &lock_waiter, task_thread_info(task));
 
 	/* add waiting tasks to the end of the waitqueue (FIFO): */
 	list_add_tail(&waiter.list, &lock->wait_list);

-- 
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