/*
 * kernel/mutex-debug.c
 *
 * Debugging code for mutexes
 *
 * Started by Ingo Molnar:
 *
 *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
 *
 * lock debugging, locking tree, deadlock detection started by:
 *
 *  Copyright (C) 2004, LynuxWorks, Inc., Igor Manyilov, Bill Huey
 *  Released under the General Public License (GPL).
 */
#include <linux/mutex.h>
#include <linux/delay.h>
#include <linux/export.h>
#include <linux/poison.h>
#include <linux/sched.h>
#include <linux/spinlock.h>
#include <linux/kallsyms.h>
#include <linux/interrupt.h>
#include <linux/debug_locks.h>

#include "mutex-debug.h"

/*
 * Must be called with lock->wait_lock held.
 */
void debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter)
{
	memset(waiter, MUTEX_DEBUG_INIT, sizeof(*waiter));
	waiter->magic = waiter;
	waiter->lock  = lock;
	INIT_LIST_HEAD(&waiter->list);
}

void debug_mutex_wake_waiter(struct mutex *lock, struct mutex_waiter *waiter)
{
	SMP_DEBUG_LOCKS_WARN_ON(!spin_is_locked(&lock->wait_lock));
	DEBUG_LOCKS_WARN_ON(list_empty(&lock->wait_list));
	DEBUG_LOCKS_WARN_ON(waiter->magic != waiter);
	DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
}

void debug_mutex_free_waiter(struct mutex_waiter *waiter)
{
	DEBUG_LOCKS_WARN_ON(!list_empty(&waiter->list));
	memset(waiter, MUTEX_DEBUG_FREE, sizeof(*waiter));
}

void debug_mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter,
			    struct task_struct *task)
{
	SMP_DEBUG_LOCKS_WARN_ON(!spin_is_locked(&lock->wait_lock));

	/* Mark the current thread as blocked on the lock: */
	spin_lock(&task->blocked_on_ptrlock);
	task->blocked_on = waiter;
	spin_unlock(&task->blocked_on_ptrlock);
}

void mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter,
			 struct task_struct *task)
{
	DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
	DEBUG_LOCKS_WARN_ON(waiter->task != task);
	DEBUG_LOCKS_WARN_ON(task->blocked_on != waiter);

	spin_lock(&task->blocked_on_ptrlock);
	task->blocked_on = NULL;
	spin_unlock(&task->blocked_on_ptrlock);

	list_del_init(&waiter->list);
	waiter->task = NULL;
}

void debug_mutex_unlock(struct mutex *lock)
{
	if (likely(debug_locks)) {
		DEBUG_LOCKS_WARN_ON(lock->magic != lock);

		if (!lock->owner)
			DEBUG_LOCKS_WARN_ON(!lock->owner);
		else
			DEBUG_LOCKS_WARN_ON(lock->owner != current);

		DEBUG_LOCKS_WARN_ON(!lock->wait_list.prev && !lock->wait_list.next);
	}

	/*
	 * __mutex_slowpath_needs_to_unlock() is explicitly 0 for debug
	 * mutexes so that we can do it here after we've verified state.
	 */
	mutex_clear_owner(lock);
	atomic_set(&lock->count, 1);
}

void debug_mutex_init(struct mutex *lock, const char *name,
		      struct lock_class_key *key)
{
#ifdef CONFIG_DEBUG_LOCK_ALLOC
	/*
	 * Make sure we are not reinitializing a held lock:
	 */
	debug_check_no_locks_freed((void *)lock, sizeof(*lock));
	lockdep_init_map(&lock->dep_map, name, key, 0);
#endif
	lock->magic = lock;

	spin_lock_init(&lock->owner_lock);
	lock->owner_info.pid = NULL;
	lock->owner_info.ip = 0;
}

/***
 * mutex_destroy - mark a mutex unusable
 * @lock: the mutex to be destroyed
 *
 * This function marks the mutex uninitialized, and any subsequent
 * use of the mutex is forbidden. The mutex must not be locked when
 * this function is called.
 */
void mutex_destroy(struct mutex *lock)
{
	DEBUG_LOCKS_WARN_ON(mutex_is_locked(lock));
	lock->magic = NULL;
}

EXPORT_SYMBOL_GPL(mutex_destroy);

int debug_mutex_task_blocked_by(struct task_struct *task,
				struct callerinfo *owner_info)
{
	struct mutex_waiter *waiter;
	struct callerinfo *oi;
	unsigned long flags;
	struct mutex *lock;
	int ret;

	/*
	 * The locking procedure here is a bit delicate, since the waiter
	 * lives on the stack of the waiting task, and basically the general
	 * assumption is that only the waiting task may mess with it.
	 *
	 * But here, we're accessing the waiter out-of-context by following
	 * the task's .blocking_on pointer.  Dereferencing it thus requires
	 * protection by holding an extra pointer lock.
	 *
	 * Since we're out-of-context, we also have to store a lock pointer in
	 * the waiter data, and make sure that the waiting task doesn't change
	 * it while we hold the lock.
	 */

	ret = spin_trylock_irqsave(&task->blocked_on_ptrlock, flags);
	if (!ret)
		/*
		 * Blocking or unblocking in progress;
		 * consider this "not blocked", at least not
		 * in a critical way.
		 */
		goto notblocking;

	waiter = task->blocked_on;
	if (!waiter) {
		spin_unlock_irqrestore(&task->blocked_on_ptrlock, flags);
		goto notblocking;
	}

	lock = waiter->lock;
	oi = &lock->owner_info;

	ret = spin_trylock(&lock->owner_lock);
	if (!ret) {
		spin_unlock_irqrestore(&task->blocked_on_ptrlock, flags);
		return -EBUSY;
	}

	owner_info->pid = get_pid(oi->pid);
	owner_info->ip = oi->ip;

	spin_unlock(&lock->owner_lock);
	spin_unlock_irqrestore(&task->blocked_on_ptrlock, flags);

	return 0;

notblocking:
	owner_info->pid = NULL;
	owner_info->ip = 0;
	return 0;
}

void show_blocking_mutex_holder(struct task_struct *task)
{
	struct callerinfo mutex_owner;
	struct task_struct *ownertask;
	int ret;

	if (!task)
		return;

	ret = debug_mutex_task_blocked_by(task, &mutex_owner);
	if (ret == 0 && mutex_owner.pid) {
		printk("Task %s[%u] is blocked on a mutex\n",
				task->comm,
				task_pid_nr(task));
		printk("Blocking mutex is held by: PID %d, taken at %pS\n",
				pid_nr(mutex_owner.pid),
				(void *)mutex_owner.ip);

		ownertask = get_pid_task(mutex_owner.pid, PIDTYPE_PID);
		if (ownertask) {
			printk("Stack dump of holding task %s[%u]:\n",
					ownertask->comm,
					task_pid_nr(ownertask));
			show_stack(ownertask, NULL);
			put_task_struct(ownertask);
		} else {
			printk("Task holding mutex not found\n");
		}

		put_pid(mutex_owner.pid);
	}
}