The proper behavior to store task's pid and get this task 
later is to get the struct pid pointer and get the task
with the pid_task() call.

Make it for rt_mutex_waiter->deadlock_task_pid field.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

---
 kernel/rtmutex-debug.c  |   12 +++++++++---
 kernel/rtmutex_common.h |    2 +-
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/kernel/rtmutex-debug.c b/kernel/rtmutex-debug.c
index 56d73cb..40ec85c 100644
--- a/kernel/rtmutex-debug.c
+++ b/kernel/rtmutex-debug.c
@@ -130,7 +130,7 @@ void debug_rt_mutex_deadlock(int detect, struct rt_mutex_waiter *act_waiter,
 
 	task = rt_mutex_owner(act_waiter->lock);
 	if (task && task != current) {
-		act_waiter->deadlock_task_pid = task->pid;
+		act_waiter->deadlock_task_pid = get_pid(task_pid(task));
 		act_waiter->deadlock_lock = lock;
 	}
 }
@@ -142,9 +142,12 @@ void debug_rt_mutex_print_deadlock(struct rt_mutex_waiter *waiter)
 	if (!waiter->deadlock_lock || !rt_trace_on)
 		return;
 
-	task = find_task_by_pid(waiter->deadlock_task_pid);
-	if (!task)
+	rcu_read_lock();
+	task = pid_task(waiter->deadlock_task_pid, PIDTYPE_PID);
+	if (!task) {
+		rcu_read_unlock();
 		return;
+	}
 
 	TRACE_OFF_NOLOCK();
 
@@ -173,6 +176,7 @@ void debug_rt_mutex_print_deadlock(struct rt_mutex_waiter *waiter)
 		current->comm, task_pid_nr(current));
 	dump_stack();
 	debug_show_all_locks();
+	rcu_read_unlock();
 
 	printk("[ turning off deadlock detection."
 	       "Please report this trace. ]\n\n");
@@ -203,10 +207,12 @@ void debug_rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
 	memset(waiter, 0x11, sizeof(*waiter));
 	plist_node_init(&waiter->list_entry, MAX_PRIO);
 	plist_node_init(&waiter->pi_list_entry, MAX_PRIO);
+	waiter->deadlock_task_pid = NULL;
 }
 
 void debug_rt_mutex_free_waiter(struct rt_mutex_waiter *waiter)
 {
+	put_pid(waiter->deadlock_task_pid);
 	TRACE_WARN_ON(!plist_node_empty(&waiter->list_entry));
 	TRACE_WARN_ON(!plist_node_empty(&waiter->pi_list_entry));
 	TRACE_WARN_ON(waiter->task);
diff --git a/kernel/rtmutex_common.h b/kernel/rtmutex_common.h
index 2d3b835..e124bf5 100644
--- a/kernel/rtmutex_common.h
+++ b/kernel/rtmutex_common.h
@@ -51,7 +51,7 @@ struct rt_mutex_waiter {
 	struct rt_mutex		*lock;
 #ifdef CONFIG_DEBUG_RT_MUTEXES
 	unsigned long		ip;
-	pid_t			deadlock_task_pid;
+	struct pid		*deadlock_task_pid;
 	struct rt_mutex		*deadlock_lock;
 #endif
 };
-- 
1.5.3.4