Don't operate with pid_t in rtmutex tester

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>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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		*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
 };