[IA64] Only unwind non-running tasks.

Unwinding a running task has proven problematic.

In one instance, the running task was attempting to unwind itself and
received an interrupt between when get_wchan allocated local variables on
the stack and when unw_init_from_blocked_task was called which resulted
in unw_init_frame_info to place this tasks task_struct pointer over the
switch stack's ar_bspstore entry.
Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/process.c

@@ -763,6 +763,9 @@ get_wchan (struct task_struct *p)
 	unsigned long ip;
 	int count = 0;
 
+	if (!p || p == current || p->state == TASK_RUNNING)
+		return 0;
+
 	/*
 	 * Note: p may not be a blocked task (it could be current or
 	 * another process running on some other CPU.  Rather than
@@ -773,6 +776,8 @@ get_wchan (struct task_struct *p)
 	 */
 	unw_init_from_blocked_task(&info, p);
 	do {
+		if (p->state == TASK_RUNNING)
+			return 0;
 		if (unw_unwind(&info) < 0)
 			return 0;
 		unw_get_ip(&info, &ip);