procfs: fix /proc/<pid>/stat stack pointer for kernel threads

Fix a small issue for the stack pointer in /proc/<pid>/stat.  In case of a
kernel thread the value of the printed stack pointer should be 0.

Signed-off-by: Stefani Seibold <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/proc/array.c

@@ -571,7 +571,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
 		rsslim,
 		mm ? mm->start_code : 0,
 		mm ? mm->end_code : 0,
-		(permitted) ? task->stack_start : 0,
+		(permitted && mm) ? task->stack_start : 0,
 		esp,
 		eip,
 		/* The signal information here is obsolete.