sched: Document task_struct::personality field

Signed-off-by: Andrei Epure <epure.andrei@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1365701429-4721-1-git-send-email-epure.andrei@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/sched.h

@@ -1105,8 +1105,10 @@ struct task_struct {
 	int exit_code, exit_signal;
 	int pdeath_signal;  /*  The signal sent when the parent dies  */
 	unsigned int jobctl;	/* JOBCTL_*, siglock protected */
-	/* ??? */
+
+	/* Used for emulating ABI behavior of previous Linux versions */
 	unsigned int personality;
+
 	unsigned did_exec:1;
 	unsigned in_execve:1;	/* Tell the LSMs that the process is doing an
 				 * execve */