Re: [PATCH] simplify/fix first_tid()

[Oleg Nesterov <oleg@tv-sign.ru>]

"Eric W. Biederman" wrote:
> 
> Oleg Nesterov <oleg@tv-sign.ru> writes:
> 
> >> So we really still need the nr_threads test in there so we don't
> >> traverse the list twice everytime through readdir.
> >
> > How so? We don't do it twice?
> 
> In general user space does.  Because a read of 0 bytes signifies
> the end of a directory.
> 
> So we have 2 trips through proc_task_readdir initiated by user
> space.

Oh, thanks, you are right.

[PATCH] simplify-fix-first_tid-fix

Restore a stupidly deleted optimization.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- MM/fs/proc/base.c~	2006-03-21 01:08:10.000000000 +0300
+++ MM/fs/proc/base.c	2006-03-21 01:14:36.000000000 +0300
@@ -2190,6 +2190,11 @@ static struct task_struct *first_tid(str
 			goto found;
 	}
 
+	/* If nr exceeds the number of threads there is nothing todo */
+	pos = NULL;
+	if (nr && nr >= get_nr_threads(leader))
+		goto out;
+
 	/* If we haven't found our starting place yet start
 	 * with the leader and walk nr threads forward.
 	 */