Message-ID: <441F0352.758F0321@tv-sign.ru>
Date: Mon, 20 Mar 2006 22:32:34 +0300
From: Oleg Nesterov <oleg@tv-sign.ru>
MIME-Version: 1.0
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Andrew Morton <akpm@osdl.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] simplify/fix first_tid()
References: <441DB045.87C4134C@tv-sign.ru>
		<m1fyldvvvo.fsf@ebiederm.dsl.xmission.com>
		<441EF4D7.AEC1AE8C@tv-sign.ru> <m1y7z5uepz.fsf@ebiederm.dsl.xmission.com>
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"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.
 	 */
-
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