From owner-freebsd-hackers@FreeBSD.ORG  Sat Jan 10 06:08:24 2004
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 01F1A16A4CE
	for <FreeBSD-hackers@FreeBSD.org>;
	Sat, 10 Jan 2004 06:08:24 -0800 (PST)
Received: from Vitsch.net (b74143.upc-b.chello.nl [212.83.74.143])
	by mx1.FreeBSD.org (Postfix) with ESMTP id D3D8243D41
	for <FreeBSD-hackers@FreeBSD.org>;
	Sat, 10 Jan 2004 06:08:21 -0800 (PST)
	(envelope-from Danovitsch@Vitsch.net)
Received: from FreeBSD.Danovitsch.LAN (b83007.upc-b.chello.nl [212.83.83.7])
	by Vitsch.net (8.12.3p2/8.11.3) with ESMTP id i0AE82Xe034592
	for <FreeBSD-hackers@FreeBSD.org>;
	Sat, 10 Jan 2004 15:08:02 +0100 (CET)
	(envelope-from Danovitsch@Vitsch.net)
Content-Type: text/plain;
  charset="us-ascii"
From: "Daan Vreeken [PA4DAN]" <Danovitsch@Vitsch.net>
To: FreeBSD-hackers@FreeBSD.org
Date: Sat, 10 Jan 2004 15:08:22 +0100
User-Agent: KMail/1.4.3
MIME-Version: 1.0
Content-Transfer-Encoding: quoted-printable
Message-Id: <200401101508.22640.Danovitsch@Vitsch.net>
Subject: kernel threads and printf locking question
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
	<freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
	<mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sat, 10 Jan 2004 14:08:24 -0000

Hi,

I am writing a kernel module in which I have created a kernel thread with=
=20
kthread_create. For debugging I have added a couple of printf's in the=20
thread-routine. Running the module on a single-proc system works fine, bu=
t=20
when running it on one of my SMP machines the console freezes after a cou=
ple=20
of seconds.

I have been looking through the archives and through some other drivers (=
 for=20
example randomdev.c uses a kthread and printf's from it ). I found a vers=
ion=20
of randomdev.c with google that lock's Giant while calling printf, but=20
randomdev.c in my src-tree has no locking there. (I'm using 5.1-RELEASE)
Right now I have changed all printf's in my module into a macro-function =
that=20
checks if ( curproc =3D=3D our thread ) and locks Giant if true, then pri=
ntf's.=20
(since some of the routines get called both from the thread and from othe=
r=20
places.)

What is the current state of printf-locking when called from a kernel thr=
ead?=20
Is locking Giant the only possible way to avoid problems on SMP systems, =
or=20
is there a more fine-grained printf lock available? (on 5.1-RELEASE or=20
-current)

thanks,
Daan