From owner-freebsd-threads@FreeBSD.ORG  Fri Jun 11 06:29:22 2004
Return-Path: <owner-freebsd-threads@FreeBSD.ORG>
Delivered-To: freebsd-threads@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP
	id 7436216A4CE; Fri, 11 Jun 2004 06:29:22 +0000 (GMT)
Received: from mail.mcneil.com (rrcs-west-24-199-45-54.biz.rr.com
	[24.199.45.54])	by mx1.FreeBSD.org (Postfix) with ESMTP
	id 6526943D41; Fri, 11 Jun 2004 06:29:22 +0000 (GMT)
	(envelope-from sean@mcneil.com)
Received: from localhost (localhost.mcneil.com [127.0.0.1])
	by mail.mcneil.com (Postfix) with ESMTP id 44A83FD059;
	Thu, 10 Jun 2004 23:29:20 -0700 (PDT)
Received: from mail.mcneil.com ([127.0.0.1])
 by localhost (server.mcneil.com [127.0.0.1]) (amavisd-new, port 10024)
 with ESMTP id 38633-08; Thu, 10 Jun 2004 23:29:19 -0700 (PDT)
Received: from [24.199.45.54] (mcneil.com [24.199.45.54])
	by mail.mcneil.com (Postfix) with ESMTP id BF4BAFD01A;
	Thu, 10 Jun 2004 23:29:19 -0700 (PDT)
From: Sean McNeil <sean@mcneil.com>
To: David Xu <davidxu@freebsd.org>
In-Reply-To: <40C94B1E.8030202@freebsd.org>
References: <1086931276.38487.35.camel@server.mcneil.com>
	 <40C94B1E.8030202@freebsd.org>
Content-Type: text/plain
Message-Id: <1086935359.85387.14.camel@server.mcneil.com>
Mime-Version: 1.0
X-Mailer: Ximian Evolution 1.4.6 
Date: Thu, 10 Jun 2004 23:29:19 -0700
Content-Transfer-Encoding: 7bit
X-Virus-Scanned: by amavisd-new at mcneil.com
cc: freebsd-threads@freebsd.org
Subject: Re: signal handler priority issue
X-BeenThere: freebsd-threads@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: Threading on FreeBSD <freebsd-threads.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-threads>,
	<mailto:freebsd-threads-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-threads>
List-Post: <mailto:freebsd-threads@freebsd.org>
List-Help: <mailto:freebsd-threads-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-threads>,
	<mailto:freebsd-threads-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 11 Jun 2004 06:29:22 -0000

On Thu, 2004-06-10 at 23:03, David Xu wrote:
> I think there is a race in GC_suspend_handler,
> code between sem_post and sigsuspend has race, let me demostrate:
> 
> Master : pthread_kill(slave1, SIGUSR1);
> Master : semwait
> Slave1 : sempost
> Master : semwait return
> Master : pthread_kill(slave, SIGUSR2);
> Master : pthread_kill(slave2, SIGUSR1);
> ...
> Slave1 : scheduler switched to slave1, found there
>           is SIGUSR2 in pending set
> Slave1 : invoke SIGUSR2 handler withinsa_handler
> Slave1 : SIGUSR2 handler return
> Slave1 : sigsuspend SIGUSR2
>           because SIGUSR2 was already handled, it hangs
>           in sigsuspend, and never return.
> 
> It seems the code has the race bug. I think you should
> use sigaction and set additional mask for SIGUSR1.
> code looks like this:
> 
> struct sigaction sa;
> 
> sigemptyset(&sa.sa_mask);
> sigaddset(&sa.sa_mask, SIGUSR2);
> sa.sa_handler = GC_suspend_handler;
> sigaction(SIGUSR1, &sa, NULL);
> 
> this code will block out SIGUSR2 in GC_suspend_handler,
> and when you call sigsuspend for SIGUSR2, it should return
> if there is SIGUSR2 pending or it SIGUSR2 comes later.

Actually, what I think is happening now is that the sigaction for
SIGUSR2 is being called but the sigsuspend isn't being release.