From owner-freebsd-hackers@FreeBSD.ORG Mon Jul 13 18:44:43 2009 Return-Path: Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 7236B106567D; Mon, 13 Jul 2009 18:44:43 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id 42C6D8FC20; Mon, 13 Jul 2009 18:44:43 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from bigwig.baldwin.cx (66.111.2.69.static.nyinternet.net [66.111.2.69]) by cyrus.watson.org (Postfix) with ESMTPSA id E5A2346B7E; Mon, 13 Jul 2009 14:44:42 -0400 (EDT) Received: from jhbbsd.hudson-trading.com (unknown [209.249.190.8]) by bigwig.baldwin.cx (Postfix) with ESMTPA id 03ECF8A096; Mon, 13 Jul 2009 14:44:42 -0400 (EDT) From: John Baldwin To: freebsd-hackers@freebsd.org Date: Mon, 13 Jul 2009 14:17:53 -0400 User-Agent: KMail/1.9.7 References: <4A4740B8.8090205@embedded-brains.de> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200907131417.53876.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.0.1 (bigwig.baldwin.cx); Mon, 13 Jul 2009 14:44:42 -0400 (EDT) X-Virus-Scanned: clamav-milter 0.95.1 at bigwig.baldwin.cx X-Virus-Status: Clean X-Spam-Status: No, score=-2.5 required=4.2 tests=AWL,BAYES_00,RDNS_NONE autolearn=no version=3.2.5 X-Spam-Checker-Version: SpamAssassin 3.2.5 (2008-06-10) on bigwig.baldwin.cx Cc: Sebastian Huber , hackers@freebsd.org, Robert Watson Subject: Re: callout(9) and Giant lock X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 13 Jul 2009 18:44:43 -0000 On Sunday 28 June 2009 11:57:05 am Robert Watson wrote: > > On Sun, 28 Jun 2009, Sebastian Huber wrote: > > > suppose that a certain time event triggered several callout functions. What > > happens if the first of these callout functions blocks on the Giant lock? > > Does this delay all further callout functions until the Giant lock is > > available for the first callout function? What happens if one of the callout > > function blocks forever? Does this deadlock the system? > > Callouts are marked as MPSAFE or non-MPSAFE when registered. If non-MPSAFE, > we will acquire Giant automatically for the callout, but I believe we'll also > try and sort non-MPSAFE callouts behind MPSAFE ones in execution order to > minimize latency for MPSAFE callouts. Most callouts acquire locks of some > sort, and stalling any callout indefinitely will stall the entire callout > thread indefinitely, which in turn could lead to a variety of odd behaviors > and potentially (although not necessarily) deadlock. FWIW, we do not actually sort the callouts in this manner, so all callouts will be blocked until Giant is acquired. -- John Baldwin