From owner-svn-src-user@FreeBSD.ORG Tue May 26 18:38:08 2009 Return-Path: Delivered-To: svn-src-user@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 8DD6B106567A; Tue, 26 May 2009 18:38:08 +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 5F4C28FC1B; Tue, 26 May 2009 18:38:08 +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 13D5546B82; Tue, 26 May 2009 14:38:08 -0400 (EDT) Received: from jhbbsd.hudson-trading.com (unknown [209.249.190.8]) by bigwig.baldwin.cx (Postfix) with ESMTPA id E45FA8A02B; Tue, 26 May 2009 14:38:06 -0400 (EDT) From: John Baldwin To: Kip Macy Date: Tue, 26 May 2009 14:37:48 -0400 User-Agent: KMail/1.9.7 References: <200905222145.n4MLjhm3019802@svn.freebsd.org> <200905260830.36831.jhb@freebsd.org> <3c1674c90905261118y282d9b0fn7d54630f507d8363@mail.gmail.com> In-Reply-To: <3c1674c90905261118y282d9b0fn7d54630f507d8363@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Message-Id: <200905261437.49148.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.0.1 (bigwig.baldwin.cx); Tue, 26 May 2009 14:38:06 -0400 (EDT) X-Virus-Scanned: clamav-milter 0.95 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: src-committers@freebsd.org, svn-src-user@freebsd.org Subject: Re: svn commit: r192604 - in user/kmacy/releng_7_2_fcs/sys: dev/hwpmc sys X-BeenThere: svn-src-user@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "SVN commit messages for the experimental " user" src tree" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 May 2009 18:38:09 -0000 On Tuesday 26 May 2009 2:18:00 pm Kip Macy wrote: > On Tue, May 26, 2009 at 5:30 AM, John Baldwin wrote: > > On Friday 22 May 2009 5:45:43 pm Kip Macy wrote: > >> Author: kmacy > >> Date: Fri May 22 21:45:43 2009 > >> New Revision: 192604 > >> URL: http://svn.freebsd.org/changeset/base/192604 > >> > >> Log: > >> =A0 - remove pmc_kthread_mtx > >> =A0 - replace sleep/wakeup on kthread with a condvar > > > > If you do not sleep on the kthread/kproc when waiting for a kthread to > > exit, then you open up a race window. =A0Usually this matters more for > > any kthreads that live in a module since the race allows the module to > > be unmapped before the thread is finished executing code from the module > > resulting in a fatal page fault in the kernel. >=20 >=20 > Yes, that is why the kthread explicitly calls cv_signal after clearing > the kthread pointer. Umm, that doesn't help. Your kthread's main routine is "physically" locate= d=20 in your kld. It needs to get into the text of kthread_exit() before it is= =20 safe for your module to unload, and so you have to sleep on the kthread/kpr= oc=20 pointer to wait for the wakeup in kthread_exit() to fire. You could have=20 easily used msleep_spin() for this w/o hacking up condvar's to support spin= =20 locks too, FWIW. =2D-=20 John Baldwin