From owner-svn-src-all@FreeBSD.ORG Thu May 21 15:54:10 2009 Return-Path: Delivered-To: svn-src-all@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 3DB7E1065740; Thu, 21 May 2009 15:54:09 +0000 (UTC) (envelope-from scottl@samsco.org) Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57]) by mx1.freebsd.org (Postfix) with ESMTP id D95128FC08; Thu, 21 May 2009 15:54:08 +0000 (UTC) (envelope-from scottl@samsco.org) Received: from phobos.local (pooker.samsco.org [168.103.85.57]) by pooker.samsco.org (8.14.2/8.14.2) with ESMTP id n4LFs1rf080561; Thu, 21 May 2009 09:54:02 -0600 (MDT) (envelope-from scottl@samsco.org) Message-ID: <4A157919.7040103@samsco.org> Date: Thu, 21 May 2009 08:54:01 -0700 From: Scott Long User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-US; rv:1.8.1.13) Gecko/20080313 SeaMonkey/1.1.9 MIME-Version: 1.0 To: "M. Warner Losh" References: <3bbf2fe10905210629p46c7a204v6863aaba77354462@mail.gmail.com> <200905210942.35555.jhb@freebsd.org> <20090521.094100.70797067.imp@bsdimp.com> In-Reply-To: <20090521.094100.70797067.imp@bsdimp.com> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-4.6 required=3.8 tests=ALL_TRUSTED,AWL,BAYES_00 autolearn=ham version=3.1.8 X-Spam-Checker-Version: SpamAssassin 3.1.8 (2007-02-13) on pooker.samsco.org Cc: src-committers@FreeBSD.org, jhb@FreeBSD.org, svn-src-all@FreeBSD.org, attilio@FreeBSD.org, svn-src-head@FreeBSD.org, rwatson@FreeBSD.org, kostikbel@gmail.com Subject: Re: svn commit: r192535 - head/sys/kern X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 21 May 2009 15:54:11 -0000 M. Warner Losh wrote: > In message: > Robert Watson writes: > : On Thu, 21 May 2009, John Baldwin wrote: > : > : >>>> Move the M_WAITOK flag in notify() into an M_NOWAIT one in order to > : > match > : >>>> the behaviour alredy present with the further malloc() call in > : >>>> devctl_notify(). > : >>>> This fixes a bug in the CAM layer where the camisr handler finished to > : >>>> call camperiphfree() (and subsequently destroy_dev() resulting in a new > : >>>> dev notify) while the xpt lock is held. > : >>> This is wrong. You cannot call destroy_dev() while holding any mutex. > : >>> Taking this into account, it makes no sense to use M_NOWAIT in notify(). > : >> > : >> As long as devctl_notify() also calls M_NOWAIT and if not available skips > : >> "silently" it just does the same thing, I think this approach is more > : >> consistent. > : >> > : >> It remains, though, the fact to fix CAM when calling destroy_dev(). Maybe > : >> we should add a witness_warn() there? > : > > : > I agree with kib, this should be reverted and CAM fixed instead. I also > : > agree that M_NOWAIT use should be limited where possible. > : > : devctl_notify() probably needs to grow a sleepable flag, or perhaps we need > : two variations, one that can sleep. > > devctl_notify() has expanded well beyond its original needs. Having > an extra case for sleeping is the wrong way to solve this problem. > Really. We're adding hacks on hacks on hacks here and we need to step > back and think. > > I specifically didn't put in CDEV notifications into devd when I > originally did it because one can get the same notification via > kevents on /dev. Maybe the right answer is to remove this stuff > entirely and update devd to do that instead? It isn't a lot of code, > and should provide equivalent functionality without needing to change > the rules of the game when it comes to destroy_dev(). Especially this > close to the code slush... > > Comments? > > Warner Very much in agreement here. I would also love to have destroy_dev() and make_dev() be locking-neutral. Having sleepable locks in leaf APIs is unpleasant for consumers of those APIs. Scott