From owner-freebsd-current@freebsd.org Thu Feb 11 10:40:34 2016 Return-Path: Delivered-To: freebsd-current@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id A5776AA48AF for ; Thu, 11 Feb 2016 10:40:34 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 24389F76 for ; Thu, 11 Feb 2016 10:40:33 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id u1BAeStO056717 (version=TLSv1 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Thu, 11 Feb 2016 12:40:29 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua u1BAeStO056717 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id u1BAeR7P056707; Thu, 11 Feb 2016 12:40:27 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Thu, 11 Feb 2016 12:40:27 +0200 From: Konstantin Belousov To: Hans Petter Selasky Cc: Greg Quinlan , "freebsd-current@freebsd.org" Subject: Re: Open Sound System - OSS "soundon" command causes KERNEL PANIC FreeBSD-11 Message-ID: <20160211104027.GP91220@kib.kiev.ua> References: <56BB0BDB.2090203@selasky.org> <872763758.2494245.1455156152295.JavaMail.yahoo@mail.yahoo.com> <56BC3041.7050203@selasky.org> <20160211101418.GO91220@kib.kiev.ua> <56BC604C.4060206@selasky.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56BC604C.4060206@selasky.org> User-Agent: Mutt/1.5.24 (2015-08-30) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 11 Feb 2016 10:40:34 -0000 On Thu, Feb 11, 2016 at 11:19:56AM +0100, Hans Petter Selasky wrote: > On 02/11/16 11:14, Konstantin Belousov wrote: > > On Thu, Feb 11, 2016 at 07:54:57AM +0100, Hans Petter Selasky wrote: > >> On 02/11/16 03:02, Greg Quinlan wrote: > >>> Hi HPS, > >>> Note: Does not happen on FreeBSD 10.1-Stable! > >>> > >> > >> Yes, that's because WITNESS is off in 10.x by default. > >> > >> Does the attached patch solve your problem? > > > > No, the patch below does not solve the issue, it only papers over it. > > I object against committing this change. > > For cases where the returned pointer is not deferred, but only checked > for a module's presence in the kernel you don't need a lock to protect > anything. Maybe make a separate API for this? How checking for bool (i.e. == NULL) would fix anything ? The fact that the module is loaded could be invalidated in parallel, so the answer you get is already wrong. The bool value you obtained is equally wrong. > > > > > Issue is that, if called unlocked, the result from module_lookupbyname() > > could become invalid right after receiving. It is the duty of the caller > > of the function to ensure that the result is still valid, and the only > > way to achieve it is to own the lock around the whole code region which > > calls the function and utilizes its result. > > > > A bug is in the OSS code. > > Yes, so why not factor out the solution? Maybe more port KLD's will trip > over this? Solution is for OSS code to take a lock around the whole region where the answer is needed.