Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751660AbdGZUDR (ORCPT ); Wed, 26 Jul 2017 16:03:17 -0400 Received: from quartz.orcorp.ca ([184.70.90.242]:34226 "EHLO quartz.orcorp.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751053AbdGZUDP (ORCPT ); Wed, 26 Jul 2017 16:03:15 -0400 Date: Wed, 26 Jul 2017 14:03:06 -0600 From: Jason Gunthorpe To: Greg Kroah-Hartman Cc: Ben Hutchings , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Stefan Berger , Jarkko Sakkinen Subject: Re: [PATCH 4.4 40/57] tpm: Provide strong locking for device removal Message-ID: <20170726200306.GB2692@obsidianresearch.com> References: <20170719111249.973558472@linuxfoundation.org> <20170719111251.592825675@linuxfoundation.org> <1501023361.12197.191.camel@codethink.co.uk> <20170726195636.GD30597@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170726195636.GD30597@kroah.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Broken-Reverse-DNS: no host name found for IP address 10.0.0.156 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1762 Lines: 46 On Wed, Jul 26, 2017 at 12:56:37PM -0700, Greg Kroah-Hartman wrote: > On Tue, Jul 25, 2017 at 11:56:01PM +0100, Ben Hutchings wrote: > > On Wed, 2017-07-19 at 13:12 +0200, Greg Kroah-Hartman wrote: > > > 4.4-stable review patch. If anyone has any objections, please let me know. > > > > > > > > > From: Jason Gunthorpe > > > > > > commit 4e26195f240d73150e8308ae42874702e3df8d2c upstream. > > > > > > Add a read/write semaphore around the ops function pointers so > > > ops can be set to null when the driver un-registers. > > [...] > > > @@ -49,10 +99,10 @@ struct tpm_chip *tpm_chip_find_get(int c > > > if (chip_num != TPM_ANY_NUM && chip_num != pos->dev_num) > > > continue; > > > > > > - if (try_module_get(pos->dev.parent->driver->owner)) { > > > + /* rcu prevents chip from being free'd */ > > > + if (!tpm_try_get_ops(pos)) > > [...] > > > > But an RCU read-side critical section is an atomic context, and > > semaphore operations can block! Fixed upstream by: > > > > commit 15516788e581eb32ec1c50e5f00aba3faf95d817 > > Author: Stefan Berger > > Date: Mon Feb 29 08:53:02 2016 -0500 > > > > tpm: Replace device number bitmap with IDR > > Ugh, that's a big patch. > > Jason, Stefan, and Jarkko, what do you think? Should I also take this > for 4.4-stable? 15516 is part of the series that included 4e26, I wouldn't take that series piecemeal, as Ben observes.. I think it would be safer to avoid all these backport patches and instead restructure the important TPM shutdown patch so that it is 'less safe'. This would mean there is a chance that the another TPM user could send a command after shutdown, but realistically that is not likely to happen. Jason