From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752306Ab3LRAKk (ORCPT ); Tue, 17 Dec 2013 19:10:40 -0500 Received: from v094114.home.net.pl ([79.96.170.134]:61752 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751493Ab3LRAKj (ORCPT ); Tue, 17 Dec 2013 19:10:39 -0500 From: "Rafael J. Wysocki" To: Tejun Heo Cc: "Rafael J. Wysocki" , Jens Axboe , tomaz.solc@tablix.org, aaron.lu@intel.com, linux-kernel@vger.kernel.org, Oleg Nesterov , Greg Kroah-Hartman , Fengguang Wu Subject: Re: [PATCH] libata, freezer: avoid block device removal while system is frozen Date: Wed, 18 Dec 2013 01:23:57 +0100 Message-ID: <18258432.12ryrov20c@vostro.rjw.lan> User-Agent: KMail/4.10.5 (Linux/3.12.0-rc6+; KDE/4.10.5; x86_64; ; ) In-Reply-To: <20131217123643.GE29989@htj.dyndns.org> References: <20131213174932.GA27070@htj.dyndns.org> <2427190.pZk9AIZAjc@vostro.rjw.lan> <20131217123643.GE29989@htj.dyndns.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tuesday, December 17, 2013 07:36:43 AM Tejun Heo wrote: > Hello, Rafael. > > On Tue, Dec 17, 2013 at 03:38:05AM +0100, Rafael J. Wysocki wrote: > > On Friday, December 13, 2013 03:40:34 PM Tejun Heo wrote: > > > Hello, > > > > > > So, this is the laughable workaround that I came up with. Seriously, > > > this is tragic. :( > > > > > > Thanks. > > > > > > ------- 8< ------- > > > Freezable kthreads and workqueues are fundamentally problematic in > > > that they effectively introduce a big kernel lock widely used in the > > > kernel and have already been the culprit of several deadlock > > > scenarios. This is the latest occurrence. > > > > OK, so I'm too tired now to go through all that, but I'll look at it tomorrow. > > > > The rule of thumb is to get rid of freezable kernel threads in the first > > place if possible anyway if they are causing problems to happen. > > Yes, that'd be awesome. In fact, getting rid of all kernel freezables > in non-low-level-drivers would be a great step forward. Agreed. > That said, we need something easily backportable so I think we probably need > this bandaid for immediate fix for now. Well, we need something, but I have a couple of concerns about this particular patch (I'll reply to it with comments shortly). Thanks, Rafael