From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756105Ab3LRWBH (ORCPT ); Wed, 18 Dec 2013 17:01:07 -0500 Received: from v094114.home.net.pl ([79.96.170.134]:62629 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750961Ab3LRWBF (ORCPT ); Wed, 18 Dec 2013 17:01:05 -0500 From: "Rafael J. Wysocki" To: Tejun Heo Cc: Dave Chinner , Jens Axboe , tomaz.solc@tablix.org, aaron.lu@intel.com, linux-kernel@vger.kernel.org, Oleg Nesterov , Greg Kroah-Hartman , Fengguang Wu Subject: Re: Writeback threads and freezable Date: Wed, 18 Dec 2013 23:14:24 +0100 Message-ID: <1639602.dY4DbMiF4F@vostro.rjw.lan> User-Agent: KMail/4.10.5 (Linux/3.12.0-rc6+; KDE/4.10.5; x86_64; ; ) In-Reply-To: <20131218114343.GA4324@htj.dyndns.org> References: <20131213174932.GA27070@htj.dyndns.org> <20131218003510.GD20579@dastard> <20131218114343.GA4324@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 Wednesday, December 18, 2013 06:43:43 AM Tejun Heo wrote: [...] > If filesystems need an indication that the underlying device is no > longer functional, please go ahead and add it, but please keep in mind > all these are completely asynchronous. Nothing guarantees you that > such events would happen in any specific order. IOW, you can be at > *ANY* point in your warm unplug path and the device is hot unplugged, > which essentially forces all the code paths to be ready for the worst, > and that's exactly why there isn't much effort in trying to separate > out warm and hot unplug paths. Yes. Devices can go away at any point without notice. Even PCI devices that have never been assumed to be hot-removable. Any piece of code in the kernel needs to be prepared to deal with such situations. Thanks, Rafael