From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753241Ab3LQMfF (ORCPT ); Tue, 17 Dec 2013 07:35:05 -0500 Received: from mail-qe0-f54.google.com ([209.85.128.54]:48966 "EHLO mail-qe0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751021Ab3LQMfB (ORCPT ); Tue, 17 Dec 2013 07:35:01 -0500 Date: Tue, 17 Dec 2013 07:34:57 -0500 From: Tejun Heo To: "Rafael J. Wysocki" Cc: Nigel Cunningham , "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 Message-ID: <20131217123457.GD29989@htj.dyndns.org> References: <20131213174932.GA27070@htj.dyndns.org> <52AB9509.1080004@nigelcunningham.com.au> <20131214203121.GB4020@htj.dyndns.org> <8951916.gd5Uu6GpK1@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8951916.gd5Uu6GpK1@vostro.rjw.lan> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, Rafael. On Tue, Dec 17, 2013 at 03:34:00AM +0100, Rafael J. Wysocki wrote: > No, it isn't. [I guess it was originally, but it has not been the case > for a very long time.] It is about getting user space interactions (all of Heh... no wonder people are all so confused about this thing. > the sysfs/ioctl/mmap/read/write/you-name-it thingies user space can do to > devices) when we're calling device suspend/resume routines. The reason is > that otherwise all of them would have had to do a "oh, are we suspending by > the way?" check pretty much on every code path that can be triggered by > user space. Freezing userland is fine. I have no problem with that but up until now the only use case that seems fundamentally valid to me is freezing IO processing kthread in a driver as a cheap way to implement suspend/resume. At this point, given the general level of confusion, it seems to be costing more than benefiting. > > Does that mean that it's safe to unfreeze before invoking resume? > > No, it isn't. So, are you saying it's really about giving device drivers easy way to implement suspend/resume? If that's the case, let's please make it *way* more specific and clear - ie. things like helpers to implement suspend/resume hooks trivially or whatnot. Freezable kthreads (and now workqueues) have been becoming a giant mess for a while now. Thanks. -- tejun