From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755520Ab2K2VUq (ORCPT ); Thu, 29 Nov 2012 16:20:46 -0500 Received: from hydra.sisk.pl ([212.160.235.94]:36453 "EHLO hydra.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753602Ab2K2VUp (ORCPT ); Thu, 29 Nov 2012 16:20:45 -0500 From: "Rafael J. Wysocki" To: Toshi Kani Cc: linux-acpi@vger.kernel.org, Hanjun Guo , Vasilis Liaskovitis , isimatu.yasuaki@jp.fujitsu.com, wency@cn.fujitsu.com, lenb@kernel.org, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Tang Chen Subject: Re: [RFC PATCH v3 0/3] acpi: Introduce prepare_remove device operation Date: Thu, 29 Nov 2012 22:25:30 +0100 Message-ID: <7256354.mIkI9CW3OY@vostro.rjw.lan> User-Agent: KMail/4.9.3 (Linux/3.7.0-rc7; KDE/4.9.3; x86_64; ; ) In-Reply-To: <1354222577.7776.22.camel@misato.fc.hp.com> References: <1353693037-21704-1-git-send-email-vasilis.liaskovitis@profitbricks.com> <1354221570.7776.11.camel@misato.fc.hp.com> <1354222577.7776.22.camel@misato.fc.hp.com> 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 Thursday, November 29, 2012 01:56:17 PM Toshi Kani wrote: > On Thu, 2012-11-29 at 13:39 -0700, Toshi Kani wrote: > > On Thu, 2012-11-29 at 21:30 +0100, Rafael J. Wysocki wrote: > > > On Thursday, November 29, 2012 10:03:12 AM Toshi Kani wrote: > > > > On Thu, 2012-11-29 at 11:15 +0100, Rafael J. Wysocki wrote: > > > > > On Wednesday, November 28, 2012 11:41:36 AM Toshi Kani wrote: > > > > > > 1. Validate phase - Verify if the request is a supported operation. All > > > > > > known restrictions are verified at this phase. For instance, if a > > > > > > hot-remove request involves kernel memory, it is failed in this phase. > > > > > > Since this phase makes no change, no rollback is necessary to fail. > > > > > > > > > > Actually, we can't do it this way, because the conditions may change between > > > > > the check and the execution. So the first phase needs to involve execution > > > > > to some extent, although only as far as it remains reversible. > > > > > > > > For memory hot-remove, we can check if the target memory ranges are > > > > within ZONE_MOVABLE. We should not allow user to change this setup > > > > during hot-remove operation. Other things may be to check if a target > > > > node contains cpu0 (until it is supported), the console UART (assuming > > > > we cannot delete it), etc. We should avoid doing rollback as much as we > > > > can. > > > > > > Yes, we can make some checks upfront as an optimization and fail early if > > > the conditions are not met, but for correctness we need to repeat those > > > checks later anyway. Once we've decided to go for the eject, the conditions > > > must hold whatever happens. > > > > Agreed. > > BTW, it is not an optimization I am after for this phase. There are > many error cases during hot-plug operations. It is difficult to assure > that rollback is successful for every error condition in terms of > testing and maintaining the code. So, it is easier to fail beforehand > when possible. OK, but as I said it is necessary to ensure that the conditions will be met in the next phases as well if we don't fail. Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.