From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752068AbdGGQlo (ORCPT <rfc822;w@1wt.eu>);
        Fri, 7 Jul 2017 12:41:44 -0400
Received: from Galois.linutronix.de ([146.0.238.70]:33026 "EHLO
        Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1750882AbdGGQln (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 7 Jul 2017 12:41:43 -0400
Date: Fri, 7 Jul 2017 18:41:32 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: Juergen Gross <jgross@suse.com>
cc: jeffy.chen@rock-chips.com,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        xen-devel <xen-devel@lists.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: Problem with commit bf22ff45bed664aefb5c4e43029057a199b7070c
In-Reply-To: <dc3e7811-e3f8-1cf9-d556-1ac57288daa5@suse.com>
Message-ID: <alpine.DEB.2.20.1707071747380.1871@nanos>
References: <dc3e7811-e3f8-1cf9-d556-1ac57288daa5@suse.com>
User-Agent: Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, 7 Jul 2017, Juergen Gross wrote:

> Commit bf22ff45bed664aefb5c4e43029057a199b7070c ("genirq: Avoid
> unnecessary low level irq function calls") breaks Xen guest
> save/restore handling.
> 
> The main problem are the PV devices using Xen event channels as
> interrupt sources which are represented as an "irq chip" in the kernel.
> When saving the guest the event channels are masked internally. At
> restore time event channels are re-established and unmasked via
> irq_startup(). Unfortunately above commit will let the unmask operation
> be a nop as the irq handling doesn't know about the masking done before.

Rightfully so. Making assumptions about the inner workings of core code is
always wrong.

> I have a patch repairing the issue, but I'm not sure if this way to do
> it would be accepted. I have exported mask_irq() and I'm doing the
> masking now through this function. Would the attached patch be
> acceptable? Or is there a better way to solve the problem?

Without looking at the patch (too lazy to fiddle with attachments right
now), this is definitely wrong. I'll have a look later tonight.

Thanks,

	tglx