Date: Fri, 11 Mar 2016 12:26:08 +0100 (CET)
From: Anna-Maria Gleixner <anna-maria@linutronix.de>
To: David Vrabel <david.vrabel@citrix.com>
cc: linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>, rt@linutronix.de
Subject: Re: [Xen-devel] [PATCH] xen/events/fifo: Add missing hotplug notifier
 transition
In-Reply-To: <56E2A3B6.2060208@citrix.com>
Message-ID: <alpine.DEB.2.11.1603111219450.5298@hypnos>
References: <1457686822-39117-1-git-send-email-anna-maria@linutronix.de> <56E2A3B6.2060208@citrix.com>
User-Agent: Alpine 2.11 (DEB 23 2013-08-11)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1056
Lines: 31

On Fri, 11 Mar 2016, David Vrabel wrote:

> On 11/03/16 09:00, Anna-Maria Gleixner wrote:
> > The evtchn_fifo_cpu_notification() hotplug callback lacks handling of
> > the CPU_UP_CANCELED case. That means, if CPU_UP_PREPARE fails, the
> > handle of the fifo events is not dropped.
> > 
> > Add handling for CPU_UP_CANCELED transition to drop the fifo events
> > handle.
> 
> __evtchn_fifo_handle_events() does not releases resources, it processes
> any pending events for this CPU.
> 
> This patch would only be necessary if a CPU in CPU_UP_CANCELED state may
> have had unmasked interrupts.  If so you would need:

Thanks for the explanation

> case CPU_UP_CANCELED:
>           if (per_cpu(cpu_control_block, cpu))
>               __evtchn_fifo_handle_events(cpu, true);
>           break;
> 
> To handle the case where the control block allocation or initialization
> failed during CPU_UP_PREPARE.

This would not be necessary, because if the CPU_UP_PREPARE of this
notifier fails, the CPU_UP_CANCELLED of this notifier will not be
invoked.

Anna-Maria