Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754626Ab0LOOuL (ORCPT ); Wed, 15 Dec 2010 09:50:11 -0500 Received: from www.tglx.de ([62.245.132.106]:38645 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754520Ab0LOOuJ (ORCPT ); Wed, 15 Dec 2010 09:50:09 -0500 Date: Wed, 15 Dec 2010 15:49:27 +0100 (CET) From: Thomas Gleixner To: Jan Kiszka cc: Jan Kiszka , Avi Kivity , Marcelo Tosatti , "linux-kernel@vger.kernel.org" , kvm , Tom Lyon , Alex Williamson , "Michael S. Tsirkin" Subject: Re: [PATCH v3 2/4] genirq: Inform handler about line sharing state In-Reply-To: <4D08CE44.6000407@siemens.com> Message-ID: References: <4D07F70A.30209@web.de> <4D08CE44.6000407@siemens.com> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2252 Lines: 62 On Wed, 15 Dec 2010, Jan Kiszka wrote: > Am 15.12.2010 14:04, Thomas Gleixner wrote: > > On Wed, 15 Dec 2010, Jan Kiszka wrote: > >> Am 14.12.2010 21:54, Thomas Gleixner wrote: > >>> On Mon, 13 Dec 2010, Jan Kiszka wrote: > >>>> @@ -943,6 +950,9 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id) > >>>> /* Make sure it's not being used on another CPU: */ > >>>> synchronize_irq(irq); > >>>> > >>>> + if (single_handler) > >>>> + desc->irq_data.drv_status &= ~IRQS_SHARED; > >>>> + > >>> > >>> What's the reason to clear this flag outside of the desc->lock held > >>> region. > >> > >> We need to synchronize the irq first before clearing the flag. > >> > >> The problematic scenario behind this: An IRQ started in shared mode, > >> this the line was unmasked after the hardirq. Now we clear IRQS_SHARED > >> before calling into the threaded handler. And that handler may now think > >> that the line is still masked as IRQS_SHARED is set. > > > > That should read "not set" I guess. > > Can't remember who wrote this, but that guy might have been too tired > for clear sentences: Yes, of course, we could run into troubles, if > IRQS_SHARED was _not_ set while the IRQ line is unmasked between hard > and threaded handler. Right. As a side note, the current implementation requires that you lookup irq_data.drv_status for every invocation of the handler or have a reference to irq_data.drv_status somewhere locally, which I don't like either. I have an evil and nasy idea how to avoid that, need to look how ugly it gets. Worst case we need to go back to that notification thing which I wanted really avoid in the first place. Though I like the register_mutex idea which came out of this a lot as it allows us to reduce desc->lock held and interrupt disabled regions quite nicely. /me goes back to stare at the code > > Hmm, needs more thoughts :( > > Be warned, might be painful. Bah, my brain became pain resistant when I started hacking that code. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/