Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752026Ab2JBLZc (ORCPT ); Tue, 2 Oct 2012 07:25:32 -0400 Received: from mail-wg0-f44.google.com ([74.125.82.44]:43041 "EHLO mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751226Ab2JBLZa (ORCPT ); Tue, 2 Oct 2012 07:25:30 -0400 Date: Tue, 2 Oct 2012 13:25:24 +0200 From: Ingo Molnar To: Alexander Gordeev Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Thomas Gleixner , Bjorn Helgaas , Suresh Siddha , Yinghai Lu , Jeff Garzik , Matthew Wilcox , x86@kernel.org, linux-pci@vger.kernel.org, linux-ide@vger.kernel.org Subject: Re: [PATCH v3 -tip 1/5] x86, MSI: Support multiple MSIs in presense of IRQ remapping Message-ID: <20121002112524.GA12420@gmail.com> References: <20121002045518.GA7756@gmail.com> <20121002110630.GA2258@dhcp-26-207.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121002110630.GA2258@dhcp-26-207.brq.redhat.com> 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 Content-Length: 2153 Lines: 65 * Alexander Gordeev wrote: > On Tue, Oct 02, 2012 at 06:55:18AM +0200, Ingo Molnar wrote: > > Thanks for the review, Ingo. > > > > @@ -584,8 +586,12 @@ int __irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node, > > > #define irq_alloc_desc_from(from, node) \ > > > irq_alloc_descs(-1, from, 1, node) > > > > > > +#define irq_alloc_descs_from(from, cnt, node) \ > > > + irq_alloc_descs(-1, from, cnt, node) > > > + > > > > Please use inlines instead of macros. Might transform the one > > above it as well in the process. > > You mean here do not introduce irq_alloc_descs_from, but rather use > irq_alloc_descs() directly? My suggestion is to add irq_alloc_descs_from() as a (very simple) inline function and change irq_alloc_desc_from() to be an inline function as well. > > > +int irq_can_alloc_irqs(unsigned int from, unsigned int cnt) > > > +{ > > > + unsigned int start; > > > + int ret = 0; > > > + > > > + if (!cnt) > > > + return -EINVAL; > > > + > > > + mutex_lock(&sparse_irq_lock); > > > + start = bitmap_find_next_zero_area(allocated_irqs, IRQ_BITMAP_BITS, > > > + from, cnt, 0); > > > + mutex_unlock(&sparse_irq_lock); > > > + if (start + cnt > nr_irqs) > > > + ret = irq_can_expand_nr_irqs(start + cnt); > > > + return ret; > > > > How is this supposed to work wrt. races? > > It is not supposed. Just a quick check if there are enough bits before an > attempt to allocate memory in __create_irqs(). Otherwise __create_irqs() > might allocate irq_cfg's, then realize there are no bits, then deallocate > and fail. > > But strictly speaking, irq_can_alloc_irqs() is unnecessary. Why complicate it if it's unnecessary? The function is inviting wrong logic: it *cannot* tell whether there are enough bits, because the check is racy. So I'd suggest to keep this out - this will further simplify the patches. Thanks, Ingo -- 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/