From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6FAB9C43331 for ; Thu, 2 Apr 2020 19:17:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4129920737 for ; Thu, 2 Apr 2020 19:17:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389460AbgDBTRn (ORCPT ); Thu, 2 Apr 2020 15:17:43 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:38889 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726963AbgDBTRn (ORCPT ); Thu, 2 Apr 2020 15:17:43 -0400 Received: from p5de0bf0b.dip0.t-ipconnect.de ([93.224.191.11] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1jK5LQ-0001k9-Kr; Thu, 02 Apr 2020 21:17:40 +0200 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 15EA1100D52; Thu, 2 Apr 2020 21:17:40 +0200 (CEST) From: Thomas Gleixner To: Marcelo Schmitt , linux-kernel@vger.kernel.org Cc: lars@metafoo.de Subject: Re: [RFC] genirq: prevent allocated_irqs from being smaller than NR_IRQS In-Reply-To: <20200402150820.GB5886@smtp.gmail.com> References: <20200402150820.GB5886@smtp.gmail.com> Date: Thu, 02 Apr 2020 21:17:40 +0200 Message-ID: <87k12xn1d7.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Marcelo, Marcelo Schmitt writes: > #ifdef CONFIG_SPARSE_IRQ > # define IRQ_BITMAP_BITS (NR_IRQS + 8196) > #else > # define IRQ_BITMAP_BITS NR_IRQS > #endif > > The thing I'm troubled about is that BITS_TO_LONGS divides > IRQ_BITMAP_BITS by sizeof(long) * 8, which makes it possible for the > size of allocated_irqs to be smaller than NR_IRQS. No. It calculates the number of longs which are required to store IRQ_BITMAP_BITS bits. And it does not only divide, it also takes the reminder into account. One byte fits 8 bits. Multiplied with sizeof(long) tells you how many bits fit into a long: Unsurprisingly that 32 on 32bit and 64 on 64bit systems. > By the way, is there any mailing list for IRQ related discussions? > I couldn't find one at vger.kernel.org. The MAINTAINERS file tells you: IRQ SUBSYSTEM L: linux-kernel@vger.kernel.org So you picked the right one. Thanks, tglx