From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755644AbdKOIgq (ORCPT ); Wed, 15 Nov 2017 03:36:46 -0500 Received: from mail.santannapisa.it ([193.205.80.98]:22052 "EHLO mail.santannapisa.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751617AbdKOIgh (ORCPT ); Wed, 15 Nov 2017 03:36:37 -0500 Date: Wed, 15 Nov 2017 09:36:29 +0100 From: luca abeni To: Matthew Wilcox Cc: Peter Zijlstra , Daniel Bristot de Oliveira , Ingo Molnar , linux-kernel@vger.kernel.org Subject: Re: New sparse warnings from sched.h Message-ID: <20171115093629.79f8ab74@sweethome> In-Reply-To: <20171114204135.GA23685@bombadil.infradead.org> References: <20171114204135.GA23685@bombadil.infradead.org> X-Mailer: Claws Mail 3.14.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Tue, 14 Nov 2017 12:41:35 -0800 Matthew Wilcox wrote: > commit 799ba82de01e7543f6b2042e1a739f3a20255f23 > Author: luca abeni > Date: Thu Sep 7 12:09:31 2017 +0200 > > sched/deadline: Use C bitfields for the state flags > > Ask the compiler to use a single bit for storing true / false > values, instead of wasting the size of a whole int value. > Tested with gcc 5.4.0 on x86_64, and the compiler produces the > expected Assembly (similar to the Assembly code generated when > explicitly accessing the bits with bitmasks, "&" and "|"). > > produces four warnings from sparse for every file which includes > sched.h: > > ./include/linux/sched.h:476:62: error: dubious one-bit signed bitfield > ./include/linux/sched.h:477:62: error: dubious one-bit signed bitfield > ./include/linux/sched.h:478:62: error: dubious one-bit signed bitfield > ./include/linux/sched.h:479:62: error: dubious one-bit signed bitfield > > This seems like the trivial fix (untested): [...] I think Dan Carpenter sent a similar patch (and I replied agreeing with it). I believe in this particular case signed integers are safe, but if "unsigned int" is the preferred style in the kernel I agree with the change. Thanks, Luca > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > index a5dc7c98b0a2..21991d668d35 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -473,10 +473,10 @@ struct sched_dl_entity { > * conditions between the inactive timer handler and the > wakeup > * code. > */ > - int dl_throttled : 1; > - int dl_boosted : 1; > - int dl_yielded : 1; > - int dl_non_contending : 1; > + unsigned int dl_throttled : 1; > + unsigned int dl_boosted : 1; > + unsigned int dl_yielded : 1; > + unsigned int dl_non_contending : 1; > > /* > * Bandwidth enforcement timer. Each -deadline task has its