From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757929AbdKOPLF (ORCPT ); Wed, 15 Nov 2017 10:11:05 -0500 Received: from mail-wm0-f67.google.com ([74.125.82.67]:39684 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751117AbdKOPK5 (ORCPT ); Wed, 15 Nov 2017 10:10:57 -0500 X-Google-Smtp-Source: AGs4zMYj9q0xMgNCz9wO2ygtJya973cPH7TCpQ6AHy1kyB27O71jDU1FkZwozBBmTpw2w/6WFC11pw== Date: Wed, 15 Nov 2017 16:10:52 +0100 From: Ingo Molnar To: Matthew Wilcox Cc: luca abeni , Peter Zijlstra , Daniel Bristot de Oliveira , linux-kernel@vger.kernel.org Subject: Re: New sparse warnings from sched.h Message-ID: <20171115151052.27y2uzwwxlu4vtr2@gmail.com> References: <20171114204135.GA23685@bombadil.infradead.org> <20171115082743.6nvdz3yk6ln2ftc5@gmail.com> <20171115145445.GA319@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171115145445.GA319@bombadil.infradead.org> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Matthew Wilcox wrote: > On Wed, Nov 15, 2017 at 09:27:43AM +0100, Ingo Molnar wrote: > > * 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): > > > > > > > > > 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 > > > > Mind sending a proper patch with a SOB once it's tested? > > I'd be more than happy to do that. I have no idea what this code is, > what it's used for, or how to test it, so I'll have to rely on somebody > else to test it. Oh, I thought you wanted to test whether it fixes the Sparse bug. Converting these bitfields from signed to unsigned should have no effect on the deadline scheduler. I.e. I basically only need your Signed-off-by. Thnaks, Ingo