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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 55047C433EF for ; Wed, 2 Mar 2022 18:44:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244673AbiCBSpA (ORCPT ); Wed, 2 Mar 2022 13:45:00 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54006 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244691AbiCBSox (ORCPT ); Wed, 2 Mar 2022 13:44:53 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 55C8FD04B4 for ; Wed, 2 Mar 2022 10:44:09 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=aB+E32SV8Widsy5hZm4SDjs3y2zV+hJliWd8+r+tQKc=; b=WlHj8/DcuQg8olNKD9pOlLvOcP EGN3ab2VLYSQocFmXfUHF72DLsPPNYkZ3b/ZN3nKLOPC90xJyqGR8QPdJbLlQ0rsvUnhBlcLkXqWL X8I5/cbUsC0wbrXpGGHo3atu0s/SxAdYjy7gYt4racnUp+KgGoqMXS6BPDq8lrMGQNXGX3y/qe28F 4x4ogm/OLsxX/+Ls5WHetLay8R0eVsSuXbO0k5Az3UD+CJ7xrcdEzCKuqBRjxse19yt9891w+RX/1 KM3jVC6UzpwCE78hgfeYP8Hv0FAHmd+0OlqcoWgrqTShXN+Vg1rsqbBqOKcfdDdSw7t5+qK/eGIfn wetp6sIQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1nPTx7-00AtAW-3b; Wed, 02 Mar 2022 18:43:57 +0000 Date: Wed, 2 Mar 2022 18:43:57 +0000 From: Matthew Wilcox To: Kees Cook Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Linus Torvalds , linux-kernel@vger.kernel.org Subject: Re: [PATCH 00/19] Enable -Wshadow=local for kernel/sched Message-ID: References: <20220302043451.2441320-1-willy@infradead.org> <202203021030.EEEF58C2@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202203021030.EEEF58C2@keescook> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 02, 2022 at 10:32:23AM -0800, Kees Cook wrote: > On Wed, Mar 02, 2022 at 04:34:32AM +0000, Matthew Wilcox (Oracle) wrote: > > I thought I'd choose one of the more core parts of the kernel to > > demonstrate the value of -Wshadow. It found two places where there are > > shadowed variables that are at least confusing. For all I know they're > > buggy and my resolution of these warnings is wrong. > > > > The first 12 patches just untangle the unclean uses of __ret in wait.h > > & friends. Then 4 patches to fix problems in headers that are noticed > > by kernel/sched. Two patches fix the two places in kernel/sched/ > > with shadowed variables and the final patch adds -Wshadow=local to > > the Makefile. > > You are my hero. I was pulling my hair out trying to figure out how > to deal with this a few months ago, and the use of UNIQUE_ID was the > key. Yay! > > > I'm quite certain this patch series isn't going in as-is. But maybe > > it'll inspire some patches that can go in. > > I think it's pretty darn close. One thing that can be done to test the > results for the first 12 patches is to do a binary comparison -- these > changes _should_ have no impact on the final machine code. (It'll > totally change the debug sections, etc, but the machine code should be > the same.) Peter pointed out that I got confused about which __ret was being referred to: +#define __wait_event_freezable_timeout(wq_head, condition, timeout, __ret) \ + ___wait_event(wq_head, ___wait_cond_timeout(condition, __ret), \ + TASK_INTERRUPTIBLE, 0, timeout, \ + __ret = freezable_schedule_timeout(__ret), UNIQUE_ID) so now that internal variable is UNIQUE_ID, whatever that is but the condition argument was supposed to look at that but you explicitly pulled that out ie "__ret = freezable_schedule_timeout(__ret)" is supposed to refer to the inner __ret, not the outer __ret. Which was the opposite of what I thought was supposed to happen. We can fix this, of course. Something like ... #define ___wait_event_freezable_timeout(wq_head, condition, timeout, ret) \ ___wait_event(wq_head, ___wait_cond_timeout(condition, ret), \ TASK_INTERRUPTIBLE, 0, timeout, \ ret = freezable_schedule_timeout(ret), ret) #define __wait_event_freezable_timeout(wq_head, condition, timeout) \ ___wait_event_freezable_timeout(wq_head, condition, timeout, UNIQUE_ID) ... and now all the 'ret' refer to the thing that they look like they're referring to.