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 3C79BC7EE2C for ; Wed, 24 May 2023 09:30:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230147AbjEXJaJ (ORCPT ); Wed, 24 May 2023 05:30:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240733AbjEXJ35 (ORCPT ); Wed, 24 May 2023 05:29:57 -0400 Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D32FF90; Wed, 24 May 2023 02:29:55 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 8A1A41FDB1; Wed, 24 May 2023 09:29:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1684920594; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VGQvzW+Ai0N6JzBCRDYD9ANjB+5pdCPWrZ/ZW6bNATU=; b=QmaO7/TVEdXRc2ZfW5QqKJSzNMUOmxWIDNB6OGRYC4BOUI6i1qLOjTEYkOSHYIzQ7sUreX mIr9MO8/EQ1lobHYc7RfSpu+vaQccIjpuEhrs/ondR/SO5UIbQsQBbqOcvGfTwDjObM6A1 CumCX5lRKXxKuDWKqoq44uH22oiUs6g= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1684920594; h=from:from:reply-to:reply-to:date:date:message-id:message-id:to:to: cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VGQvzW+Ai0N6JzBCRDYD9ANjB+5pdCPWrZ/ZW6bNATU=; b=Jm2FeBO6CN2J5Qdpaen4fp8Cs5uhaO/2fEkgDQxqFrP+kzx7uw37gi6NTJn+3EpK/YCnxM 2XGRcs4yVazvXrBQ== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 5055D13425; Wed, 24 May 2023 09:29:54 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id 2t7mEhLZbWQzAQAAMHmgww (envelope-from ); Wed, 24 May 2023 09:29:54 +0000 Date: Wed, 24 May 2023 11:23:47 +0200 From: David Sterba To: Qu Wenruo Cc: Stephen Zhang , clm@fb.com, josef@toxicpanda.com, dsterba@suse.com, linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org, zhangshida@kylinos.cn, k2ci Subject: Re: [PATCH] btrfs: fix uninitialized warning in btrfs_log_inode Message-ID: <20230524092346.GI32559@suse.cz> Reply-To: dsterba@suse.cz References: <20230516013430.2712449-1-zhangshida@kylinos.cn> <20230522215144.GS32559@twin.jikos.cz> <409455a1-560f-24d0-e28f-74c665668050@gmx.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <409455a1-560f-24d0-e28f-74c665668050@gmx.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 23, 2023 at 06:47:39PM +0800, Qu Wenruo wrote: > On 2023/5/23 05:51, David Sterba wrote: > > On Wed, May 17, 2023 at 05:07:55PM +0800, Stephen Zhang wrote: > >> Qu Wenruo 于2023年5月17日周三 15:47写道： > >>> On 2023/5/16 09:34, zhangshida wrote: > >>>> From: Shida Zhang > >>>> > >>>> This fixes the following warning reported by gcc 10 under x86_64: > >>> > >>> Full gcc version please. > >> > >> it's "gcc (Debian 10.2.1-6) 10.2.1 20210110". > >> > >>> Especially you need to check if your gcc10 is the latest release. > >>> > >>> If newer gcc (12.2.1) tested without such error, it may very possible to > >>> be a false alert. > >>> > >>> And in fact it is. > >>> > >>> @first_dir_index would only be assigned to @last_range_start if > >>> last_range_end != 0. > >>> > >>> Thus the loop must have to be executed once, and @last_range_start won't > >>> be zero. > >>> > >> > >> Yup, I know it's a false positive. What I don't know is the criterion > >> that decides whether it is a good patch. > > > > If you have analyzed the code and found out that it was indeed a false > > positive then please state that in the changelog. Fixing it still makes > > sense so the compiler version and briefly explaining why you fix it that > > way makes it a good patch. > > > >> That is, > >> it doesn't look so good because it is a false alert and the latest gcc > >> can get rid of such warnings, based on what you said( if I understand > >> correctly). > >> Or, > >> It looks okay because the patch can make some older gcc get a cleaner > >> build and do no harm to the original code logic. > > > > In general I agree here. > > > >> In fact, I've seen Linus complaining about the warning generated by > >> some gcc version in another thread. > >> > >> https://lore.kernel.org/linux-xfs/168384265493.22863.2683852857659893778.pr-tracker-bot@kernel.org/T/#t > > > > I share the POV for warning fixes, I'd rather see new reports after > > fixing the previous ones than reminding everybody to update. > > Or can we only enable -Wmaybe-uninitialized only for certain builds? > Like binding it with CONFIG_BTRFS_DEBUG? > > So far all warning are false alerts, and I'm really not a fan of false > alerts. Josef found some real bugs with this warning enabled and then we decided it would be a good idea to have it enabled for all builds. If we don't do it by default then the chances that people will use it are low. > The -Wmaybe-uninitialized option doesn't look that reliable on older > compilers, and for developers we're more or less using uptodate > toolchains anyway. Yeah the warning is speculative so the compilers can report more false positives. I still have some very old test setups and the compiler gets updated rarely, IIRC I went from 4.x to 7.x and now there's 10.x so I might send some warning fixes myself. Over time I'd like to enable more warnings just for fs/btrfs/.