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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 D46B9C33CB3 for ; Fri, 17 Jan 2020 21:27:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ABF582072E for ; Fri, 17 Jan 2020 21:27:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="ivmlj8nN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729107AbgAQV1B (ORCPT ); Fri, 17 Jan 2020 16:27:01 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:34805 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729081AbgAQV1A (ORCPT ); Fri, 17 Jan 2020 16:27:00 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1579296419; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=2vnulubJD8mSbDRt53yuy9p1BI2iN8qpqQuvtoRp26c=; b=ivmlj8nNlBxGwwJHQU8C/JORg5GLy7wUyKY2MpBcC7vU90EDoXynTGrFeCvrbyTfMIqRN5 6/jpkTUkM79tRH9CXo1N1SWNDzcTTuOtdAqzNs3KGXZFyjGYTWaZHmP8gDHxcxn8fpUg4P o6lXyQeEJd8HK29wxyx9gCt5HOswtQ4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-111-EKAgyNHDPSSLzbE8S-KphQ-1; Fri, 17 Jan 2020 16:26:54 -0500 X-MC-Unique: EKAgyNHDPSSLzbE8S-KphQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 004D1DBA6; Fri, 17 Jan 2020 21:26:53 +0000 (UTC) Received: from treble (ovpn-123-54.rdu2.redhat.com [10.10.123.54]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7556B5D9CD; Fri, 17 Jan 2020 21:26:51 +0000 (UTC) Date: Fri, 17 Jan 2020 15:26:49 -0600 From: Josh Poimboeuf To: Marco Elver Cc: David Sterba , Randy Dunlap , Stephen Rothwell , Linux Next Mailing List , Linux Kernel Mailing List , Linux Btrfs , Peter Zijlstra Subject: Re: linux-next: Tree for Dec 6 (objtool, lots in btrfs) Message-ID: <20200117212649.opf4lt4w4jgwmrt7@treble> References: <20191212184725.db3ost7rcopotr5u@treble> <20191213235054.6k2lcnwa63r26zwi@treble> <20191214054515.ougsr5ykhl3vvy57@treble> <20191217152511.GG3929@suse.cz> <20200117172629.yqowxl642hdx4vcm@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Jan 17, 2020 at 09:28:27PM +0100, Marco Elver wrote: > On Fri, 17 Jan 2020 at 18:26, Josh Poimboeuf wrote: > > > > On Tue, Dec 17, 2019 at 04:25:11PM +0100, David Sterba wrote: > > > On Fri, Dec 13, 2019 at 11:05:18PM -0800, Randy Dunlap wrote: > > > > OK, that fixes most of them, but still leaves these 2: > > > > > > > > btrfs006.out:fs/btrfs/extent_io.o: warning: objtool: __set_extent_bit()+0x536: unreachable instruction > > > > > > Hard to read from the assembly what C statement is it referring to. I > > > think there are also several functions inlined, I don't see anything > > > suspicious inside __set_extent_bit itself. > > > > > > > btrfs006.out:fs/btrfs/relocation.o: warning: objtool: add_tree_block()+0x501: unreachable instruction > > > > > > Probably also heavily inlined, the function has like 50 lines, a few > > > non-trivial function calls but the offset in the warning suggests a > > > larger size. > > > > > > While browsing the callees I noticed that both have in common a function > > > that is supposed to print and stop at fatal errors. They're > > > extent_io_tree_panic (extent_io.c) and backref_tree_panic > > > (relocation.c). Both call btrfs_panic which is a macro: > > > > > > 3239 #define btrfs_panic(fs_info, errno, fmt, args...) \ > > > 3240 do { \ > > > 3241 __btrfs_panic(fs_info, __func__, __LINE__, errno, fmt, ##args); \ > > > 3242 BUG(); \ > > > 3243 } while (0) > > > > > > There are no conditionals and BUG has the __noreturn annotation > > > (unreachable()) so all is in place and I don't have better ideas what's > > > causing the reports. > > > > I think KCSAN is somehow disabling GCC's detection of implicit noreturn > > functions -- or at least some calls to them. So GCC is inserting dead > > code after the calls. BUG() uses __builtin_unreachable(), so GCC should > > know better. > > > > If this is specific to KCSAN then I might just disable these warnings > > for KCSAN configs. > > I noticed that this is also a CC_OPTIMIZE_FOR_SIZE config. I recently > sent some patches to turn some inlines into __always_inlines because > CC_OPTIMIZE_FOR_SIZE decides to not inline functions that should > always be inlined. > > I noticed that 'assfail' is a 'static inline' function and you > mentioned earlier that GCC seems to not be able to determine if it > returns or not. If CC_OPTIMIZE_FOR_SIZE decides to not inline, then > maybe this could be a problem? It could also be the compiler having > some trouble here with the CC_OPTIMIZE_FOR_SIZE + KCSAN combination. Even for a non-inlined static function, GCC typically detects when it's implicitly "noreturn", and optimizes the call sites accordingly. And that has also been true even for CC_OPTIMIZE_FOR_SIZE in the past. So something changed apparently. (KCSAN was just a guess.) -- Josh