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=-11.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 1761AC49361 for ; Fri, 18 Jun 2021 23:05:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F12926109E for ; Fri, 18 Jun 2021 23:05:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232885AbhFRXHf (ORCPT ); Fri, 18 Jun 2021 19:07:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:44942 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230024AbhFRXHd (ORCPT ); Fri, 18 Jun 2021 19:07:33 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id CF02961078; Fri, 18 Jun 2021 23:05:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1624057523; bh=G+jqxlyGbiQRmuv7Op8PGzyCrvARiAzvbUMuCk+sATc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=pOi4gQgxN2WAWNlxGZJM51qtNaMiRMYNHNfglrR3HfsVUfJRLEScpil9/7sMpfTeT 7NHmX29rFhAqjTql30Tyku39E/6ZbllF46qHXSMzn1BcfomPQEjQh15+BD/I1WXuRB OQ8N3WiGQ7IBF/31k/d3ikA0FkAlG0FI6mlhzCU6AInm+wRUfIOkeB6sOi1GWrmikP drC/Icm25Vv/2gE1NlREMbWEPx66/a3z9y7hrVEx9fxnBVptemp0f6VKMf19vAVPF3 zBP+seiGKRYoNmbk1Fl6K1+XPPDn5OnNZRk8bKLAmMR8fltnlm5S1/i1wOJZs+Pyxr NwSVkNEcAln3A== Date: Fri, 18 Jun 2021 16:05:17 -0700 From: Nathan Chancellor To: "Aneesh Kumar K.V" Cc: Andrew Morton , Matthew Wilcox , Naresh Kamboju , linux-next@vger.kernel.org, clang-built-linux@googlegroups.com, lkft-triage@lists.linaro.org, linux-kernel@vger.kernel.org, Nick Desaulniers , Arnd Bergmann , Stephen Rothwell Subject: Re: [next] [clang] x86_64-linux-gnu-ld: mm/mremap.o: in function `move_pgt_entry': mremap.c:(.text+0x763): undefined reference to `__compiletime_assert_342' Message-ID: References: <6f3c5317-2877-9a57-0126-e9305f000269@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6f3c5317-2877-9a57-0126-e9305f000269@linux.ibm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 18, 2021 at 10:32:42AM +0530, Aneesh Kumar K.V wrote: > On 6/17/21 11:32 PM, Nathan Chancellor wrote: > > Rebuilt the CC list because most people were added based on the > > incorrect bisect result. > > > > On Thu, Jun 17, 2021 at 02:51:49PM +0100, Matthew Wilcox wrote: > > > On Thu, Jun 17, 2021 at 06:15:45PM +0530, Naresh Kamboju wrote: > > > > On Thu, 17 Jun 2021 at 17:41, Naresh Kamboju wrote: > > > > > x86_64-linux-gnu-ld: mm/mremap.o: in function `move_pgt_entry': > > > > > mremap.c:(.text+0x763): undefined reference to `__compiletime_assert_342' > > > > > > > > The git bisect pointed out the first bad commit. > > > > > > > > The first bad commit: > > > > commit 928cf6adc7d60c96eca760c05c1000cda061604e > > > > Author: Stephen Boyd > > > > Date: Thu Jun 17 15:21:35 2021 +1000 > > > > module: add printk formats to add module build ID to stacktraces > > > > > > Your git bisect probably went astray. There's no way that commit > > > caused that regression. > > > > My bisect landed on commit 83f85ac75855 ("mm/mremap: convert huge PUD > > move to separate helper"). flush_pud_tlb_range() evaluates to > > BUILD_BUG() when CONFIG_TRANSPARENT_HUGEPAGE is unset but this function > > is present just based on the value of > > CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD. > > > > $ make -skj(nproc) ARCH=x86_64 CC=clang O=build/x86_64 distclean allnoconfig mm/mremap.o > > > > $ llvm-readelf -s build/x86_64/mm/mremap.o &| rg __compiletime_assert > > 21: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND __compiletime_assert_337 > > > > $ rg TRANSPARENT_ build/x86_64/.config > > 450:CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE=y > > 451:CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD=y > > 562:# CONFIG_TRANSPARENT_HUGEPAGE is not set > > > > Not sure why this does not happen on newer clang versions, presumably > > something with inlining decisions? Still seems like a legitimate issue > > to me. > > > > gcc 10 also doesn't give a build error. I guess that is because we evaluate > > if (pud_trans_huge(*old_pud) || pud_devmap(*old_pud)) { > > to if (0) with CONFIG_TRANSPARENT_HUGEPAGE disabled. > > switching that to if (1) do results in BUILD_BUG triggering. Thanks for pointing that out. I think what happens with clang-10 and clang-11 is that move_huge_pud() gets inlined into move_pgt_entry() but then the compiler does not figure out that the HPAGE_PUD case is dead so the code sticks around, where as GCC and newer clang versions can figure that out and eliminate that case. > Should we fix this ? Yes, I believe that we should. > modified mm/mremap.c > @@ -336,7 +336,7 @@ static inline bool move_normal_pud(struct vm_area_struct > *vma, > } > #endif > > -#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD > +#if defined(CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD) && > defined(CONFIG_TRANSPARENT_HUGEPAGE) > static bool move_huge_pud(struct vm_area_struct *vma, unsigned long > old_addr, > unsigned long new_addr, pud_t *old_pud, pud_t *new_pud) > { That works or we could mirror what has already been done for the HPAGE_PMD case. No personal preference. diff --git a/mm/mremap.c b/mm/mremap.c index 9a7fbec31dc9..5989d3990020 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -460,7 +460,8 @@ static bool move_pgt_entry(enum pgt_entry entry, struct vm_area_struct *vma, new_entry); break; case HPAGE_PUD: - moved = move_huge_pud(vma, old_addr, new_addr, old_entry, + moved = IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && + move_huge_pud(vma, old_addr, new_addr, old_entry, new_entry); break; Cheers, Nathan