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=-13.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 26A25C0650E for ; Wed, 3 Jul 2019 11:23:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 050C9218A0 for ; Wed, 3 Jul 2019 11:23:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727013AbfGCLXT (ORCPT ); Wed, 3 Jul 2019 07:23:19 -0400 Received: from foss.arm.com ([217.140.110.172]:44794 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726255AbfGCLXT (ORCPT ); Wed, 3 Jul 2019 07:23:19 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 6045E344; Wed, 3 Jul 2019 04:23:18 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 76C263F703; Wed, 3 Jul 2019 04:23:17 -0700 (PDT) Date: Wed, 3 Jul 2019 12:23:12 +0100 From: Mark Rutland To: Nathan Huckleberry Cc: catalin.marinas@arm.com, will@kernel.org, clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2] arm64: mm: Fix dead assignment of old_pte Message-ID: <20190703112139.GA29570@lakrids.cambridge.arm.com> References: <20190702234135.78780-1-nhuck@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190702234135.78780-1-nhuck@google.com> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 02, 2019 at 04:41:35PM -0700, Nathan Huckleberry wrote: > When analyzed with the clang static analyzer the > following warning occurs > > line 251, column 2 > Value stored to 'old_pte' is never read > > This warning is repeated every time pgtable.h is > included by another file and produces ~3500 > extra warnings. > > Moving old_pte into preprocessor guard. > > Cc: clang-built-linux@googlegroups.com > Signed-off-by: Nathan Huckleberry > --- > Changes from v1 -> v2 > * Added scope to avoid [-Wdeclaration-after-statement] > arch/arm64/include/asm/pgtable.h | 27 ++++++++++++++++----------- > 1 file changed, 16 insertions(+), 11 deletions(-) As Will asked, does this also trigger in linux-next? I rewrote this code to avoid to only perform the READ_ONCE() when we'd use the value, and IIUC that may be sufficient to avoid the warning: https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?h=for-next/core&id=9b604722059039a1a3ff69fb8dfd024264046024 Thanks, Mark. > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h > index fca26759081a..12b7f08db40d 100644 > --- a/arch/arm64/include/asm/pgtable.h > +++ b/arch/arm64/include/asm/pgtable.h > @@ -238,8 +238,6 @@ extern void __sync_icache_dcache(pte_t pteval); > static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, > pte_t *ptep, pte_t pte) > { > - pte_t old_pte; > - > if (pte_present(pte) && pte_user_exec(pte) && !pte_special(pte)) > __sync_icache_dcache(pte); > > @@ -248,16 +246,23 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr, > * hardware updates of the pte (ptep_set_access_flags safely changes > * valid ptes without going through an invalid entry). > */ > - old_pte = READ_ONCE(*ptep); > - if (IS_ENABLED(CONFIG_DEBUG_VM) && pte_valid(old_pte) && pte_valid(pte) && > - (mm == current->active_mm || atomic_read(&mm->mm_users) > 1)) { > - VM_WARN_ONCE(!pte_young(pte), > - "%s: racy access flag clearing: 0x%016llx -> 0x%016llx", > - __func__, pte_val(old_pte), pte_val(pte)); > - VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte), > - "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx", > - __func__, pte_val(old_pte), pte_val(pte)); > + #if IS_ENABLED(CONFIG_DEBUG_VM) > + { > + pte_t old_pte; > + > + old_pte = READ_ONCE(*ptep); > + if (pte_valid(old_pte) && pte_valid(pte) && > + (mm == current->active_mm || > + atomic_read(&mm->mm_users) > 1)) { > + VM_WARN_ONCE(!pte_young(pte), > + "%s: racy access flag clearing: 0x%016llx -> 0x%016llx", > + __func__, pte_val(old_pte), pte_val(pte)); > + VM_WARN_ONCE(pte_write(old_pte) && !pte_dirty(pte), > + "%s: racy dirty state clearing: 0x%016llx -> 0x%016llx", > + __func__, pte_val(old_pte), pte_val(pte)); > + } > } > + #endif > > set_pte(ptep, pte); > } > -- > 2.22.0.410.gd8fdbe21b5-goog > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel