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 B8F72C433F5 for ; Wed, 2 Feb 2022 06:53:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245108AbiBBGxR (ORCPT ); Wed, 2 Feb 2022 01:53:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50852 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244694AbiBBGwj (ORCPT ); Wed, 2 Feb 2022 01:52:39 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 72CC3C061751 for ; Tue, 1 Feb 2022 22:08:07 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id D3FBDB83008 for ; Wed, 2 Feb 2022 06:08:05 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 41E52C004E1; Wed, 2 Feb 2022 06:08:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1643782084; bh=HvguaN/KnZ4Mt0Cs/C294n4Y3l8Qu7MGLAl0oB6BX8A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Dmv/O/fu5NnmFseISuSg9qnGKsfJ+GJKJEkZ8vZjnaF7XparyJocs3xwnglIv0Hn5 B1wgm/vqIf/RxYTIDwPtrBlHm3BO4o6YI+3tR8ymy0ODR19N+P8gfPYcYM+2NG0s8V 8WotdaRor7WyMp4yCgDoyYtMDcvJoviH0w1CojQD0LqJrxP3tRdUHh7PmL+o8/5M+o CC2Q9zJjwOcN20qyU5og1CQA1Lu8COT6nL/CQHFZZJEi6MSAoUZZpMn5cGD6G9RXrr R8yI1HFyuMiZRXrLLvh+IQYvxo2RLmd8/sLF+OSLlIfJV8h999dPQP4g++k3yHuadB 8KI7BZDO14UYg== Date: Wed, 2 Feb 2022 08:07:55 +0200 From: Mike Rapoport To: Waiman Long Cc: Andrew Morton , "Kirill A. Shutemov" , Ingo Molnar , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Justin Forbes , Rafael Aquini Subject: Re: [PATCH] mm/sparsemem: Fix 'mem_section' will never be NULL gcc 12 warning Message-ID: References: <20220201192924.672675-1-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220201192924.672675-1-longman@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 01, 2022 at 02:29:24PM -0500, Waiman Long wrote: > The gcc 12 compiler reports a warning on the following code: > > static inline struct mem_section *__nr_to_section(unsigned long nr) > { > #ifdef CONFIG_SPARSEMEM_EXTREME > if (!mem_section) > return NULL; > #endif > : > > With CONFIG_SPARSEMEM_EXTREME on, the mem_section definition is > > extern struct mem_section **mem_section; > > Obviously, mem_section cannot be NULL, but *mem_section can be if memory > hasn't been allocated for the dynamic mem_section[] array yet. Fix this > warning by checking for "!*mem_section" instead. Hmm, if mem_section cannot be NULL, it means if will be never allocated, no? static void __init memory_present(int nid, unsigned long start, unsigned long end) { unsigned long pfn; #ifdef CONFIG_SPARSEMEM_EXTREME if (unlikely(!mem_section)) { unsigned long size, align; size = sizeof(struct mem_section *) * NR_SECTION_ROOTS; align = 1 << (INTERNODE_CACHE_SHIFT); mem_section = memblock_alloc(size, align); if (!mem_section) panic("%s: Failed to allocate %lu bytes align=0x%lx\n", __func__, size, align); } #endif ... > > Fixes: 83e3c48729d9 ("mm/sparsemem: Allocate mem_section at runtime for CONFIG_SPARSEMEM_EXTREME=y") > Signed-off-by: Waiman Long > --- > include/linux/mmzone.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index aed44e9b5d89..bd1b19925f3b 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1390,7 +1390,7 @@ static inline unsigned long *section_to_usemap(struct mem_section *ms) > static inline struct mem_section *__nr_to_section(unsigned long nr) > { > #ifdef CONFIG_SPARSEMEM_EXTREME > - if (!mem_section) > + if (!*mem_section) > return NULL; > #endif > if (!mem_section[SECTION_NR_TO_ROOT(nr)]) > -- > 2.27.0 > > -- Sincerely yours, Mike.