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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E8BCAC433F5 for ; Thu, 4 Nov 2021 13:36:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C6C85611C4 for ; Thu, 4 Nov 2021 13:36:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231265AbhKDNij (ORCPT ); Thu, 4 Nov 2021 09:38:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:38702 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230409AbhKDNic (ORCPT ); Thu, 4 Nov 2021 09:38:32 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 377C561108; Thu, 4 Nov 2021 13:35:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1636032954; bh=OfNAx9rQwiK+QscXJpdjavO2stFix0dG6j0x3xEKe1Q=; h=From:To:Cc:Subject:Date:From; b=RVwruqXOchb8HPnX9zYesjc5taffYzUjt7Ru/SD0ohD4UwUbooowtwoIEJPTiuRIV IKwwp2rfndBuNSLtgY/JjNhXQCExn0GZRbkzR+l30BdDCOOTJG0kHY0iqqYiHWJSNg GvgTwB99X/O68fnjRVr9IMIrHSBO0b9xG2WcXLBr3mkZ0t/Byfce148xWoj6fHuCWL 8XawY1nWvhDKfpPaNCakCh1OTddYg8NaMxoBoTpMcEkeSguYgDDoBD/pLAZoVIYajs /5CNVLT0BdybSBmlu0SzRe7GCGlRV6go/ehR2J2mm1y6x4VwjdB1p71cTfOLE0biVg NxcuD+n38m5Zg== From: Arnd Bergmann To: Andrew Morton Cc: Arnd Bergmann , "Uladzislau Rezki (Sony)" , Stephen Rothwell , Nicholas Piggin , Michal Hocko , "Paul E. McKenney" , Chen Wandun , David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] mm: vmap: avoid -Wsequence-point warning Date: Thu, 4 Nov 2021 14:35:40 +0100 Message-Id: <20211104133549.1150058-1-arnd@kernel.org> X-Mailer: git-send-email 2.29.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Arnd Bergmann gcc warns about potentially undefined behavior in an array index: mm/vmalloc.c: In function 'vmap_pfn_apply': mm/vmalloc.c:2800:58: error: operation on 'data->idx' may be undefined [-Werror=sequence-point] 2800 | *pte = pte_mkspecial(pfn_pte(data->pfns[data->idx++], data->prot)); | ~~~~~~~~~^~ arch/arm64/include/asm/pgtable-types.h:25:37: note: in definition of macro '__pte' 25 | #define __pte(x) ((pte_t) { (x) } ) | ^ arch/arm64/include/asm/pgtable.h:80:15: note: in expansion of macro '__phys_to_pte_val' 80 | __pte(__phys_to_pte_val((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)) | ^~~~~~~~~~~~~~~~~ mm/vmalloc.c:2800:30: note: in expansion of macro 'pfn_pte' 2800 | *pte = pte_mkspecial(pfn_pte(data->pfns[data->idx++], data->prot)); | ^~~~~~~ This only appeared in one randconfig build so far, and I don't know what caused it, but moving the index increment out of the expression at least addresses the warning. Fixes: 3e9a9e256b1e ("mm: add a vmap_pfn function") Signed-off-by: Arnd Bergmann --- Not sure if it's worth doing a deeper analysis of how the compiler thinks this might go wrong, it would appear that it thinks 'pte' might be an alias for 'data' here, but only in some configurations. If you want to try reproducing it, the .config that triggered it is https://pastebin.com/caeKD1Wv --- mm/vmalloc.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index d2a00ad4e1dd..cdac02aab6b1 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2797,7 +2797,9 @@ static int vmap_pfn_apply(pte_t *pte, unsigned long addr, void *private) if (WARN_ON_ONCE(pfn_valid(data->pfns[data->idx]))) return -EINVAL; - *pte = pte_mkspecial(pfn_pte(data->pfns[data->idx++], data->prot)); + *pte = pte_mkspecial(pfn_pte(data->pfns[data->idx], data->prot)); + data->idx++; + return 0; } -- 2.29.2