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Silva" X-Patchwork-Id: 11534783 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D868E92A for ; Thu, 7 May 2020 19:17:41 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A70E5221F7 for ; Thu, 7 May 2020 19:17:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="qtcvF+cD" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A70E5221F7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id CC48E900003; Thu, 7 May 2020 15:17:40 -0400 (EDT) Delivered-To: linux-mm-outgoing@kvack.org Received: by kanga.kvack.org (Postfix, from userid 40) id C75A2900002; Thu, 7 May 2020 15:17:40 -0400 (EDT) X-Original-To: int-list-linux-mm@kvack.org X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B6408900003; Thu, 7 May 2020 15:17:40 -0400 (EDT) X-Original-To: linux-mm@kvack.org X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0039.hostedemail.com [216.40.44.39]) by kanga.kvack.org (Postfix) with ESMTP id 9E738900002 for ; Thu, 7 May 2020 15:17:40 -0400 (EDT) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 59D688248D51 for ; Thu, 7 May 2020 19:17:40 +0000 (UTC) X-FDA: 76790882280.19.straw95_8bd2bf37282f X-Spam-Summary: 2,0,0,98756690b6b73b55,d41d8cd98f00b204,gustavoars@kernel.org,,RULES_HIT:41:355:379:800:960:967:973:988:989:1260:1277:1312:1313:1314:1345:1437:1516:1518:1519:1534:1541:1593:1594:1595:1596:1711:1730:1747:1777:1792:2194:2198:2199:2200:2393:2525:2553:2559:2564:2682:2685:2693:2859:2933:2937:2939:2942:2945:2947:2951:2954:3022:3138:3139:3140:3141:3142:3353:3865:3866:3867:3868:3870:3871:3874:3934:3936:3938:3941:3944:3947:3950:3953:3956:3959:4321:4605:5007:6117:6261:6653:9025:10004:10400:10450:10455:11026:11658:11914:12043:12048:12296:12297:12517:12519:12555:12986:13069:13161:13229:13311:13357:13439:13895:14181:14394:14721:19904:19999:21067:21080:21433:21451:21524:21627:21740:21972:30012:30054:30070:30090,0,RBL:198.145.29.99:@kernel.org:.lbl8.mailshell.net-62.2.0.100 64.100.201.201,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fp,MSBL:0,DNSBL:neutral,Custom_rules:0:0:0,LFtime:24,LUA_SUMMARY:none X-HE-Tag: straw95_8bd2bf37282f X-Filterd-Recvd-Size: 3314 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf40.hostedemail.com (Postfix) with ESMTP for ; Thu, 7 May 2020 19:17:39 +0000 (UTC) Received: from embeddedor (unknown [189.207.59.248]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CA96F21835; Thu, 7 May 2020 19:17:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588879058; bh=2vhh4CWf1qAP4IS40XgtchAprraO0Zj46YURZXgZFxA=; h=Date:From:To:Cc:Subject:From; b=qtcvF+cDY/ipaTvvUakxHaYOOOaLgEwR9HV2QmMIlhIR8wkeEVlREwC4/m9YLnpft XUg3iDrYlcwaHkUM01QM7nxWmLwBhWKL3XSCKnQ7vLzN+RM4UHK7fkrd3MLhQu59Q5 6/yuMeKWhbTEuuN8BZs5eR0etQ7bh6DWI1umxTsY= Date: Thu, 7 May 2020 14:22:04 -0500 From: "Gustavo A. R. Silva" To: Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH] slab: Replace zero-length array with flexible-array Message-ID: <20200507192204.GA16270@embeddedor> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva Acked-by: David Rientjes --- mm/slab.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/slab.h b/mm/slab.h index 207c83ef6e06..815e4e9a94cd 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -34,7 +34,7 @@ struct kmem_cache { struct memcg_cache_array { struct rcu_head rcu; - struct kmem_cache *entries[0]; + struct kmem_cache *entries[]; }; /*