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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 D646FC4BA0A for ; Wed, 26 Feb 2020 04:06:18 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 91DC821927 for ; Wed, 26 Feb 2020 04:06:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="FIZTPvRn" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 91DC821927 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 313786B0003; Tue, 25 Feb 2020 23:06:18 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 2C47C6B0005; Tue, 25 Feb 2020 23:06:18 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 201C66B0006; Tue, 25 Feb 2020 23:06:18 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0115.hostedemail.com [216.40.44.115]) by kanga.kvack.org (Postfix) with ESMTP id 0A9DD6B0003 for ; Tue, 25 Feb 2020 23:06:18 -0500 (EST) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id A1FC38248076 for ; Wed, 26 Feb 2020 04:06:17 +0000 (UTC) X-FDA: 76530940794.17.nail04_8e0fe60766c5f X-HE-Tag: nail04_8e0fe60766c5f X-Filterd-Recvd-Size: 2295 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf26.hostedemail.com (Postfix) with ESMTP for ; Wed, 26 Feb 2020 04:06:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=Qu2aPURbegdzfjSgtAkPb+TbG3uomn1JGpoqTQmr/0g=; b=FIZTPvRn3595XVQory0Jhecsta 7XjC4muiAu+9tLTT/ALg6Wttpv6fpY+HJQLq4Y7fPKXszStHmceKhxiLlF1bAsyYbTkoxvhVa2khJ 9fjlkcmhi2t2MCy94H98F65UBVbwCWVYf771eZCuA6YrXgSl6j4GB5amo8hdAFdl1BBwd1gHUb+yY u2uQJm3Rx3cxA5GHwL120ApkFqoadtRq0F6StjPiuJNO6aHI5WyUtnsP+xpSPRGBIzXbEKsHHj3Ss 8KFa64/bKLds0lA1SsVnuQb2afuoHhuDBWIBtIBf4c5G7gGkMxWRQ1rhktcynjjdGFkqFFY5MS1Ro sLtvsvsA==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j6nxc-0007Kc-S7; Wed, 26 Feb 2020 04:06:12 +0000 Date: Tue, 25 Feb 2020 20:06:12 -0800 From: Matthew Wilcox To: Qian Cai Cc: akpm@linux-foundation.org, elver@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] mm/vmscan: fix data races at kswapd_classzone_idx Message-ID: <20200226040612.GW24185@bombadil.infradead.org> References: <20200226035827.1285-1-cai@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200226035827.1285-1-cai@lca.pw> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Feb 25, 2020 at 10:58:27PM -0500, Qian Cai wrote: > pgdat->kswapd_classzone_idx could be accessed concurrently in > wakeup_kswapd(). Plain writes and reads without any lock protection > result in data races. Fix them by adding a pair of READ|WRITE_ONCE() as > well as saving a branch (compilers might well optimize the original code > in an unintentional way anyway). While at it, also take care of > pgdat->kswapd_order and non-kswapd threads in allow_direct_reclaim(). I don't understand why the usages of kswapd_classzone_idx in kswapd() and kswapd_try_to_sleep() don't need changing too? kswapd_classzone_idx() looks safe to me, but I'm prone to missing stupid things that compilers are allowed to do.