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 B4AF2C4BA06 for ; Wed, 26 Feb 2020 01:30:01 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4F70A20658 for ; Wed, 26 Feb 2020 01:30:01 +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="G2lnM6jJ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4F70A20658 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 956C16B0003; Tue, 25 Feb 2020 20:30:00 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 8E0B66B0005; Tue, 25 Feb 2020 20:30:00 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7A92E6B0006; Tue, 25 Feb 2020 20:30:00 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0130.hostedemail.com [216.40.44.130]) by kanga.kvack.org (Postfix) with ESMTP id 5F66E6B0003 for ; Tue, 25 Feb 2020 20:30:00 -0500 (EST) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 31AC9181AC9B6 for ; Wed, 26 Feb 2020 01:30:00 +0000 (UTC) X-FDA: 76530546960.23.stage75_574b1fea21a41 X-HE-Tag: stage75_574b1fea21a41 X-Filterd-Recvd-Size: 2458 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf42.hostedemail.com (Postfix) with ESMTP for ; Wed, 26 Feb 2020 01:29:59 +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=f0M9pTXksi/4gAdPbOMhWiXGju+Jg2ed8su13b9OEus=; b=G2lnM6jJj1akbMJAyGC37MnXzJ O6MCG2g4Myrkqv+/4A5AdEgf3m6KJPl4eeI62mVAGs/AXIo3l37SrV6qZ/aB9nSNPtpz2/FjVa29l A3EWCc+3b0q++puV9gruRmIZTtb4yudjw/NgTbo6WUU5r+K/lfECbtKswv319+mTC5AXKFCEoR6Le 7zHyLP3lJpdQZqOV49IykmyDLwsWIEdLE8XME8gmlydvnw9EG/xQAPfSyGrr8Bkyys97fPKmw4Ojb CQ8sZ7ePfd1et9+ZNVI/FGBsH7LQneHNo++MSf4OmQLfv6BdMyWQrsonz5NFl+YCW54YIWu3Sjr8D At5rGWNw==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j6lWK-0004C5-HK; Wed, 26 Feb 2020 01:29:52 +0000 Date: Tue, 25 Feb 2020 17:29:52 -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] mm/vmscan: fix data races at kswapd_classzone_idx Message-ID: <20200226012952.GV24185@bombadil.infradead.org> References: <1582649726-15474-1-git-send-email-cai@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1582649726-15474-1-git-send-email-cai@lca.pw> X-Bogosity: Ham, tests=bogofilter, spamicity=0.001338, 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 11:55:26AM -0500, Qian Cai wrote: > - if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES) > - pgdat->kswapd_classzone_idx = classzone_idx; > - else > - pgdat->kswapd_classzone_idx = max(pgdat->kswapd_classzone_idx, > - classzone_idx); > + if (READ_ONCE(pgdat->kswapd_classzone_idx) == MAX_NR_ZONES || > + READ_ONCE(pgdat->kswapd_classzone_idx) < classzone_idx) > + WRITE_ONCE(pgdat->kswapd_classzone_idx, classzone_idx); > + > pgdat->kswapd_order = max(pgdat->kswapd_order, order); Doesn't this line have the exact same problem you're "solving" above? Also, why would you do this crazy "f(READ_ONCE(x)) || g(READ_ONCE(x))? Surely you should be stashing READ_ONCE(x) into a local variable? And there are a _lot_ of places which access kswapd_classzone_idx without a lock. Are you sure this patch is sufficient?