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 3EF1FC3F68F for ; Mon, 10 Feb 2020 17:25:17 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0BD0620842 for ; Mon, 10 Feb 2020 17:25:16 +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="culiPi1Q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0BD0620842 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 9F0746B00E2; Mon, 10 Feb 2020 12:25:16 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 9A2066B00EB; Mon, 10 Feb 2020 12:25:16 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8DEA66B0132; Mon, 10 Feb 2020 12:25:16 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0065.hostedemail.com [216.40.44.65]) by kanga.kvack.org (Postfix) with ESMTP id 728EA6B00E2 for ; Mon, 10 Feb 2020 12:25:16 -0500 (EST) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 0032B181AC9CB for ; Mon, 10 Feb 2020 17:25:15 +0000 (UTC) X-FDA: 76474893432.04.night56_4b04729aee421 X-HE-Tag: night56_4b04729aee421 X-Filterd-Recvd-Size: 2015 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) by imf46.hostedemail.com (Postfix) with ESMTP for ; Mon, 10 Feb 2020 17:25:15 +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=FKWDJRQkvccelSptVw0DM+3Z0/fjsynGFQORnsVICQc=; b=culiPi1QCROeF4470hWIw1cPqD ulAoApdWZj7NpYbaioAxNM6Pbe6LDQa2IxTm8sjfw0f9+pVtPDOrpP1Ym+tBrQpeoBGXIkjRitGKM 6t3OBa2V4+mFxqAUhW3NJ010fV7ju+coEejm/lQP98xawvj4rCzMkJQlDOG+Ky08L4LRMIAKTZfu9 8zlrp0pdp5Zn94Bju8ph2HAWgeTldnk4n+8m1qhDv/lUo7YyoWF6E6EAuyTjgacegQ0KHiKhQHx99 PI1Vy4TsALOqFyM6Nd5vLHCcxKYAEJ16aCYaq37fOINoLINIVDG/3mgY9ZPq82h0WGIogihYIPHQb 8Vto2tDg==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j1Co3-0003NN-NZ; Mon, 10 Feb 2020 17:25:11 +0000 Date: Mon, 10 Feb 2020 09:25:11 -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 -next] mm/filemap: fix a data race in filemap_fault() Message-ID: <20200210172511.GL8731@bombadil.infradead.org> References: <1581354029-20154-1-git-send-email-cai@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1581354029-20154-1-git-send-email-cai@lca.pw> X-Bogosity: Ham, tests=bogofilter, spamicity=0.009752, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Feb 10, 2020 at 12:00:29PM -0500, Qian Cai wrote: > @@ -2622,7 +2622,7 @@ void filemap_map_pages(struct vm_fault *vmf, > if (page->index >= max_idx) > goto unlock; > > - if (file->f_ra.mmap_miss > 0) > + if (data_race(file->f_ra.mmap_miss > 0)) > file->f_ra.mmap_miss--; How is this safe? Two threads can each see 1, and then both decrement the in-memory copy, causing it to end up at -1.