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=-8.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 543F1C352A2 for ; Thu, 6 Feb 2020 04:53:37 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 0EAED20838 for ; Thu, 6 Feb 2020 04:53:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="iiZGxzok" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0EAED20838 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nvidia.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id B06DE6B0003; Wed, 5 Feb 2020 23:53:36 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id AB7C36B0006; Wed, 5 Feb 2020 23:53:36 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 9CC586B0007; Wed, 5 Feb 2020 23:53:36 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0234.hostedemail.com [216.40.44.234]) by kanga.kvack.org (Postfix) with ESMTP id 82B376B0003 for ; Wed, 5 Feb 2020 23:53:36 -0500 (EST) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 3448B181AEF15 for ; Thu, 6 Feb 2020 04:53:36 +0000 (UTC) X-FDA: 76458484032.30.help60_76b08da2beb5e X-HE-Tag: help60_76b08da2beb5e X-Filterd-Recvd-Size: 5829 Received: from hqnvemgate26.nvidia.com (hqnvemgate26.nvidia.com [216.228.121.65]) by imf03.hostedemail.com (Postfix) with ESMTP for ; Thu, 6 Feb 2020 04:53:35 +0000 (UTC) Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate26.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Wed, 05 Feb 2020 20:53:20 -0800 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Wed, 05 Feb 2020 20:53:34 -0800 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Wed, 05 Feb 2020 20:53:34 -0800 Received: from [10.2.168.158] (172.20.13.39) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Thu, 6 Feb 2020 04:53:34 +0000 Subject: Re: [PATCH -next] mm: mark a intentional data race in page_zonenum() To: Qian Cai , CC: , , , , References: <20200206035235.2537-1-cai@lca.pw> X-Nvconfidentiality: public From: John Hubbard Message-ID: <480a7dde-f678-c07b-2231-4da8e0a38753@nvidia.com> Date: Wed, 5 Feb 2020 20:50:34 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.2 MIME-Version: 1.0 In-Reply-To: <20200206035235.2537-1-cai@lca.pw> X-Originating-IP: [172.20.13.39] X-ClientProxiedBy: HQMAIL107.nvidia.com (172.20.187.13) To HQMAIL107.nvidia.com (172.20.187.13) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1580964800; bh=xAf0FzCgCZHzZBkZwyyUZaACb8F7IA6ZF9/a+cOMFxI=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=iiZGxzokIV7dKwk6orbh4Tjn8nC+D33QxqoUVsITyYoSSxF5mhX/T7W8eMjYYs6hn x64npC1JSBOvWe4AnCkEoZposuV8JiGphnHJbLPPafWCuJ10+iBR0zjjvNnRlbgmSW TOvlSZdyh2wFhoV42fmwn3uvxScnqFx+vtq9+1rALq0366RB0e2QZ6Bh45jI2i9ptG 5epxWT5W2AGT+z3IjCzXuoGsHxNjPH737YJN+2uFm+QkoSWg0pR99spBxVxmS1vBwh PUpweoGCLjsaySHVedk+T0egYyRE1kTDF+LeDb283491HlZKcSax7uxFezMSWoLswS q/5tBsLKWnbSw== 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: On 2/5/20 7:52 PM, Qian Cai wrote: > The commit 07d802699528 ("mm: devmap: refactor 1-based refcounting for > ZONE_DEVICE pages") introduced a data race as page->flags could be Hi, I really don't think so. This "race" was there long before that commit. Anyway, more below: > accessed concurrently as noticied by KCSAN, > > BUG: KCSAN: data-race in page_cpupid_xchg_last / put_page > > write (marked) to 0xfffffc0d48ec1a00 of 8 bytes by task 91442 on cpu 3: > page_cpupid_xchg_last+0x51/0x80 > page_cpupid_xchg_last at mm/mmzone.c:109 (discriminator 11) > wp_page_reuse+0x3e/0xc0 > wp_page_reuse at mm/memory.c:2453 > do_wp_page+0x472/0x7b0 > do_wp_page at mm/memory.c:2798 > __handle_mm_fault+0xcb0/0xd00 > handle_pte_fault at mm/memory.c:4049 > (inlined by) __handle_mm_fault at mm/memory.c:4163 > handle_mm_fault+0xfc/0x2f0 > handle_mm_fault at mm/memory.c:4200 > do_page_fault+0x263/0x6f9 > do_user_addr_fault at arch/x86/mm/fault.c:1465 > (inlined by) do_page_fault at arch/x86/mm/fault.c:1539 > page_fault+0x34/0x40 > > read to 0xfffffc0d48ec1a00 of 8 bytes by task 94817 on cpu 69: > put_page+0x15a/0x1f0 > page_zonenum at include/linux/mm.h:923 > (inlined by) is_zone_device_page at include/linux/mm.h:929 > (inlined by) page_is_devmap_managed at include/linux/mm.h:948 > (inlined by) put_page at include/linux/mm.h:1023 > wp_page_copy+0x571/0x930 > wp_page_copy at mm/memory.c:2615 > do_wp_page+0x107/0x7b0 > __handle_mm_fault+0xcb0/0xd00 > handle_mm_fault+0xfc/0x2f0 > do_page_fault+0x263/0x6f9 > page_fault+0x34/0x40 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 69 PID: 94817 Comm: systemd-udevd Tainted: G W O L 5.5.0-next-20200204+ #6 > Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 > > Both the read and write are done only with the non-exclusive mmap_sem > held. Since the read only check for a specific bit in the flag, even if Perhaps a clearer explanation is that the read of the page flags is always looking at a bit range (zone number: up to 3 bits) that is not being written to by the writer. > load tearing happens, it will be harmless, so just mark it as an > intentional data races using the data_race() macro. > > Signed-off-by: Qian Cai > --- > include/linux/mm.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 52269e56c514..cafccad584c2 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -920,7 +920,7 @@ vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf); > > static inline enum zone_type page_zonenum(const struct page *page) > { > - return (page->flags >> ZONES_PGSHIFT) & ZONES_MASK; > + return data_race((page->flags >> ZONES_PGSHIFT) & ZONES_MASK); I don't know about this. Lots of the kernel is written to do this sort of thing, and adding a load of "data_race()" everywhere is...well, I'm not sure if it's really the best way. I wonder: could we maybe teach this kcsan thing to understand a few of the key idioms, particularly about page flags, instead of annotating all over the place? thanks, -- John Hubbard NVIDIA > } > > #ifdef CONFIG_ZONE_DEVICE >