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=-17.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 B9F8BC433FE for ; Tue, 14 Sep 2021 08:31:41 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 66235610D1 for ; Tue, 14 Sep 2021 08:31:41 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 66235610D1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 058346B006C; Tue, 14 Sep 2021 04:31:41 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 00581900002; Tue, 14 Sep 2021 04:31:40 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E36336B0072; Tue, 14 Sep 2021 04:31:40 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0213.hostedemail.com [216.40.44.213]) by kanga.kvack.org (Postfix) with ESMTP id D6F296B006C for ; Tue, 14 Sep 2021 04:31:40 -0400 (EDT) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 6FF2F2D4D8 for ; Tue, 14 Sep 2021 08:31:40 +0000 (UTC) X-FDA: 78585510360.04.97BDE09 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf06.hostedemail.com (Postfix) with ESMTP id EEE70801A8A7 for ; Tue, 14 Sep 2021 08:31:39 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id 59D4860EE0; Tue, 14 Sep 2021 08:31:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1631608297; bh=oX/5ZZdm4wVN44TRFscoqvKnha+6+V0peernKrQWcE4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Ie7BWsEUv3r+l0ENRqwgNjhdGuC9pt94fhz0OuDHBqqnLw8nHJ/XdNbiDCkmZuKW2 XJ4kGbGz2LWrEVYz5yVbCYxt4DYMs04PmldjuXQgYnj5F8v1xEJEc0pP4bsfI7Dagk WV+o8uIsv2Vujzx9hrjCANSGZVPc59sBKXwHcZJs5njm1qgriaxifGXLx7YalV1jwY Tugv6pIz6s5WBcdTd4ZaTC2Ds0c0CvSHSfFB3oQ1YO7jEWi3hriUJUe5YE0DXFTKpq IerDrBh0Zi39qu8OemUaq7/vHwc5l6gs3nSJtPRBXPZXkEPhxOoiGk0/8hJRcJVZzl A1ulA2DzhHvIQ== Date: Tue, 14 Sep 2021 09:31:32 +0100 From: Will Deacon To: Marco Elver Cc: Andrew Morton , linux-mm@kvack.org, "Kirill A . Shutemov" , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, kernel test robot Subject: Re: [PATCH] mm: fix data race in PagePoisoned() Message-ID: <20210914083132.GA5891@willie-the-truck> References: <20210913113542.2658064-1-elver@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210913113542.2658064-1-elver@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: EEE70801A8A7 X-Stat-Signature: e8aqrf86ncie1yifdoq6thd6tist7db7 Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Ie7BWsEU; spf=pass (imf06.hostedemail.com: domain of will@kernel.org designates 198.145.29.99 as permitted sender) smtp.mailfrom=will@kernel.org; dmarc=pass (policy=none) header.from=kernel.org X-HE-Tag: 1631608299-983323 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 Mon, Sep 13, 2021 at 01:35:43PM +0200, Marco Elver wrote: > PagePoisoned() accesses page->flags which can be updated concurrently: > > | BUG: KCSAN: data-race in next_uptodate_page / unlock_page > | > | write (marked) to 0xffffea00050f37c0 of 8 bytes by task 1872 on cpu 1: > | instrument_atomic_write include/linux/instrumented.h:87 [inline] > | clear_bit_unlock_is_negative_byte include/asm-generic/bitops/instrumented-lock.h:74 [inline] > | unlock_page+0x102/0x1b0 mm/filemap.c:1465 > | filemap_map_pages+0x6c6/0x890 mm/filemap.c:3057 > | ... > | read to 0xffffea00050f37c0 of 8 bytes by task 1873 on cpu 0: > | PagePoisoned include/linux/page-flags.h:204 [inline] > | PageReadahead include/linux/page-flags.h:382 [inline] > | next_uptodate_page+0x456/0x830 mm/filemap.c:2975 > | ... > | CPU: 0 PID: 1873 Comm: systemd-udevd Not tainted 5.11.0-rc4-00001-gf9ce0be71d1f #1 > > To avoid the compiler tearing or otherwise optimizing the access, use > READ_ONCE() to access flags. > > Link: https://lore.kernel.org/all/20210826144157.GA26950@xsang-OptiPlex-9020/ > Reported-by: kernel test robot > Signed-off-by: Marco Elver > Cc: Will Deacon > Cc: Kirill A. Shutemov > --- > include/linux/page-flags.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h > index a558d67ee86f..628ab237665e 100644 > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -206,7 +206,7 @@ static __always_inline int PageCompound(struct page *page) > #define PAGE_POISON_PATTERN -1l > static inline int PagePoisoned(const struct page *page) > { > - return page->flags == PAGE_POISON_PATTERN; > + return READ_ONCE(page->flags) == PAGE_POISON_PATTERN; > } Acked-by: Will Deacon Thanks for writing up the patch! Will