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=ham 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 A8585C433F5 for ; Tue, 14 Sep 2021 08:31:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8792660234 for ; Tue, 14 Sep 2021 08:31:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230086AbhINIcz (ORCPT ); Tue, 14 Sep 2021 04:32:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:37014 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229458AbhINIcy (ORCPT ); Tue, 14 Sep 2021 04:32:54 -0400 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) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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