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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 CF0F9C433DB for ; Mon, 11 Jan 2021 22:21:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 81E2922D05 for ; Mon, 11 Jan 2021 22:21:05 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 81E2922D05 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id CBDF98D005B; Mon, 11 Jan 2021 17:21:04 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id C6E1C8D0051; Mon, 11 Jan 2021 17:21:04 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BACB58D005B; Mon, 11 Jan 2021 17:21:04 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0055.hostedemail.com [216.40.44.55]) by kanga.kvack.org (Postfix) with ESMTP id A43778D0051 for ; Mon, 11 Jan 2021 17:21:04 -0500 (EST) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 5D076180AD81A for ; Mon, 11 Jan 2021 22:21:04 +0000 (UTC) X-FDA: 77694915648.30.hair15_4f13fb427510 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin30.hostedemail.com (Postfix) with ESMTP id 388EC180B3AA7 for ; Mon, 11 Jan 2021 22:21:04 +0000 (UTC) X-HE-Tag: hair15_4f13fb427510 X-Filterd-Recvd-Size: 3340 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by imf41.hostedemail.com (Postfix) with ESMTP for ; Mon, 11 Jan 2021 22:21:01 +0000 (UTC) IronPort-SDR: vKy5ExzsFXMu5hCI1gOeH+FXrgKn75cALnJaR/qSPT7N2/AfhanEVn1aM0/6S20EYi0GJBvadI j/0Z9aPCR9xw== X-IronPort-AV: E=McAfee;i="6000,8403,9861"; a="178040008" X-IronPort-AV: E=Sophos;i="5.79,339,1602572400"; d="scan'208";a="178040008" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Jan 2021 14:20:59 -0800 IronPort-SDR: 6pIQeWH++WIe5oa7r6R4Yn0mC8sPjVDU2XZ0A2/jSZOf5nG9czsXeUsatRR7hFe9qglLiP6g72 UUxZF1tWmcUA== X-IronPort-AV: E=Sophos;i="5.79,339,1602572400"; d="scan'208";a="381170169" Received: from agluck-desk2.sc.intel.com (HELO agluck-desk2.amr.corp.intel.com) ([10.3.52.68]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 11 Jan 2021 14:20:58 -0800 Date: Mon, 11 Jan 2021 14:20:57 -0800 From: "Luck, Tony" To: Andy Lutomirski Cc: Borislav Petkov , x86@kernel.org, Andrew Morton , Peter Zijlstra , Darren Hart , Andy Lutomirski , linux-kernel@vger.kernel.org, linux-edac@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery Message-ID: <20210111222057.GA2369@agluck-desk2.amr.corp.intel.com> References: <20210111214452.1826-2-tony.luck@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Content-Transfer-Encoding: quoted-printable 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, Jan 11, 2021 at 02:11:56PM -0800, Andy Lutomirski wrote: >=20 > > On Jan 11, 2021, at 1:45 PM, Tony Luck wrote: > >=20 > > =EF=BB=BFRecovery action when get_user() triggers a machine check use= s the fixup > > path to make get_user() return -EFAULT. Also queue_task_work() sets = up > > so that kill_me_maybe() will be called on return to user mode to send= a > > SIGBUS to the current process. > >=20 > > But there are places in the kernel where the code assumes that this > > EFAULT return was simply because of a page fault. The code takes some > > action to fix that, and then retries the access. This results in a se= cond > > machine check. > >=20 > > While processing this second machine check queue_task_work() is calle= d > > again. But since this uses the same callback_head structure that > > was used in the first call, the net result is an entry on the > > current->task_works list that points to itself. >=20 > Is this happening in pagefault_disable context or normal sleepable faul= t context? If the latter, maybe we should reconsider finding a way for t= he machine check code to do its work inline instead of deferring it. The first machine check is in pagefault_disable() context. static int get_futex_value_locked(u32 *dest, u32 __user *from) { int ret; pagefault_disable(); ret =3D __get_user(*dest, from); pagefault_enable(); return (ret =3D=3D -ENXIO) ? ret : ret ? -EFAULT : 0; } -Tony