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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 6A8FFC433E6 for ; Fri, 22 Jan 2021 12:08:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 36A7423444 for ; Fri, 22 Jan 2021 12:08:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727807AbhAVME2 (ORCPT ); Fri, 22 Jan 2021 07:04:28 -0500 Received: from elvis.franken.de ([193.175.24.41]:42480 "EHLO elvis.franken.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727823AbhAVKyi (ORCPT ); Fri, 22 Jan 2021 05:54:38 -0500 Received: from uucp (helo=alpha) by elvis.franken.de with local-bsmtp (Exim 3.36 #1) id 1l2u4h-0006yq-02; Fri, 22 Jan 2021 11:53:55 +0100 Received: by alpha.franken.de (Postfix, from userid 1000) id 5D1DCC0BF1; Fri, 22 Jan 2021 11:49:48 +0100 (CET) Date: Fri, 22 Jan 2021 11:49:48 +0100 From: Thomas Bogendoerfer To: linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Mark Rutland Subject: Re: [PATCH] MIPS: mm: abort uaccess retries upon fatal signal Message-ID: <20210122104948.GB8146@alpha.franken.de> References: <20210121160416.111298-1-tsbogend@alpha.franken.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210121160416.111298-1-tsbogend@alpha.franken.de> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Thu, Jan 21, 2021 at 05:04:16PM +0100, Thomas Bogendoerfer wrote: > When there's a fatal signal pending, MIPS's do_page_fault() > implementation returns. The intent is that we'll return to the > faulting userspace instruction, delivering the signal on the way. > > However, if we take a fatal signal during fixing up a uaccess, this > results in a return to the faulting kernel instruction, which will be > instantly retried, resulting in the same fault being taken forever. As > the task never reaches userspace, the signal is not delivered, and the > task is left unkillable. While the task is stuck in this state, it can > inhibit the forward progress of the system. > > To avoid this, we must ensure that when a fatal signal is pending, we > apply any necessary fixup for a faulting kernel instruction. Thus we > will return to an error path, and it is up to that code to make forward > progress towards delivering the fatal signal. > > [ Description taken from commit 746a272e4414 ("ARM: 8692/1: mm: abort > uaccess retries upon fatal signal") ] > > Signed-off-by: Thomas Bogendoerfer > --- > arch/mips/mm/fault.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) applied to mips-next. Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]