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=-13.8 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 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 D5D16C4332B for ; Fri, 22 Jan 2021 10:25:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A3F72239EE for ; Fri, 22 Jan 2021 10:25:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727823AbhAVKPI (ORCPT ); Fri, 22 Jan 2021 05:15:08 -0500 Received: from foss.arm.com ([217.140.110.172]:39546 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727851AbhAVKMq (ORCPT ); Fri, 22 Jan 2021 05:12:46 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id BDA58139F; Fri, 22 Jan 2021 02:12:00 -0800 (PST) Received: from C02TD0UTHF1T.local (unknown [10.57.41.42]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 179393F719; Fri, 22 Jan 2021 02:11:59 -0800 (PST) Date: Fri, 22 Jan 2021 10:11:57 +0000 From: Mark Rutland To: Thomas Bogendoerfer Cc: linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] MIPS: mm: abort uaccess retries upon fatal signal Message-ID: <20210122101157.GB29124@C02TD0UTHF1T.local> 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> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 FWIW, this looks right to me, from a scan of the no_context path. I don't have any MIPS system to test on, but FWIW: Acked-by: Mark Rutland Thanks for spinning this! Mark. > --- > arch/mips/mm/fault.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/arch/mips/mm/fault.c b/arch/mips/mm/fault.c > index 7c871b14e74a..e7abda9c013f 100644 > --- a/arch/mips/mm/fault.c > +++ b/arch/mips/mm/fault.c > @@ -156,8 +156,11 @@ static void __kprobes __do_page_fault(struct pt_regs *regs, unsigned long write, > */ > fault = handle_mm_fault(vma, address, flags, regs); > > - if (fault_signal_pending(fault, regs)) > + if (fault_signal_pending(fault, regs)) { > + if (!user_mode(regs)) > + goto no_context; > return; > + } > > if (unlikely(fault & VM_FAULT_ERROR)) { > if (fault & VM_FAULT_OOM) > -- > 2.29.2 >