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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 AC563C433E6 for ; Mon, 22 Feb 2021 12:05:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7974C60C3E for ; Mon, 22 Feb 2021 12:05:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230169AbhBVMF0 (ORCPT ); Mon, 22 Feb 2021 07:05:26 -0500 Received: from foss.arm.com ([217.140.110.172]:43800 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230087AbhBVMEn (ORCPT ); Mon, 22 Feb 2021 07:04:43 -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 699E71FB; Mon, 22 Feb 2021 04:03:55 -0800 (PST) Received: from [10.37.8.9] (unknown [10.37.8.9]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 6D31F3F70D; Mon, 22 Feb 2021 04:03:53 -0800 (PST) Subject: Re: [PATCH v13 4/7] arm64: mte: Enable TCO in functions that can read beyond buffer limits To: Catalin Marinas Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, Andrew Morton , Will Deacon , Dmitry Vyukov , Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Branislav Rankov , Andrey Konovalov , Lorenzo Pieralisi References: <20210211153353.29094-1-vincenzo.frascino@arm.com> <20210211153353.29094-5-vincenzo.frascino@arm.com> <20210212172128.GE7718@arm.com> From: Vincenzo Frascino Message-ID: Date: Mon, 22 Feb 2021 12:08:07 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210212172128.GE7718@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/12/21 5:21 PM, Catalin Marinas wrote: >> + >> + /* >> + * This function is called on each active smp core at boot >> + * time, hence we do not need to take cpu_hotplug_lock again. >> + */ >> + static_branch_enable_cpuslocked(&mte_async_mode); >> } > Sorry, I missed the cpuslocked aspect before. Is there any reason you > need to use this API here? I suggested to add it to the > mte_enable_kernel_sync() because kasan may at some point do this > dynamically at run-time, so the boot-time argument doesn't hold. But > it's also incorrect as this function will be called for hot-plugged > CPUs as well after boot. > > The only reason for static_branch_*_cpuslocked() is if it's called from > a region that already invoked cpus_read_lock() which I don't think is > the case here. I agree with your analysis on why static_branch_*_cpuslocked() is needed, in fact cpus_read_lock() takes cpu_hotplug_lock as per comment on top of the line of code. If I try to take that lock when enabling the secondary cores I end up in the situation below: [ 0.283402] smp: Bringing up secondary CPUs ... .... [ 5.890963] Call trace: [ 5.891050] dump_backtrace+0x0/0x19c [ 5.891212] show_stack+0x18/0x70 [ 5.891373] dump_stack+0xd0/0x12c [ 5.891531] dequeue_task_idle+0x28/0x40 [ 5.891686] __schedule+0x45c/0x6c0 [ 5.891851] schedule+0x70/0x104 [ 5.892010] percpu_rwsem_wait+0xe8/0x104 [ 5.892174] __percpu_down_read+0x5c/0x90 [ 5.892332] percpu_down_read.constprop.0+0xbc/0xd4 [ 5.892497] cpus_read_lock+0x10/0x1c [ 5.892660] static_key_enable+0x18/0x3c [ 5.892823] mte_enable_kernel_async+0x40/0x70 [ 5.892988] kasan_init_hw_tags_cpu+0x50/0x60 [ 5.893144] cpu_enable_mte+0x24/0x70 [ 5.893304] verify_local_cpu_caps+0x58/0x120 [ 5.893465] check_local_cpu_capabilities+0x18/0x1f0 [ 5.893626] secondary_start_kernel+0xe0/0x190 [ 5.893790] 0x0 [ 5.893975] bad: scheduling from the idle thread! [ 5.894065] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G W 5.11.0-rc7-10587-g22cd50bcfcf-dirty #6 and the kernel panics. Note: there is a look of msg drop in between enabling the secondary and the first clean stack trace. -- Regards, Vincenzo