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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS 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 23093C43381 for ; Mon, 4 Mar 2019 17:22:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EA75F206BA for ; Mon, 4 Mar 2019 17:22:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727246AbfCDRWB (ORCPT ); Mon, 4 Mar 2019 12:22:01 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:36344 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726098AbfCDRWA (ORCPT ); Mon, 4 Mar 2019 12:22:00 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 48209A78; Mon, 4 Mar 2019 09:22:00 -0800 (PST) Received: from [10.1.196.50] (e108454-lin.cambridge.arm.com [10.1.196.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7917E3F703; Mon, 4 Mar 2019 09:21:59 -0800 (PST) Subject: Re: [PATCH] tty/sysrq: Convert show_lock to raw_spinlock_t To: linux-kernel@vger.kernel.org Cc: jslaby@suse.com, gregkh@linuxfoundation.org, "linux-rt-users@vger.kernel.org" References: <20190304172053.17340-1-julien.grall@arm.com> From: Julien Grall Message-ID: <545fb96e-0f07-758e-5c79-a725e74e3387@arm.com> Date: Mon, 4 Mar 2019 17:21:57 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190304172053.17340-1-julien.grall@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (CC correctly linux-rt-users) On 04/03/2019 17:20, Julien Grall wrote: > At the moment show_lock is implemented using spin_lock_t and called from > an interrupt context on Arm64. The following backtrace was triggered by: > > 42sh# echo l > /proc/sysrq-trigger > > [ 4432.073756] sysrq: SysRq : Show backtrace of all active CPUs > [ 4432.403422] BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:974 > [ 4432.403424] sysrq: CPU6: > [ 4432.403426] in_atomic(): 1, irqs_disabled(): 128, pid: 2410, name: kworker/u16:2 > > [...] > > [ 4432.403581] Call trace: > [ 4432.403584] dump_backtrace+0x0/0x148 > [ 4432.403586] show_stack+0x14/0x20 > [ 4432.403588] dump_stack+0x9c/0xd4 > [ 4432.403592] ___might_sleep+0x1cc/0x298 > [ 4432.403595] rt_spin_lock+0x5c/0x70 > [ 4432.403596] showacpu+0x34/0x68 > [ 4432.403599] flush_smp_call_function_queue+0xd4/0x278 > [ 4432.403602] generic_smp_call_function_single_interrupt+0x10/0x18 > [ 4432.403605] handle_IPI+0x26c/0x668 > [ 4432.403607] gic_handle_irq+0x9c/0xa0 > [ 4432.403609] el1_irq+0xb4/0x13c > > With RT-patches, spin_lock can now sleep and therefore cannot be used from > interrupt context. Use a raw_spin_lock instead to prevent the lock to > sleep. > > Signed-off-by: Julien Grall > --- > drivers/tty/sysrq.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c > index 1f03078ec352..8473557c7ab2 100644 > --- a/drivers/tty/sysrq.c > +++ b/drivers/tty/sysrq.c > @@ -208,7 +208,7 @@ static struct sysrq_key_op sysrq_showlocks_op = { > #endif > > #ifdef CONFIG_SMP > -static DEFINE_SPINLOCK(show_lock); > +static DEFINE_RAW_SPINLOCK(show_lock); > > static void showacpu(void *dummy) > { > @@ -218,10 +218,10 @@ static void showacpu(void *dummy) > if (idle_cpu(smp_processor_id())) > return; > > - spin_lock_irqsave(&show_lock, flags); > + raw_spin_lock_irqsave(&show_lock, flags); > pr_info("CPU%d:\n", smp_processor_id()); > show_stack(NULL, NULL); > - spin_unlock_irqrestore(&show_lock, flags); > + raw_spin_unlock_irqrestore(&show_lock, flags); > } > > static void sysrq_showregs_othercpus(struct work_struct *dummy) > -- Julien Grall