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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 746E3EB64DA for ; Wed, 12 Jul 2023 13:23:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To:Subject: MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=BXAfV6XOl0tIRVCD7UOmw7yXWpBSgG87LowqCCxnFvo=; b=DZWrpaejIcpGWj aCDsQE+04zimQGQvTmdXEcoUHvN4acahnLS8fjTQFs/25KLd5X1OcHKEsijRaPZYfJ5XiAYhvSMBN cvrpvgoCBye4tMbOH9voxy/oqoNPKYFUka0Hup0+2DOx2N4H9Zbia6E9TU/wvcPtiCDXM3ymKr+qs Q5cxS2qIg+uFCh4ZMu7zIZV7DM6KN+y93onug8MEigevc+trVsp6kddni6w9nXBDRmf+bw4wqrONQ 1eD12NKqqxQtZEMAuGZo6J/UiRhc2OPw/brbnwHoVZmT68fNc3TbmX0dFF7QzNepFIWeF0ZOHwmdC DDV8vXIfTDYvmVebC/Iw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qJZnk-0003zH-3D; Wed, 12 Jul 2023 13:22:41 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qJZni-0003y5-15 for linux-arm-kernel@lists.infradead.org; Wed, 12 Jul 2023 13:22:40 +0000 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 326EAD75; Wed, 12 Jul 2023 06:23:12 -0700 (PDT) Received: from [10.57.36.71] (unknown [10.57.36.71]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D6A363F67D; Wed, 12 Jul 2023 06:22:27 -0700 (PDT) Message-ID: <06877064-51df-d162-0da2-aaa710e0fefe@arm.com> Date: Wed, 12 Jul 2023 14:22:26 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH] coresight: etm3x: convert struct etm_drvdata's spinlock to raw_spinlock To: James Clark , Greg Kroah-Hartman , quanyang.wang@windriver.com Cc: Alexander Shishkin , Tingwei Zhang , Mathieu Poirier , Kim Phillips , Sebastian Siewior , Thomas Gleixner , Steven Rostedt , linux-rt-users@vger.kernel.org, coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20230711070536.3944458-1-quanyang.wang@windriver.com> <2023071134-mardi-lyricist-e5b0@gregkh> <85a706fb-1072-0c59-e08c-8bb27e069991@arm.com> From: Suzuki K Poulose In-Reply-To: <85a706fb-1072-0c59-e08c-8bb27e069991@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230712_062238_509369_71E1F7B5 X-CRM114-Status: GOOD ( 17.65 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 11/07/2023 16:45, James Clark wrote: > > > On 11/07/2023 15:05, Greg Kroah-Hartman wrote: >> On Tue, Jul 11, 2023 at 03:05:36PM +0800, quanyang.wang@windriver.com wrote: >>> From: Quanyang Wang >>> >>> For PREEMPT_RT kernel, spinlock_t locks become sleepable. The functions >>> etm_dying_cpu and etm_starting_cpu which call spin_lock/unlock run in >>> an irq-disabled context, this will trigger the following calltrace: >>> >>> BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46 >>> in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 25, name: migration/1 >>> preempt_count: 1, expected: 0 >>> RCU nest depth: 0, expected: 0 >>> 1 lock held by migration/1/25: >>> #0: 82a7587c (&drvdata->spinlock){....}-{2:2}, at: etm_dying_cpu+0x28/0x54 >>> Preemption disabled at: >>> [<801ec760>] cpu_stopper_thread+0x94/0x120 >>> CPU: 1 PID: 25 Comm: migration/1 Not tainted 6.1.35-rt10-yocto-preempt-rt #30 >>> Hardware name: Xilinx Zynq Platform >>> Stopper: multi_cpu_stop+0x0/0x174 <- __stop_cpus.constprop.0+0x48/0x88 >>> unwind_backtrace from show_stack+0x18/0x1c >>> show_stack from dump_stack_lvl+0x58/0x70 >>> dump_stack_lvl from __might_resched+0x14c/0x1c0 >>> __might_resched from rt_spin_lock+0x4c/0x84 >>> rt_spin_lock from etm_dying_cpu+0x28/0x54 >>> etm_dying_cpu from cpuhp_invoke_callback+0x140/0x33c >>> cpuhp_invoke_callback from __cpuhp_invoke_callback_range+0xa4/0x104 >>> __cpuhp_invoke_callback_range from take_cpu_down+0x7c/0xa8 >>> take_cpu_down from multi_cpu_stop+0x15c/0x174 >>> multi_cpu_stop from cpu_stopper_thread+0x9c/0x120 >>> cpu_stopper_thread from smpboot_thread_fn+0x31c/0x360 >>> smpboot_thread_fn from kthread+0x100/0x124 >>> kthread from ret_from_fork+0x14/0x2c >>> >>> Convert struct etm_drvdata's spinlock to raw_spinlock to fix it. >> >> wait, why will a raw_spinlock fix this? Why not fix the root problem >> here, that of calling these locks inproperly in irq context? >> >> How is changing to a raw_spinlock going to fix the above splat? >> >> thanks, >> >> greg k-h >> > > If it's just etm_starting_cpu() and etm_dying_cpu() as mentioned in the > commit message then can those spinlocks be removed? > > Surely there can't be any concurrent access to the per-cpu data when the > hotplug callbacks are called? Accessing the per-cpu data is not a problem. The spinlocks are there to protect the accesses to drvdata->mode. etm_starting_cpu() would try to enable the etm (i.e., start the tracing) if the mode is not DISABLED. Especially for SYSFS mode, this could be controlled from a different CPU, affecting the mode. I think we may still be able to avoid this lock, by allowing the modifications to the mode performed via enable_hw/disable_hw on the CPU. That way, there cannot be concurrent modifications to the mode for a given ETM bound to the CPU. Suzuki _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel