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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 6E0F9C282CB for ; Tue, 5 Feb 2019 11:20:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 44AD52070B for ; Tue, 5 Feb 2019 11:20:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728135AbfBELUC (ORCPT ); Tue, 5 Feb 2019 06:20:02 -0500 Received: from foss.arm.com ([217.140.101.70]:39896 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727949AbfBELUC (ORCPT ); Tue, 5 Feb 2019 06:20:02 -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 8B2E480D; Tue, 5 Feb 2019 03:20:01 -0800 (PST) Received: from [10.1.196.93] (en101.cambridge.arm.com [10.1.196.93]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A05A73F675; Tue, 5 Feb 2019 03:19:59 -0800 (PST) Subject: Re: [PATCH 1/5] perf/arm-cci: Fix CPU hotplug race avoidance To: robin.murphy@arm.com, will.deacon@arm.com, mark.rutland@arm.com Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, peterz@infradead.org, tglx@linutronix.de, bigeasy@linutronix.de, Meng.Li@windriver.com References: <606ff8c3f7f35ccdcb4b52a49f692fb20e27359c.1549299188.git.robin.murphy@arm.com> From: Suzuki K Poulose Message-ID: <3ebabec2-5423-9aca-19aa-7cd96353efd6@arm.com> Date: Tue, 5 Feb 2019 11:19:55 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <606ff8c3f7f35ccdcb4b52a49f692fb20e27359c.1549299188.git.robin.murphy@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 Robin, On 04/02/2019 17:09, Robin Murphy wrote: > The arm-cci probe logic faces a cyclic dependency wherein it has to pick > a valid CPU to associate with before registering the PMU device, has to > have the PMU state initialised before handling hotplug events in case it > must be migrated, but has to have the hotplug notifier registered before > the chosen CPU may go offline lest things get out of sync. The present > code has tried to solve the races by using get_cpu() to pick the current > CPU and prevent it from disappearing while the other two registrations > are performed, but that results in taking mutexes with preemption > disabled, which makes certain configurations very unhappy: > > [ 1.983337] BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:2004 > [ 1.983340] in_atomic(): 1, irqs_disabled(): 0, pid: 1, name: swapper/0 > [ 1.983342] Preemption disabled at: > [ 1.983353] [] cci_pmu_probe+0x1dc/0x488 > [ 1.983360] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.18.20-rt8-yocto-preempt-rt #1 > [ 1.983362] Hardware name: ZynqMP ZCU102 Rev1.0 (DT) > [ 1.983364] Call trace: > [ 1.983369] dump_backtrace+0x0/0x158 > [ 1.983372] show_stack+0x24/0x30 > [ 1.983378] dump_stack+0x80/0xa4 > [ 1.983383] ___might_sleep+0x138/0x160 > [ 1.983386] __might_sleep+0x58/0x90 > [ 1.983391] __rt_mutex_lock_state+0x30/0xc0 > [ 1.983395] _mutex_lock+0x24/0x30 > [ 1.983400] perf_pmu_register+0x2c/0x388 > [ 1.983404] cci_pmu_probe+0x2bc/0x488 > [ 1.983409] platform_drv_probe+0x58/0xa8 > > However, we don't actually mind being preempted or migrated at this > point; all that really matters is that whichever CPU we pick does not > get offlined before we're done. Thus, do the robust thing and instead > take the lock to inhibit CPU hotplug for the duration. This also > revealed an additional race in assigning the global pointer too late > relative to the hotplug notifier, so that gets fixed in the process. > > Reported-by: "Li, Meng" > Signed-off-by: Robin Murphy Thanks for fixing the issues. Reviewed-by: Suzuki K Poulose