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=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS autolearn=unavailable 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 1C16EC4360F for ; Thu, 4 Apr 2019 10:42:30 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id DEF6420855 for ; Thu, 4 Apr 2019 10:42:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="gB25iPrH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DEF6420855 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=XTdWKL524LV1+G5DKWTrGj+4iaJTG2S1zodbdcuBztI=; b=gB25iPrHpER0JfBdfuJeZnb2a yNBWaQdWfyDXkWOqOeMdw7mqRtHhLpLpHp2I2Yk2pBrP+L7RIq6ZoNe+rZNXmeuEkZsVBHzaBImaz 2uCjabagX/O8CD9ig59ck90kl/itWIaMD742AmXQeLzWS6oHcBkNow891BaxoKrcfT5kI/XvfHMFD /DM08vJWVH6tYIzzNrnGLU5/GjQJc0u7vlsgkCY+UXaFIHCOKAL1unNNDhwIfuazdB/0Fjhidr1Ss r6O4viZeDfaFiOUMSKU/g6aUayEcszFOo5f+RdV6xIXFEV87d+Pe3KxNE3x4UY1LkZrGULQ49/0NQ uZJd5ob6Q==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hBzpC-0006Q9-9t; Thu, 04 Apr 2019 10:42:26 +0000 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hBzp8-0006Pj-Re for linux-arm-kernel@lists.infradead.org; Thu, 04 Apr 2019 10:42:24 +0000 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 8CB52A78; Thu, 4 Apr 2019 03:42:22 -0700 (PDT) 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 D8DB13F557; Thu, 4 Apr 2019 03:42:20 -0700 (PDT) Subject: Re: [PATCH v2 1/2] perf/arm-cci: Remove broken race mitigation To: robin.murphy@arm.com, will.deacon@arm.com References: From: Suzuki K Poulose Message-ID: Date: Thu, 4 Apr 2019 11:42:19 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190404_034222_903663_58A6E68A X-CRM114-Status: GOOD ( 19.30 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, peterz@infradead.org, bigeasy@linutronix.de, linux-kernel@vger.kernel.org, clabbe.montjoie@gmail.com, tglx@linutronix.de, Meng.Li@windriver.com, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 03/04/2019 18:10, Robin Murphy wrote: > Uncore PMU drivers face an awkward cyclic dependency wherein: > > - They have to pick a valid online CPU to associate with before > registering the PMU device, since it will get exposed to userspace > immediately. > - The PMU registration has to be be at least partly complete before > hotplug events can be handled, since trying to migrate an > uninitialised context would be bad. > - The hotplug handler has to be ready as soon as a CPU is chosen, lest > it go offline without the user-visible cpumask value getting updated. > > The arm-cci driver has tried to solve this by using get_cpu() to pick > the current CPU and prevent it from disappearing while both > 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 > > It is not feasible to resolve all the possible races outside of the perf > core itself, so address the immediate bug by following the example of > nearly every other PMU driver and not even trying to do so. Registering > the hotplug notifier first should minimise the window in which things > can go wrong, so that's about as much as we can reasonably do here. This > also revealed an additional race in assigning the global pointer too > late relative to the hotplug notifier, which gets fixed in the process. > > Reported-by: "Li, Meng" > Reported-by: Corentin Labbe > Signed-off-by: Robin Murphy Thanks for fixing this. Reviewed-by: Suzuki K Poulose _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel