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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E0321C6FD1D for ; Thu, 30 Mar 2023 03:53:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229661AbjC3DxU (ORCPT ); Wed, 29 Mar 2023 23:53:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34354 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229588AbjC3DxS (ORCPT ); Wed, 29 Mar 2023 23:53:18 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4B80B4C15; Wed, 29 Mar 2023 20:53:17 -0700 (PDT) Received: from canpemm500009.china.huawei.com (unknown [172.30.72.56]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4Pn8dT2LXCzKqdc; Thu, 30 Mar 2023 11:52:45 +0800 (CST) Received: from [10.67.102.169] (10.67.102.169) by canpemm500009.china.huawei.com (7.192.105.203) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.21; Thu, 30 Mar 2023 11:53:15 +0800 CC: , , , , , , , , , , Subject: Re: [PATCH 1/4] hwtracing: hisi_ptt: Make cpumask only present online CPUs To: Jonathan Cameron References: <20230315094316.26772-1-yangyicong@huawei.com> <20230315094316.26772-2-yangyicong@huawei.com> <20230328172409.000021f5@Huawei.com> From: Yicong Yang Message-ID: <94e7d85a-d580-94c5-ae2c-fe6a77c21487@huawei.com> Date: Thu, 30 Mar 2023 11:53:14 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: <20230328172409.000021f5@Huawei.com> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.102.169] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To canpemm500009.china.huawei.com (7.192.105.203) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 2023/3/29 0:24, Jonathan Cameron wrote: > On Wed, 15 Mar 2023 17:43:13 +0800 > Yicong Yang wrote: > >> From: Yicong Yang >> >> perf will try to start PTT trace on every CPU presented in cpumask sysfs >> attribute and it will fail to start on offline CPUs(see the comments in >> perf_event_open()). But the driver is using cpumask_of_node() to export >> the available cpumask which may include offline CPUs and may fail the >> perf unintendedly. Fix this by only export the online CPUs of the node. > > There isn't clear documentation that I can find for cpumask_of_node() > and chasing through on arm64 (which is what we care about for this driver) > it's maintained via numa_add_cpu() numa_remove_cpu() > Those are called in arch/arm64/kernel/smp.c in locations that are closely coupled > with set_cpu_online(cpu, XXX); > https://elixir.bootlin.com/linux/v6.3-rc4/source/arch/arm64/kernel/smp.c#L246 > https://elixir.bootlin.com/linux/v6.3-rc4/source/arch/arm64/kernel/smp.c#L303 > > Now there are races when the two might not be in sync but in this case > we are just exposing the result to userspace, so chances of a race > after this sysfs attribute has been read seems much higher to me and > I don't think we can do anything about that. > > Is there another path that I'm missing where online and node masks are out > of sync? > maybe no. This patch maybe incorrect and I need more investigation, so let's me drop it from the series. Tested and everything seems fine now. I found this problem and referred to commit 064f0e9302af ("mm: only display online cpus of the numa node") which might be the same problem. But seems unnecessary that cpumask_of_node() already include online CPUs only. Thanks. > Jonathan > > >> >> Fixes: ff0de066b463 ("hwtracing: hisi_ptt: Add trace function support for HiSilicon PCIe Tune and Trace device") >> Signed-off-by: Yicong Yang > >> --- >> drivers/hwtracing/ptt/hisi_ptt.c | 13 +++++++++++-- >> 1 file changed, 11 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/hwtracing/ptt/hisi_ptt.c b/drivers/hwtracing/ptt/hisi_ptt.c >> index 30f1525639b5..0a10c7ec46ad 100644 >> --- a/drivers/hwtracing/ptt/hisi_ptt.c >> +++ b/drivers/hwtracing/ptt/hisi_ptt.c >> @@ -487,9 +487,18 @@ static ssize_t cpumask_show(struct device *dev, struct device_attribute *attr, >> char *buf) >> { >> struct hisi_ptt *hisi_ptt = to_hisi_ptt(dev_get_drvdata(dev)); >> - const cpumask_t *cpumask = cpumask_of_node(dev_to_node(&hisi_ptt->pdev->dev)); >> + cpumask_var_t mask; >> + ssize_t n; >> >> - return cpumap_print_to_pagebuf(true, buf, cpumask); >> + if (!alloc_cpumask_var(&mask, GFP_KERNEL)) >> + return 0; >> + >> + cpumask_and(mask, cpumask_of_node(dev_to_node(&hisi_ptt->pdev->dev)), >> + cpu_online_mask); >> + n = cpumap_print_to_pagebuf(true, buf, mask); >> + free_cpumask_var(mask); >> + >> + return n; >> } >> static DEVICE_ATTR_RO(cpumask); >> > > . >