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=-12.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 14B60C433DF for ; Thu, 6 Aug 2020 20:40:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 10FCA221E5 for ; Thu, 6 Aug 2020 20:40:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726396AbgHFUkU (ORCPT ); Thu, 6 Aug 2020 16:40:20 -0400 Received: from foss.arm.com ([217.140.110.172]:48080 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725272AbgHFUkU (ORCPT ); Thu, 6 Aug 2020 16:40:20 -0400 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 8D93E30E; Thu, 6 Aug 2020 13:40:19 -0700 (PDT) Received: from [10.57.35.143] (unknown [10.57.35.143]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 414D43F7D7; Thu, 6 Aug 2020 13:40:18 -0700 (PDT) Subject: Re: [tip: perf/core] perf/core: Fix endless multiplex timer To: Greg KH Cc: "stable@vger.kernel.org" , linux-kernel@vger.kernel.org, Andi Kleen , Kan Liang , "Peter Zijlstra (Intel)" , x86 References: <20200305123851.GX2596@hirez.programming.kicks-ass.net> <158470908175.28353.4859180707604949658.tip-bot2@tip-bot2> <20200806185353.GA2942033@kroah.com> From: Robin Murphy Message-ID: <3a89fe47-e143-885a-d116-d3805e0712a0@arm.com> Date: Thu, 6 Aug 2020 21:40:17 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200806185353.GA2942033@kroah.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-08-06 19:53, Greg KH wrote: > On Thu, Aug 06, 2020 at 07:11:24PM +0100, Robin Murphy wrote: >> On 2020-03-20 12:58, tip-bot2 for Peter Zijlstra wrote: >>> The following commit has been merged into the perf/core branch of tip: >>> >>> Commit-ID: 90c91dfb86d0ff545bd329d3ddd72c147e2ae198 >>> Gitweb: https://git.kernel.org/tip/90c91dfb86d0ff545bd329d3ddd72c147e2ae198 >>> Author: Peter Zijlstra >>> AuthorDate: Thu, 05 Mar 2020 13:38:51 +01:00 >>> Committer: Peter Zijlstra >>> CommitterDate: Fri, 20 Mar 2020 13:06:22 +01:00 >>> >>> perf/core: Fix endless multiplex timer >>> >>> Kan and Andi reported that we fail to kill rotation when the flexible >>> events go empty, but the context does not. XXX moar >>> >>> Fixes: fd7d55172d1e ("perf/cgroups: Don't rotate events for cgroups unnecessarily") >> >> Can this patch (commit 90c91dfb86d0 ("perf/core: Fix endless multiplex >> timer") upstream) be applied to stable please? For PMU drivers built as >> modules, the bug can actually kill the system, since the runaway hrtimer >> loop keeps calling pmu->{enable,disable} after all the events have been >> closed and dropped their references to pmu->module. Thus legitimately >> unloading the module once things have got into this state quickly results in >> a crash when those callbacks disappear. >> >> (FWIW I spent about two days fighting with this while testing a new driver >> as a module against the 5.3 kernel installed on someone else's machine, >> assuming it was a bug in my code...) > > What exactly kernel(s) do you wish for it to be applied to? It's > already in the latest stable releases of 5.7.y. Sorry, I implicitly meant 5.4.y there - the buggy commit was merged in 5.3, the fix in 5.7, so I think that's the only "stable" branch in between that warrants explicit action. Apologies if I'm getting the terminology wrong. Cheers, Robin.