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=-6.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 0D5D6C433E0 for ; Wed, 10 Feb 2021 18:11:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C7C5A64DC3 for ; Wed, 10 Feb 2021 18:11:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232715AbhBJSLY (ORCPT ); Wed, 10 Feb 2021 13:11:24 -0500 Received: from mail.kernel.org ([198.145.29.99]:54090 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233571AbhBJSBI (ORCPT ); Wed, 10 Feb 2021 13:01:08 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 171A864E6F; Wed, 10 Feb 2021 18:00:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1612980027; bh=Zk7OqLQIa9Im9RmLh/iXB3llwfY7isgcOwpCyCEnmTQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RHhw7Ixm9JO/VgrXA5FpKhv2NNlOfhg2fKBr0WGqmhQM1acwzEJgsl/ErZLllTftO NozAltpMUklKOGdpyBaLNL79Z1uPPl5n7nKzfpEVFy8J8Py7QHjX0FuXGHolAwAnP6 JMEhTob/3Tweom/dFQOHCH1iCXSLraw23EIayN6MtI9w5hpTzrAI2G1cA1ssus2Tn+ LOxE3T/mFOb9E8YGYgpFV/SVnH/m3uNL8DoHi1hFlX2mG48+A+VKsI+A0lsIylSMp2 7XqZ6yJaxvAY99GbHvaAF0P73glsX6b6SJE0rA//ivheIHRU/pwXSNMWStzW5/UdfA kHIQyZNacCHkQ== Date: Wed, 10 Feb 2021 13:00:25 -0500 From: Sasha Levin To: Mathieu Desnoyers Cc: Greg Kroah-Hartman , stable , Theodore Tso , linux-kernel , Chris Mason , Tejun Heo , Jens Axboe , rostedt , Michael Jeanson Subject: Re: [stable 4.4, 4.9, 4.14, 4.19 LTS] Missing fix "memcg: fix a crash in wb_workfn when a device disappears" Message-ID: <20210210180025.GE4035784@sasha-vm> References: <537870616.15400.1612973059419.JavaMail.zimbra@efficios.com> <2071967108.15704.1612977931149.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <2071967108.15704.1612977931149.JavaMail.zimbra@efficios.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 10, 2021 at 12:25:31PM -0500, Mathieu Desnoyers wrote: >----- On Feb 10, 2021, at 12:09 PM, Greg Kroah-Hartman gregkh@linuxfoundation.org wrote: > >> On Wed, Feb 10, 2021 at 11:04:19AM -0500, Mathieu Desnoyers wrote: >>> Hi, >>> >>> While reconciling the lttng-modules writeback instrumentation with its >>> counterpart >>> within the upstream Linux kernel, I notice that the following commit introduced >>> in >>> 5.6 is present in stable branches 5.4 and 5.5, but is missing from LTS stable >>> branches >>> for 4.4, 4.9, 4.14, 4.19: >>> >>> commit 68f23b89067fdf187763e75a56087550624fdbee >>> ("memcg: fix a crash in wb_workfn when a device disappears") >>> >>> Considering that this fix was CC'd to the stable mailing list, is there any >>> reason why it has not been integrated into those LTS branches ? >> >> Yes, it doesn't apply at all. If you think this is needed, I will >> gladly take backported and tested patches. >> >> But why do you think this is needed in older kernels? Have you hit >> this in real-life? > >No, I have not hit this in real-life. Looking at the patch commit message, >the conditions needed to trigger this issue are very specific: memcg must >be enabled, and a device must be hotremoved while writeback is going on, >with writeback tracing active. > >AFAIU memcg was present in those LTS releases and devices can be hotremoved >(please correct me if I'm wrong here), so all the preconditions appear to be >met. > >Considering that I don't have the setup ready to reproduce this issue, I will >have to defer to the original patch authors for a properly tested backport, >if it happens to be relevant at all. > >I just though reporting what appears to be a missing fix in LTS branches >would be the right thing to do. Looks like it doesn't apply due to churn with tracepoints, I think it's fixable. Let me try and get something for <=4.19. -- Thanks, Sasha