To: vikas.shivappa@linux.intel.com
Cc: stable@vger.kernel.org, linux-kernel@vger.kernel.org,
        tglx@linutronix.de, ravi.v.shankar@intel.com, tony.luck@intel.com,
        fenghua.yu@intel.com, peterz@infradead.org, eranian@google.com,
        ak@linux.intel.com, davidcc@google.com, mingo@redhat.com,
        hpa@zytor.com, x86@kernel.org, 1733662@bugs.launchpad.net,
        "Roderick W. Smith" <rod.smith@canonical.com>
From: Joseph Salisbury <joseph.salisbury@canonical.com>
Subject: [REGRESSION][v4.14.y][v4.15] x86/intel_rdt/cqm: Improve limbo list
 processing
Message-ID: <84b8d891-6217-f56d-8ec0-313f7eb317c9@canonical.com>
Date: Fri, 12 Jan 2018 11:22:44 -0500
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Sender: linux-kernel-owner@vger.kernel.org

Hi Vikas,

A kernel bug report was opened against Ubuntu [0].  After a kernel
bisect, it was found that reverting the following commit resolved this bug:

commit 24247aeeabe99eab13b798ccccc2dec066dd6f07
Author: Vikas Shivappa <vikas.shivappa@linux.intel.com>
Date:   Tue Aug 15 18:00:43 2017 -0700

    x86/intel_rdt/cqm: Improve limbo list processing


The regression was introduced as of v4.14-r1 and still exists with
current mainline.  The trace with v4.15-rc7 is in comment #44[1].

I was hoping to get your feedback, since you are the patch author.  Do
you think gathering any additional data will help diagnose this issue,
or would it be best to submit a revert request?


Thanks,

Joe
[0] http://pad.lv/1733662
[1]
https://bugs.launchpad.net/ubuntu/+source/linux-hwe/+bug/1733662/comments/44