linux-kernel - Re: [REGRESSION][v4.14.y][v4.15] x86/intel_rdt/cqm: Improve limbo list processing

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Date:   Sun, 14 Jan 2018 12:35:45 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Joseph Salisbury <joseph.salisbury@...onical.com>
cc:     vikas.shivappa@...ux.intel.com, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, ravi.v.shankar@...el.com,
        tony.luck@...el.com, fenghua.yu@...el.com, peterz@...radead.org,
        eranian@...gle.com, ak@...ux.intel.com, davidcc@...gle.com,
        mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        1733662@...s.launchpad.net,
        "Roderick W. Smith" <rod.smith@...onical.com>
Subject: Re: [REGRESSION][v4.14.y][v4.15] x86/intel_rdt/cqm: Improve limbo
 list processing

On Fri, 12 Jan 2018, Joseph Salisbury wrote:

> 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@...ux.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?

That stinks like a use after free. Can you run with KASAN enabled?

Thanks,

	tglx