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

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Message-ID: <alpine.DEB.2.20.1801161909020.2366@nanos>
Date:   Tue, 16 Jan 2018 19:09:33 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Joseph Salisbury <joseph.salisbury@...onical.com>
cc:     "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "vikas.shivappa@...ux.intel.com" <vikas.shivappa@...ux.intel.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "eranian@...gle.com" <eranian@...gle.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "davidcc@...gle.com" <davidcc@...gle.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "1733662@...s.launchpad.net" <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 Tue, 16 Jan 2018, Joseph Salisbury wrote:
> On 01/16/2018 08:32 AM, Shankar, Ravi V wrote:
> > Vikas on vacation until end of the month. Fenghua will look into this
> > issue.
> >
> > On Jan 16, 2018, at 5:09 AM, Thomas Gleixner <tglx@...utronix.de
> > <mailto:tglx@...utronix.de>> wrote:
> >
> >>
> >> Vikas, Fenghua can you please look at that ASAP?
> >>
> >> On Sun, 14 Jan 2018, Thomas Gleixner wrote:
> >>
> >>> 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
> >>>> <mailto: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
> 
> 
> Here is some data wiht KASAN enabled:
> https://bugs.launchpad.net/ubuntu/+source/linux-hwe/+bug/1733662/comments/51
> 
> Are there any specific logs you would like to see, or specific actions
> executed?

No, the KASAN output is pretty clear where the issue is.

Thanks,

	tglx