linux-kernel - RE: [PATCH RT] nvdimm: make lane acquirement RT aware

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Message-ID: <597B109EC20B76429F71A8A97770610D12A649C1@ALA-MBD.corp.ad.wrs.com>
Date:   Mon, 18 Mar 2019 11:48:28 +0000
From:   "Liu, Yongxin" <Yongxin.Liu@...driver.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "pagupta@...hat.com" <pagupta@...hat.com>,
        "Gortmaker, Paul" <Paul.Gortmaker@...driver.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
Subject: RE: [PATCH RT] nvdimm: make lane acquirement RT aware


> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org [mailto:linux-kernel-
> owner@...r.kernel.org] On Behalf Of Sebastian Andrzej Siewior
> Sent: Monday, March 18, 2019 19:40
> To: Liu, Yongxin
> Cc: linux-kernel@...r.kernel.org; linux-rt-users@...r.kernel.org;
> tglx@...utronix.de; rostedt@...dmis.org; dan.j.williams@...el.com;
> pagupta@...hat.com; Gortmaker, Paul; linux-nvdimm@...ts.01.org
> Subject: Re: [PATCH RT] nvdimm: make lane acquirement RT aware
> 
> On 2019-03-18 01:41:10 [+0000], Liu, Yongxin wrote:
> >
> > Consider the recursive call to nd_region_acquire_lane() in the
> following situation.
> > Will there be a dead lock?
> >
> >
> >     Thread A                    Thread B
> >        |                           |
> >        |                           |
> >      CPU 1                       CPU 2
> >        |                           |
> >        |                           |
> >  get lock for Lane 1         get lock for Lane 2
> >        |                           |
> >        |                           |
> >  migrate to CPU 2            migrate to CPU 1
> >        |                           |
> >        |                           |
> >  wait lock for Lane 2        wait lock for Lane 1
> >        |                           |
> >        |                           |
> >        _____________________________
> >                    |
> >                 dead lock ?
> 
> Bummer. That would dead lock indeed.
> Is it easily possible to recognize the recursive case?

Not easily. I don't have test case for recursive call. 
For now, just code analysis.


Yongxin

> >
> > Thanks,
> > Yognxin
> 
> Sebastian