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

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Message-ID: <20190318114017.tazjaegln2obt3zg@linutronix.de>
Date:   Mon, 18 Mar 2019 12:40:17 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     "Liu, Yongxin" <Yongxin.Liu@...driver.com>
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

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? 

> 
> Thanks,
> Yognxin

Sebastian