RE: [PATCH RT] nvdimm: make lane acquirement RT aware

[Liu, Yongxin]

> -----Original Message-----
> From: linux-kernel-owner@xxxxxxxxxxxxxxx [mailto:linux-kernel-
> owner@xxxxxxxxxxxxxxx] On Behalf Of Sebastian Andrzej Siewior
> Sent: Monday, March 18, 2019 19:40
> To: Liu, Yongxin
> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-rt-users@xxxxxxxxxxxxxxx;
> tglx@xxxxxxxxxxxxx; rostedt@xxxxxxxxxxx; dan.j.williams@xxxxxxxxx;
> pagupta@xxxxxxxxxx; Gortmaker, Paul; linux-nvdimm@xxxxxxxxxxxx
> 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