netdev - RE: [PATCH v2] ravb: Fixed the problem that rmmod can not be done

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Date:   Fri, 31 Jul 2020 10:18:09 +0000
From:   "ashiduka@...itsu.com" <ashiduka@...itsu.com>
To:     'Sergei Shtylyov' <sergei.shtylyov@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org" 
        <linux-renesas-soc@...r.kernel.org>
Subject: RE: [PATCH v2] ravb: Fixed the problem that rmmod can not be done

Hi Sergei,

I understand that the commit log needs to be corrected.
(Shimoda-san's point is also correct)

If there is anything else that needs to be corrected, please point it out.

>    That seems a common pattern, inlluding the Renesas sh_eth
> driver...

Yes.
If I can get an R-Car Gen2 board, I will also fix sh_eth driver.

>    No, the driver's remove() method calls ravb_mdio_release() and
> that one calls
> free_mdio_bitbang() that calls module_put(); the actual reason lies
> somewehre deeper than this...

No.
Running rmmod calls delete_module() in kernel/module.c before ravb_mdio_release() is called.
delete_module()
   -> try_stop_module()
     -> try_release_module_ref()
In try_release_module_ref(), check refcnt and if it is counted up, ravb_mdio_release() is not
called and rmmod is terminated.

Thanks & Best Regards,
Yuusuke Ashizuka <ashiduka@...itsu.com>

> -----Original Message-----
> From: Sergei Shtylyov <sergei.shtylyov@...il.com>
> Sent: Friday, July 31, 2020 1:04 AM
> To: Ashizuka, Yuusuke/芦塚 雄介 <ashiduka@...itsu.com>
> Cc: netdev@...r.kernel.org; linux-renesas-soc@...r.kernel.org
> Subject: Re: [PATCH v2] ravb: Fixed the problem that rmmod can not
> be done
> 
> Hello!
> 
> On 7/30/20 1:01 PM, Yuusuke Ashizuka wrote:
> 
> > ravb is a module driver, but I cannot rmmod it after insmod it.
> 
>    Modular. And "insmod'ing it".
> 
> > ravb does mdio_init() at the time of probe, and module->refcnt
> is incremented
> > by alloc_mdio_bitbang() called after that.
> 
>    That seems a common pattern, inlluding the Renesas sh_eth
> driver...
> 
> > Therefore, even if ifup is not performed, the driver is in use
> and rmmod cannot
> > be performed.
> 
>    No, the driver's remove() method calls ravb_mdio_release() and
> that one calls
> free_mdio_bitbang() that calls module_put(); the actual reason lies
> somewehre deeper
> than this... Unfortunately I don't have the affected hardware
> anymore... :-(
> 
> [...]
> 
> MBR, Sergei