linux-kernel - Re: [PATCH net 1/2] net: ravb: Fix missing rtnl lock in suspend path

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Message-ID: <cdf4e312-92bc-44f3-a049-bd3ddf3222e1@tuxon.dev>
Date: Thu, 23 Jan 2025 16:17:58 +0200
From: Claudiu Beznea <claudiu.beznea@...on.dev>
To: Kory Maincent <kory.maincent@...tlin.com>
Cc: Paul Barker <paul.barker.ct@...renesas.com>,
 Niklas Söderlund <niklas.soderlund@...natech.se>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Mikhail Ulyanov <mikhail.ulyanov@...entembedded.com>,
 Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 Niklas Söderlund <niklas.soderlund+renesas@...natech.se>,
 Claudiu Beznea <claudiu.beznea.uj@...renesas.com>, netdev@...r.kernel.org,
 linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net 1/2] net: ravb: Fix missing rtnl lock in suspend path

On 23.01.2025 16:08, Kory Maincent wrote:
> On Thu, 23 Jan 2025 13:33:30 +0200
> Claudiu Beznea <claudiu.beznea@...on.dev> wrote:
> 
>> Hi, Kory,
>>
>> On 22.01.2025 18:19, Kory Maincent wrote:
>>> Fix the suspend path by ensuring the rtnl lock is held where required.
>>> Calls to ravb_open, ravb_close and wol operations must be performed under
>>> the rtnl lock to prevent conflicts with ongoing ndo operations.
> 
>>
>> I've test it. Looks good.
>>
>> Thank you for your patch. However, I think this could be simplified. The
>> locking scheme looks complicated to me. E.g., this one works too:
>>
>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c
>> b/drivers/net/ethernet/renesas/ravb_main.c
>> index bc395294a32d..cfe4f0f364f3 100644
>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
>> @@ -3217,10 +3217,16 @@ static int ravb_suspend(struct device *dev)
>>
>>         netif_device_detach(ndev);
>>
>> -       if (priv->wol_enabled)
>> -               return ravb_wol_setup(ndev);
>> +       if (priv->wol_enabled) {
>> +               rtnl_lock();
>> +               ret = ravb_wol_setup(ndev);
>> +               rtnl_unlock();
>> +               return ret;
>> +       }
> 
> What happen if wol_enabled flag changes it state between the rtnl_lock and the
> if condition? We will be in the wrong path.

wol_enabled flag can't change in this suspend phase. The user space tasks
are fronzen when ravb_suspend() is called.

Thank you,
Claudiu

> 
> Regards,