linux-kernel - Re: [PATCH net-next 06/17] net: dsa: Call driver's setup callback after setting up its switchdev notifier

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Date:   Wed, 3 Apr 2019 12:58:40 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     f.fainelli@...il.com, vivien.didelot@...il.com,
        davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linus.walleij@...aro.org,
        georg.waibel@...sor-technik.de
Subject: Re: [PATCH net-next 06/17] net: dsa: Call driver's setup callback
 after setting up its switchdev notifier

On 4/3/19 12:03 AM, Andrew Lunn wrote:
> On Sun, Mar 31, 2019 at 08:42:21PM +0300, Vladimir Oltean wrote:
>> This allows the driver to perform some manipulations of its own during
>> setup, using generic code.
>> One current usage scenario is for the driver to request DSA to set up
>> 802.1Q based switch tagging for its ports.
>>
>> Signed-off-by: Vladimir Oltean <olteanv@...il.com>
>> Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
>> ---
>>   net/dsa/dsa2.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
>> index c00ee464afc7..5beceb18b7e2 100644
>> --- a/net/dsa/dsa2.c
>> +++ b/net/dsa/dsa2.c
>> @@ -360,14 +360,14 @@ static int dsa_switch_setup(struct dsa_switch *ds)
>>   	if (err)
>>   		return err;
>>   
>> -	err = ds->ops->setup(ds);
>> -	if (err < 0)
>> -		return err;
>> -
>>   	err = dsa_switch_register_notifier(ds);
>>   	if (err)
>>   		return err;
> 
> It seems that notifiers are the important thing here? Maybe state that
> in the commit message?
> 
> I'm also wondering how safe this is in general. If we have not yet
> called the driver setup, the switch is potentially not yet ready to
> actually handle an requests that come via the notifier. If such
> notifiers can only come from the driver itself, it should be
> safe. However, if they could come from the rest of the stack, i could
> see bad things happening.
> 
>      Andrew
> 

Hi Andrew,

Correct me if I'm wrong, but the switchdev notifiers coming from the 
stack are coming through a net device, and the slave net devices are 
only created in dsa_port_setup, which is later than the code I'm 
modifying anyway? Do you have an example of potentially racy situation 
caused by this change?

Thanks,
-Vladimir