Subject: Re: [PATCH 1/1] net: Add rtnl_lock for netif_device_attach/detach

From: "Li, ZhenHua" <[email-masked]>
Date: Mon, 21 Apr 2014 14:30:06 +0800

The comment is trying to explain why add a lock here.

On 04/19/2014 03:01 AM, Sergei Shtylyov wrote:
> Hello.
>
> On 04/16/2014 11:08 AM, Li, Zhen-Hua wrote:
>
>> From: "Li, Zhen-Hua" <[email-masked]>
>
>> As netif_running is called in netif_device_attach/detach. There 
>> should be
>> rtnl_lock/unlock called, to avoid dev stat change during 
>> netif_device_attach
>> and detach being called.
>> I checked NIC some drivers,  some of them have 
>> netif_device_attach/detach
>> called between rtnl_lock/unlock, while some drivers do not.
>
>> This patch is tring to find a generic way to fix this for all NIC 
>> drivers.
>
>> Signed-off-by: Li, Zhen-Hua <[email-masked]>
>> ---
>>   net/core/dev.c |   18 ++++++++++++++++++
>>   1 file changed, 18 insertions(+)
>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 5b3042e..795bbc5 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -2190,10 +2190,19 @@ EXPORT_SYMBOL(__dev_kfree_skb_any);
>>    */
>>   void netif_device_detach(struct net_device *dev)
>>   {
>> +    /**
>
>   Hm, why kernel-doc style comment here?
>
>> +     * As netif_running is called , rtnl_lock and unlock are needed to
>> +     * avoid __LINK_STATE_START bit changes during this function call.
>> +     */
>> +    int need_unlock;
>> +
>> +    need_unlock = rtnl_trylock();
>>       if (test_and_clear_bit(__LINK_STATE_PRESENT, &dev->state) &&
>>           netif_running(dev)) {
>>           netif_tx_stop_all_queues(dev);
>>       }
>> +    if (need_unlock)
>> +        rtnl_unlock();
>>   }
>>   EXPORT_SYMBOL(netif_device_detach);
>>
>> @@ -2205,11 +2214,20 @@ EXPORT_SYMBOL(netif_device_detach);
>>    */
>>   void netif_device_attach(struct net_device *dev)
>>   {
>> +    /**
>
>   ... and here?
>
>> +     * As netif_running is called , rtnl_lock and unlock are needed to
>> +     * avoid __LINK_STATE_START bit changes during this function call.
>> +     */
>
> WBR, Sergei
>