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Date:	Mon, 21 Apr 2014 15:54:42 +0400
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	"Li, ZhenHua" <zhen-hual@...com>
CC:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Veaceslav Falico <vfalico@...hat.com>,
	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Jiri Pirko <jiri@...nulli.us>,
	stephen hemminger <stephen@...workplumber.org>,
	Jerry Chu <hkchu@...gle.com>,
	Sathya Perla <sathya.perla@...lex.com>,
	Subbu Seetharaman <subbu.seetharaman@...lex.com>,
	Ajit Khaparde <ajit.khaparde@...lex.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] net: Add rtnl_lock for netif_device_attach/detach

Hello.

On 21-04-2014 10:30, Li, ZhenHua wrote:

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

    I can read, thanks. :-)
    I was wondering about the kernel-doc comment style you've used; AFAIK, 
it's only good for documenting functions and data structures. The normal 
multi-line comment style in the networking code is this:

/* bla
  * bla
  */

>>> From: "Li, Zhen-Hua" <zhen-hual@...com>

>>> 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 <zhen-hual@...com>
>>> ---
>>>   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

    Space before comma not needed.

>>> +     * 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

    Space before comma not needed.

>>> +     * avoid __LINK_STATE_START bit changes during this function call.
>>> +     */

WBR, Sergei

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