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

[Li, ZhenHua]

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" <zhen-hual@xxxxxx>
>
> > 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@xxxxxx>
> > ---
> >   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

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