Re: [PATCH v1 net] net: macb: Use rcu_dereference() for idev->ifa_list in macb_suspend().

[Vineeth Karumanchi <vineeth.karumanchi@amd.com>]

On 08/08/24 10:15 am, Kuniyuki Iwashima wrote:
> From: Vineeth Karumanchi <vineeth.karumanchi@amd.com>
> Date: Thu, 8 Aug 2024 09:53:42 +0530
>> Hi Kuniyuki,
>>
>> On 08/08/24 9:30 am, Kuniyuki Iwashima wrote:
>>> In macb_suspend(), idev->ifa_list is fetched with rcu_access_pointer()
>>> and later the pointer is dereferenced as ifa->ifa_local.
>>>
>>> So, idev->ifa_list must be fetched with rcu_dereference().
>>>
>>
>> Is there any functional breakage ?
> 
> rcu_dereference() triggers lockdep splat if not called under
> rcu_read_lock().
> 
> Also in include/linux/rcupdate.h:
> 
> /**
>   * rcu_access_pointer() - fetch RCU pointer with no dereferencing
> ...
>   * It is usually best to test the rcu_access_pointer() return value
>   * directly in order to avoid accidental dereferences being introduced
>   * by later inattentive changes.  In other words, assigning the
>   * rcu_access_pointer() return value to a local variable results in an
>   * accident waiting to happen.
> 
> 
>> I sent initial patch with rcu_dereference, but there is a review comment:
>>
>> https://lore.kernel.org/netdev/a02fac3b21a97dc766d65c4ed2d080f1ed87e87e.camel@redhat.com/
> 
> I guess the following ifa_local was missed then ?

I am ok to use rcu_dereference(), just curios why the check 
idev->ifa_list was removed ?


vineeth