Re: [PATCH net-next 3/3] vrf: Remove unnecessary synchronize_rcu() invocations

[David Ahern <dsahern@kernel.org>]

On 3/24/26 2:39 PM, Eric Dumazet wrote:
> On Tue, Mar 24, 2026 at 8:56 AM Ido Schimmel <idosch@nvidia.com> wrote:
>>
>> vrf_rtable_release() and vrf_rt6_release() are called as part of the VRF
>> device's ndo_uninit() callback. As such, an RCU grace period passes
>> between the removal of the VRF slaves and the closing of the VRF device
>> until these functions are invoked.
>>
>> Therefore, it should not be possible for any concurrent RCU readers to
>> try and acquire a reference on the dst entry while we are potentially
>> releasing the last reference via dst_release().
>>
>> Given the above, the synchronize_rcu() invocations in these functions
>> seem unnecessary and only add unnecessary delay when deleting VRF
>> devices. Remove them.
>>
>> Reviewed-by: Petr Machata <petrm@nvidia.com>
>> Signed-off-by: Ido Schimmel <idosch@nvidia.com>
>> ---
>>  drivers/net/vrf.c | 2 --
>>  1 file changed, 2 deletions(-)
>>
>> diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
>> index bfc9ea91ac20..75edb8eba87f 100644
>> --- a/drivers/net/vrf.c
>> +++ b/drivers/net/vrf.c
>> @@ -753,7 +753,6 @@ static void vrf_rt6_release(struct net_device *dev, struct net_vrf *vrf)
>>         struct rt6_info *rt6 = rtnl_dereference(vrf->rt6);
>>
>>         RCU_INIT_POINTER(vrf->rt6, NULL);
> 
> We could argue that the vrf->rt6 clearing is not needed,
> or should be done before the RCU grace period mentioned in the
> changelog started ?
> 

AIUI Ido's point is that the synchronize_net() in
unregister_netdevice_many_notify() occurs before the ndo_uninit call
making the synchronize_rcu here unnecessary. There is also a second
synchronize_net after it.

I get your point about skipping the clearing the poiniters.