Re: [PATCH][net-next] net: vrf: switch to synchronize_net() when releasing routes

[Ido Schimmel <idosch@nvidia.com>]

On Wed, Mar 11, 2026 at 02:26:57PM +0100, Eric Dumazet wrote:
> On Wed, Mar 11, 2026 at 2:19 PM Ido Schimmel <idosch@nvidia.com> wrote:
> >
> > On Tue, Mar 10, 2026 at 06:53:31AM -0400, lirongqing wrote:
> > > From: Li RongQing <lirongqing@baidu.com>
> > >
> > > Replace synchronize_rcu() with synchronize_net() in vrf_rtable_release()
> > > and vrf_rt6_release().
> > >
> > > synchronize_net() is RTNL-aware and can use the more efficient
> > > synchronize_rcu_expedited() when the RTNL lock is held, avoiding
> > > potentially long wait times for a standard RCU grace period.
> > >
> > > Since these release functions are called during device teardown where
> > > the RTNL lock is typically held, this change reduces the time spent
> > > in RTNL critical sections and speeds up VRF device deletion.
> > >
> > > Signed-off-by: Li RongQing <lirongqing@baidu.com>
> > > ---
> > >  drivers/net/vrf.c | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
> > > index 8c009bc..92a0f4b 100644
> > > --- a/drivers/net/vrf.c
> > > +++ b/drivers/net/vrf.c
> > > @@ -755,7 +755,7 @@ static void vrf_rt6_release(struct net_device *dev, struct net_vrf *vrf)
> > >       struct dst_entry *dst;
> > >
> > >       RCU_INIT_POINTER(vrf->rt6, NULL);
> > > -     synchronize_rcu();
> > > +     synchronize_net();
> >
> > I might be missing something, but why do we need synchronize_rcu() here?
> > The code below calls dst_release() which will only free the dst entry
> > after an RCU grace period (assuming we dropped the last reference).
> 
> Agreed, this could/should have been removed after
> 
> commit 4f04256c983a4f115417d2009b44dcb7d70a6375
> Author: David Ahern <dsahern@gmail.com>
> Date:   Fri Aug 11 17:11:14 2017 -0700
> 
>     net: vrf: Drop local rtable and rt6_info
> 
>     The VRF cached rtable and rt6_info for local traffic are no longer
>     needed and actually prevent local traffic through enslaved devices.
>     Remove them.
> 
> 
> 
> >
> > Also, I think that instead of using net->loopback_dev the code can be
> > converted to use dst_dev_put() before dst_release().
> >
> 
> Maybe in a separate patch ;)

Yes, separate patch. Another thing that can be simplified in this area
is the NULL check in vrf_rtable_release(). I don't see how that can
happen. It is necessary in the case of vrf_rt6_release() due to
'ipv6.disable=1'.

Li RongQing, can you take care of these changes?

1. Remove NULL check in vrf_rtable_release().

2. Convert vrf_rtable_release() and vrf_rt6_release() to use
dst_dev_put() before dst_release(), instead of using
'net->loopback_dev'.

3. Remove synchronize_rcu() from both vrf_rtable_release() and
vrf_rt6_release().

Thanks