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

On Wed, Mar 25, 2026 at 08:17:30AM -0600, David Ahern wrote:

On 3/24/26 2:39 PM, Eric Dumazet wrote:

quoted

On Tue, Mar 24, 2026 at 8:56 AM Ido Schimmel [off-list ref] wrote:

quoted

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.

We can probably remove more code than just the synchronize_rcu() calls.
Looking into that right now.