Hi Eric,
On Thu, Nov 17, 2022 at 01:58:18PM -0800, Eric Dumazet wrote:
> On Wed, Nov 16, 2022 at 7:16 PM Joel Fernandes (Google)
> <joel@xxxxxxxxxxxxxxxxx> wrote:
> >
> > In a networking test on ChromeOS, we find that using the new CONFIG_RCU_LAZY
> > causes a networking test to fail in the teardown phase.
> >
> > The failure happens during: ip netns del <name>
> >
> > Using ftrace, I found the callbacks it was queuing which this series fixes. Use
> > call_rcu_flush() to revert to the old behavior. With that, the test passes.
> >
> > Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
> > ---
> > net/ipv4/devinet.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> > index e8b9a9202fec..98b20f333e00 100644
> > --- a/net/ipv4/devinet.c
> > +++ b/net/ipv4/devinet.c
> > @@ -328,7 +328,7 @@ static void inetdev_destroy(struct in_device *in_dev)
> > neigh_parms_release(&arp_tbl, in_dev->arp_parms);
> > arp_ifdown(dev);
> >
> > - call_rcu(&in_dev->rcu_head, in_dev_rcu_put);
> > + call_rcu_flush(&in_dev->rcu_head, in_dev_rcu_put);
> > }
>
> For this one, I suspect the issue is about device refcount lingering ?
>
> I think we should release refcounts earlier (and only delegate the
> freeing part after RCU grace period, which can be 'lazy' just fine)
>
> Something like:
The below diff where you reduce refcount before RCU grace period, also makes the
test pass.
If you are Ok with it, I can roll it into a patch with your Author tag and my
Tested-by. Let me know what you prefer?
Also, looking through the patch, I don't see any issue. One thing is
netdev_put() now happens before a grace period, instead of after. But I don't
think that's an issue.
thanks!
- Joel
>
> diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
> index e8b9a9202fecd913137f169f161dfdccc16f7edf..e0258aef4211ec6a72d062963470a32776e6d010
> 100644
> --- a/net/ipv4/devinet.c
> +++ b/net/ipv4/devinet.c
> @@ -234,13 +234,21 @@ static void inet_free_ifa(struct in_ifaddr *ifa)
> call_rcu(&ifa->rcu_head, inet_rcu_free_ifa);
> }
>
> +static void in_dev_free_rcu(struct rcu_head *head)
> +{
> + struct in_device *idev = container_of(head, struct in_device, rcu_head);
> +
> + kfree(rcu_dereference_protected(idev->mc_hash, 1));
> + kfree(idev);
> +}
> +
> void in_dev_finish_destroy(struct in_device *idev)
> {
> struct net_device *dev = idev->dev;
>
> WARN_ON(idev->ifa_list);
> WARN_ON(idev->mc_list);
> - kfree(rcu_dereference_protected(idev->mc_hash, 1));
> +
> #ifdef NET_REFCNT_DEBUG
> pr_debug("%s: %p=%s\n", __func__, idev, dev ? dev->name : "NIL");
> #endif
> @@ -248,7 +256,7 @@ void in_dev_finish_destroy(struct in_device *idev)
> if (!idev->dead)
> pr_err("Freeing alive in_device %p\n", idev);
> else
> - kfree(idev);
> + call_rcu(&idev->rcu_head, in_dev_free_rcu);
> }
> EXPORT_SYMBOL(in_dev_finish_destroy);
>
> @@ -298,12 +306,6 @@ static struct in_device *inetdev_init(struct
> net_device *dev)
> goto out;
> }
>
> -static void in_dev_rcu_put(struct rcu_head *head)
> -{
> - struct in_device *idev = container_of(head, struct in_device, rcu_head);
> - in_dev_put(idev);
> -}
> -
> static void inetdev_destroy(struct in_device *in_dev)
> {
> struct net_device *dev;
> @@ -328,7 +330,7 @@ static void inetdev_destroy(struct in_device *in_dev)
> neigh_parms_release(&arp_tbl, in_dev->arp_parms);
> arp_ifdown(dev);
>
> - call_rcu(&in_dev->rcu_head, in_dev_rcu_put);
> + in_dev_put(in_dev);
> }
>
> int inet_addr_onlink(struct in_device *in_dev, __be32 a, __be32 b)
