RE: [PATCH net v2] net: openvswitch: fix race on port output

[Felix Hüttner]

On Tue, Apr 4, 2023 at 10:03 AM Eric Dumazet wrote:
> On Tue, Apr 4, 2023 at 9:33 AM Felix Huettner
> <felix.huettner@mail.schwarz> wrote:
> >
> > assume the following setup on a single machine:
> > 1. An openvswitch instance with one bridge and default flows
> > 2. two network namespaces "server" and "client"
> > 3. two ovs interfaces "server" and "client" on the bridge
> > 4. for each ovs interface a veth pair with a matching name and 32 rx and
> >    tx queues
> > 5. move the ends of the veth pairs to the respective network namespaces
> > 6. assign ip addresses to each of the veth ends in the namespaces (needs
> >    to be the same subnet)
> > 7. start some http server on the server network namespace
> > 8. test if a client in the client namespace can reach the http server
> >
> > when following the actions below the host has a chance of getting a cpu
> > stuck in a infinite loop:
> > 1. send a large amount of parallel requests to the http server (around
> >    3000 curls should work)
> > 2. in parallel delete the network namespace (do not delete interfaces or
> >    stop the server, just kill the namespace)
> >
>
> > Fixes: 7f8a436eaa2c ("openvswitch: Add conntrack action")
> > Co-developed-by: Luca Czesla <luca.czesla@mail.schwarz>
> > Signed-off-by: Luca Czesla <luca.czesla@mail.schwarz>
> > Signed-off-by: Felix Huettner <felix.huettner@mail.schwarz>
> > ---
> > v2:
> >   - replace BUG_ON with DEBUG_NET_WARN_ON_ONCE
> >   - use netif_carrier_ok() instead of checking for NETREG_REGISTERED
> > v1: https://lore.kernel.org/netdev/ZCaXfZTwS9MVk8yZ@kernel-bug-kernel-bug/
> >
> >  net/core/dev.c            | 1 +
> >  net/openvswitch/actions.c | 2 +-
> >  2 files changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index 253584777101..37b26017f458 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -3199,6 +3199,7 @@ static u16 skb_tx_hash(const struct net_device *dev,
> >         }
> >
> >         if (skb_rx_queue_recorded(skb)) {
> > +               DEBUG_NET_WARN_ON_ONCE(unlikely(qcount == 0));
>
> No need for unlikely(), it is already done in DEBUG_NET_WARN_ON_ONCE()
>
> Thanks.

Thanks for the feedback. Will include that in v3.
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