netdev - Re: [PATCH net-next 09/11] can: gw: switch cangw_pernet

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Date:   Mon, 7 Feb 2022 09:54:17 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Oliver Hartkopp <socketcan@...tkopp.net>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        David Ahern <dsahern@...nel.org>,
        Marc Kleine-Budde <mkl@...gutronix.de>
Subject: Re: [PATCH net-next 09/11] can: gw: switch cangw_pernet_exit() to
 batch mode

On Mon, Feb 7, 2022 at 9:41 AM Oliver Hartkopp <socketcan@...tkopp.net> wrote:
>
>
>
> On 07.02.22 18:17, Eric Dumazet wrote:
> > From: Eric Dumazet <edumazet@...gle.com>
> >
> > cleanup_net() is competing with other rtnl users.
> >
> > Avoiding to acquire rtnl for each netns before calling
> > cgw_remove_all_jobs() gives chance for cleanup_net()
> > to progress much faster, holding rtnl a bit longer.
> >
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> > Cc: Oliver Hartkopp <socketcan@...tkopp.net>
> > Cc: Marc Kleine-Budde <mkl@...gutronix.de>
> > ---
> >   net/can/gw.c | 9 ++++++---
> >   1 file changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/net/can/gw.c b/net/can/gw.c
> > index d8861e862f157aec36c417b71eb7e8f59bd064b9..24221352e059be9fb9aca3819be6a7ac4cdef144 100644
> > --- a/net/can/gw.c
> > +++ b/net/can/gw.c
> > @@ -1239,16 +1239,19 @@ static int __net_init cangw_pernet_init(struct net *net)
> >       return 0;
> >   }
> >
> > -static void __net_exit cangw_pernet_exit(struct net *net)
> > +static void __net_exit cangw_pernet_exit_batch(struct list_head *net_list)
> >   {
> > +     struct net *net;
> > +
> >       rtnl_lock();
> > -     cgw_remove_all_jobs(net);
> > +     list_for_each_entry(net, net_list, exit_list)
> > +             cgw_remove_all_jobs(net);
>
> Instead of removing the jobs for ONE net namespace it seems you are
> remove removing the jobs for ALL net namespaces?
>
> Looks wrong to me.

I see nothing wrong in my patch.

I think you have to look more closely at ops_exit_list() in
net/core/net_namespace.c


BTW, the sychronize_rcu() call in cgw_remove_all_jobs is definitely
bad, you should absolutely replace it by call_rcu() or kfree_rcu()

>
> Best regards,
> Oliver
>
>
> >       rtnl_unlock();
> >   }
> >
> >   static struct pernet_operations cangw_pernet_ops = {
> >       .init = cangw_pernet_init,
> > -     .exit = cangw_pernet_exit,
> > +     .exit_batch = cangw_pernet_exit_batch,
> >   };
> >
> >   static __init int cgw_module_init(void)