netdev - Re: Refcount mismatch when unregistering netdevice from kernel

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Message-ID: <CAADnVQ+AbH0Xs_fF5mESb2i-TCL0T-inpAX+gtggDbHhA+9djA@mail.gmail.com>
Date:   Thu, 11 Feb 2021 11:21:26 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Wei Wang <weiwan@...gle.com>
Cc:     David Ahern <dsahern@...il.com>, stranche@...eaurora.org,
        Eric Dumazet <eric.dumazet@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Subash Abhinov Kasiviswanathan <subashab@...eaurora.org>
Subject: Re: Refcount mismatch when unregistering netdevice from kernel

On Tue, Jan 5, 2021 at 11:11 AM Wei Wang <weiwan@...gle.com> wrote:
>
> On Mon, Jan 4, 2021 at 8:58 PM David Ahern <dsahern@...il.com> wrote:
> >
> > On 1/4/21 8:05 PM, stranche@...eaurora.org wrote:
> > >
> > > We're able to reproduce the refcount mismatch after some experimentation
> > > as well.
> > > Essentially, it consists of
> > > 1) adding a default route (ip -6 route add dev XXX default)
> > > 2) forcing the creation of an exception route via manually injecting an
> > > ICMPv6
> > > Packet Too Big into the device.
> > > 3) Replace the default route (ip -6 route change dev XXX default)
> > > 4) Delete the device. (ip link del XXX)
> > >
> > > After adding a call to flush out the exception cache for the route, the
> > > mismatch
> > > is no longer seen:
> > > diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
> > > index 7a0c877..95e4310 100644
> > > --- a/net/ipv6/ip6_fib.c
> > > +++ b/net/ipv6/ip6_fib.c
> > > @@ -1215,6 +1215,7 @@ static int fib6_add_rt2node(struct fib6_node *fn,
> > > struct fib6_info *rt,
> > >                 }
> > >                 nsiblings = iter->fib6_nsiblings;
> > >                 iter->fib6_node = NULL;
> > > +               rt6_flush_exceptions(iter);
> > >                 fib6_purge_rt(iter, fn, info->nl_net);
> > >                 if (rcu_access_pointer(fn->rr_ptr) == iter)
> > >                         fn->rr_ptr = NULL;
> >
> > Ah, I see now. rt6_flush_exceptions is called by fib6_del_route, but
> > that won't handle replace.
> >
> > If you look at fib6_purge_rt it already has a call to remove pcpu
> > entries. This call to flush exceptions should go there and the existing
> > one in fib6_del_route can be removed.
> >
> Thanks for catching this!
> Agree with this proposed fix.

Looks like this fix never landed?
Is it still needed or there was an alternative fix merged?