netdev - Re: selftests: net: pmtu.sh: Unable to handle kernel paging request at virtual address

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Date: Tue,  5 Sep 2023 19:10:59 +0800
From: Hillf Danton <hdanton@...a.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Netdev <netdev@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Naresh Kamboju <naresh.kamboju@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: selftests: net: pmtu.sh: Unable to handle kernel paging request at virtual address

On Mon, 4 Sep 2023 13:29:57 +0200 Eric Dumazet <edumazet@...gle.com>
> On Sun, Sep 3, 2023 at 5:57=E2=80=AFAM Hillf Danton <hdanton@...a.com>
> > On Thu, 31 Aug 2023 15:12:30 +0200 Eric Dumazet <edumazet@...gle.com>
> > > --- a/net/core/dst.c
> > > +++ b/net/core/dst.c
> > > @@ -163,8 +163,13 @@ EXPORT_SYMBOL(dst_dev_put);
> > >
> > >  void dst_release(struct dst_entry *dst)
> > >  {
> > > -       if (dst && rcuref_put(&dst->__rcuref))
> > > +       if (dst && rcuref_put(&dst->__rcuref)) {
> > > +               if (!(dst->flags & DST_NOCOUNT)) {
> > > +                       dst->flags |= DST_NOCOUNT;
> > > +                       dst_entries_add(dst->ops, -1);
> >
> > Could this add happen after the rcu sync above?
> >
> I do not think so. All dst_release() should happen before netns removal.

	cpu2                    cpu3
	====                    ====
	cleanup_net()           __sys_sendto
	                        sock_sendmsg()
	                        udpv6_sendmsg()
	synchronize_rcu();
				dst_release()

Could this one be an exception?