From: Stephen Hemminger <stephen@networkplumber•org>
To: Cong Wang <amwang@redhat•com>
Cc: netdev@vger•kernel.org, "David S. Miller" <davem@davemloft•net>
Subject: Re: [Patch net-next] vxlan: do real refcnt for vn_sock
Date: Tue, 28 May 2013 21:22:00 -0700 [thread overview]
Message-ID: <20130528212200.798261d7@nehalam.linuxnetplumber.net> (raw)
In-Reply-To: <1369793333.12227.4.camel@cr0>
On Wed, 29 May 2013 10:08:53 +0800
Cong Wang <amwang@redhat•com> wrote:
> On Tue, 2013-05-28 at 08:22 -0700, Stephen Hemminger wrote:
> > On Tue, 28 May 2013 19:07:22 +0800
> > Cong Wang <amwang@redhat•com> wrote:
> >
> > > From: Cong Wang <amwang@redhat•com>
> > >
> > > In commit 553675fb5e9ce3d71a (vxlan: listen on multiple ports),
> > > we use kfree_rcu() to free ->vn_sock, but a) there is no use
> > > of RCU API to access this filed, b) RCU is not enough to do refcnt
> > > here, because in vxlan_leave_group() we drop RTNL lock before
> > > locking the socket, it could be possible that this field is
> > > freed during this period.
> > >
> > > So, instead making things complex, just do basic refcnt for
> > > the ->vn_sock, like we do for others.
> > >
> ...
> >
> > Not needed all access is under RTNL
>
> I know, this is why I had a patch (not posted) which adds the missing
> rtnl_dereference(), but even if we had these, it is still not correct.
>
> As I explained in the changelog, vxlan_leave_group() has a problem,
> because it releases rtnl lock before locking the socket, _and_ it is
> called after vxlan_dellink() which schedules a work to cleanup the
> struct. Therefore the ->vn_sock could be freed right after rtnl lock is
> released.
>
> Am I miss anything?
Ignoring your IPv6 code for now...
With IPV4:
refcnt is incremented when socket is incremented in newlink (RTNL held).
refcnt is decremented in by dellink (RTNL held) and socket is deleted from list
leave_group doesn't happen until work queue is fired.
rtnl_dereference is fine, but hardly necessary when the call hierarchy is so obvious.
The problem you describe won't be fixed by just converting it to atomic,
I think you need add a dev_hold()/dev_put to vxlan_stop to prevent
device from being deleted when rtnl_lock is dropped.
next prev parent reply other threads:[~2013-05-29 4:22 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-28 11:07 [Patch net-next] vxlan: do real refcnt for vn_sock Cong Wang
2013-05-28 15:22 ` Stephen Hemminger
2013-05-29 2:08 ` Cong Wang
2013-05-29 4:22 ` Stephen Hemminger [this message]
2013-05-29 4:34 ` Cong Wang
2013-05-29 4:01 ` Cong Wang
2013-05-29 4:41 ` Stephen Hemminger
2013-05-29 5:14 ` Cong Wang
2013-05-29 8:39 ` Cong Wang
2013-05-31 2:55 ` Cong Wang
2013-05-31 3:56 ` Stephen Hemminger
2013-05-31 4:12 ` Cong Wang
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