Re: [PATCH RFC 9/9] sunrpc: don't upgrade passive net reference in xs_create_sock

[Trond Myklebust]

On Mon, 2025-03-17 at 17:36 -0400, Jeff Layton wrote:
> On Mon, 2025-03-17 at 21:28 +0000, Trond Myklebust wrote:
> > On Mon, 2025-03-17 at 17:00 -0400, Jeff Layton wrote:
> > > With the move to having sunrpc client xprts not hold active
> > > references
> > > to the net namespace, there is no need to upgrade the socket's
> > > reference
> > > in xs_create_sock. Just keep the passive reference instead.
> > > 
> > > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
> > > ---
> > >  net/sunrpc/xprtsock.c | 3 ---
> > >  1 file changed, 3 deletions(-)
> > > 
> > > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> > > index
> > > 83cc095846d356f24aed26e2f98525662a6cff1f..0c3d7552f772d6f8477a3ae
> > > d8f0
> > > c513b62cdf589 100644
> > > --- a/net/sunrpc/xprtsock.c
> > > +++ b/net/sunrpc/xprtsock.c
> > > @@ -1941,9 +1941,6 @@ static struct socket *xs_create_sock(struct
> > > rpc_xprt *xprt,
> > >  		goto out;
> > >  	}
> > >  
> > > -	if (protocol == IPPROTO_TCP)
> > > -		sk_net_refcnt_upgrade(sock->sk);
> > > -
> > >  	filp = sock_alloc_file(sock, O_NONBLOCK, NULL);
> > >  	if (IS_ERR(filp))
> > >  		return ERR_CAST(filp);
> > > 
> > 
> > Is this not going to reintroduce the bug described by
> > https://lore.kernel.org/netdev/67b72aeb.050a0220.14d86d.0283.GAE@xxxxxxxxxx/T/#u
> > ?
> > 
> > As I understand it, the problem has nothing to do with whether or
> > not
> > NFS or the RPC layer holds a reference to the net namespace, but
> > rather
> > whether there are still packets in the socket queues at the time
> > when
> > that net namespace is being freed.
> > 
> > 
> 
> I don't think so. That syzkaller report was closed by this patch:
> 
>     5c70eb5c593d net: better track kernel sockets lifetime
> 
> That says:
> 
>     "To fix this, make sure that kernel sockets own a reference on
> net
> passive."
> 
> With this, we still do keep a passive reference on the net in the
> socket, which I think is enough.

No. You just removed that by reverting the patch that assigns the
passive reference.

> 
> That said, I'd appreciate a look at this from the netdev folks.

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx