Re: [PATCH 1/1] SUNRPC: Ensure XPRT_CONNECTED is cleared while handling TCP RST

[Scott Mayhew <smayhew@redhat.com>]

On Wed, 12 Dec 2018, Trond Myklebust wrote:

> On Wed, 2018-12-12 at 08:51 -0500, Dave Wysochanski wrote:
> > Commit 9b30889c548a changed the handling of TCP_CLOSE inside
> > xs_tcp_state_change.  Prior to this change, the XPRT_CONNECTED bit
> > was cleared unconditionally inside xprt_disconnect_done, similar
> > to the handling of TCP_CLOSE_WAIT.  After the change the clearing
> > of XPRT_CONNECTED depends on successfully queueing a work based
> > xprt_autoclose which depends on XPRT_LOCKED and may not happen.
> > This is significant in the case of an unexpected RST from the
> > server, as the client will only see xs_tcp_state_change called with
> > sk_state == TCP_CLOSE.  Restore the unconditional clear_bit on
> > XPRT_CONNECTED while handling TCP_CLOSE and make it consistent
> > with handling TCP_CLOSE_WAIT.
> > 
> > Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
> > ---
> >  net/sunrpc/xprtsock.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> > index 8a5e823e0b33..b9789036051d 100644
> > --- a/net/sunrpc/xprtsock.c
> > +++ b/net/sunrpc/xprtsock.c
> > @@ -1492,6 +1492,7 @@ static void xs_tcp_state_change(struct sock
> > *sk)
> >  		if (sk->sk_err)
> >  			xprt_wake_pending_tasks(xprt, -sk->sk_err);
> >  		/* Trigger the socket release */
> > +		clear_bit(XPRT_CONNECTED, &xprt->state);
> >  		xs_tcp_force_close(xprt);
> >  	}
> >   out:
> 
> Hi Dave,
> 
> This isn't needed for 4.20 or newer because call_transmit() will now
> always call xprt_end_transmit().

Dave's script can also produce a hang on 4.20, but for a different
reason... if xs_reset_transport() is called on an xprt that has
XPRT_WRITE_SPACE set, then no further RPC tasks will be able to lock the
transport or connect it.  Clearing XPRT_WRITE_SPACE in
xs_sock_reset_connection_flags() seems to fix that. I don't know if
XPRT_WRITE_SPACE counts as a "connection flag" though.

-Scott

> I suggest that a stable fix do
> something similar (perhaps conditional on the error returned by
> xprt_transmit()?).
> 
> Cheers
>   Trond
> 
> -- 
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@hammerspace.com
> 
>