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Message-ID: <1544636846.3750.2.camel@redhat.com>
Subject: Re: [PATCH 1/1] SUNRPC: Ensure XPRT_CONNECTED is cleared while
 handling TCP RST
From:   Dave Wysochanski <dwysocha@redhat.com>
To:     Trond Myklebust <trondmy@hammerspace.com>,
        "anna.schumaker@netapp.com" <anna.schumaker@netapp.com>
Cc:     "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>
Date:   Wed, 12 Dec 2018 12:47:26 -0500
In-Reply-To: <03049f893dfd265abb90fd2692bc41e1534f85d0.camel@hammerspace.com>
References: <20181212135157.4489-1-dwysocha@redhat.com>
         <20181212135157.4489-2-dwysocha@redhat.com>
         <03049f893dfd265abb90fd2692bc41e1534f85d0.camel@hammerspace.com>
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On Wed, 2018-12-12 at 16:56 +0000, 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(). I suggest that a stable fix do
> something similar (perhaps conditional on the error returned by
> xprt_transmit()?).
> 

Can you explain the handling in xs_tcp_state_change - why
XPRT_CONNECTED would need to remain set longer in the case of handling
TCP_CLOSE case rather than TCP_CLOSE_WAIT?  It seems like if we get an
RST we'll go directly to TCP_CLOSE and why would the XPRT_CONNECTED bit
getting cleared need to be delayed in that case?

I will look into the approach you mention though at the moment I do not
see how it helps because the underlying issue seems to be clearing of
the XPRT_CONNECTED bit.

Thanks.