Re: [PATCH 4/5] NFSD/SUNRPC: Check rpc_xprt out of xs_setup_bc_tcp

[Kinglong Mee <kinglongmee@gmail.com>]

On 01/10/2014 01:27 AM, Trond Myklebust wrote:
> 
> On Jan 9, 2014, at 11:26, Dr Fields James Bruce <bfields@fieldses.org> wrote:
> 
>> On Thu, Jan 09, 2014 at 06:33:10PM +0800, Kinglong Mee wrote:
>>> Besides checking rpc_xprt out of xs_setup_bc_tcp,
>>> increase it's reference (it's important).
>>
>> This sounds wrong to me: the presence of a backchannel can't prevent the
>> client's connection from going away.  Instead, when the connection dies,
>> any associated backchannels should be immediately destroyed.
> 
> Hi Bruce,
> 
> The right way to deal with this is to have knfsd shut down the rpc_client
> when it detects the TCP disconnection event. 

Yes, that's right.
Knfsd has do it as you said.

When getting xprt's status of XPT_CLOSE in svc_recv/svc_handle_xprt, 
knfsd will delete the xprt by svc_delete_xprt.

In svc_delete_xprt, knfsd calls call_xpt_users to notify those users of the xprt.
So, nfsd4_conn_lost will be called to free the connection.
After freeing connection, nfsd4_probe_callback will update the callback for the client.
And, the clp->cl_cb_client will be shutdown in nfsd4_process_cb_update.

At last, all using of the xprt will be released.
I have test it, that's OK. 

> The xprt->count shouldn’t be an issue here: 
> it has nothing to do with the socket connection state.

The xprt of backchannel, there are two references, 
1. rpc_clnt
2. svc_xprt

For rpc_clnt, initialize the xprt->count in xs_setup_bc_tcp,
or increase it in create_backchannel_client, and, decrease in rpc_free_client.

For svc_xprt, increase it in xs_setup_bc_tcp, and decrease in svc_xprt_free.

thanks,
Kinglong Mee