SUNRPC: Prevent hang on NFS mount with xprtsec=[m]tls

Engineers at Hammerspace noticed that sometimes mounting with
"xprtsec=tls" hangs for a minute or so, and then times out, even
when the NFS server is reachable and responsive.

kTLS shuts off data_ready callbacks if strp->msg_ready is set to
mitigate data_ready callbacks when a full TLS record is not yet
ready to be read from the socket.

Normally msg_ready is clear when the first TLS record arrives on
a socket. However, I observed that sometimes tls_setsockopt() sets
strp->msg_ready, and that prevents forward progress because
tls_data_ready() becomes a no-op.

Moreover, Jakub says: "If there's a full record queued at the time
when [tlshd] passes the socket back to the kernel, it's up to the
reader to read the already queued data out." So SunRPC cannot
expect a data_ready call when ingress data is already waiting.

Add an explicit poll after SunRPC's upper transport is set up to
pick up any data that arrived after the TLS handshake but before
transport set-up is complete.

Reported-by: Steve Sears <[email protected]>
Suggested-by: Jakub Kacinski <[email protected]>
Fixes: 75eb6af ("SUNRPC: Add a TCP-with-TLS RPC transport class")
Tested-by: Mike Snitzer <[email protected]>
Reviewed-by: Mike Snitzer <[email protected]>
Cc: [email protected]
Signed-off-by: Chuck Lever <[email protected]>
Signed-off-by: Anna Schumaker <[email protected]>

Author: chucklever

net/sunrpc/xprtsock.c

@@ -2740,6 +2740,11 @@ static void xs_tcp_tls_setup_socket(struct work_struct *work)
 	}
 	rpc_shutdown_client(lower_clnt);
 
+	/* Check for ingress data that arrived before the socket's
+	 * ->data_ready callback was set up.
+	 */
+	xs_poll_check_readable(upper_transport);
+
 out_unlock:
 	current_restore_flags(pflags, PF_MEMALLOC);
 	upper_transport->clnt = NULL;