core: The brick process is getting crash during upcall event (#4256)

A brick process may crash while it try to send upcall notification
to the client and client disconnect is being process.

Solution: Avoid upcall event notification to the client if disconnect
        is being process for the same client.

Fixes: #4255
Change-Id: I80478d7f4a038b04a10fb21a1290b4309e9fe4dd

Signed-off-by: Mohit Agrawal <[email protected]>

Author: mohit84

xlators/protocol/server/src/server.c

@@ -1469,6 +1469,12 @@ server_process_event_upcall(xlator_t *this, void *data)
             if (!client || strcmp(client->client_uid, client_uid))
                 continue;
 
+           /* Avoid upcall notification to client if disconnect is in
+              progress
+            */
+            if (GF_ATOMIC_GET(xprt->disconnect_progress))
+                continue;
+
             xprt_found = _gf_true;
             rpc_transport_ref(xprt);
             break;