telemetry: fix race on callbacks list

[ upstream commit 0489602 ]

The list_commands() function accessed the callbacks list,
but did not take the lock. This may have caused inconsistencies if
callbacks were being registered at the same time.
This is now fixed to lock before iterating the list,
and unlock afterwards.

Fixes: f387487 ("telemetry: add default callback commands")

Reported-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Ciara Power <ciara.power@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>

lib/librte_telemetry/telemetry.c

@@ -95,8 +95,10 @@ list_commands(const char *cmd __rte_unused, const char *params __rte_unused,
 	int i;
 
 	rte_tel_data_start_array(d, RTE_TEL_STRING_VAL);
+	rte_spinlock_lock(&callback_sl);
 	for (i = 0; i < num_callbacks; i++)
 		rte_tel_data_add_array_string(d, callbacks[i].cmd);
+	rte_spinlock_unlock(&callback_sl);
 	return 0;
 }