rpc: minor cleanup of scheduler callback code

Try to make the comment here a little more clear and concise.

Also, this macro definition seems unnecessary.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/sched.h

@@ -135,7 +135,6 @@ struct rpc_task_setup {
 #define RPC_IS_SWAPPER(t)	((t)->tk_flags & RPC_TASK_SWAPPER)
 #define RPC_DO_ROOTOVERRIDE(t)	((t)->tk_flags & RPC_TASK_ROOTCREDS)
 #define RPC_ASSASSINATED(t)	((t)->tk_flags & RPC_TASK_KILLED)
-#define RPC_DO_CALLBACK(t)	((t)->tk_callback != NULL)
 #define RPC_IS_SOFT(t)		((t)->tk_flags & RPC_TASK_SOFT)
 
 #define RPC_TASK_RUNNING	0

net/sunrpc/sched.c

@@ -626,19 +626,15 @@ static void __rpc_execute(struct rpc_task *task)
 		/*
 		 * Execute any pending callback.
 		 */
-		if (RPC_DO_CALLBACK(task)) {
-			/* Define a callback save pointer */
+		if (task->tk_callback) {
 			void (*save_callback)(struct rpc_task *);
 
 			/*
-			 * If a callback exists, save it, reset it,
-			 * call it.
-			 * The save is needed to stop from resetting
-			 * another callback set within the callback handler
-			 * - Dave
+			 * We set tk_callback to NULL before calling it,
+			 * in case it sets the tk_callback field itself:
 			 */
-			save_callback=task->tk_callback;
-			task->tk_callback=NULL;
+			save_callback = task->tk_callback;
+			task->tk_callback = NULL;
 			save_callback(task);
 		}