SUNRPC: Merge svc_do_enqueue_xprt() into svc_enqueue_xprt()

Neil says:
"These functions were separated in commit 0971374 ("SUNRPC:
Reduce contention in svc_xprt_enqueue()") so that the XPT_BUSY check
happened before taking any spinlocks.

We have since moved or removed the spinlocks so the extra test is
fairly pointless."

I've made this a separate patch in case the XPT_BUSY change has
unexpected consequences and needs to be reverted.

Suggested-by: Neil Brown <neilb@suse.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: chucklever

net/sunrpc/svc_xprt.c

@@ -32,7 +32,6 @@ static int svc_deferred_recv(struct svc_rqst *rqstp);
 static struct cache_deferred_req *svc_defer(struct cache_req *req);
 static void svc_age_temp_xprts(struct timer_list *t);
 static void svc_delete_xprt(struct svc_xprt *xprt);
-static void svc_xprt_do_enqueue(struct svc_xprt *xprt);
 
 /* apparently the "standard" is that clients close
  * idle connections after 5 minutes, servers after
@@ -267,12 +266,12 @@ void svc_xprt_received(struct svc_xprt *xprt)
 	}
 
 	/* As soon as we clear busy, the xprt could be closed and
-	 * 'put', so we need a reference to call svc_xprt_do_enqueue with:
+	 * 'put', so we need a reference to call svc_xprt_enqueue with:
 	 */
 	svc_xprt_get(xprt);
 	smp_mb__before_atomic();
 	clear_bit(XPT_BUSY, &xprt->xpt_flags);
-	svc_xprt_do_enqueue(xprt);
+	svc_xprt_enqueue(xprt);
 	svc_xprt_put(xprt);
 }
 EXPORT_SYMBOL_GPL(svc_xprt_received);
@@ -412,6 +411,8 @@ static bool svc_xprt_ready(struct svc_xprt *xprt)
 	smp_rmb();
 	xpt_flags = READ_ONCE(xprt->xpt_flags);
 
+	if (xpt_flags & BIT(XPT_BUSY))
+		return false;
 	if (xpt_flags & (BIT(XPT_CONN) | BIT(XPT_CLOSE)))
 		return true;
 	if (xpt_flags & (BIT(XPT_DATA) | BIT(XPT_DEFERRED))) {
@@ -424,7 +425,12 @@ static bool svc_xprt_ready(struct svc_xprt *xprt)
 	return false;
 }
 
-static void svc_xprt_do_enqueue(struct svc_xprt *xprt)
+/**
+ * svc_xprt_enqueue - Queue a transport on an idle nfsd thread
+ * @xprt: transport with data pending
+ *
+ */
+void svc_xprt_enqueue(struct svc_xprt *xprt)
 {
 	struct svc_pool *pool;
 	struct svc_rqst	*rqstp = NULL;
@@ -468,18 +474,6 @@ static void svc_xprt_do_enqueue(struct svc_xprt *xprt)
 	put_cpu();
 	trace_svc_xprt_enqueue(xprt, rqstp);
 }
-
-/*
- * Queue up a transport with data pending. If there are idle nfsd
- * processes, wake 'em up.
- *
- */
-void svc_xprt_enqueue(struct svc_xprt *xprt)
-{
-	if (test_bit(XPT_BUSY, &xprt->xpt_flags))
-		return;
-	svc_xprt_do_enqueue(xprt);
-}
 EXPORT_SYMBOL_GPL(svc_xprt_enqueue);
 
 /*