net/smc: Add comment for smc_tx_pending

The previous patch introduces a lock-free version of smc_tx_work() to
solve unnecessary lock contention, which is expected to be held lock.
So this adds comment to remind people to keep an eye out for locks.
Suggested-by: Stefan Raspl <raspl@linux.ibm.com>
Signed-off-by: Tony Lu <tonylu@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/smc/smc_tx.c

@@ -611,6 +611,10 @@ int smc_tx_sndbuf_nonempty(struct smc_connection *conn)
 	return rc;
 }
 
+/* Wakeup sndbuf consumers from process context
+ * since there is more data to transmit. The caller
+ * must hold sock lock.
+ */
 void smc_tx_pending(struct smc_connection *conn)
 {
 	struct smc_sock *smc = container_of(conn, struct smc_sock, conn);
@@ -626,7 +630,8 @@ void smc_tx_pending(struct smc_connection *conn)
 }
 
 /* Wakeup sndbuf consumers from process context
- * since there is more data to transmit
+ * since there is more data to transmit in locked
+ * sock.
  */
 void smc_tx_work(struct work_struct *work)
 {