According to the man page of TCP_CORK [1], if set, don't send out
partial frames. All queued partial frames are sent when option is
cleared again.

When applications call setsockopt to disable TCP_CORK, this call is
protected by lock_sock(), and tries to mod_delayed_work() to 0, in order
to send pending data right now. However, the delayed work smc_tx_work is
also protected by lock_sock(). There introduces lock contention for
sending data.

To fix it, send pending data directly which acts like TCP, without
lock_sock() protected in the context of setsockopt (already lock_sock()ed),
and cancel unnecessary dealyed work, which is protected by lock.

[1] https://linux.die.net/man/7/tcp

Signed-off-by: Tony Lu <tonylu@linux.alibaba.com>
---
  net/smc/af_smc.c |  4 ++--
  net/smc/smc_tx.c | 25 +++++++++++++++----------
  net/smc/smc_tx.h |  1 +
  3 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index ffab9cee747d..ef021ec6b361 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c

@@ -2600,8 +2600,8 @@ static int smc_setsockopt(struct socket *sock, int level, int optname,
  		    sk->sk_state != SMC_CLOSED) {
  			if (!val) {
  				SMC_STAT_INC(smc, cork_cnt);
-				mod_delayed_work(smc->conn.lgr->tx_wq,
-						 &smc->conn.tx_work, 0);
+				smc_tx_pending(&smc->conn);
+				cancel_delayed_work(&smc->conn.tx_work);
  			}
  		}
  		break;

diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index be241d53020f..7b0b6e24582f 100644
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c

@@ -597,27 +597,32 @@ int smc_tx_sndbuf_nonempty(struct smc_connection *conn)
  	return rc;
  }
  
-/* Wakeup sndbuf consumers from process context
- * since there is more data to transmit
- */
-void smc_tx_work(struct work_struct *work)
+void smc_tx_pending(struct smc_connection *conn)