net/smc: remove unneeded atomic operations in smc_tx_sndbuf_nonempty

JIRA: https://issues.redhat.com/browse/RHEL-73484

commit e7bed88
Author: Li RongQing <lirongqing@baidu.com>
Date:   Thu Nov 23 09:45:37 2023 +0800

    net/smc: remove unneeded atomic operations in smc_tx_sndbuf_nonempty

    The commit dcd2cf5 ("net/smc: add autocorking support") adds an
    atomic variable tx_pushing in smc_connection to make sure only one can
    send to let it cork more and save CDC slot. since smc_tx_pending can be
    called in the soft IRQ without checking sock_owned_by_user() at that
    time, which would cause a race condition because bh_lock_sock() did
    not honor sock_lock()

    After commit 6b88af8 ("net/smc: don't send in the BH context if
    sock_owned_by_user"), the transmission is deferred to when sock_lock()
    is held by the user. Therefore, we no longer need tx_pending to hold
    message.

    So remove atomic variable tx_pushing and its operation, and
    smc_tx_sndbuf_nonempty becomes a wrapper of __smc_tx_sndbuf_nonempty,
    so rename __smc_tx_sndbuf_nonempty back to smc_tx_sndbuf_nonempty

    Suggested-by: Alexandra Winter <wintera@linux.ibm.com>
    Co-developed-by: Dust Li <dust.li@linux.alibaba.com>
    Signed-off-by: Dust Li <dust.li@linux.alibaba.com>
    Signed-off-by: Li RongQing <lirongqing@baidu.com>
    Reviewed-by: Alexandra Winter <wintera@linux.ibm.com>

    diff v4: remove atomic variable tx_pushing
    diff v3: improvements in the commit body and comments
    diff v2: fix a typo in commit body and add net-next subject-prefix

     net/smc/smc.h    |  1 -
     net/smc/smc_tx.c | 30 +-----------------------------
     2 files changed, 1 insertion(+), 30 deletions(-)

    Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Mete Durlu <mdurlu@redhat.com>

Author: Mete Durlu

net/smc/smc.h

@@ -196,7 +196,6 @@ struct smc_connection {
 						 * - dec on polled tx cqe
 						 */
 	wait_queue_head_t	cdc_pend_tx_wq; /* wakeup on no cdc_pend_tx_wr*/
-	atomic_t		tx_pushing;     /* nr_threads trying tx push */
 	struct delayed_work	tx_work;	/* retry of smc_cdc_msg_send */
 	u32			tx_off;		/* base offset in peer rmb */
 

net/smc/smc_tx.c

@@ -638,7 +638,7 @@ static int smcd_tx_sndbuf_nonempty(struct smc_connection *conn)
 	return rc;
 }
 
-static int __smc_tx_sndbuf_nonempty(struct smc_connection *conn)
+int smc_tx_sndbuf_nonempty(struct smc_connection *conn)
 {
 	struct smc_sock *smc = container_of(conn, struct smc_sock, conn);
 	int rc = 0;
@@ -672,34 +672,6 @@ static int __smc_tx_sndbuf_nonempty(struct smc_connection *conn)
 	return rc;
 }
 
-int smc_tx_sndbuf_nonempty(struct smc_connection *conn)
-{
-	int rc;
-
-	/* This make sure only one can send simultaneously to prevent wasting
-	 * of CPU and CDC slot.
-	 * Record whether someone has tried to push while we are pushing.
-	 */
-	if (atomic_inc_return(&conn->tx_pushing) > 1)
-		return 0;
-
-again:
-	atomic_set(&conn->tx_pushing, 1);
-	smp_wmb(); /* Make sure tx_pushing is 1 before real send */
-	rc = __smc_tx_sndbuf_nonempty(conn);
-
-	/* We need to check whether someone else have added some data into
-	 * the send queue and tried to push but failed after the atomic_set()
-	 * when we are pushing.
-	 * If so, we need to push again to prevent those data hang in the send
-	 * queue.
-	 */
-	if (unlikely(!atomic_dec_and_test(&conn->tx_pushing)))
-		goto again;
-
-	return rc;
-}
-
 /* Wakeup sndbuf consumers from process context
  * since there is more data to transmit. The caller
  * must hold sock lock.