net/smc: remove unneeded atomic operations in smc_tx_sndbuf_nonempty

The commit dcd2cf5f2fc0 ("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 6b88af839d20 ("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>

diff --git a/net/smc/smc.h b/net/smc/smc.h
index e377980b84145dea53844b0ba080fd2fb25f80c0..cd51261b7d9e2839f930438c3c5b77a9d1279aa9 100644 (file)
--- a/net/smc/smc.h
+++ b/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 */
 

diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index 3b0ff3b589c70fc88614cd0f5b8667d3e48622cb..214ac3cbcf9ad37cea2062a9400658e40803578c 100644 (file)
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c
@@ -621,7 +621,7 @@ 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;
@@ -655,34 +655,6 @@ out:
        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.