When application sending data more than sndbuf_space, there have chances
application will sleep in epoll_wait, and will never be wakeup again. This
is caused by a race between smc_poll and smc_cdc_tx_handler.
application tasklet
smc_tx_sendmsg(len > sndbuf_space) |
epoll_wait for EPOLL_OUT,timeout=0 |
smc_poll |
if (!smc->conn.sndbuf_space) |
| smc_cdc_tx_handler
| atomic_add sndbuf_space
| smc_tx_sndbuf_nonfull
| if (!test_bit SOCK_NOSPACE)
| do not sk_write_space;
set_bit SOCK_NOSPACE; |
return mask=0; |
Application will sleep in epoll_wait as smc_poll returns 0. And
smc_cdc_tx_handler will not call sk_write_space because the SOCK_NOSPACE
has not be set. If there is no inflight cdc msg, sk_write_space will not be
called any more, and application will sleep in epoll_wait forever.
So set SOCK_NOSPACE when send_remaining but no sndbuf_space left in
smc_tx_sendmsg, to ensure call sk_write_space in smc_cdc_tx_handler
even when the above race happens.
Fixes: 6889b36da78a ("net/smc: don't wait for send buffer space when data was already sent")
Signed-off-by: Guangguan Wang <guangguan.wang@xxxxxxxxxxxxxxxxx>
Reviewed-by: Wen Gu <guwen@xxxxxxxxxxxxxxxxx>
Reviewed-by: D. Wythe <alibuda@xxxxxxxxxxxxxxxxx>
---
net/smc/smc_tx.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/net/smc/smc_tx.c b/net/smc/smc_tx.c
index 214ac3cbcf9a..60cfec8eb255 100644
--- a/net/smc/smc_tx.c
+++ b/net/smc/smc_tx.c
@@ -222,8 +222,11 @@ int smc_tx_sendmsg(struct smc_sock *smc, struct msghdr *msg, size_t len)
conn->local_tx_ctrl.prod_flags.urg_data_pending = 1;
if (!atomic_read(&conn->sndbuf_space) || conn->urg_tx_pend) {
- if (send_done)
+ if (send_done) {
+ sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
+ set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
return send_done;
+ }
rc = smc_tx_wait(smc, msg->msg_flags);
if (rc)
goto out_err;
--
2.24.3 (Apple Git-128)
