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 check sndbuf_space again after NOSPACE flag is set to break the race.
Fixes: 8dce2786a290 ("net/smc: smc_poll improvements")
Signed-off-by: Guangguan Wang <guangguan.wang@xxxxxxxxxxxxxxxxx>
Suggested-by: Paolo Abeni <pabeni@xxxxxxxxxx>
---
net/smc/af_smc.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index 9d76e902fd77..4ab86141e4b4 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -2881,6 +2881,13 @@ __poll_t smc_poll(struct file *file, struct socket *sock,
} else {
sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
+
+ if (sk->sk_state != SMC_INIT) {
+ /* Race breaker the same way as tcp_poll(). */
+ smp_mb__after_atomic();
+ if (atomic_read(&smc->conn.sndbuf_space))
+ mask |= EPOLLOUT | EPOLLWRNORM;
+ }
}
if (atomic_read(&smc->conn.bytes_to_rcv))
mask |= EPOLLIN | EPOLLRDNORM;
--
2.24.3 (Apple Git-128)
