From: Guangguan Wang <guangguan.wang@linux.alibaba.com> mainline inclusion from mainline-v6.13-rc4 commit 679e9ddcf90dbdf98aaaa71a492454654b627bcb category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/IC914B Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- 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@linux.alibaba.com> Suggested-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Wang Liang <wangliang74@huawei.com> --- 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 49f6ffdf0498..02abaf96f390 100644 --- a/net/smc/af_smc.c +++ b/net/smc/af_smc.c @@ -2827,6 +2827,13 @@ static __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; -- 2.34.1