5.4-stable review patch. If anyone has any objections, please let me know.
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From: Guangguan Wang guangguan.wang@linux.alibaba.com
[ Upstream commit 679e9ddcf90dbdf98aaaa71a492454654b627bcb ]
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: Sasha Levin sashal@kernel.org --- 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 e070b0e2a30c..1373a0082b5a 100644 --- a/net/smc/af_smc.c +++ b/net/smc/af_smc.c @@ -1660,6 +1660,13 @@ 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;