From: Wen Gu guwen@linux.alibaba.com
[ Upstream commit 2153bd1e3d3dbf6a3403572084ef6ed31c53c5f0 ]
The SMC fallback is incomplete currently. There may be some wait queue entries remaining in smc socket->wq, which should be removed to clcsocket->wq during the fallback.
For example, in nginx/wrk benchmark, this issue causes an all-zeros test result:
server: nginx -g 'daemon off;' client: smc_run wrk -c 1 -t 1 -d 5 http://11.200.15.93/index.html
Running 5s test @ http://11.200.15.93/index.html 1 threads and 1 connections Thread Stats Avg Stdev Max ± Stdev Latency 0.00us 0.00us 0.00us -nan% Req/Sec 0.00 0.00 0.00 -nan% 0 requests in 5.00s, 0.00B read Requests/sec: 0.00 Transfer/sec: 0.00B
The reason for this all-zeros result is that when wrk used SMC to replace TCP, it added an eppoll_entry into smc socket->wq and expected to be notified if epoll events like EPOLL_IN/ EPOLL_OUT occurred on the smc socket.
However, once a fallback occurred, wrk switches to use clcsocket. Now it is clcsocket->wq instead of smc socket->wq which will be woken up. The eppoll_entry remaining in smc socket->wq does not work anymore and wrk stops the test.
This patch fixes this issue by removing remaining wait queue entries from smc socket->wq to clcsocket->wq during the fallback.
Link: https://www.spinics.net/lists/netdev/msg779769.html Signed-off-by: Wen Gu guwen@linux.alibaba.com Reviewed-by: Tony Lu tonylu@linux.alibaba.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/smc/af_smc.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)
diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c index ac8265e35b2d2..04bf8088872a9 100644 --- a/net/smc/af_smc.c +++ b/net/smc/af_smc.c @@ -513,12 +513,26 @@ static void smc_link_save_peer_info(struct smc_link *link,
static void smc_switch_to_fallback(struct smc_sock *smc) { + wait_queue_head_t *smc_wait = sk_sleep(&smc->sk); + wait_queue_head_t *clc_wait = sk_sleep(smc->clcsock->sk); + unsigned long flags; + smc->use_fallback = true; if (smc->sk.sk_socket && smc->sk.sk_socket->file) { smc->clcsock->file = smc->sk.sk_socket->file; smc->clcsock->file->private_data = smc->clcsock; smc->clcsock->wq.fasync_list = smc->sk.sk_socket->wq.fasync_list; + + /* There may be some entries remaining in + * smc socket->wq, which should be removed + * to clcsocket->wq during the fallback. + */ + spin_lock_irqsave(&smc_wait->lock, flags); + spin_lock(&clc_wait->lock); + list_splice_init(&smc_wait->head, &clc_wait->head); + spin_unlock(&clc_wait->lock); + spin_unlock_irqrestore(&smc_wait->lock, flags); } }