@@ -562,6 +562,10 @@ static void smc_stat_fallback(struct smc_sock *smc)
static void smc_switch_to_fallback(struct smc_sock *smc, int reason_code)
{
+ 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;
smc->fallback_rsn = reason_code;
smc_stat_fallback(smc);
@@ -571,6 +575,16 @@ static void smc_switch_to_fallback(struct smc_sock *smc, int reason_code)
smc->clcsock->file->private_data = smc->clcsock;
smc->clcsock->wq.fasync_list =
smc->sk.sk_socket->wq.fasync_list;
+
+ /* There might be some wait queue 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_irqsave(&clc_wait->lock, flags);
+ list_splice_init(&smc_wait->head, &clc_wait->head);
+ spin_unlock_irqrestore(&clc_wait->lock, flags);
+ spin_unlock_irqrestore(&smc_wait->lock, flags);
}
}
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://lore.kernel.org/all/db9acf73-abef-209e-6ec2-8ada92e2cfbc@linux.ibm.com/ Signed-off-by: Wen Gu <guwen@linux.alibaba.com> Reviewed-by: Tony Lu <tonylu@linux.alibaba.com> --- net/smc/af_smc.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)