Re: [PATCH net] net/smc: Transfer remaining wait queue entries during fallback
From: Heiko Carstens <hca@linux.ibm.com>
Date: 2021-11-12 14:02:20
Also in:
linux-s390, lkml
On Fri, Nov 12, 2021 at 11:30:39AM +0800, Wen Gu wrote: ...
quoted hunk ↗ jump to hunk
+ 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);
No idea if the rest of the patch makes sense, however this usage of spin_lock_irqsave() is not correct. The second spin_lock_irqsave() would always save a state with irqs disabled into "flags", and therefore this path would always be left with irqs disabled, regardless if irqs were enabled or disabled when entering. You need to change it to something like
+ 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);